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.