Differential voluntary feed intake and whole transcriptome profiling in the hypothalamus of young sheep offered CP and phosphorus-deficient diets

A reduction in voluntary feed intake is observed in ruminants consuming nutrient-deficient diets, such as those with a low CP or P content, and has been attributed to active metabolic regulation, rather than a physical constraint. The hypothalamus is the key integrator of feed intake regulation in mammals. The objectives of this experiment were to (1) establish a model of metabolic feed intake regulation in ruminants consuming diets of variable CP and P content, and (2) determine key biochemical pathways and influential points of regulation within the hypothalamus. Merino wethers [n = 40; 23.7 ± 1.4 kg liveweight (mean ± SD)] were fed one of five dietary treatments (n = 8/treatment) for 63 days in individual pens. The treatments included targeted combinations of high (H) and low (L) CP (110 and 55 g/kg DM) and high and low P (2.5 and 0.7 g/kg DM) with 9 MJ metabolisable energy (ME) per kg DM which were fed ad libitum (UMEI; unrestricted ME intake) resulting in four experimental diets (HCP-HP-UMEI, LCP-HP-UMEI, HCP-LP-UMEI and LCP-LP-UMEI). An additional nutritional treatment (HCP-HP-RMEI) restricted intake of the HCP-HP diet to an equivalent ME intake of wethers consuming the LCP-LP-UMEI treatment. Wethers offered the LCP-HP-UMEI, HCP-LP-UMEI and LCP-LP-UMEI treatments consumed 42, 32 and 49% less total DM (P ≤ 0.05), respectively than the HCP-HP-UMEI treatment, and this was not attributable to any physical limitation of the rumen. Plasma concentrations of urea nitrogen and inorganic phosphate indicated that these nutrient deficiencies were successfully established. To assess potential mechanisms, RNA-seq was conducted on samples from the arcuate nucleus (ARC), ventromedial hypothalamus and lateral hypothalamus of the wethers, yielding a total of 301, 8 and 148 differentially expressed genes across all pairwise comparisons, respectively. The expression of NPY, AGRP and CARTPT, known for their regulatory role in mammalian feed intake regulation, had a similar transcriptional response in the ARC of wethers consuming nutrient-deficient treatments and those consuming a ME-restricted treatment, despite these wethers expressing behaviours indicative of satiated and hungry states, respectively. In addition, genes involved with glycolysis (TPI1), the citric acid cycle (CS, OGDH, GLUD1, GOT1) and oxidative phosphorylation (COX5A, ATP5MC1, ATP5F1B, ATP5MC3) were downregulated in the ARC of wethers fed a nutrient deficient (LCP-LP-UMEI) relative to the non-deficient (HCP-HP-UMEI) treatment. In summary, a model for voluntary feed intake restriction was established to determine genome-wide molecular changes in the hypothalamus of young ruminants.

Improving live weight gain of crossbred Limousin bulls with cassava peel silage

There is a growing demand for beef products across developing countries. Formulating rations to include locally available waste products has the potential to increase the live weight gain (LWG) of cattle and improve the livelihoods of smallholder farmers; however, upper limit inclusion levels of cassava peel products require investigation. An experiment evaluated the effect of using cassava peel silage (CPS) at the DM inclusion levels of 30, 40, 50, 60 and 70% (with the remainder protein meals and maize stover in the diet) on the LWG of crossbred Limousin × Ongole bulls (269 ± 48.8 kg). Thirty bulls, approximately two years of age, were allocated in a completely randomised block design with six blocks based on initial live weight (LW) and five treatments based on level of CPS. The combination of CPS (with 2% urea of the CPS) and protein meals significantly affected LWG with the highest values obtained at levels of 30 and 50% inclusion of CPS (1.16-1.35 kg/day) (P < 0.05). Polynomial analysis of LWG data revealed the optimal LWG is theoretically achieved at 37% CPS with a LWG of 1.31 kg/day; however, LWG was similar from 30 to 50% inclusion levels and then declined. There was little significant difference at CPS inclusion levels of 30-60%, for DM intake (DMI) which ranged from 2.3 to 2.6% LW, organic matter (OM) digestibility (77.8-81.6%), feed conversion ratio (FCR) (6.56-7.56 kg DM/kg LWG) and feed cost of gain (Indonesia rupiah (IDR)/kg LW 18 612 - 21 398). At a high (70%) level of CPS inclusion, these values were markedly changed when compared to the 30% inclusion level of CPS. Feed treatments did not affect rumen pH, NH₃-N, concentration or molar percentage of volatile fatty acids or protozoal population (P < 0.05). Rumen pH measured three hours after morning feed ranged from 6.7 to 6.8 and NH₃-N ranged from 14.1 to 19.3 mg NH₃-N/dl. It was concluded that inclusion of CPS up to 60% mixed with protein meals and urea and 20% maize stover maximised LWG and profitability of the production system.

Formulating diets based on whole cassava tuber (Manihot esculenta) and gliricidia (Gliricidia sepium) increased feed intake, liveweight gain and income over feed cost of Ongole and Bali bulls fed low quality forage in Central Sulawesi, Indonesia

Context Formulating rations with high energy and protein feeds such as cassava tuber and gliricidia, is an important strategy to increase liveweight gain (LWG) of bulls and improve profitability of smallholder farmers in Indonesia. Aims Two on-farm experiments were conducted to evaluate the effect of increasing the supplementation level of a mixture of cassava (Manihot esculenta) whole root tuber powder and fresh gliricidia (Gliricidia sepium) on feed intake and LWG of Ongole and Bali bulls given fresh corn stover and elephant grass, respectively. Methods Two experiments were conducted, each with five treatments: a basal diet of fresh corn stover (Experiment 1 for Ongole bulls) or elephant grass (Experiment 2 for Bali bulls) fed ad libitum or this diet supplemented with a combination of cassava tuber (whole root tuber including peel, sun-dried and ground) and fresh, chopped gliricidia (1:1) on estimated dry matter (DM) basis, at DM levels of 0.4, 0.8, 1,2 and 1.6% liveweight (LW)/day. Each experiment was run for 18 weeks, consisting of a two week adaptation and 16 week experimental period. Parameters measured included basal DM intake, supplement DM intake, total DM intake, total water intake, faecal pH, daily LWG, feed conversion ratio (FCR) and income over feed cost (IOFC). Key results Increasing supplement level linearly (P &lt; 0.05) decreased basal diet intake, but linearly increased total DM intake and LWG (P &lt; 0.05) in both breeds. Basal diet DM intake was reduced at the rate of 0.43 kg/kg of supplement DM consumed for both Ongole and Bali bulls. Water intake and faecal pH were not affected (P &gt; 0.05) by increasing supplement intake. Inclusion of cassava tuber and gliricidia supplement up to 1.6% LW/day, increased total feed DM intake (up to 3.28 and 3.18% LW/day, for Ongole and Bali bulls, respectively) and LWG (maximum Ongole bulls 0.69 kg/day and Bali bulls 0.46 kg/day). Daily income over feed cost (IOFC) increased significantly (P &lt; 0.05) in association with increased supplement intake in both Experiments 1 and 2. Using the derived model without supplementation, the value of IOFC was only IDR 7802/day and IDR 7687/day, for Experiments 1 and 2, respectively. The highest IOFC was achieved at a supplement intake of 1.6% LW/day with values of IDR 13949/day and IDR 12543/day for Experiments 1 and 2 respectively. Conclusions The addition of a cassava tuber and gliricidia mixture up to 1.6% LW/day increased LWG and profit for smallholders fattening bulls. Implications Formulating a ration with cassava tuber and gliricidia can be economically beneficial in cattle fattening systems in Indonesia.

Formulating rations with cassava meal to promote high live weight gain in crossbred Limousin bulls

Formulating rations with high energy and protein feeds such as cassava and locally sourced protein meals is an important strategy to increase live weight gain (LWG) of crossbred bulls in Indonesia. Current systems of production for Indonesian smallholders fatten bulls using cut and carry. Formulating a diet for an optimal combination of available feeds will increase production and potential profitability for smallholders. An experiment was conducted to evaluate the effect of using cassava meal in the diet at levels of 70C, 60C, 50C, 40C and 30C% (with most of the remainder being the protein meals) on the LWG of Limousin × Ongole bulls so as to determine the optimum combination of cassava meal and protein meals for LWG. Thirty bulls were allocated in a completely randomized block design with 6 blocks based on initial live weight (LW) and 5 treatments based on level of cassava meal. The combination of cassava meal (with 2% urea) and protein meals significantly affected LWG with the highest (1.35 kg/day) recorded at 40C (40% cassava meal, 40% protein meals and 20% maize stover). The LWG and nutrient intake increased curvilinearly with decreasing cassava meal and increasing protein meals (P < 0.05). Measured cassava meal inclusion in the final ration as a consequence of the changes in intake was 60, 56, 47, 37 and 28% for the designated 70C, 60C, 50C, 40C and 30C treatments, respectively. Dry matter intake reached 96 g/kg^0.75 per day or equal to 2.24% LW at this 40% level of inclusion. At the 70C treatment with 60% cassava meal and 9% protein meals, DM digestibility (69.1%) was lowest and that value increased as the proportion of cassava meal decreased and was highest at the 40C treatment (75.8%). Feed treatments significantly affected rumen pH, ammonia N (NH₃N) and volatile fatty acid concentrations (P < 0.05). There was no significant effect on protozoal population (P > 0.05). Rumen pH ranged from 6.3 to 6.9. It was concluded that a combination of 40% dried cassava meal and 40% protein meals with roughage (20%) maximized intake and LWG and beyond that level of cassava meal inclusion, LWG and intake decreased markedly.

Defoliation dynamics, pasture intake and milk production of dairy cows grazing lucerne pastures in a partial mixed-ration system

The effect of lucerne pasture allocation on defoliation dynamics, pasture intake and animal production was investigated in a subtropical partial mixed-ration dairy system. The study took place at the Gatton Research Dairy, south-eastern Queensland, with a 28-day adaptation period followed by an 8-day treatment period during November and December 2016. Twenty-four multiparous Holstein Friesian dairy cows were offered 11 kg of dry matter (DM)/cow.day as partial mixed-ration dairy system, and four levels of daily pasture allocation measured to 5-cm residual pasture height (averaging 30.6, 20.5, 15.1 and 10.9 kg DM/cow.day). Cows with lower allocations were forced to graze further down the vertical plane and pasture intake and milk yield significantly (P &lt; 0.001) declined. Cows grazed the top grazing stratum (TGS) across 80% of the pasture area before re-grazing another area of the paddock, regardless of the allocation level. Pasture intake (kg DM/ha) of the TGS was at least 2.9 times higher than that of the lower strata, regardless of allocation level. Therefore, the decline in pasture intake is explained by the transition from grazing the TGS to grazing lower strata. When the horizontal utilisation of the TGS approached 100%, the proportion of ungrazed, uncontaminated pasture approached 0% of the area, and intake and milk production declined. Grazing management strategies for lucerne should allocate pasture to lactating dairy cows to achieve horizontal utilisations approaching 0% for proportion of ungrazed, uncontaminated pasture to maximise intake and production. Secondary grazing herds or mechanical methods should be used to remove residual pasture to the ideal height for pasture regrowth.

Effect of quantity and source of rumen nitrogen on the efficiency of microbial protein synthesis in steers consuming tropical forage

Low values for the efficiency of microbial protein synthesis (EMPS) in cattle consuming tropical forages are related to low rumen degradable crude protein (RDP) intakes. This study examined the effect on the EMPS of the quantity and source of nitrogen (N) supplied to the rumen of eight entire and four rumen-fistulated Brahman steers consuming mature tropical grass hay (57.3 g crude protein/kg DM). Four treatment diets were fed in a Latin square design and included a basal diet of mature pangola grass (Digitaria eriantha) hay (control) and hay plus supplements estimated to provide 150 g RDP/kg digestible organic matter intake (DOMI), as urea or casein, or 300 g RDP/kg DOMI as casein. The EMPS was only increased (P < 0.05) above that for the control diet (167 vs 123 g microbial crude protein (MCP)/kg DOMI) when RDP was provided at the highest rate of 293 g/kg DOMI. This increase was also associated with an ~4-fold increase in the concentration of NH3-N (277 vs 73 mg/L) and of branched-chain volatile fatty acids (44 vs 10 mmol/mol of total volatile fatty acids) in rumen fluid of the steers. However, the source of rumen degradable N (urea or casein) had no effect on the EMPS (109–115 g MCP/kg DOMI) when supplied at ~150 g RDP/kg DOMI. There was no effect of treatment on in vivo neutral detergent fibre digestibility (599 g/kg DM) or the rate (0.037/h) or extent (potential degradable fraction: 636 g/kg OM) of in sacco disappearance of pangola grass hay. In addition, rumen particle dilution rate was unaffected by treatment (0.022/h) and rumen fluid dilution rate, although showing some treatment differences (0.048–0.062/h), was poorly correlated with EMPS. It was concluded that only high amounts of RDP supply to the rumen, in the form of true protein, resulted in increased EMPS whereas at the lower intakes of RDP formulated to achieve EMPS in the range suggested in the feeding standards (130–170 g MCP/kg DOMI) there was no difference in providing the RDP as non-protein N or degradable-protein.

Supplementation of cattle fed tropical grasses with microalgae increases microbial protein production and average daily gain

A series of 3 experiments were conducted to evaluate the use of microalgae as supplements for ruminants consuming low-CP tropical grasses. In Exp. 1, the chemical composition and in vitro protein degradability of 9 algae species and 4 protein supplements were determined. In Exp. 2, rumen function and microbial protein (MCP) production were determined in steers fed speargrass hay alone or supplemented with , , , or cottonseed meal (CSM). In Exp. 3, DMI and ADG were determined in steers fed speargrass hay alone or supplemented with increasing amounts of NPN (urea combined with ammonia sulfate), CSM, or . In Exp. 1, the CP content of and (675 and 580 g/kg DM) was highest among the algae species and higher than the other protein supplements evaluated, and sp. had the highest crude lipid (CL) content (198 g/kg DM). In Exp. 2, supplementation increased speargrass hay intake, the efficiency of MCP production, the fractional outflow rate of digesta from the rumen, the concentration of NHN, and the molar proportion of branched-chain fatty acids in the rumen fluid of steers above all other treatments. acceptance by steers was low and this resulted in no significant difference to unsupplemented steers for all parameters measured for this algae supplement. In Exp. 3, ADG linearly increased with increasing supplementary N intake from both and NPN, with no difference between the 2 supplements. In contrast, ADG quadratically increased with increasing supplementary N intake from CSM. It was concluded that and may potentially be used as protein sources for cattle grazing low-CP pastures.

Responses to various protein and energy supplements by steers fed low-quality tropical hay. 1. Comparison of response surfaces for young steers

Response curves were established for different supplements, offered at intakes ranging from 0 to 20 g/kg liveweight (W).day to young Bos indicus crossbred steers fed low-quality Rhodes grass (Chloris gayana) hay ad libitum in two pen experiments. Supplements included protein meals of varying rumen-degradability (cottonseed meal (CSM) or fishmeal), as well as ‘energy sources’ comprising grains of high and low ruminal starch degradability (barley and sorghum) and a highly fermentable sugar source (molasses), with all diets adjusted for rumen-degradable nitrogen and mineral content. Unsupplemented steers gained 0.08 and 0.15 kg/day, in Experiments 1 and 2, respectively. Growth of steers increased linearly with intake of ‘energy source’ supplements in increasing order of molasses, sorghum and barley (all differences P < 0.05). Steer growth rate also increased linearly with fishmeal, albeit over a narrow intake range (0–4.1 g/kg W.day), whereas the response with CSM was asymptotic, showing a steep response at low intake before levelling at ~1.2 kg/day. All supplement types were associated with a linear reduction in hay intake by the steers (energy substitution) where the reduction was greater (P < 0.05) for barley and molasses (not different) than for sorghum (P < 0.05), and for fishmeal compared with CSM (P < 0.05). In concurrent metabolism studies with the same rations, organic matter digestibility of the total ration (561–578 g/kg DM, unsupplemented) was increased linearly by barley and molasses (both P < 0.05) but was unaffected by CSM and sorghum supplements. The efficiency of microbial protein synthesis in steers increased linearly, from 91 g microbial crude protein/kg digestible organic matter (unsupplemented), in both molasses and CSM-supplemented steers, with the trend for a higher response to molasses (P = 0.05), and appeared most closely related to digestible organic matter intake. The response curves from these studies provide the practical framework upon which to formulate rations for cattle grazing low-quality forages.

Efficiency of rumen microbial protein synthesis in cattle grazing tropical pastures as estimated by a novel technique

The efficiency of microbial protein synthesis (EMPS) in cattle grazing a range of tropical pasture types was examined using a new method of intra-jugular infusion of chromium–EDTA to estimate urinary excretion of purine derivatives. Seven pasture types were studied in south-eastern Queensland, Australia, over a 13-month period. These included native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii) studied in the early wet, the wet–dry transition and the dry season; introduced tropical grass (C4) pasture (Bothriochloa insculpta) in the mid-wet season; two introduced tropical legume species (C3; Lablab purpureus and Clitoria ternatea); and the temperate-grass (C3) pasture, ryegrass (Lolium multiflorum). There was a large range in EMPS across pasture types, with a range of 26–209 g microbial crude protein per kilogram digestible organic matter intake (DOMI). Estimated rumen-degradable protein (RDP) supply (42–525 g/kg DOMI) was the major factor associated with EMPS across the range of pasture types studied. EMPS in steers grazing all tropical grass pastures was low (&lt;130 g/kg DOMI) and limited by RDP supply. Negative linear relationships (P &lt; 0.05) between EMPS and concentrations of both neutral detergent fibre and acid detergent fibre in extrusa were evident. However, non-fibre carbohydrate in extrusa, total non-structural carbohydrate concentration in plucked pasture leaf, rumen fluid and particle dilution rate, protozoal concentration in rumen fluid and rumen fluid pH were not correlated with EMPS. It was concluded that EMPS was well below 130 g microbial crude protein per kilogram DOMI when cattle grazed unfertilised, tropical grass pastures in south-eastern Queensland and that RDP was the primary limiting nutrient. High EMPS was associated with a very high RDP, vastly in excess of RDP requirements by microbes.

Responses to various protein and energy supplements by steers fed low-quality tropical hay. 2. Effect of stage of maturity of steers

Dose response curves to various supplements were established in two pen-feeding experiments (Exp1 and Exp2) with Bos indicus crossbred steers of two age groups (Young, 10–12 months; Old, 33–36 months) fed low-quality tropical grass hays ad libitum. Diets included supplements based on (Exp1) cottonseed meal (CSM; intake (as fed) 0–10 g/kg liveweight (W).day) and a barley mix (Bar; 0–20 g/kg W.day) and (Exp2) a molasses mix (MUP) and a Bar mix, both fed at 0–20 g/kg W.day. Urea was provided with the Bar mixes and urea/copra meal with the MUP mix. Growth rates of Young steers increased linearly with Bar and MUP supplements but asymptotically with CSM whereas those of Old steers increased asymptotically with all supplement types. With supplement intake expressed on a liveweight basis (g/kg W.day), responses were greater for both steer age groups with CSM compared with Bar (Young, P < 0.001; Old, P < 0.01) and Bar compared with MUP treatments (Young, P < 0.01; Old, P < 0.05). Furthermore, Old steers outperformed their Young counterparts with both CSM (P < 0.05) and Bar (P < 0.001) supplements fed in Exp1 and with Bar and MUP supplements (P < 0.01) fed in Exp2. When supplement intake was expressed in absolute terms (kg/day), growth responses were not different between age groups for different supplements except that Old steers had a higher daily W gain on Bar than their Young counterparts (P < 0.05). Intake of hay (W-corrected) was higher for Young compared with Old steers without supplement but was variably reduced for both steer groups with increasing supplement intake. The results of these experiments have implications for supplement formulation for steers at different stages of maturity grazing low-quality forages.

Immediate and residual effects of heat stress and restricted intake on milk protein and casein composition and energy metabolism

The effects of heat stress on dairy production can be separated into 2 distinct causes: those effects that are mediated by the reduced voluntary feed intake associated with heat stress, and the direct physiological and metabolic effects of heat stress. To distinguish between these, and identify their effect on milk protein and casein concentration, mid-lactation Holstein-Friesian cows (n = 24) were housed in temperature-controlled chambers and either subjected to heat stress [HS; temperature-humidity index (THI) ~78] or kept in a THI<70 environment and pair-fed with heat-stressed cows (TN-R) for 7 d. A control group of cows was kept in a THI<70 environment with ad libitum feeding (TN-AL). A subsequent recovery period (7 d), with THI<70 and ad libitum feeding followed. Intake accounted for only part of the effects of heat stress. Heat stress reduced the milk protein concentration, casein number, and casein concentration and increased the urea concentration in milk beyond the effects of restriction of intake. Under HS, the proportion in total casein of αS1-casein increased and the proportion of αS2-casein decreased. Because no effect of HS on milk fat or lactose concentration was found, these effects appeared to be the result of specific downregulation of mammary protein synthesis, and not a general reduction in mammary activity. No residual effects were found of HS or TN-R on milk production or composition after THI<70 and ad libitum intake were restored. Heat-stressed cows had elevated blood concentrations of urea and Ca, compared with TN-R and TN-AL. Cows in TN-R had higher serum nonesterified fatty acid concentrations than cows in HS. It was proposed that HS and TN-R cows may mobilize different tissues as endogenous sources of energy.

Spirulina (Spirulina platensis) algae supplementation increases microbial protein production and feed intake and decreases retention time of digesta in the rumen of cattle

Cattle consuming pastures low in protein have low liveweight gain due to low rumen degradable protein (RDP) supply and thus low microbial crude protein (MCP) production and efficiency of MCP production [EMCP, g MCP/kg digestible organic matter (DOM)]. Nitrogen supplements can increase MCP production and EMCP of cattle grazing low protein pastures. The objective of this study was to compare the effects of supplementation with a non-protein-N source (NPN), in this case urea and ammonium sulfate (US), with a single-cell algal protein source (Spirulina platensis), on intake, microbial protein supply and digestibility in cattle. Nine cannulated Bos indicus steers [initial liveweight 250.1 ± 10.86 (s.d.) kg] were fed Mitchell grass hay (Astrebla spp; 6.1 g N, 746 g NDF/kg DM) ad libitum and were supplied with increasing amounts of US (0, 6, 13, 19 and 33 g US DM/kg hay DM) or Spirulina 0, 0.5, 1.4, 2.5 and 6.1 g Spirulina DM/kg W.day in an incomplete Latin square design. The response of MCP production and EMCP to increasing amounts of the two supplements was different, with a greater response to Spirulina evident. The MCP production was predicted to peak at 140 and 568 g MCP/day (0.64 and 2.02 g MCP/kg W.day) for the US and Spirulina supplements, respectively. The highest measured EMCP were 92 and 166 g MCP/kg DOM for the US and Spirulina treatments at 170 and 290 g RDP/kg DOM, respectively, or a Spirulina intake of 5.7 g DM/kg W.day. Increasing RDP intake from US and Spirulina resulted in an increase in Mitchell grass hay intake and rumen NH3-N concentration and reduced the retention time of liquid and particulate markers and digesta DM, NDF and lignin in the rumen with greater changes due to Spirulina. Total DM intake peaked at a Spirulina supplement level of 4.6 g Spirulina DM/kg W.day with a 2.3-fold higher DOM intake than Control steers. Rumen NH3-N concentrations reached 128 and 264 mg NH3-N/L for the US and Spirulina treatments with a significant increase in the concentration of branched-chain fatty acids for the Spirulina treatment. The minimum retention time of liquid (Cr-EDTA; 23 and 13 h) and particulate (Yb; 34 and 22 h) markers in the rumen were significantly lower for Spirulina compared with US and lower than unsupplemented animals at 24 and 34 h for Cr-EDTA and Yb, respectively. Spirulina could be provided safely at much higher N intakes than NPN supplements. The results suggest that, at an equivalent RDP supply, Spirulina provided greater increases than US in MCP production, EMCP and feed intake of Bos indicus cattle consuming low protein forage and could also be fed safely at higher levels of N intake.

Effect of varying the proportion of molasses in the diet on intake, digestion and microbial protein production by steers

The present experiment was conducted to determine the efficiency of microbial protein production in the rumen and intake by cattle fed high-molasses diets. Intake and microbial crude protein (MCP) production were measured along with the concentration of rumen ammonia-nitrogen (N) and volatile fatty acids (VFA), pH and the rate of digestion of roughage in the rumen. Eight Brahman crossbred steers weighing 211 ± 19.3 (± s.d.) kg were used in a double 4 × 4 Latin square design. Steers were allocated to one of four total mixed rations: control (pangola hay only), 25M (25% molasses/urea mix + 75% hay), 50M (50% molasses/urea + 50% hay), and 75M (75% molasses/urea + 25% hay). The production and efficiency of production of MCP (EMCP) of the diet increased quadratically as the level of molasses in the diet increased. The EMCP from the molasses/urea mix was estimated as 166 g MCP/kg digestible organic matter (DOM), a relatively high value. Intake of dry matter (DM) and DOM increased quadratically, reaching a peak when molasses was ~50% (as fed) of the ration. Digestibility of DM increased quadratically and that of neutral detergent fibre decreased linearly with increasing level of molasses in the diet. Molasses inclusion in the diet had no effect on rumen pH, ammonia and VFA concentration in the rumen fluid, plasma urea-N, urine pH or ruminal fractional outflow rate of ytterbium-labelled particles and Cr-EDTA. It was concluded that a diet with a high level of molasses (>50%) and supplemented with adequate N had high EMCP, and that low MCP production was not a factor limiting intake or performance of cattle consuming high-molasses diets.

Predicting feed intake and liveweight gain of Ongole (Bos indicus) cattle in Indonesia

We evaluated the precision and accuracy of equations from the Australian Ruminant Feeding Standards (ARFS) and the Large Ruminant Nutrition System (LRNS) in predicting the performance of Ongole (Bos indicus) cattle under Indonesian conditions. A database was constructed using information from 121 cattle in five different pen-feeding experiments. Cattle included mature cows and growing bulls, and they were fed a range of diets commonly used by Indonesian farmers. We compared observed and predicted dry matter intake and daily liveweight gain. Model predictions were evaluated for precision and accuracy using mean bias, mean square prediction error and regression of observed against predicted values. Across all experiments, the LRNS provided the better estimates of intake and growth. While both models included animal age, sex, weight and body condition score, the LRNS provided better estimates of metabolisable energy requirements for maintenance of liveweight, feed quality and efficiency of energy utilisation. The LRNS model also better accounted for environmental conditions by including correction factors for minimum night temperature and relative humidity, in addition to average daily temperatures. Based on our results, the LRNS model appears suitable for use in Indonesian beef-production systems.

Evaluation of village-based diets for increasing the weight and condition of Ongole (Bos indicus) and Bali (Bos javanicus) cows in Indonesia

The aim of this research was to compare different feeding strategies to increase the weight and body condition score (BCS) of Ongole (Bos indicus) and Bali (Bos javanicus) cows kept by smallholder farmers in Indonesia. Thirty mature, non-pregnant, non-lactating Ongole and Bali cows were allocated to one of three treatment groups in a randomised block design, with five cows of each breed per treatment. The experiment consisted of a 2-week adaptation period and 24-week experimental period. In Weeks 1–17 cows were offered one of three diets; rice straw ad libitum plus gliricidia (Gliricidia sepium) at 3 g DM/kg W.day (RSG3), rice straw at 10 g DM/kg W.day plus gliricidia at 10 g DM/kg W.day, or elephant grass (Pennisetum purpureum) ad libitum. During Weeks 18–24 the cows previously fed the RSG3 diet were offered rice straw ad libitum plus rice bran at 10 g DM/kg W.day. There was no change to diets of the other groups. Feeding untreated rice straw plus gliricidia or rice bran only provided enough metabolisable energy for maintenance of both breeds. Ongole and Bali cows consuming elephant grass gained weight at 0.25 and 0.33 kg/day, respectively. However, even at these higher growth rates it would still take ~4–6 months for cows to gain 1 BCS unit (1–5 scale). Maintaining a good BCS would be a better management strategy.

Metabolisable energy requirements for maintenance and gain of liveweight of Bali cattle (Bos javanicus)

A series of liveweight gain (LWG), feed and water intake and digestibility experiments were conducted across eastern Indonesia. Thirty-six datasets of LWG, feed and water intake, and diet characteristics were used to determine the nutritional requirements of growing Bali cattle fed a wide range of diets that varied in crude protein content and apparent dry matter digestibility. Regression of average daily LWG against estimated metabolisable energy (ME) intake was conducted, and the ME requirements for maintenance of liveweight (LW, 0 kg/day) and LWG were determined. It was estimated that the ME required to maintain LW of this class of Bali cattle, across the range of diets evaluated, was 0.47 MJ ME/kg LW0.75.day and that 34 MJ ME was required for each kg LWG, or 29 g LWG/MJ ME. The relationship between estimated ME intake and LWG was not affected by the crude protein content of the diet. The data demonstrate that ME requirements for maintenance of LW of Bali cattle are comparable with values for other cattle species, but that this class of Bali cattle is generally less efficient in the use of ME for LWG across the range of diets evaluated.

Digestion of forages in the rumen is increased by the amount but not the type of protein supplement

Three polyester bag experiments were conducted with fistulated Bos indicus steers to determine the effect of the amount and type of nitrogen (N) supplement on the digestion rate of forages different in quality. In Experiment 1, test substrates were incubated in polyester bags in the rumen of steers fed ryegrass, pangola grass, speargrass and Mitchell grass hays in a 4 by 4 Latin-square design. In Experiment 2, test substrates were incubated in polyester bags in the rumen of steers fed speargrass hay supplemented with urea and ammonium sulfate (US), branched-chain amino acids with US (USAA), casein, cottonseed meal, yeast and Chlorella algae in a 7 by 3 incomplete Latin-square design. In Experiment 3, test substrates were incubated in polyester bags in the rumen of steers fed Mitchell grass hay supplemented with increasing amounts of US or Spirulina algae (Spirulina platensis). The test substrates used in all experiments were speargrass, Mitchell grass, pangola grass or ryegrass hays. Digestion rate of the ryegrass substrate was higher than that of the speargrass substrate (P < 0.05) in Experiment 1. Supplementation with various N sources increased the degradation rate and effective degradability of all incubated substrates above that apparent in Control steers (P < 0.05; Experiment 2). Supplementation of US and Spirulina increased degradation rate and effective degradability of ryegrass, pangola grass and Mitchell grass substrates above that apparent in Control steers (P < 0.05; Experiment 3). However, there was no further response on digestion rate of the substrates in increasing supplementation levels either for US or Spirulina. In conclusion, rate of digestion was affected by forage physical and anatomical properties. Supplementation with various N sources increased rate of digestion when the Control forage ration was very low in N but once a minimum level of N supplementation was reached, irrespective of form of N or other potential growth factors, there was no further increase in rate of digestion.

Long-term growth of male and female Bali cattle fed Sesbania grandiflora

This study examined the long-term growth of male and female Bali cattle (Bos javanicus) fed a diet consisting solely of Sesbania grandiflora (sesbania) or sesbania with rice bran. Twelve male (71.6 ± 2.2 kg mean liveweight and standard error of the mean; LW) and six female (80.3 ± 2.8 kg LW) weaned Bali cattle, ~6 months of age at the commencement were used in this experiment. LW, wither height (WH), hip height and chest circumference (girth) were measured from ~6 to 27 months of age. Dry matter intake and the concentration of glucose, urea and insulin-like growth factor-1 in the plasma were measured at ~9, 18 and 27 months of age. There was no difference in LW gain of male and female Bali cattle between 6 and 18 months of age but males had a greater average LW gain (0.40 kg/day) than females (0.22 kg/day) between 18 and 27 months of age. Overall females displayed a curvilinear growth path in LW, WH and girth between 6 and 27 months of age, while males displayed a linear growth path in LW and girth but curvilinear in WH over the same age. Dry matter intake did not differ with stage of development or between male and female cattle. The plasma urea concentration declined in male Bali cattle with stage of development but was constant in female cattle across the experiment. The concentration of insulin-like growth factor-1 in the plasma increased with age and tended to be greater in male (268 ng/mL) than female (222 ng/mL) Bali cattle. In conclusion, Bali cattle display sexual dimorphism in growth after ~18 months of age, which is important to consider when developing feeding strategies across the full growth path.

Immediate, cumulative and residual effects of short- and long-term low plane of nutrition on milk protein and casein composition

Immediate and residual effects of two lengths of low plane of nutrition (PON) on the synthesis of milk protein and protein fractions were studied at the Mutdapilly Research Station, in south-east Queensland. Thirty-six multiparous Holstein-Friesian cows, between 46 and 102 days in milk (DIM) initially, were used in a completely randomised design experiment with three treatments. All cows were fed on a basal diet of ryegrass pasture (7.0 kg DM/cow.day), barley-sorghum concentrate mix (2.7 kg DM/cow.day) and a canola meal-mineral mix (1.3 kg DM/cow.day). To increase PON, 5.0 kg DM/cow.day supplemental maize and forage sorghum silage was added to the basal diet. The three treatments were (C) high PON (basal diet + supplemental silage); (L9) low PON (basal diet only) for a period of 9 weeks; and (L3) low PON (basal diet only) for a period of 3 weeks. The experiment comprised three periods (1) covariate – high PON, all groups (5 weeks), (2) period of low PON for either 3 weeks (L3) or 9 weeks (L9), and (3) period of high PON (all groups) to assess ability of cows to recover any production lost as a result of treatments (5 weeks). The low PON treatment periods for L3 and L9 were end-aligned so that all treatment groups began Period 3 together. Although there was a significant effect of L9 on yields of milk, protein, fat and lactose, and concentrations of true protein, whey protein and urea, these were not significantly different from L3. There were no residual effects of L3 or L9 on protein concentration or nitrogen distribution after 5 weeks of realimentation. There was no significant effect of low PON for 3 or 9 weeks on casein concentration or composition.

Liveweight gain and feed intake of weaned Bali cattle fed grass and tree legumes in West Nusa Tenggara, Indonesia

Two experiments were conducted with weaned entire male Bali cattle (Bos javanicus) between 6 and 12 months of age. A randomised block design was used in both experiments, which consisted of four treatments (diets), with five replicates (animals) per treatment. In both experiments, the average daily liveweight gain (LWG), feed and water intake and diet digestibility were determined over 8 or 10 weeks, with chest girth and wither height measured at the commencement and end of the experiments. In Experiment 1, the treatments were fresh native grass, native grass supplemented with fresh sesbania, fresh sesbania and fresh sesbania supplemented with rice bran. In Experiment 2, the treatments were sole diets of leucaena hay, sesbania hay, moringa hay or gliricidia hay supplemented with sesbania hay. In Experiment 1, animals fed sesbania supplemented with rice bran had higher DM intake than did animals fed the other three diets. DM digestibility (DMD) was significantly lower for weaners fed the native grass diet than for those fed the other diets. Animals fed sesbania or sesbania supplemented with rice bran had a higher LWG (0.34 and 0.43 kg/day, respectively) and estimated metabolisable energy (ME) intake (0.71 and 0.80 MJ of ME/kg W0.75.day, respectively) than did animals fed native grass alone (0.03 kg/day; 0.58 MJ of ME/kg W0.75.day) or native grass supplemented with sesbania (0.07 kg/day; 0.64 MJ of ME/kg W0.75.day). In Experiment 2, animals fed gliricidia hay had the lowest DM intake. DM intake of animals fed moringa hay was higher than that of animals fed gliricidia hay, but lower than the intake of animals fed sesbania hay or leucaena hay. DMD of the sesbania and leucaena hay diets was lower than that of the gliricidia and moringa hay diets. Animals fed leucaena and sesbania hays had a higher LWG (0.47 and 0.43 kg/day, respectively) and estimated ME intake (0.75 and 0.78 MJ of ME/kg W0.75.day, respectively) than did animals fed moringa hay (0.22 kg/day; 0.66 MJ ME/kg W0.75.day) or gliricidia hay supplemented with sesbania hay (0.0 kg/day; 0.48 MJ ME/kg W0.75.day). In conclusion, tree legumes can safely be fed to growing Bali cattle as the sole component of the diet and some of them will increase LWGs above that of native grasses, which are typically fed to Bali cattle in villages.

Rice straw, cassava by-products and tree legumes provide enough energy and nitrogen for liveweight maintenance of Brahman (Bos indicus) cows in Indonesia

The aim of this experiment was to test the effectiveness of two diets in increasing liveweight (LW) and body condition score (BCS) of Brahman cows in Indonesia. Diets were based on rice straw, with additional energy and nitrogen (N) provided in the form of onggok (a cassava by-product) plus urea or a tree legume. Thirty mature, non-pregnant, non-lactating Brahman crossbred cows (288 kg LW, BCS 2/5) were allocated to one of two treatment groups. Cows were kept in individual pens for 21 weeks and offered one of two diets; (1) urea-supplemented rice straw ad libitum plus 10 g onggok DM/kg LW.day, or (2) untreated rice straw ad libitum plus 5 g onggok DM/kg LW.day and 5 g Gliricidia sepium DM/kg LW.day. The urea supplement provided no advantages over using locally available N sources such as gliricidia, with both supplement types meeting the rumen-degradable N requirements of the cows. Cows on both diets gained weight at a similar rate (0.19 kg/day) for the first 15 weeks of the experiment. Liveweight gain in Weeks 16–21 was only 0.04 kg/day, despite an increase in total feed intake and energy content of the diets compared with Weeks 1–15. Liveweight of cows stabilised during Weeks 16–21 at 304 kg, BCS 2.2. While our results demonstrate that Brahman cows can maintain LW on rice straw-based diets, they may not be able to maintain a BCS sufficient for good reproduction rates (i.e. BCS 3 or higher on 1–5 scale). Better quality diets containing higher levels of energy are required for cows to gain and maintain a suitable BCS.

The liveweight gain response of heifers to supplements of molasses or maize while grazing irrigated Leucaena leucocephala/Digitaria eriantha pastures in north-west Australia

This experiment in the Ord River Irrigation area (ORIA) of north Western Australia evaluated the liveweight gain of cattle rotationally grazing leucaena (Leucaena leucocephala cv. Cunningham)/pangola (Digitaria eriantha cv. Steudel) pastures alone, or supplemented with four levels of molasses (1.25, 2.50, 3.75, 5.00 kg molasses/head.day, as fed or fresh weight basis) or two levels of cracked maize supplementation (0.75, 1.50 kg/head.day, as fed or fresh weight basis). Seventy Bos indicus cross heifers [~12 months of age, mean initial weight 252 ± 3.8 (s.e.) kg] were allocated to the seven treatments and two replicates of each treatment (five cattle per replicate plus five additional similar heifers) with the stocking rate set at 6.25 head/ha. The experiment was conducted over 106 days of the dry season (August–November). Each replicate paddock of 0.4 ha was rotationally grazed with 10 animals with a 7-day grazing period and a 21-day regrowth period for each rotation. The mean herbage mass, residual herbage mass and herbage allowance for the experiment were 3.78 t DM/ha, 3.07 t DM/ha and 7.32 kg DM/100 kg liveweight, respectively. Pangola contributed a mean of 0.79 of the herbage mass. There was a significant quadratic response of liveweight gain to level of molasses supplement (P < 0.0087) with an optimum liveweight gain of 1.08 kg/head.day at a supplement level of 2.65 kg molasses/head.day or 8.9 g/kg LW.day derived from the quadratic equation. The quadratic equation was: Liveweight gain = 0.763(±0.0644) + 0.241(±0.0658) * M – 0.046(±0.0126) * M2 (where M is level of molasses supplement kg/head.day). There was no significant response to level of maize supplement. There were no significant differences between treatments in the concentration of rumen ammonia N or volatile fatty acids or in the molar proportion of volatile fatty acids. It was concluded that molasses can be used effectively to increase the liveweight gain of cattle grazing leucaena/pangola pasture at a level of ~8.9 g/kg LW.day.

The effect of sucrose addition on intake of a tropical grass hay by sheep

Increasing levels of sucrose (15, 30, 45, and 60% of the total dry matter intake, DMI) were added to a Control diet of a tropical grass hay (pangola grass, Digitaria eriantha) to examine the effect on DMI and digestible organic matter intake (DOMI). A pelleted lucerne (Medicago sativa) diet provided a positive Control diet with a higher metabolisable energy intake. There were positive linear and quadratic effects of sucrose addition on DMI and DOMI, reflecting increasing values from Control to 45% sucrose, which then decreased for 60% sucrose. Intake values at 45% sucrose were equivalent to 49% (DMI) and 60% (DOMI) of those shown by animals fed on pelleted lucerne. At the same time there was a decrease in hay intake and neutral detergent fibre digestibility. Rumen concentration of butyric acid increased with sucrose addition. Eating pattern changed with increasing sucrose inclusion in that meals extended over the whole day rather than most food being consumed within 5 h as occurred with the high roughage diet. Intake of sucrose was similar for all diets by 5 h, but by 24 h high sucrose diets had resulted in a higher intake of sucrose. It was suggested that the underlying characteristics of the neutral detergent fibre present in the diet regulate intake by posing a limit, which cannot be overridden.

Liquid-phase denaturant gradient gel electrophoresis profiles of rumen bacteria from Brahman cross steers selected into two groups on the basis of post-weaning liveweight gain on low crude protein pasture

Two experiments were conducted to evaluate the relationship between rumen liquid-associated bacterial community structures and post-weaning liveweight gain (LWG) of Brahman crossbred steers. Bacterial diversity was assessed using denaturant gradient gel electrophoresis (DGGE). In Experiment 1, 16 steers were selected from a group of 100 steers by pairing steers with the same weaning weight, but different LWG 90 days after weaning (n = 8 highest growth, 0.21 ± 0.01 kg/day; and n = 8 lowest growth –0.07 ± 0.01 kg/day). Thereafter, steers were allocated to a 28-day pen study and fed Mitchell grass (Astrebla spp.) hay to examine DM intake and digestibility, rumen parameters and rumen microbial community in these two groups. Rumen fluid samples were taken by stomach tube 3 h after feeding on the last day of the pen phase. In Experiment 2, 12 pairs of weaned steers were selected from a group of 203 steers on the same basis as Experiment 1. The post-weaning LWG were 0.20 ± 0.03 and 0.02 ± 0.03 kg/day for the 12 highest and 12 lowest growth animals selected, respectively. Steers then grazed dry season Sabi grass (Urochloa mosambicensis) dominant pasture for 21 days, before rumen sampling 3 h after morning grazing by stomach tubing on the last day. In Experiment 1, there were no significant differences between the two groups in DM intake, digestibility, ruminal pH, total volatile fatty acid (VFA) concentration or the VFA proportion. In Experiments 1 and 2, rumen ammonia-N concentration was similar between LWG groups and there was no evidence of a relationship between liquid-phase DGGE profiles of rumen bacteria and high or low post-weaning LWG using multivariate analyses. Furthermore, the number of detected DGGE bands, the Shannon–Wiener and evenness indexes were not different between LWG groups. This DGGE analysis of the most abundant groups of rumen fluid-associated bacteria suggests that microbial populations were not related with the differences observed in post-weaning LWG within a group of weaners fed low crude protein diets.

Liveweight gain and feed intake of weaned Bali cattle fed a range of diets in Central Sulawesi, Indonesia

Three experiments were conducted to determine liveweight (W) gain and feed and water intake of weaned Bali cattle offered a range of feed types. In each experiment, 18 weaned entire male Bali cattle were allocated to three treatment groups in a completely randomised block design, with six replicates (animals) per treatment. The dietary treatments were: Experiment 1, native grass fed ad libitum, native grass supplemented with rice bran at 10 g dry matter (DM)/kg W.day and native grass supplemented with a mixture of rice bran and copra meal in equal proportions fed at 10 g DM/kg W.day; Experiment 2, elephant grass hay fed ad libitum, elephant grass supplemented with gliricidia at 10 g DM/kg W.day, and gliricidia fed ad libitum; and Experiment 3, corn stover fed ad libitum, corn stover supplemented with gliricidia at 10 g DM/kg W.day, and corn stover supplemented with rice bran/copra meal in equal amounts (w/w) at 10 g DM/kg W.day. Each experiment was 10 weeks in duration, consisting of a 2-week preliminary period for adaptation to diets and an 8-week experimental period for the measurement of W change, feed and water intake and digestibility of the diet. Growth rates of 6–12-month-old, entire male Bali cattle fed a range of local diets ranged from 0.10 and 0.40 kg/day. Lowest growth rates occurred when the cattle were given the basal diets of native grass (0.104 kg/day), elephant grass (0.174 kg/day) and corn stover (0.232 kg/day). With the addition of supplements such as rice bran, rice bran/copra meal or gliricidia to these basal diets liveweight gains increased to between 0.225 and 0.402 kg/day. Forage DM intake was reduced with these supplements by on average 22.6% while total DM intake was increased by an average of 10.5%. The growth rate on gliricidia alone was 0.269 kg/day and feed DM intake was 28.0 g/kg W.day. Water intake was not affected by supplement type or intake. In conclusion, inclusion of small quantities of locally available, high quality feed supplements provide small-holder farmers with the potential to increase growth rates of Bali calves from 0.1 to 0.2 kg/day, under prevailing feeding scenarios, to over 0.4 kg/day.

The level of tree legumes required to meet the maintenance energy requirements of Ongole (Bos indicus) cows fed rice straw in Indonesia

Improving the productivity and profitability of smallholder cattle enterprises in Indonesia requires greater and more efficient utilisation of underutilised feed resources such as rice straw. The experiment tested the hypothesis that an Ongole cow with low energy requirements can maintain weight (W) on a rice straw-based diet with the addition of a small amount of tree legumes. Thirty-two Ongole cross (Bos indicus) cows were allocated to one of four treatments in a randomised block design with eight cows per treatment. Cows were offered untreated rice straw ad libitum with four levels of tree legumes (0, 11, 21, and 42 g DM/kg W0.75.day) for 20 weeks. Feed intake was determined daily and liveweight was measured every second week. There was no difference in total feed intake between the treatment groups (P > 0.05). Intake of tree legumes was higher when more was offered (P < 0.05), but cows did not consume all of the legumes offered to them. The inclusion of tree legumes in the diet had no effect on organic matter digestibility, ME content of the diet, liveweight gain or estimated energy balance of the cows (P > 0.05). Rice straw alone contained insufficient ME and rumen-degradable N to meet the maintenance requirements of the cows. From the regression relating liveweight change and ME intake for all cows across all diets, the inclusion of tree legumes in the diet at ~12 g DM/kg W0.75.day or 2.8 g DM/kg W.day was enough to meet the energy requirements for maintenance of Ongole cows fed rice straw ad libitum.

Nutritional research to meet future challenges

Nutrition is a mature science with well established principles for energy, protein and mineral metabolism based on known metabolic pathways. The quantitative requirements are summarised within various international feeding standards and models. However, when these are applied to specific circumstances, especially in northern Australia, the response of the animal to nutrient supply does not always agree with that predicted from the feeding standards or the error of prediction is not sufficiently accurate for practical use. There is a need for the continual testing of these relationships within production systems. Molecular methods have the potential to discover new metabolic relationships within tissues and characterise the microbial ecology and its relationship to rumen function. Suitable problem models based on growth, meat quality, reproduction, milk and fibre production, and environmental consequences need to be identified. We suggest that production systems designed to meet market weight for age specifications, growth paths and compensatory growth, skeletal growth, parasites, fatty acid isomers, adaptation to low crude protein diets, rumen microbial ecology, epigenetics, remote data acquisition and animal management, greenhouse gas emission, and C balance of various production systems are important problem models, the research of which will benefit the future of the livestock industries in Australia.

Intake, retention time in the rumen and microbial protein production of Bos indicus steers consuming grasses varying in crude protein content

Feed intake, rumen function, microbial protein (MCP) production and the efficiency of MCP production were determined in steers fed four different forage hays varying markedly in crude protein content. Low quality tropical forage (speargrass and Mitchell grass) hays had lower crude protein content, higher neutral detergent fibre content and lower digestibility than a medium quality tropical forage (pangola grass) hay and a temperate forage (ryegrass) hay. Steers fed speargrass and Mitchell grass hays had lower MCP production (80 and 170 g MCP/day, respectively) and efficiency of MCP production [78 and 79 g MCP/kg digestible organic matter (DOM), respectively] than steers fed pangola grass (328 g MCP/day; 102 g MCP/kg DOM) and ryegrass (627 g MCP/day; 135 g MCP/kg DOM) hays, which was directly related to the supply of DOM and rumen degradable protein. Intake was greatest for ryegrass hay, followed by pangola grass, Mitchell grass and speargrass hays [17.6, 15.6, 10.1 and 5.5 g DM/kg W.day, respectively]. The retention time of DM in the rumen was 72.1, 47.7, 28.6 and 19.1 h for speargrass, Mitchell grass, pangola grass and ryegrass hays, respectively, with a similar trend apparent for the retention time of neutral detergent fibre, lignin, chromium-EDTA and ytterbium labelled digesta. The difference in the protein : energy ratio of absorbed substrates (measured as efficiency of MCP production) did not appear to account for all the differences in intake, nor did a purely physical mechanism.

Effect of the concentration of Spirulina (Spirulina platensis) algae in the drinking water on water intake by cattle and the proportion of algae bypassing the rumen

Spirulina, a freshwater microalgae, has previously been shown to increase the efficiency of microbial protein production in cattle fed hay with a low crude protein content. The present study was carried out to determine the effect of increasing the concentration of Spirulina in the drinking water on the intake of water and the amount of water containing Spirulina bypassing the rumen of cattle. Five rumen-cannulated steers were given a fixed amount of pangola grass hay (14 g DM/kg W.day–1) and water containing 0, 1, 2, 2.7 and 3.5% (w/w) Spirulina in an incomplete Latin square design. Water intake by the control steers (0% Spirulina) was 29.7 and 49.3 g/kg W for the first drinking event after it was made available and over 24 h, respectively. For steers receiving the algae, intake of water plus Spirulina increased linearly (P < 0.01) from 42.7 to 60.2 g/kg W during the first drinking event, as the concentration of Spirulina in the drinking water increased, but over 24 h was not affected by Spirulina concentration and averaged 74.4 g/kg W. The bypass of water through the rumen, as determined using chromium-EDTA as a marker, averaged 20.5 ± 1.2% and was not affected by the concentration of Spirulina in the drinking water. Increasing inclusion of Spirulina was associated with a decrease in rumen pH, an increase in urea concentration in blood serum, and an increase in ammonia-N concentration, propionate and branched-chain fatty acids, and a decrease in butyrate proportions in rumen fluid. Spirulina inclusion in the drinking water increased water intake and may provide a potential safe and inexpensive alternative to urea for extensively grazed ruminants.

Sampling requirements for predicting cattle diet quality using faecal near-infrared reflectance spectroscopy (F.NIRS) in heterogeneous tropical rangeland pastures

Faecal near-infrared reflectance spectroscopy (F.NIRS) provides predictive information on cattle diets and nutritional levels, useful for livestock management or for research purposes. Potential errors exist throughout the entire F.NIRS process, including the collection method. The accepted collection method involves aggregating equal amounts of faecal material from 5 to 15 animals, mixing and removing a single sample for analysis. The adequacy of this method was tested by collecting and analysing up to 70 samples from individual cattle in different paddocks. Two methods were used to determine sample size based on observed variability in dietary attributes. Variability of dietary non-grass material and crude protein content increased with paddock size, so required sample size also increased. For dietary F.NIRS predictions to be used for research, our results suggest from 20 to 51 samples are needed in small to large paddocks to accurately predict the proportion of dietary non-grass material, from 12 to 50 samples for crude protein content and from 6 to 34 samples for dry matter digestibility. Composite samples from 15 cattle provided representative means in less than 50% of the situations investigated using biologically significant precision levels, but would be adequate for management of animal nutrition. Analysis of individual samples provided additional measures of range and variability which were also informative.

Effect of treatment of cocoa-pods with Aspergillus niger on liveweight gain and cocoa-pod intake of Bali (Bos sondaicus) cattle in South-East Sulawesi

Cocoa-pods, a by-product of the cocoa industry, could potentially be used as a feed resource for ruminants in eastern Indonesia. However, little is known regarding the optimal amount to be included in the diet or the effect of treatment with Aspergillus niger on cocoa-pod quality. In this experiment the effect of rate of inclusion (0 or 10 g DM/kg liveweight.day or ad libitum) of A. niger-treated or untreated cocoa-pods in the diet on intake and liveweight gain of Bali cattle (Bos sondaicus) was investigated. Ad libitum intake of cocoa-pods was greater when they were treated with A. niger (17.1 ± 0.07 g DM/kg liveweight.day; mean ± s.e.m.) compared with untreated cocoa-pods (13.9 ± 0.19 g DM/kg liveweight.day) when offered as the sole component of the diet. The digestibility of A. niger-treated cocoa-pods (448.9 ± 23.7 g/kg) was not different to untreated cocoa-pods (422.9 ± 13.9 g/kg) when fed ad libitum, which was lower than native grass (527.2 ± 10.7 g/kg). Animals offered A. niger-treated cocoa-pods lost less liveweight than animals offered untreated cocoa-pods when offered ad libitum (–0.104 ± 0.02 and –0.280 ± 0.02 kg/day, respectively), and grew faster when included in the diet at 10 g DM/kg liveweight.day (0.233 ± 0.02 and 0.129 ± 0.02 kg/day, respectively). In conclusion, in areas where cocoa plantations exist, cocoa-pods may be a useful feed resource for ruminants when fed at low levels of inclusion in the diet. The treatment of cocoa-pods with A. niger will result in increased liveweight gain. However, it is unlikely such treatments will be adopted by small-holder farmers due to the increased requirements for inputs, such as time, labour, funds, equipment, and technical skills.

Chronic improvement of amino acid nutrition stimulates initiation of global messenger ribonucleic acid translation in tissues of sheep without affecting protein elongation

Initiation of mRNA translation and elongation of the polypeptide chain are 2 regulated processes responsible for the short-term postprandial acceleration of protein synthesis in animal tissues. It is known that a chronic increase in the absorptive supply of AA stimulates protein synthesis in ruminant animals, but effects on translation initiation and elongation are unknown. To determine whether initiation or elongation phases of global mRNA translation are affected by chronic elevation of AA supply, 24 ewe lambs of 25.9 +/- 2.5 kg of BW were randomly allocated to 4 treatment groups of 6 lambs each. All lambs received a basal diet of barley and hay at 1.2 times maintenance ME intake. Treatments were an intravenous (i.v.) saline infusion as a control, i.v. infusion of 6 essential AA (EAA; Arg, Lys, His, Thr, Met, Cys) for 10 d, i.v. infusion of the same EAA excluding Met and Cys (EAA-SAA) for 10 d, and an oral drench of fishmeal twice daily for 17 d. Fishmeal supplementation supplied an extra 719 mg of N x kg(-0.75) x d(-1) and N retention was increased 519 mg x kg(-0.75) x d(-1) over the control. The EAA treatment supplied an extra 343 mg of N x kg(-0.75) x d(-1) directly into the blood, and N balance was increased by 268 mg x kg(-0.75) x d(-1). Deletion of Met plus Cys from EAA had no effect on N balance. The results indicate that Met plus Cys did not limit body protein gain on the basal diet alone or the basal diet plus 6 AA. Protein fractional synthesis rates in liver, duodenum, skin, rumen, semimembranosus, and LM were measured by a flooding dose procedure using L-[ring-2,6-(3)H]-Phe. Ribosome transit times were estimated from the ratio of nascent to total protein-bound radioactivities. Fishmeal and EAA treatments had no effect on RNA, DNA, or protein contents of tissues, but fractional synthesis rate, translational efficiency, and concentrations of active ribosomes were consistently elevated. Ribosome transit time was not affected by long-term AA supply. We conclude that the chronic stimulation of protein synthesis by long-term i.v. infusion of EAA or supplementation with an undegradable protein source is brought about by an improvement in the rate of initiation of mRNA translation with no change in the rate of polypeptide chain elongation.

Protein elongation rates in tissues of growing and adult sheep

To identify the relative roles of translation initiation and elongation in the long term control of protein synthesis in ovine tissues, fractional synthesis rates (FSR) and ribosomal transit times (RTT) were measured in vivo in 24 ewe lambs at 3 levels of intake [maintenance (M), 1.5M, and 2M] and 8 mature ewes at 2M intake. After 17 to 25 d on treatment, animals were given an i.v. flooding dose of l-[ring-2,6-(3)H]phenylalanine and tissues were collected for analysis of radioactivity in free protein, total protein, and nascent ribosome-associated proteins. Ribosome transit time (the inverse of elongation rate) averaged 83, 393, 183, 241, 85, and 113 s for liver, duodenum, skin, rumen, semimembranosus, and LM, respectively. In response to an increased level of intake, protein FSR increased (P < 0.01) in all tissues except rumen and was attributed to greater translational efficiency. There was no effect (P > 0.50) of intake on RTT in these tissues, and the estimated proportion of ribosomes attached to and actively translating mRNA was increased (P < 0.07), indicating that an upregulation of initiation was responsible for the greater FSR. Mature ewes exhibited lower (P < 0.10) protein FSR in all tissues compared with lambs, which was related to a decline in the RNA:protein ratio in all tissues except for liver and duodenum. In all tissues but liver and semimembranosus, RTT increased (P < 0.10) with age. The lower elongation rate was not considered to have influenced the protein synthetic rate, but it caused an increase in the proportion of ribosomes actively translating mRNA. It is anticipated that this work will provide direction to future studies of the molecular mechanisms of chronic FSR control.

Ruminal protein degradability of a range of tropical pastures

The rumen degradability parameters of the diet selected by two to four oesophageal-fistulated Brahman steers grazing a range of tropical pastures were determined by incubation of extrusa in nylon bags suspended in the rumen of rumen-fistulated (RF) Brahman steers. The effective protein degradability (Edg) was determined by measuring the rate of disappearance of neutral detergent insoluble nitrogen (NDIN) less acid detergent insoluble nitrogen (ADIN) in the incubated extrusa. Six to eight RF steers also grazed each of the pastures along with the oesophageal-fistulated steers, to allow determination of key rumen parameters and rumen particulate matter fractional outflow rates (FOR). The seven pastures studied included: native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii), studied in the early wet (NPEW), the wet/dry transition (NPT) and the dry (NPD) seasons; introduced tropical grass (C4) pasture (Bothriochloa insculpta), studied in the mid wet season (BB); the introduced tropical legumes (C3), Lablab purpureus (LL) and Clitoria ternatea (BP); and the temperate grass (C3) pasture, ryegrass (Lolium multiflorum, RG). Using the measured particle FOR values in calculations, the Edg estimates were very high for both C4 and C3 species: 0.82–0.91 and 0.95–0.98 g/g crude protein (CP), respectively. Substitution of an assumed FOR (kp = 0.02/h) for the measured values for each pasture type did not markedly affect estimates of Edg. However, C4 tropical grasses had much lower effective rumen degradable protein (ERDP) fractions (23–66 g/kg DM) than the C3 pasture species RG and LL (356 and 243 g/kg DM, respectively). This was associated with a lower potential degradability and degradation rate of organic matter (OM) in sacco, lower in vitro organic matter digestibility (IVOMD) and CP concentrations in the extrusa, and lower ammonia-N and branched-chain fatty acid concentrations in rumen fluid for the tropical grasses. As tropical grass pastures senesced, there was a decline in Edg, the ERDP and rumen undegradable protein (UDP) fractions, the potential degradability and degradation rate of OM and the IVOMD. These results provide useful data for estimating protein supply to cattle grazing tropical pastures.

Marker concentration patterns of labelled leaf and stem particles in the rumen of cattle grazing bermuda grass (Cynodon dactylon) analysed by reference to a raft model

Large (>1600 μm), ingestively masticated particles of bermuda grass (Cynodon dactylon L. Pers.) leaf and stem labelled with 169Yb and 144Ce respectively were inserted into the rumen digesta raft of heifers grazing bermuda grass. The concentration of markers in digesta sampled from the raft and ventral rumen were monitored at regular intervals over approximately 144 h. The data from the two sampling sites were simultaneously fitted to two pool (raft and ventral rumen–reticulum) models with either reversible or sequential flow between the two pools. The sequential flow model fitted the data equally as well as the reversible flow model but the reversible flow model was used because of its greater application. The reversible flow model, hereafter called the raft model, had the following features: a relatively slow age-dependent transfer rate from the raft (means for a gamma 2 distributed rate parameter for leaf 0.0740 v. stem 0.0478 h-1), a very slow first order reversible flow from the ventral rumen to the raft (mean for leaf and stem 0.010 h-1) and a very rapid first order exit from the ventral rumen (mean of leaf and stem 0.44 h-1). The raft was calculated to occupy approximately 0.82 total rumen DM of the raft and ventral rumen pools. Fitting a sequential two pool model or a single exponential model individually to values from each of the two sampling sites yielded similar parameter values for both sites and faster rate parameters for leaf as compared with stem, in agreement with the raft model. These results were interpreted as indicating that the raft forms a large relatively inert pool within the rumen. Particles generated within the raft have difficulty escaping but once into the ventral rumen pool they escape quickly with a low probability of return to the raft. It was concluded that the raft model gave a good interpretation of the data and emphasized escape from and movement within the raft as important components of the residence time of leaf and stem particles within the rumen digesta of cattle.

A comparison of the excretion rate of endogenous purine derivatives in the urine of Bos indicus and Bos taurus steers

Estimates of microbial crude protein (MCP) production by ruminants, using a method based on the excretion of purine derivatives in urine, require an estimate of the excretion of endogenous purine derivatives (PD) by the animal. Current methods allocate a single value to all cattle. An experiment was carried out to compare the endogenous PD excretion in Bos taurus and high-content B. indicus (hereafter, B. indicus) cattle. Five Holstein–Friesian (B. taurus) and 5 Brahman (> 75% B. indicus) steers (mean liveweight 326 ± 3.0 kg) were used in a fasting study. Steers were fed a low-quality buffel grass (Cenchrus ciliaris; 59.4 g crude protein/kg dry matter) hay at estimated maintenance requirements for 19 days, after which hay intake was incrementally reduced for 2 days and the steers were fasted for 7 days. The excretion of PD in urine was measured daily for the last 6 days of the fasting period and the mean represented the daily endogenous PD excretion. Excretion of endogenous PD in the urine of B. indicus steers was less than half that of the B. taurus steers (190 µmol/kg W0.75.day v. 414 µmol/kg W0.75.day; combined s.e. 37.2 µmol/kg W0.75.day; P < 0.001). It was concluded that the use of a single value for endogenous PD excretion is inappropriate for use in MCP estimations and that subspecies-specific values would improve precision.

Glucose Metabolism in Steers Receiving High Fibre Diets and Glucose Infusion Into Abomasum

Abstract dalam bentuk hard copy

Elevation of feed intake in parasite-infected lambs by central administration of a cholecystokinin receptor antagonist

The role of cholecystokinin (CCK) in modulating feed intake depression in parasite-infected lambs was investigated using CCK receptor antagonists (L364-718 and loxiglumide). Four experiments were carried out using ewe lambs infected with 4000 Trichostrongylus colubriformis larvae/d or non-infected controls (n8, live weight 25 kg). Animals were fed daily on a nutritionally complete pelleted diet and had free access to water. In the first experiment, infected and non-infected animals were injected subcutaneously with CCK antagonist (100 micrograms L364-718) or carrier alone as a single dose. In the second experiment, CCK antagonist (loxiglumide: 0, 5, 10 or 20 mg/kg live weight) was injected into a jugular vein immediately before feeding. In the third experiment, animals were infused continuously with the CCK antagonist (loxiglumide; 10 mg/kg per h) for 10 min before feeding and for the first 2 h of feeding. In the final experiment, lambs were fitted with an indwelling cerebral ventricular cannula and infused with a CCK antagonist (loxiglumide, 162 micrograms/min), CCK agonist (CCK-8, 2.5 pmol/min), loxiglumide plus CCK-8 or sterile saline solution alone via the cannula for 30 min before feeding and for the first 60 min of feeding. In all the experiments short-term feed intake was recorded at 10 and 15 min intervals for the first and second hours of feeding respectively, then at hourly intervals for the remainder of the 8 h recording period. Peripheral injection with L364-718 or loxiglumide did not elevate feed intake in either the infected or non-infected animals. However, feed intake was increased (P < 0.05) in the short term by central infusion of loxiglumide, this effect being greater in the infected animals and apparently due to an elevation in intake during the second hour of feeding. CCK-8 depressed short term feed intake only in the infected animals (P < 0.05). Total daily feed consumption was not influenced by any of the pharmacological agents. The results indicate an involvement of central CCK receptors in regulation of feed intake depression following gastrointestinal parasitism of sheep and the possibility of a similar role in non-infected sheep. They do not support the singular importance of a peripheral action of CCK in determining satiety.

Predictions of food intake in ruminants from analyses of food composition

Equations used to predict intake by cattle from some chemical or physical characteristic of food were examined. The equations are empirical or mechanistic in nature. Mechanistic equations are not used widely, usually only in a research context. The input to mechanistic models requires too much time to quantify to be used routinely. Empirical relationships form the basis of most feeding standards and are based on a wide variety of prescribed characteristics (digestibility, chemical composition, etc.), but the underlying principle is a relationship between intake and digestibility. Equations are modified to take account of feed types, animal weight and physiological state, rumen modifiers, hormone implants, environmental conditions, and whether grazing or hand fed. Quite significant differences exist between the equations in the intakes they predict in response to variation in weight, breed type, and feed digestibility. Equations can be very precise in their prediction when used with feed types and breed types on which they are based. Near infrared reflectance (NIR) offers the most potential for long-term development of equations. At present, NIR is used largely to determine chemical composition because of speed of operation, but long-term storage of data is simple, allowing further associative relationships to be developed readily. More sophisticated statistical procedures being employed to improve the precision of the relationships between intake and prescribed characteristics of food and NIR will be vitally important as they enable extra parameters to be incorporated at no extra cost or time for analysis.

Method for close arterial infusion of the lactating mammary gland

A simple method of catheterizing an artery which supplies the ipsilateral side of the mammary gland of a high-producing dairy cow is described. The preparation allows infusion of the mammary gland with nutrients or endocrine factors locally, but does not require general anaesthesia or deep surgical dissection. Following a preliminary experiment involving infusion of acetate, the catheters were removed and the cows returned to the milking herd. Key words: Cow, mammary gland, arterial infusion, acetate

Protein and energy utilization by ruminants at pasture

Low live weight gain of cattle in the wet season of tropical areas was identified as a major limitation to achieving annual growth rates from tropical pasture systems sufficient to meet new market specifications of young animals of high carcass weight. Both protein and energy are limiting nutrients for growth. Net transfer of feed protein to the intestines is often not complete, and losses occur with grasses and legumes when CP content exceeds 210 g of CP/kg of digestible OM. This protein loss is important because a collation of experimental data indicated that cattle consuming low- and high-quality pasture and silage-based diets all responded to extra protein. The response was less for the higher-quality forage. The role of legumes in supplying this protein was investigated and, unless legumes can increase total DMI by at least 30%, they will not supply sufficient intestinal protein to increase live weight gain by about 300 g/d. The problem with legumes and some grasses is the loss of protein from the rumen, and increasing energy supply to the rumen, either through improved digestibility or energy supplements, is a strategy that could be used to reduce this. Strategies to increase the proportion of escape protein would be successful, but incorporation of lowly degradable protein fractions into legumes may be more difficult because of the level of expression of these protein fractions required for a significant live weight gain response. Cattle entering the wet season usually exhibit compensatory growth and are exposed to high ambient temperatures and often to high humidity. Intestinal protein above that stipulated in feeding standards may be beneficial in these circumstances, and more emphasis should be placed on the ability of legumes to supply protein postruminally. At present the protein delivery capacity of agronomically competitive legumes seems to be inadequate for the higher growth rates required in production systems, and supplements of energy and protein will be needed to achieve these higher targets until new cultivars appear.

The intake, digestion and protein degradation of grazed herbage by early-weaned lambs

Sixty-four intact lambs and twenty-four lambs fitted with a duodenal cannula were weaned at 6 weeks of age and grazed pure species swards of either lucerne (Medicago sativa), white clover ((Trifolium repens), ryegrass (Lolium perenne) or prairie grass (Bromus catharticus) for 6 weeks. Intake and duodenal digesta flow were estimated when lambs were 8 and 12 weeks of age. Lambs grazing the two legume species grew at a similar rate, as did lambs grazing the two grass species. Legumes promoted a 38% higher growth rate than grasses. The higher growth rate of lambs grazing legumes was associated with a 36% higher digestible organic matter intake (DOMI; 29.5 and 21.7 g/kg body-weight per d for legume and grass respectively) and a 33% higher duodenal non-ammonia-nitrogen (NAN) flow (1.22 and 0.92 g/kg body-weight per d respectively). There was no species difference in the site of organic matter digestion; on average 0.56 of DOMI was apparently digested in the rumen and 0.77 of DOMI was truly digested in the rumen. There was no difference in duodenal NAN flow, relative to DOMI (average, 43 g/kg) or to organic matter apparently digested in the rumen (80 g/kg). Similarly, there was no difference in microbial N flow relative to duodenal NAN (0.50 g/g) and organic matter apparently (41 g/kg) or truly (29 g/kg) digested in the rumen. It was concluded that the higher growth rates achieved by lambs grazing legumes were due to higher intakes which increased the total quantity of nutrients supplied despite more protein being lost in the rumen of lambs consuming legumes.

Nitrogen transactions along the digestive tract of lambs concurrently infected with Trichostrongylus colubriformis and Ostertagia circumcincta

Twelve lambs, paired on the basis of live weight, were cannulated in the abomasum, in the proximal jejunum approximately 4 m distal to the pylorus and in the terminal ileum. Six were infected with 3000 Trichostrongylus colubriformis and 3000 Ostertagia circumcincta larvae each day for 18 weeks and the remainder were pair-fed to individual infected lambs. All animals were offered ryegrass (Lolium perenne)-white clover (Trifolium repens) pasture, cut daily. Dry matter (DM) intake, live weight, faecal egg concentration, plasma pepsinogen and plasma protein concentrations were measured weekly. During weeks 7 and 17 after commencement of infection, the flow of digesta along the gastrointestinal tract was measured together with enteric plasma loss and true digestion and absorption of 125I-labelled albumin in the small intestine. DM intake was depressed by parasitism, being 1331, (SE 70), 423 (SE 32) and 529 (SE 52) g/d during weeks 3, 7 and 17 respectively. The flow of nitrogen at the proximal jejunum and in faeces was increased by parasitism during week 7 and at the abomasum and ileum during week 17. Plasma protein-N loss (g/d) into the gastrointestinal tract was 0.68 (SE 0.091) and 1.97 (SE 0.139) during week 7, and 0.85 (SE 0.158) and 1.96 (SE 0.396) during week 17, in control and infected sheep respectively. True digestion and absorption of albumin in the proximal small intestine, the site of infection, was very low (mean 0.08) and was not affected by parasitism. Between the abomasum and terminal ileum absorption of albumin was high (mean 0.87) and again was not affected by parasitism. It was calculated that of the total increase in endogenous protein passing from the ileum tract as a result of infection, plasma protein comprised only a small percentage (10-36%). The major proportion of digestion and absorption of protein occurred in the distal small intestine beyond the site of infection and was not affected by infection.

The effect of post-ruminal infusion of protein or energy on the pathophysiology of Trichostrongylus colubriformis infection and body composition in lambs

The effect of post-ruminal infusion of protein or energy on the pathophysiology of Trichostrongylus colubriformis infection and body composition in lambs was investigated using the comparative slaughter technique. Of 52 Dorset DownxCoopworth wether lambs (mean body weight 30.5, s.e. 0.44 kg), 8 comprised an initial slaughter group (IC), 36 were infected daily, per os, with 3000 Trichostrongylus colubriformis larvae per animal, and the remainder (C) were parasite-free controls. Groups of 12 infected animals were given either a continuous infusion (via abomasal catheter) of 50.4 g/day crude protein as sodium caseinate (PI), glucose (EI) in isocaloric amounts to PI, or a solution containing P and Na at the same rate as the caseinate infusions (SI). Uninfected controls (C) were also infused with this solution. Animals were slaughtered after 6 and 12 weeks for estimation of worm count and body composition. All animals were offered, ad libitum, meadow hay (118 g crude protein/kg dry matter (DM); 930 g organic matter/kg DM; 0.65 organic matter digestibility). DM intake of infected animals decreased by approximately 22% in PI and EI and by 32% in SI animals. Mean total metabolizable energy (ME) intake during the experiment (inclusive of infusions) was C, 0.607; PI, 0.687; EI, 0.704; SI, 0.617, s.e.d. 0.0308 MJME (kg W)-0.75 day-1. Nitrogen retention in infected sheep was increased fourfold by protein infusion and twofold by energy infusion. The rate of energy retention was reduced by infection, increased by protein infusion but only partly by energy infusion. Protein infusion reduced mean faecal egg output and mean total parasite count. Increased endogenous plasma loss into the gastrointestinal tract was similar in all infected groups. It was concluded that a major limiting factor in efficient food utilization in animals with gastrointestinal nematode infections is a parasite-induced protein rather than energy deficiency, possibly the result of increased endogenous protein losses into the gastrointestinal tract. The debilitating effect of internal parasites could be markedly reduced by increasing duodenal protein supply.

Theoretical considerations in the estimation of rumen fractional outflow rate from various sampling sites in the digestive tract

The digesta markers 103ruthenium phenanthroline (Ru-P) and 51Cr-EDTA were continuously infused into the rumen of young lambs offered clover hay ad lib. indoors or grazing pure species swards of either lucerne (Medicago sativa), white clover (Trifolium repens), ryegrass (Lolium perenne) or prairie grass (Bromus catharticus). Following the cessation of infusion the fractional outflow rate (FOR) of markers from the rumen was estimated from the rate of decline of marker concentration in rumen and abomasal digesta (Expt 1), abomasal digesta and faeces (Expt 2) and duodenal digesta and faeces (Expt 3). Estimates of FOR from the rumen were similar when based on rumen and abomasal sampling but estimates from abomasal and duodenal sampling were significantly higher than those from faeces. A simulation of a two-compartment model with variable FOR was performed to calculate faecal excretion curves following continuous marker infusion or the administration of a single marker dose into the rumen. Analysis of the descending portion of these theoretical faecal excretion curves yielded values of FOR from the rumen which differed from the values entered in the equations. The magnitude of the difference depended on the ratio of the values of FOR from the caecum and rumen entered in the equation. This suggested that the experimental variation observed in these young lambs was caused by the high FOR from the rumen in relation to the FOR from the caecum-large intestine.

The effects of a concurrent infection of Trichostrongylus colubriformis and Ostertagia circumcincta on calcium, phosphorus and magnesium transactions along the digestive tract of lambs

Twelve lambs, paired on the basis of live weight, were cannulated in the abomasum, proximal jejunum and terminal ileum. Six were infected with 3000 T. colubriformis and 3000 O. circumcincta larvae per day for 18 weeks. The other six lambs were pair-fed to the infected lambs. All animals were offered fresh ryegrass and white clover pasture, cut daily. Dry matter intake, live weight and plasma Ca, P and Mg concentrations were measured throughout the experiment. During weeks 7 and 17 post-infection, digesta flow along the gastrointestinal tract of infected and control animals was measured. Parasitism depressed dry matter intake by 60 per cent and was associated with a reduction in retention of Ca, P and Mg in both infected and control animals. During weeks 7 and 17, parasitism increased the flow of Ca past the proximal jejunum and, during week 17, the flow of P past the terminal ileum. Increased endogenous Ca and P losses, together with a net reduction in absorption of Ca and P, were associated with depressed plasma Ca and P concentrations. These findings, together with evidence of reduced addition of P to anterior regions of the tract, indicate induced Ca and P deficiency. There was evidence for compensatory absorption of Ca and P in the large intestine and distal small intestine, respectively. Magnesium metabolism was apparently not affected by parasitism.