Rate of passage of digesta in sheep. 4. Passage of marker through the alimentary tract and the biological relevance of rate-constants derived from the changes in concentration of marker in faeces

Effect of Brosimum alicastrum Foliage on Intake, Kinetics of Fermentation and Passage and Microbial N Supply in Sheep Fed Megathyrsus maximus Hay

An experiment was carried out to assess the effect of the incorporation of sun-dried foliage of Brosimum alicastrum into rations based on hay of Megathyrsus maximus on intake, rumen fermentation, kinetics of passage, microbial nitrogen supply to the small intestine, apparent digestibility in Pelibuey hair sheep. Four rations were randomly allotted to four rumen-cannulated lambs (BW = 37.4 ± 4.9 kg) using a 4 × 4 Latin square design to assess the effect of increasing levels (0, 15, 30 and 45% DM basis) of foliage of Brosimum alicastrum on a basal ration of M. maximus. Organic matter intake and water consumption increased linearly (p < 0.01) with increasing levels of B. alicastrum in the ration. The rate and potential extent of rumen fermentation of OM and CP of B. alicastrum were 10.6%/h and 86.6% and 11.4%/h and 95.2%, respectively, but no effect (p > 0.05) was found on the potential rumen degradation of DM (40.2%) or on the rate of degradation of DM (0.033%/h) of M. maximus, although a positive effect was found in the rumen degradation rate of NDF (p < 0.05). VFA and ammonia concentration in the rumen and the rate of passage of solids and liquids through the rumen (k1) increased linearly (p < 0.01) with increasing levels of B. alicastrum. Rumen pH was not affected by the incorporation of B. alicastrum (p > 0.05). Microbial nitrogen supply to the small intestine (p < 0.001), apparent digestibility of dry matter (p < 0.01) and NDF (p < 0.05) of the rations were also significantly increased as a result of the incorporation of B. alicastrum foliage. Results from this experiment suggest that the foliage of Brosimum alicastrum can be readily incorporated at around 30% of the ration of dry matter in hair sheep with beneficial effects on feed intake, rate of passage and microbial N supply to the lower tract.

Individual differences in digesta retention and their relation to chewing in cattle-A pilot investigation

While information on individual differences in digesta mean retention time (MRT) might be interesting when selecting phenotypes for digestive efficiency, MRT measurements are prohibitively labour-intensive for large-scale application. Therefore, more easily measured proxies of MRT might be helpful. We used the opportunity of an experiment applying saliva stimulant in cattle to investigate the effect of different individual chewing behaviour on fluid and particle MRT with a consistent diet. Four non-lactating cattle (670-850 kg body mass [BM]) were used in a 4 × 4 Latin square design, treated with the saliva stimulant pilocarpine in dosages of 0, 1, 2.5 and 5 mg/kg BM per day. The cattle were fed hay with dry matter intake (DMI) assigned according to their metabolic body weight. MRT in the whole gastrointestinal tract (GIT), the reticulorumen (RR) and the distal tract were measured using Co-EDTA, Cr-mordanted fibre and La-mordanted fibre as markers representing fluid, small particles (2 mm) and large particles (1 cm), respectively. The chewing behaviour was measured via noseband pressure sensor and expressed as chewing frequency (chews per time) and chewing intensity (chews per DMI), both for total chewing (ingestion plus rumination) and rumination chewing alone. The animals differed considerably in chewing behaviour and MRT measures. BM did not show a significant effect on chewing behaviour and MRT measures, though it tended to negatively correlated to total chewing intensity. Chewing intensity exerted a significant negative influence on MRT of fluid and particles in the RR, which was not the case for chewing frequency. Chewing frequency showed a significant relationship with MRT of large particles in the GIT. We suggest that chewing behaviour could influence MRT in two ways: (i) by affecting saliva production via the masticatory-salivary reflex and subsequently, the fluid inflow to the RR; (ii) by contributing to particle size reduction. Should the link between chewing behaviour and MRT be corroborated in larger studies, chewing measures, with their large interindividual variation, could emerge as an easy-to-measure proxy for MRT characteristics.

Trichostrongylus colubriformis infection damages intestine brush board cells and could negatively impact postabsorptive parameters of Santa Ines lambs

This study aimed to evaluate histological, digestive and postabsorptive physiological parameters in Santa Ines lambs infected with Trichostrongylus colubriformis and fed different levels of phosphorus. Therefore, eighteen Santa Ines, castrated male, six-month old, healthy lambs (initial body weight 22.4 ± 2.7 kg) were distributed in one of four treatments arranged in a 2 × 2 split-plot arrangement: Sufficient dietary P level and uninfected (SPui; n = 4), Sufficient dietary P level and infected (SPi; n = 5), Deficient dietary P level and uninfected (DPui; n = 4), Deficient dietary P level and infected (DPi; n = 5). Infected lambs received, orally, a single pulse dose of 40.000 T. colubriformis infective larval stage (L3). Animals were fed Tifton 85 hay (Cynodon ssp.; 60%), and cassava meal and maize gluten meal (40%). Measurement of nutrient apparent digestibility and nitrogen metabolism were performed in individual metabolic stalls. To achieve the trial results, it was measured methane emissions in respiratory chambers, urine purine derivatives, ruminal short-chain fatty acids (SCFA), histological cuts of duodenal mucosal tissues and passage rates fluxes, analyzed by external (Yb, Cr, and Co) and internal (iNDF) markers. Statistical procedures were performed in R studio. The fixed main effects of treatment and the interactions were tested by ANOVA, and means compared by Duncan's test at 5% significance. Apparent digestibility was not affected by treatments, however, nitrogen retained decreased (P < 0.01) and urinary nitrogen losses increased (P < 0.01) in infected animals. Small intestine digesta content, empty segment weight, and length were higher in infected animals (P < 0.05). Passage rate was not majorly affected by infection or dietary P levels. Methane emissions, SCFA concentrations, and purine derivative excretion were also not affected by treatments. Regarding the histology, the vilosity weight (P < 0.05), and crypt depth (P < 0.01) decreased in infected animals. In conclusion, T. colubriformis infection can damage intestinal mucosa and affect nitrogen metabolism, but did not affect the digesta transit, and nutrient digestibility. The P dietary levels did not promote any modification in GIT physiological parameters tested in this study.

Effect of induced saliva flow on fluid retention time, ruminal microbial yield and methane emission in cattle

Both in vitro and animal studies indicated that a higher dilution rate is related to a more efficient microbial synthesis and a lower methane (CH₄ ) yield. The latter could be a consequence of the former, as an increase in microbial cell synthesis offers an alternative hydrogen sink competing with methanogenesis. To test this assumption in live animals, we applied a saliva stimulant, pilocarpine, to modify liquid flow rate in cattle. Four non-lactating cows (750 ± 71 kg) were fed forage only (restricted to constant intake) in a 4 × 4 Latin square design with oral doses of 0, 1, 2.5 and 5mg pilocarpine/kg body weight and day. We quantified feed and water intake, ruminal and total tract mean retention time (MRT) of solute and particle markers, ruminal microbial yield (via urinary purine bases or metabolic faecal nitrogen), CH₄ emission, digestibility, chewing behaviour, reticular motility and rumen fluid parameters. The effect of induced saliva flow was evident by visibly increased salivation and water intake. Increasing the pilocarpine dosages resulted in a linearly decreased MRT of fluid and small particles (p < 0.001 and p< 0.05, respectively) and methane yield as related to digested DM (p < 0.05), the latter at a magnitude of 5%. No effect of treatment was found on ruminal microbial yield estimated via purine derivates. Metabolic faecal N as an indicator of microbial growth linearly correlated with pilocarpine dosages (p < 0.05). No significant relationship was found between pilocarpine dosages and large particle MRT, nutrient digestibility, ruminal pH and short-chain fatty acids. In conclusion, different from some in vitro studies, there was little indication of a reciprocal effect of CH₄ and microbial biomass production in cows fed a forage-only diet.

Stocking Rate Has No Confounding Effect on the Use of Internal and Inert Markers to Predict Botanical Composition, Diet Quality, Degradability and Passage Rate Kinetics in Sheep

Simple Summary

Internal markers are components of diets recovered to different degrees in faeces of animals. These feed components maybe helpful in predicting diet selection, nutrient intake and digestibility in animals. The development of sustainable grazing management and practices to prevent the depletion of natural grasslands as a result of overgrazing depends on the knowledge of feed intake, chemical and botanical composition of diets selected and consumed by ruminants. Determination of the botanical composition of diets selected by free ranging ruminants by visual observation is time consuming and tedious, while the use of oesophageal cannulated animals is invasive and impairs animal welfare. Therefore, it is imperative to use non-invasive methods, such as internal markers to predict feed preferences and composition of diets that ruminants consume. However, it is unclear if the accuracy of results obtained using internal markers is confounded by other factors, such as stocking rate, which is expected to determine the availability and botanical composition of pasture, which, in turn, may exert its influence on the diet selected and consumed by grazing animals. The findings of this study, however, showed that stocking rates did not affect diet selection and nutrient intake in sheep, while a combination of internal markers can be used to estimate the quality of diet selected by animals under cafeteria feeding conditions, regardless of the stocking rate used. Thus, the use of modified acid detergent fibre, acid insoluble ash and acid detergent lignin contents in feeds achieved high accuracy and precision in estimating diets selected by sheep. This approach serves as a proof of concept that these markers can be also used in free ranging animals.

Abstract

This study investigated if there is any confounding effect of stocking rate on the use of internal markers to determine and predict the dietary ingredient composition, dry matter intake (DMI) and digestibility of diets consumed by sheep. Fifteen sheep were randomly allocated to stocking rate treatments of one (SR1), two (SR2), four (SR4) and eight (SR8) sheep per pen (space allowance: 31.04 m², 15.52 m², 7.76 m² and 3.88 m² per sheep, respectively) and fed ad libitum maize stover, sorghum stover and veld hay by supplying 110% of previous day’s intake. Sheep were rotated across the treatments in four periods of 10 days. The proportion of feeds selected and total DMI were similar across all stocking rate treatments. However, diets selected by sheep in SR2 had the highest digestibility compared to other treatments. The prediction of the effective degradability of dry matter using acid detergent fibre content achieved an accuracy of 84.6%. A combination of crude protein and neutral detergent fibre contents achieved 63% accuracy in the prediction of the rate of degradation of feeds. The use of acid insoluble ash (AIA) as an internal marker to predict nutrient intake, digestibility, DMI and dietary ingredient intake accounted for 84.3%, 81.2%, 53.0% and 64.1% of the variation, respectively. The predictions of dietary feed proportions and nutrient quality selected obtained with least squares procedure using a combination of modified acid detergent fibre (MADF), acid detergent lignin (ADL) and AIA accounted for 81.0% and 72.4% of the variation, respectively. In conclusion, regardless of the different stocking rate tested in this study, a combination of MADF, ADL and AIA as internal markers can be used to estimate diet and nutrient selection by sheep using the least squares procedure. Hence, these markers can be used to predict ingredient composition of diet, diet and nutrient selection, nutrient intake and digestibility in free ranging animals.

Evaluation of source of corn silage and trace minerals on rumen characteristics and passage rate of Holstein cows

The effects of source of corn silage and trace mineral on rumen fermentation, turnover, and particle passage rates were evaluated with 8 ruminally cannulated Holstein cows averaging 83 (standard error = 5) days in milk in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments and 28-d periods. The diets consisted (dry basis) of 55% conventional (CON) or brown midrib-3 (BM3) corn silage, 2% chopped wheat straw, and 43% grain mix with either sulfate (STM) or hydroxy (HTM) source of Cu, Zn, and Mn trace minerals. The targeted supplemental amount of Cu, Zn, and Mn was 194, 1,657, and 687 mg/d, respectively. The dietary treatments were (1) CON-STM, (2) CON-HTM, (3) BM3-STM, and (4) BM3-HTM. Dietary nutrient composition of BM3 diets averaged 32.1% amylase neutral detergent fiber on an organic matter basis (aNDFom) and 6.9% undigested neutral detergent fiber at 240 h of in vitro fermentation (uNDF240om; % of dry matter), and CON diets averaged 36.2% aNDFom and 8.6% uNDF240om (% of dry matter). Data were summarized by period and analyzed as a replicated Latin square design with fixed model effects for corn silage, trace mineral, corn silage and trace mineral interaction, period within replicated square, and replicated square using the MIXED procedure of SAS (version 9.4, SAS Institute Inc., Cary, NC). Cow within replicate was a random effect. Daily mean, standard deviation, minimum, and maximum for rumen pH were unaffected by corn silage or trace mineral source. Cows fed the CON diets had greater rumen acetate percentage than cows fed the BM3 diets (65.7 vs. 64.7 molar %). In contrast, cows fed the BM3 diets had greater rumen propionate percentage than cows fed the CON diets (21.4 vs. 20.4 molar %). Total volatile fatty acid concentration was lower for cows fed STM versus HTM in BM3 diets, but not for the cows fed the CON diets. Cows fed the BM3 diets had faster turnover rate and shorter turnover time for uNDF240om than cows fed the CON diets (3.12 vs. 2.86%/h and 33.3 vs. 36.5 h, respectively). Cows fed the BM3 diets had a faster passage rate of small and medium corn silage neutral detergent fiber particles than cows fed the CON diets (5.73 vs. 5.37%/h and 4.74 vs. 4.31%/h, respectively). We observed a corn silage by source of trace mineral interaction on organic matter and uNDF240om rumen pool size and organic matter turnover. Overall, source of corn silage had a pronounced influence on rumen dynamics presumably related to greater in vitro neutral detergent fiber digestibility and lower uNDF240om content of BM3 corn silage that allowed for faster turnover of indigestible neutral detergent fiber and greater passage rate of corn silage particles. In contrast, the source of trace mineral had much less significant effects on rumen fermentation, turnover, and particle passage rates. Corn silage-based diets intended to enhance rumen fiber fermentation, turnover, and passage are more affected by source and digestibility of neutral detergent fiber than source of dietary trace minerals.

Effect of calcium oxide and soybean hull addition to feedlot diets containing dried distillers grains and corn stover on steer performance, carcass characteristics, and digestibility

The objective of this study was to determine the effect of soybean hulls (SBH) and/or calcium oxide (CaO) on rumen pH, digestibility, and performance of steers fed diets containing dried distillers grains with solubles (DDGS). In experiment 1, Angus × Simmental steers (n = 112, body weight [BW] = 364 ± 7.8 kg) were allotted to 1 of 4 diets arranged as a 2 × 2 factorial and placed in 16 pens (7 steers/pen, 4 pens/treatment, and 28 steers/treatment). Factors were SBH (0% or 30% of diet dry matter [DM]) and CaO (0% or 1%) inclusion. Basal diets contained 20% corn stover, 30% DDGS, and 4% supplement. Diets with SBH contained 14.1% or 15.0% corn and diets without SBH contained 43.9% or 44.8% corn. In experiment two, four steers (BW = 510 ± 9.8 kg) were allotted to a 4 × 4 Latin square (21 d periods) to determine the effects of CaO and SBH on ruminal pH, volatile fatty acid (VFA), nutrient digestibility, and digestion kinetics. Statistical analyses were conducted using the MIXED procedure of SAS. In experiment 1, BW did not differ among treatments (P ≥ 0.46). Overall carcass-adjusted gain did not differ due to SBH or CaO inclusion (P ≥ 0.13); however, there was an interaction (P = 0.01) where CaO improved gain in steers fed no SBH, but not in steers fed SBH. Steers fed SBH consumed more DM than steers not fed SBH (P = 0.02) and an interaction tended to occur (P = 0.06) where CaO increased dry matter intake in steers fed no SBH, but not in steers fed SBH. Calcium oxide increased hot carcass weight and yield grade (interaction; P ≤ 0.04) and tended to increase fat thickness (interaction; P = 0.08) in steers fed no SBH, but not in steers fed SBH. Dressing percentage, longissimus muscle area, % kidney, pelvic, heart fat, and marbling score did not differ among treatments (P ≥ 0.14). Total VFA concentrations were greater with SBH inclusion and with CaO addition (P < 0.01). Digestibility of DM, neutral detergent fiber (NDF), and acid detergent fiber (ADF) was greater with CaO addition (P ≤ 0.04) and NDF and ADF digestibility were greater with SBH inclusion (P < 0.001). Inclusion of SBH did not affect (P ≥ 0.26) rate of digestion (k d) or passage (k p). Addition of CaO tended to increase mean retention time (P = 0.09). An interaction between SBH inclusion and CaO addition occurred for k d (P = 0.01), where CaO increased k d in steers fed SBH, but decreased k d when steers were fed no SBH. Total N excretion tended to be lower with SBH inclusion and CaO addition (P = 0.07). In conclusion, CaO enhances performance of cattle fed corn, DDGS, and corn stover diets, but not when corn is partially replaced by a fiber-based energy feed.

Accuracy of methane emissions predicted from milk mid-infrared spectra and measured by laser methane detectors in Brown Swiss dairy cows

Since heritability of CH₄ emissions in ruminants was demonstrated, various attempts to generate large individual animal CH₄ data sets have been initiated. Predicting individual CH₄ emissions based on equations using milk mid-infrared (MIR) spectra is currently considered promising as a low-cost proxy. However, the CH₄ emission predicted by MIR in individuals still has to be confirmed by measurements. In addition, it remains unclear how low CH₄ emitting cows differ in intake, digestion, and efficiency from high CH₄ emitters. In the current study, putatively low and putatively high CH₄ emitting Brown Swiss cows were selected from the entire Swiss herdbook population (176,611 cows), using an MIR-based prediction equation. Eventually, 15 low and 15 high CH₄ emitters from 29 different farms were chosen for a respiration chamber (RC) experiment in which all cows were fed the same forage-based diet. Several traits related to intake, digestion, and efficiency were quantified over 8 d, and CH₄ emission was measured in 4 open circuit RC. Daily CH₄ emissions were also estimated using data from 2 laser CH₄ detectors (LMD). The MIR-predicted CH₄ production (g/d) was quite constant in low and high emission categories, in individuals across sites (home farm, experimental station), and within equations (first available and refined versions). The variation of the MIR-predicted values was substantially lower using the refined equation. However, the predicted low and high emitting cows (n = 28) did not differ on average in daily CH₄ emissions measured either with RC or estimated using LMD, and no correlation was found between CH₄ predictions (MIR) and CH₄ emissions measured in RC. When individuals were recategorized based on CH₄ yield measured in RC, differences between categories of 10 low and 10 high CH₄ emitters were about 20%. Low CH₄ emitting cows had a higher feed intake, milk yield, and residual feed intake, but they differed only weakly in eating pattern and digesta mean retention times. Low CH₄ emitters were characterized by lower acetate and higher propionate proportions of total ruminal volatile fatty acids. We concluded that the current MIR-based CH₄ predictions are not accurate enough to be implemented in breeding programs for cows fed forage-based diets. In addition, low CH₄ emitting cows have to be characterized in more detail using mechanistic studies to clarify in more detail the properties that explain the functional differences found in comparison with other cows.

Digestibility and Retention Time of Coastal Bermudagrass (Cynodon dactylon) Hay by Horses

Simple Summary

Longer retention of forages with increased fiber concentrations may be a compensatory digestive strategy in horses. We investigated the digestive characteristics of bermudagrass hay, a prominent warm-season grass in the southeast United States that has greater fiber concentrations than other common forages fed to horses. The morphological structure and photosynthetic pathway of warm-season grasses differ from cool-season grasses and legumes which may have important impacts on equine digestion and digesta transit through the gastrointestinal tract. The retention time of Coastal bermudagrass was longer than alfalfa or orchardgrass hay. The digestibility of Coastal bermudagrass decreased with increasing maturity, but the fiber digestibility of alfalfa and orchardgrass was similar to the earliest maturity of Coastal bermudagrass hay. The chemical composition of the plant cell wall influences diet digestibility and is a major difference between warm-season and cool-season forages. The increased retention time of Coastal bermudagrass allows for microbial fermentation to occur longer, adapting to more difficult-to-digest plant cell walls in warm-season forages. The decrease in diet digestibility when horses consume warm-season forages can be reduced by feeding early maturity forage, by harvesting hay at an earlier stage of growth or managing pastures in a vegetative state.

Abstract

Bermudagrass (Cynodon dactylon) and other warm-season grasses are known for their increased fiber concentrations and reduced digestibility relative to cool-season grasses and legumes. This study investigated the digestive characteristics and passage kinetics of three maturities of Coastal bermudagrass hay. A 5 × 5 Latin square design experiment was used to compare the digestion of five hays: alfalfa (Medicago sativa, ALF), orchardgrass (Dactylis glomerata, ORCH), and Coastal bermudagrass harvested at 4 (CB 4), 6 (CB 6), and 8 weeks of regrowth (CB 8). Horses were fed cobalt-ethylenediaminetetraacetic acid (Co-EDTA) and ytterbium (Yb) labeled neutral detergent fiber (NDF) before an 84-h total fecal collection to determine digesta retention time. Dry matter digestibility was greatest for ALF (62.1%) and least for CB 6 (36.0%) and CB 8 diets (36.8%, SEM = 2.1; p < 0.05). Mean retention time was longer (p < 0.05) for Coastal bermudagrass (particulate 31.3 h, liquid 25.3 h) compared with ORCH and ALF (28.0 h, SEM = 0.88 h; 20.7 h, SEM = 0.70 h). Further evaluation of digesta passage kinetics through mathematical modeling indicated ALF had distinct parameters compared to the other diets. Differences in digestive variables between forage types are likely a consequence of fiber physiochemical properties, warranting further investigation on forage fiber and digestive health.

Alkali addition and roughage inclusion effect on performance and carcass characteristics of feedlot steers fed diets containing 60% dried distillers grains with solubles

Three experiments were conducted to determine the effectiveness of calcium hydroxide (Ca(OH)₂) addition and roughage inclusion on digestibility, performance, and carcass characteristics of steers fed 60% dried distillers grains with solubles (DGS). Statistical analyses for studies were conducted using the MIXED procedures of SAS. In experiment 1, 48 steers (353.5 ± 7.55 kg) were allotted to individual pens and fed 1 of 3 diets (dry matter [DM] basis) containing 60% dried DGS, 20% corn silage, and 4% supplement with: 1) 14.5% corn and no Ca(OH)₂; 2) 14% corn and 2% Ca(OH)₂; and 3) 14.5% additional corn silage and no Ca(OH)₂. Steers fed Ca(OH)₂ consumed the least (P = 0.03) and steers fed added corn silage consumed the most and had the least gain:feed (P = 0.02). Gain and carcass quality were not affected by treatment (P ≥ 0.48). In experiment 2, 112 steers (375.3 ± 19.25 kg) were allotted to pens (four pens per treatment; seven steers per pen) arranged as a 2 × 2 factorial (roughage × Ca(OH)₂) and fed one of four diets (DM basis) containing 60% dried DGS, 17% corn silage, and 4% supplement with: 1) 17.5% corn silage and no Ca(OH)₂; 2) 17% corn silage and 2% Ca(OH)₂; 3) 17.25% corn stover and no Ca(OH)₂; and 4) 17% corn stover and 2% Ca(OH)₂. Added stover decreased average daily gain (ADG) compared to added corn silage (P = 0.04). Ca(OH)₂ increased ADG when steers were fed stover, but not when steers were fed only corn silage (P = 0.05; interaction). In experiment 3, six ruminally cannulated steers (initial body weight = 352 ± 14.8 kg) were randomly allotted to a 6 × 6 Latin square design to determine the effects of roughage inclusion (corn, corn silage, stover) and Ca(OH)₂ addition (0% or 2%) on ruminal characteristics. Feeding stover decreased total volatile fatty acid(s) (VFA) concentration and DM digestibility compared to corn silage or corn (P < 0.01), whereas Ca(OH)₂ resulted in greater total VFA concentrations and DM digestibility (P ≤ 0.02). Stover increased rate of DM degradation (K_d) and rate of particle outflow from the rumen (P ≤ 0.04) but decreased extent of DM digestion and mean retention time (P ≤ 0.02) compared to corn or silage. Ca(OH)₂ increased K_d (P < 0.01) and tended to increase (P = 0.06) liquid passage rate. In conclusion, added roughage did not improve performance of cattle fed 60% dried DGS. Ca(OH)₂ may decrease intake and maintain performance of cattle fed 60% dried DGS with corn silage as the roughage source and increases ADG when corn stover replaces a portion of the corn silage.

Effects of roughage quality, period of day and time lapse after meal termination on rumen digesta load in goats and sheep

OBJECTIVE

This study ascertained effects of roughage quality, period of day at meal termination and time lapse after feeding on digesta load in the rumen.

METHODS

Veld hay was untreated (poor roughage quality, PRQ), improved (improved roughage quality, IRQ) by treating with urea or semi-improved by spraying with urea (semi-improved roughage quality, SIRQ). Experiment 1a used four rumen fistulated sheep to determine in-sacco degradability. Twelve sheep (56.3±4.59 kg) were blocked by weight and randomly allocated to IRQ (n = 6) and PRQ (n = 6) to determine solid and liquid passage rates. In experiment 1b, nine sheep (37.6±9.34 kg) were blocked by weight and randomly allocated to IRQ (n = 4) and PRQ (n = 5) to determine digestibility. Sixteen sheep (36.47±9.46 kg) were blocked by body weight and randomly allocated to IRQ (n = 8) and PRQ (n = 8). Two sheep were slaughtered for each sampling time in each treatment (IRQ and PRQ) at 0, 6, 12, and 24 h after feeding to determine rumen load. In experiment 2, eighteen goats (25.4±9.08 kg) were blocked by weight and randomly allocated to IRQ (n = 6), SIRQ (n = 6), and PRQ (n = 6). Then all 18 goats were slaughtered soon after meal termination in the morning; afternoon and evening to determine the effect of period of day on rumen fill.

RESULTS

Rate of degradation and effective degradability were enhanced by improvement of roughage quality. Roughage quality had no effect on digestibility, but digestibility was higher in goats than sheep. Fractional passage rate of particles was higher for IRQ than PRQ, but similar for liquids. Digesta fractional clearance rates at 24 h after feeding were 0.018/h (IRQ) and 0.006/h (PRQ). Period of day had an influence on rumen load. Neutral detergent fibre load for goats were above 2.03 kg/100 kg body weight for all diet treatments.

CONCLUSION

Following starvation, passage rate had negligible effects on emptying of rumen load.

Effect of forage to concentrate ratio in complete diets offered to sheep on voluntary food intake and some digestive parameters

Twelve mature ewes were used to study the effect of forage: concentrate ratio in complete diets on voluntary intake and some digestive characteristics. Diets consisted of four combinations of chopped lucerne hay and a concentrate (390 g cracked barley grains, 440 g cracked maize grains and 170 g soya-bean meal per kg of concentrate) in the following proportions (fresh matter basis): 0·8:0·2 (C20), 0·6:0·4 (C40), 0·4:0·6 (C60) and 0·2:0·8 (C80). Diets were offered over two 42-day periods and, in each of them, three sheep received one of the four diets, with the restriction that no animal received the same diet in both periods. Chromium Ill-mordanted fibre was used as a marker to estimate passage rate of digest a and microbial nitrogen supply (MNS) was estimated from the urinary excretion of purine derivatives. The increase in the proportion of concentrate affected linearly (P< 0·05) the voluntary intake of food, the mean values being 36·8, 37·9, 36·3 and 30·0 g dry matter (DM) per kg live weight per day for C20, C40, C60 and C80 diets, respectively. Apparent digestibility of DM, organic matter (OM) and crude protein increased linearly (P< 0·01) with the proportion of concentrate in the diet, whereas that of cellulose evolved auadratically (P< 0·05), reaching a minimum value in the C80 diet. Digestible OM intake was unaffected (P> 0·05) by the proportion of concentrate in the diet. Both particulate passage rate from the rumen and through the caecum and proximal colon decreased linearly (P< 0·05) as concentrate proportion in the diet increased. MNS (g/day) was not affected (P> 0·05) by the diet, whereas its efficiency (g/kg digestible OM intake) tended (P< 0·10) to increase with the proportion of concentrate in the diet.

Effect of forage to concentrate ratio in the diet on ruminal fermentation and digesta flow kinetics in sheep offered food at a fixed and restricted level of intake

The effects of four diets differing in their for age: concentrate ratio (80:20, 60:40, 40: 60 and 20:80; g/100 g fresh matter) on rumen characteristics, digestibility and digesta flow kinetics were investigated. Alfalfa hay was used as forage and concentrate was composed of barley, soya-bean meal and maize. Diets were prepared by mixing all ingredients and offered to the animals as complete diets. Eight mature Merino sheep, each fitted with a rumen cannula, were offered 1·055 kg dry matter per day of the corresponding diet over two experimental periods. The daily evolution of ruminai pH, volatile fatty acids (VFA) and ammonia nitrogen (N) concentrations were measured. Digestibility was determined by total faecal collection and Cr and Co were used as markers to estimate digesta passage rates. Microbial nitrogen flow at the duodenum (MNDF) was estimated from the urinary excretion of purine derivatives (PD). The apparent digestibility of organic matter increased (P < 0·001) whereas that of all fibrous fractions decreased linearly (P < 0·05) as the proportion of concentrate in the diet increased. Rumen pH decreased linearly (P < 0·001) with increasing proportions of concentrate but total VFA concentrations were unaffected by changes in the diet (P > 0·05). Both liquid and solid digesta outflow rates from the rumen decreased quadratically (P < 0·01) as the proportion of concentrate in the diet increased. The urinary excretion of total N, urea-N and ammonia-N was unaffected (P > 0·05) by changes in the diet. In contrast, the daily urinary excretion of both allantoin and total PD increased quadratically (P < 0·05) with increasing proportions of concentrate. Consequently, the estimated MNDF increased linearly (P < 0·001) from 9·9 g/day on the high forage diet to 14·5 g/day on the high concentrate diet.

Albendazole in environment: faecal concentrations in lambs and impact on lower development stages of helminths and seed germination

Albendazole (ABZ), widely used benzimidazole anthelmintic, administered to animals enters via excrements into environment and may impact non-target organisms. Moreover, exposure of lower development stages of helminths to anthelmintics may also encourage the development of drug-resistant strains of helminths. In present project, the kinetics of ABZ (10 mg kg(-1) p.o.) and its metabolite (ABZ.SO, ABZSO2) elimination in faeces from treated Texel lambs were studied using UHPLC/MS/MS with the aim to find out their concentrations achievable in the environment. Consequently, the effect of these compounds on lower development stages of Barber's pole worm (Haemonchus contortus) and on germination of white mustard (Sinapis alba) seeds was evaluated. The results showed that ABZ concentrations in faeces excreted in 4-60 h after treatment were above the concentrations lethal for H. contortus eggs. Moreover, pre-incubation with sub-lethal doses of ABZ and ABZ.SO did not increase the resistance of H. contortus eggs and larvae to anthelmintics. On the other hand, concentrations of ABZ and ABZ.SO in faeces are so high that might have negative influence on non-target soil invertebrates. As neither ABZ nor its metabolites affect the germination of mustard seeds, phytoremediation could be considered as potential tool for detoxification of ABZ in the environment.

Effects of alternate day feeding of dried distiller's grains plus solubles in forage-fed steers on intake, ruminal fermentation and passage rates, and serum nonesterified fatty acid

Four ruminally and duodenally cannulated Holstein steers (BW = 449 ± 7.3 kg) were used to examine the effects of feeding either dried distiller's grains plus solubles (DG) or grass hay on alternate days (every other day) on intake, ruminal fermentation and passage rates, and serum NEFA in forage-fed steers. Steers were assigned to 1 of 4 dietary treatments in a 4 × 4 Latin square: 1) only hay (CON), 2) hay and 0.4% of BW as DG DM daily (DG7), 3) hay daily and 0.8% BW DG every other day (DG2), and 4) alternate day feeding of hay and 0.8% of BW as DG (DGA). Treatment periods consisted of 13 d of adaptation and 8 d of collecting digesta and blood. Over the entire collection period, DMI was decreased ( = 0.004) for DGA compared with other treatments (13.0 ± 0.8, 12.7 ± 0.8, 13.3 ± 0.8, and 10.9 ± 0.8 kg/d for CON, DG7, DG2, and DGA, respectively). Immediately after feeding on days supplement was fed to DG2 and DGA (supplemented days [SUP]), ruminal pH of DGA was less than other treatments but by the end of the day was greater than other treatments (treatment × time, < 0.001). At feeding time on nonsupplemented days (NSUP), ruminal pH of DGA steers was greater than other treatments but was similar (treatment × time, < 0.001) to DG2 and CON by 5 h after feeding. Total concentrations of VFA were similar ( = 0.09) among treatments on SUP; however, on NSUP, total VFA concentrations were least in DGA from feeding until 4 h after feeding (treatment × time, = 0.02). No differences ( ≥ 0.06) were observed among treatments for apparent ruminal, total intestinal, and total tract DM, OM, or CP digestibility. There were no differences ( = 0.36) in serum NEFA among treatments on SUP; however, on NSUP, steers fed DGA (209.5 ± 12.7 m) had greater ( < 0.01) NEFA compared with other treatments (84.4 ± 12.7, 88.0 ± 12.7, and 77.7 ± 12.7 m for CON, DG7, and DG2, respectively). The DGA feeding strategy influenced DMI and ruminal kinetics and circulating NEFA without impacting total tract digestibility.

Relative contribution of ruminal buffering systems to pH regulation in feedlot cattle fed either low- or high-forage diets

The relative contribution of ruminal short-chain fatty acid (SCFA) absorption and salivary buffering to pH regulation could potentially change under different dietary conditions. Therefore, the objective of this study was to investigate the effects of altering the ruminal supply of rapidly fermentable carbohydrate (CHO) on absorptive function and salivation in beef cattle. Eight heifers (mean BW±SD=410±14 kg) were randomly allocated to two treatments in a crossover design with 37-day periods. Dietary treatments were barley silage at 30% low forage (LF) or 70% high forage (HF) of dietary dry matter (DM), with the remainder of the diet consisting of barley grain (65% or 25% on a DM basis) and a constant level (5%) of supplement. The LF and HF diets contained 45.3% and 30.9% starch, and 4.1% and 14.0% physically effective fiber (DM basis), respectively. Ruminal pH was continuously measured from day 17 to day 23, whereas ruminal fluid was collected on day 23 to determine SCFA concentration. Ruminal liquid passage rate was determined on day 23 using Cr-ethylenediaminetetraacetic acid. Eating or resting salivation was measured by collecting masticate (days 28 and 29) or saliva samples (days 30 and 31) at the cardia, respectively. On days 30 and 31, the temporarily isolated and washed reticulo-rumen technique was used to measure total, and Cl--competitive (an indirect measure of protein-mediated transport) absorption of acetate, propionate and butyrate. As a result of the higher dietary starch content and DM intake, the ruminal supply of rapidly fermentable CHO, total ruminal SCFA concentration (118 v. 95 mM; P<0.001) and osmolality (330 v. 306 mOsm/kg; P=0.018) were greater in cattle fed LF compared with HF. In addition, feeding LF resulted in a longer duration (2.50 v. 0.09 h/day; P=0.02) and a larger area (0.44 v. 0.01 (pH×h)/day; P=0.050) that pH was below 5.5. There was no diet effect on total and Cl--competitive absorption (mmol/h and %/h) of acetate, propionate, butyrate and total SCFA (acetate+propionate+butyrate), but eating salivation was less (131 v. 152 ml/min; P=0.02), and resting salivation tended to be less (87 v. 104 ml/min; P=0.10) in cattle fed an LF diet. In summary, lower ruminal pH in cattle with greater rapidly fermentable CHO intake was attributed to an increase in SCFA production and decrease in salivation, which were not compensated for by an increase in epithelial permeability.

Effects of replacing barley grain with graded levels of wheat bran on rumen fermentation, voluntary intake and nutrient digestion in beef cattle

Friedt, A. D., McAllister, T. A., He, M. L., Penner, G. B. and McKinnon, J. J. 2014. Effects of replacing barley grain with graded levels of wheat bran on rumen fermentation, voluntary intake and nutrient digestion in beef cattle. Can. J. Anim. Sci. 94: 129–137. Abrasion-milled wheat bran (AMWB) is a relatively new by-product from wheat-based ethanol production. Few published studies are available on the nutritional value of this by-product feed for growing cattle. The objective of this trial was to evaluate the effects of replacing rolled barley with AMWB on apparent nutrient digestibility, voluntary intake and rumen fermentation parameters of beef heifers fed a backgrounding diet formulated to 1.50 and 0.91 Mcal kg−1 dry matter (DM) of NEm and NEg, respectively. Five spayed and rumen-cannulated Angus heifers (584±40 kg) were used in a 5×5 Latin square design. The control diet consisted of 36% barley silage, 24% grass hay, 8% supplement and 32% rolled barley grain (DM basis). Dietary treatments replaced barley grain with AMWB at 8, 16, 24 and 32% of the diet DM. Voluntary DM (P=0.30) and organic matter (OM) (P=0.19) intake were not affected by AMWB inclusion level. Mean rumen pH (P=0.68) as well as duration (min) (P=0.68) and area under the pH curve 5.8 (P=0.27) were not affected by AMWB. Other than acetate, which linearly increased (P=0.03) with increasing AMWB, effects on rumen volatile fatty acids or NH3-N levels were minimal. There was a linear decrease (P<0.01) in DM, OM and gross energy digestibility with increasing AMWB, while acid (P=0.01) and neutral (P=0.03) detergent fibre digestibility decreased in a quadratic manner. A similar quadratic trend (P=0.06) for decreased digestible energy content was also noted with increasing levels of AMWB. Crude protein digestibility was not affected (P=0.94) by treatment. These results indicate AMWB will not support similar gains to barley grain in growing diets due to reduced total tract nutrient utilization and lower digestible energy content.

Effects of different sources of carbohydrates on intake, digestibility, chewing, and performance of Holstein dairy cows

To investigate the effects of different sources of carbohydrates on intake, digestibility, chewing, and performance, nine lactating Holstein dairy cows (day in milk= 100±21 d; body weight=645.7 ± 26.5 kg) were allotted to a 3 × 3 Latin square design at three 23-d periods. The three treatments included 34.91% (B), 18.87% (BC), and 18.86% (BB) barley that in treatment B was partially replaced with only corn or corn plus beet pulp in treatments BC and BB, respectively. The concentration of starch and neutral detergent soluble carbohydrate varied (22.2, 20.2, and 14.5; 13.6, 15.9, and 20.1% of DM in treatments B, BC, and BB, respectively). Cows in treatment BB showed a higher DMI and improved digestibility of DM, NDF, and EE compared with treatments B or BC. Ruminal pH was higher in cows fed on BB (6.83) compared with those that received B or BC treatments (6.62 and 6.73, respectively). A lower proportion of propionate accompanied the higher pH in the BB group; however, a greater proportion of acetate and acetate: propionate ratio was observed compared with cows fed either on the B or BC diet. Moreover, cows fed on the BB diet showed the lowest ruminal passage rate and longest ruminal and total retention time. Eating time did not differ among treatments, rumination time was greater among cows fed on the BB diet compared with the others, whereas total chewing activity was greater than those fed on BC, but similar to those fed on B. The treatments showed no effect on milk yield. Partially replacing barley with corn or beet pulp resulted in an increase in milk fat and a lower protein concentration. Changing dietary NFC with that of a different degradability thus altered intake, chewing activity, ruminal environment, retention time or passage rate, and lactation performance. The results of this study showed that beet pulp with a higher NDF and a detergent-soluble carbohydrate or pectin established a more consistent ruminal mat than barley and corn, thus resulting in higher mean retention time and chewing activity, whereas no changes in 3.5% FCM and milk fat were observed.

Malic acid or orthophosphoric acid-heat treatments for protecting sunflower (Helianthus annuus) meal proteins against ruminal degradation and increasing intestinal amino acid supply

The protection of sunflower meal (SFM) proteins by treatments with solutions of malic acid (1 M) or orthophosphoric acid (0.67 M) and heat was studied in a 3 × 3 Latin-square design using three diets and three rumen and duodenum cannulated wethers. Acid solutions were applied to SFM at a rate of 400 ml/kg under continuous mixing. Subsequently, treated meals were dried in an oven at 150°C for 6 h. Diets (ingested at 75 g/kg BW0.75) were isoproteic and included 40% Italian ryegrass hay and 60% concentrate. The ratio of untreated to treated SFM in the concentrate was 100 : 0 in the control diet and around 40 : 60 in diets including acid-treated meals. The use of acid-treated meals did not alter either ruminal fermentation or composition of rumen contents and led to moderate reductions of the rumen outflow rates of untreated SFM particles, whereas it did not affect their comminution and mixing rate. In situ effective estimates of by-pass (BP) and its intestinal effective digestibility (IED) of dry matter (DM), CP and amino acids (AAs) were obtained considering both rates and correcting the particle microbial contamination in the rumen using 15N infusion techniques. Estimates of BP and IED decreased applying microbial correction, but these variations were low in agreement with the small contamination level. Protective treatments increased on average the BP of DM (48.5%) and CP (267%), mainly decreasing both the soluble fraction and the degradation rate but also increasing the undegradable fraction, which was higher using orthophosphoric acid. Protective treatments increased the IED of DM (108%) and CP, but this increase was lower using orthophosphoric acid (11.8%) than malic acid (20.7%). Concentrations of AA were similar among all meals, except for a reduction in lysine concentrations using malic acid (16.3%) or orthophosphoric acid (20.5%). Protective treatments also increased on average the BP of all AA, as well as the IED of most of them. Evidence of higher increases for those AA showing a high resistance to degradation in the untreated meal were also observed. The total supply of metabolisable AA was increased by 3.87 times for sulphur-containing AA, whereas that of lysine was increased by 2.5 times, mainly because of lysine losses with heat treatments. These treatments and especially that with malic acid would be useful to increase the protein value of these meals but their combined use with lysine-rich protein concentrates would improve the metabolisable protein profile.

Effects of supplementation frequency on ruminal fermentation and digestion by steers fed medium-quality hay and supplemented with a soybean hull and corn gluten feed blend

Reducing the frequency of supplementation to beef cattle would reduce labor and vehicle maintenance costs and could have the potential to increase profits if performance is not negatively affected. Six ruminally cannulated beef steers (362 ± 18 kg of BW) were used in a replicated 3 × 3 Latin square design to determine the effect of supplementation frequency (daily or on alternate days) on digestion and ruminal parameters when feeding medium-quality hay and supplementing with a mixture of soybean hulls and corn gluten feed. Dietary treatments consisted of ad libitum fescue hay (8.8% CP and 34.8% ADF) that was supplemented at 1% of BW daily (SD), supplemented at 2% of BW on alternate days (SA), or not supplemented (NS). The supplement (14.6% CP and 29.8% ADF) contained 47% soybean hull pellets, 47% corn gluten feed pellets, 2% feed grade limestone, and 4% molasses (as fed). Each period consisted of a 12-d adaptation phase followed by 6 d of total fecal, urine, and ort collection. All supplement offered was consumed within 2 h. Ruminal fluid was collected every 4 h for 2 d. Hay intake was reduced (P < 0.01) for SD and further reduced (P < 0.01) for SA. Hay intake was 1.54, 1.19, and 1.02% of BW (SEM ± 0.036) for NS, SD, and SA, respectively. There was a treatment (P < 0.01) × day interaction for mean ruminal pH. On the day of supplementation, ruminal pH for SA (6.13) was lower (P < 0.01) than those for both SD (6.29) and NS (6.52). However, on the day the SA treatment did not receive supplement, ruminal pH of SA (6.53) did not differ (P = 0.87) from ruminal pH of NS and was greater (P < 0.01) than that of SD. Ruminal pH of SD was lower (P < 0.01) than that of NS. Diet DM digestibility was increased (P < 0.01) by supplementation but did not differ (P = 0.58) because of frequency. Dry matter digestibility was 57.9, 64.1, and 64.6% (SEM ± 0.65) for NS, SD, and SA, respectively. The amount of N retained did not differ (P = 0.47) because of frequency (24.9 ± 5.61 and 22.0 ± 5.50 g/d for SD and SA, respectively) and was greater (P < 0.01) for the supplemented treatments than for NS (4.2 ± 3.30 g/d). When supplementing a blend of soybean hulls and corn gluten feed, producers can reduce the frequency of supplementation to every other day without reducing digestibility or N retention.

The effect of size and density on the mean retention time of particles in the reticulorumen of cattle ( Bos primigenius f. taurus), muskoxen ( Ovibos moschatus) and moose ( Alces alces)

Particle passage from the reticulorumen (RR) depends on particle density and size. Forage particle density and size are related and change over time in the RR. Particle density mainly influences sorting in the reticulum, whereas particle size influences particle retention in the fibre mat of stratified rumen contents ('filter-bed' effect). We investigated these effects independently, by inserting plastic particles of different sizes (1, 10 and 20 mm) and densities (1·03, 1·20 and 1·44 mg/ml) in the RR of cattle (Bos primigenius f. taurus) as a pilot study, and of muskoxen (Ovibos moschatus; n 4) and moose (Alces alces; n 2) both fed two diets (browse and grass). Faeces were analysed for plastic residues for 13 d after dosing to calculate mean retention times (MRT). The results confirmed previous findings of differences in absolute MRT between species. Comparing muskoxen with moose, there was no difference in the effect of particle density on the MRT between species but particle size had a more pronounced effect on the MRT in muskoxen than in moose. This indicated a stronger 'filter-bed effect' in muskoxen, in accord with the reports of stratified RR contents in this species v. the absence of RR content stratification in moose. Low-density particles were retained longer in both species fed on grass diets, indicating a contribution of forage type to the 'filter-bed effect'. The results indicate that retention based on particle size may differ between ruminant species, depending on the presence of a fibre mat in the RR, whereas the density-dependent mechanism of sedimentation in the RR is rather constant across species.

Comparative digestibility and digesta flow kinetics in two breeds of sheep

A study was conducted to compare apparent digestibility and digesta flow kinetics in the whole digestive tract in two breeds of sheep (Churra and Merino) offered alfalfa hay at about maintenance. Ten mature sheep (five Churra and five Merino) each fitted with a rumen cannula were used in the study. Apparent digestibility was determined by total faecal collection. Liquid (Co-EDTA) and solid (Cr-mordanted fibre) markers were used to estimate rumen volumes and digesta flows. There were no significant differences between Churra and Merino sheep either in dry-matter or fibre apparent digestibility (P > 0·05). Liquid and solid passage rates did not differ between breeds and the estimated total mean retention times were similar for both genotypes. The volume of liquid in the rumen was proportionately 0·14 greater in Churra than in Merino sheep, although the difference was not significant. Estimated saliva secretion was greater in Churra (11·6 (s.e. 0·77) I/day) than in Merino sheep (10·5 (s.e. 0·72) I/day) but the difference did not reach statistical significance. Solid contents of the rumen did not differ between breeds. Rumen particle density was lowest at 2 h after feeding and remained stable at other sampling times, with no significant differences between breeds. There were no significant differences between breeds in the urinary excretion of total purine derivatives but urinary excretion of allantoin and microbial nitrogen supply tended to be higher in Merino than in Churra sheep (P < 0·20). This was attributed to the smaller rumen pool size of Merino (8·0 (s.e. 0·62) kg) compared with Churra sheep (9·2 (s.e. 0·63) kg). The study indicated that there were no apparent breed differences between Churra and Merino sheep in digestibility and digesta passage when they were given a good-quality forage at a low level of intake.

Evaluation of milk allantoin excretion as an index of microbial protein supply in lactating dairy cows

The potential of milk allantoin as an index ofmicrobial protein supply was evaluated in two experiments conducted with 12 multiparous Holstein-Friesian dairy cows that examined the effects of altering the supply of metabolizable energy (ME) and fermentable metabolizable energy (FME). In the first experiment, late lactation cows received a 14·3 kg dry matter (DM) per day basal diet consisting of (g/kg DM) chopped barley straw (415), soya-bean meal (322), molassed sugar-beet pulp (197), molasses (33), urea (17) and a vitamin and mineral supplement (17) for a 21-day co-variance period. During four 16-day periods, six treatments were allocated randomly to cows, consisting of potato starch (1, 2 or 3 kg DM per day) or fat supplements (0·64, 1·27 or 1·91 kg DM per day). In the second experiment, early lactation cows received 40 kg/day (fresh weight, (FW)) of silage (307 g/kg toluene-corrected dry matter, 149 g/kg DM crude protein and 11·6 MJ/kg ME). During three 21-day periods, four treatments were evaluated consisting of supplements of either 4·1 (LI) or 8·1 (12) kg fresh weight per day of a low fat concentrate (acid hydrolysis ether extract (AHEE) 45 g/kg DM) or 3·8 (HI) or 7·5 (H2) kg fresh weight per day of a high fat concentrate (AHEE 110 g/kg DM). Both experiments showed individual cow milk allantoin concentration or excretion to be poorly correlated with urinary purine derivative excretion or calculated microbial protein supply. Use of treatment mean (TM) values dramatically improved these relationships. For pooled TM (no. = 10) values from both experiments, close relationships existed between milk allantoin excretion and concentration with milk yield (r values 0·991 and 0·883, respectively). Auto-correlation with milk yield appeared to account for milk allantoin excretion and concentration being highly correlated with urinary purine derivative excretion (r values 0·908 and 0·934, respectively) and calculated microbial protein supply (r values 0·938 and 0·945, respectively). Current experimental data indicates that measurement of milk allantoin is not a reliable indicator of microbial protein supply for individual cows.

Factors affecting the outflow of protein supplements from the rumen. 1. Feeding level

1. Two experiments were conducted with four sheep and four lactating Friesian cows to investigate the effect of food intake on the outflow of protein supplements from the rumen. Protein supplements treated with sodium dichromate were used.

2. Dichromate treatment had little or no effect on particle size distribution or density of the protein supplements. The dichromate-treated proteins were rendered completely undegradable in the rumen and the rate of outflow of chromium-treated protein from the rumen was estimated from the concentrations of chromium recovered in the faeces.

3. There were highly significant linear effects of feeding level on fractional outflow rate per h of chromium-treated protein supplements from the rumen of sheep and cows. Fractional outflow rates of chromium-treated fish meal and soya-bean meal, respectively, from the rumen of sheep were 0·0080 and 0·0076; 0·0182 and 0·0259; 0·0319 and 0·0335; and 0·0383 and 0·0385 per h at 0·2, 1·0, 1·5 and 2·0 times the energy requirements for maintenance, respectively. There were no significant differences between the two tested chromium-treated protein supplements in fractional outflow rates per h when the particle size was similar, nor any difference in particle size or density. Soya-bean meal was ground to achieve a particle size distribution similar to that of fish meal. For the dairy cows, the fractional outflow rates of fish meal from the rumen were 0·065, 0·072, 0·091 and 0·088 per h, at 1·5, 2·0, 2·5 and 3·0 times the energy requirements for maintenance.

4. There were significant differences between sheep in fractional outflow rates per h of protein supplements from the rumen due to the considerably higher values obtained for one animal.

Efficiency of utilization during pregnancy and lactation in the ewe of the protein reaching the abomasum and truly digested in the small intestine

In six experiments carried out on individually penned Finn Dorset ewes estimates were made of the quantities of non-ammonia nitrogen (NAN) reaching the abomasum and truly digested in the small intestine. For experiments 1 and 2 which each involved 33 ewes given a complete diet of milled hay and concentrates supplemented with varying amounts of a good-quality fish meal during late pregnancy, the overall regression estimate for the daily amount of truly digested NAN required for zero N retention (ewe plus conceptus) was 438 mg/kg M0·75 (441 and 434 for experiments 1 and 2 respectively). The coefficients for the efficiency of utilization of increments of truly digested NAN and maternal tissue N for net N accretion in the conceptus were 0·48 (s.e. 0·039) and 0·84 (s.e. 0·127) respectively.

In experiment 3, 24 lactating ewes had their diet supplemented with either soya-bean meal or fish meal. There was no effect of protein source on the amounts of NAN reaching the abomasum in ewes fitted with an abomasal cannula or on milk yield and these observations confirmed the unusually high degradability (measured by the polyester bag technique) of the fish-meal protein in the rumen. For experiments 4, 5 and 6 a total of 36 ewes were used to test the efficiency with which the NAN truly digested in the small intestine was used for the synthesis of milk protein. In the absence of data on the possible contribution of body tissue N to milk N the coefficient for the apparent efficiency of utilization of truly digested NAN when the ewes were given a basal diet containing approximately 10 g crude protein per MJ metabolizable energy was 0·63. For those ewes receiving the basal diet supplemented with either soya-bean meal, fish meal or blood meal the coefficients for the efficiency of utilization for the production of milk N of the increments in truly digested NAN supplied by the three protein sources were 0·61, 0·54 and 0·29 respectively. It is suggested that the low coefficient for blood meal may be due to its low content of methionine.

Rumen degradability of organic matter, nitrogen and fibre fractions in forages

Rumen degradability of dry matter (DM), organic matter (OM), nitrogen (N), neutral-detergent fibre (NDF), hemicellulose, cellulose and lignin was evaluated with the in situ technique for maize silage and cocksfoot, timothy, fescue, lucerne and meadow hays. The degradability of each of the six forages was studied separately, each forage being used in turn as the main component of the diet offered to four fistulated cows. For each forage 300 g were mordanted with sodium dichromate and placed in the rumen when the same forage was studied. Faecal grab samples were collected to measure the forage transit time. Digestibility was evaluated using both lignin as an indicator and by an in vitro method.

Rumen outflow rate was higher for cocksfoot and lucerne hays than for maize silage and the meadow, timothy and fescue hays (P < 0·01). The effective degradabilities of DM and OM were higher in maize silage, fescue and lucerne than in cocksfoot, timothy or meadow hay (P < 0·01). Effective degradability of N was highest in lucerne and lowest in timothy and meadow hay (P < 0·01). The degradability of NDF, hemicellulose and cellulose for fescue was always the highest of the six forages (P < 0·01; P < 0·05; F < 0·01 respectively).

Rumen outflow rate was statistically correlated with the c value of DM (r = 0·47), N (r = 0·54), NDF (r = 0·43) and hemicellulose (r = 0·43). High correlations were observed between rate constants of degradation of NDF and hemicellulose, cellulose or lignin (0·93, 0·75 and 0·79 respectively). The regression between in vitro and lignin-derived digestibility was highly significant (P < 0·001, r2 = 0·902 residual s.e. 0·017). The multiple regression analysis between lignin-based digestibility and degradability coefficients, effective degradability and coefficients of faecal chromium excretion was highly significant (r = 0·748; residual s.e. = 0·03).

Graded levels of Sesbania sesban and Leucaena leucocephala as supplements to teff straw given to Ethiopian Menz sheep

Two experiments were conducted to investigate the effect of supplementation with fodder tree leaves on the utilization of teff straw. This ivas aimed at testing the hypothesis that forage supplements (e.g. sesbania) that disappear faster from the rumen compared with those that disappear slowly (eg. leucaena) may elicit higher intakes of the basal diet. Experiment 1 investigated the effect of level (i.e. 0,200,300 and 400 g/kg dry matter (DM) intake) of leaves of Sesbania sesban or Leucaena leucocephala on the utilization of teff straw fed ad libitum. Seven sheep were given the seven diets in four periods following a partially balanced (7 × 4) cross-over design. In experiment 2, teff straw alone or supplemented with graded levels of sesbania (250, 350 and 450 g/kg DM intake), were fed to 16 sheep in a completely randomized block design. Intake, degradability, nitrogen (N) utilization, particulate and liquid passage rates were estimated.

In experiment 1, protein source × protein level interaction was not significant. Supplementation increased intakes of total DM (P < 0-05), organic matter (P < 0·01) and N retention (P < 0·01) but had no effect on the intake of teff straw. Supplementation with sesbania, but not with leucaena, increased (P < 0·05) the apparent digestibility of DM. Both supplements increased (P < 0·05) the fractional rate of passage from the rumen. In experiment 2, graded levels of sesbania increased DM intake (P < 0·05), fractional rate of liquid outflow (P< 0·05) and tended to increase the rate of degradation. It was concluded that the effect of fodder tree leaves on roughage intake is a function of their disappearance rate from the rumen.

Change in amino acid composition of different protein sources after rumen incubation

The effective degradability (Dg) of dry matter (DM), nitrogen (N) and amino acids (AA) in soya-bean meal (SBM), fish meal (FM), dried brewers' grains (DBG) and ensiled lucerne (EL) was measured using polyester bags suspended in the rumens of six cows given a basal diet of maize silage, hay and concentrate. Rumen outflow rate was measured using chromium-mordanted SBM.

AA were grouped into essential (EAA), non-essential (NEAA) or branched chain (BrAA). The AA concentration in DM varied from 88 g/kg DM for EL to 566 g/kg for FM. The proportion of determined AA in crude protein (CP) was similar for SBM, FM and DBG and always higher than 0·85. EL had the lowest A A concentration in CP, partly due to the presence of ammonia N (170 g/kg total N).

Methionine always had a higher, and threonine a lower Dg than total AA in all foods. Dg of other AA was generally food dependent.

SBM always had the highest EAA, BrAA, NEAA, mean AA and total N degradability, whilst FM always had the lowest Dg for EAA, BrAA, mean AA and total N, and these values were significantly different in comparison with SBM. The effective Dg of BrAA in DBG was significantly lower than in SBM and significantly higher than in FM. In EL, NEAA and mean AA Dg were significantly lower compared with SBM.

Effective Dg of total AA in SBM and EL was significantly lower than the CP Dg; this difference was not apparent in DBG or FM.

The undegraded fraction of FM and EL had a significantly higher proportion of EAA whilst DBG and EL had a higher proportion of BrAA when compared with the unexposed food. Isoleucine concentration, highest in EL, and lysine and methionine contents, highest in FM, differed significantly between the four protein source residues.

The first limiting AA after rumen incubation, in relation to casein and meat, was always methionine. The essential amino acid index of the food residues post incubation, relative to casein and meat, was lower in SBM, DBG and EL but higher in FM.

The response of store lambs to dietary supplements of fish meal 1. Effects of forage-to-concentrate ratio

Forty-eight individually-penned lambs (mean live weight 31-4 kg) were offered one of four diets, to investigate response to a supplement of fish meal (0 and 100 g dry matter (DM) per kg M) given with diets of either 60: 40 or 40: 60 forage-to-concentrate ratio. Nitrogen (N) degradability in the rumen and fractional outflow rates of protein supplements were determined. The diets were formulated such that the lambs received about 3 or 9 g undegradable rumen N per kg DM. The diets were given daily to provide sufficient metabolizable energy for maintenance and 150 g gain, and were adjusted according to live weight at weekly intervals.

Fish-meal supplementation improved daily growth over a 49-day period (P < 0·001) and enhanced N retention (P < 0·001). Live-weight gain was also marginally improved on the high-forage diets. (P < 0-05), but there was no protein supplement × forage-to-concentrate ratio interaction. Apparent digestibility of acid detergent fibre was improved by the fish-meal supplement on the high-concentrate diet.

The four diets were also given to rumen-fistulated sheep. The high-concentrate diet was associated with a higher molar proportion of propionate (P < 0·05) and a lower proportion of acetate (P < 0·001). Rumen concentrations of ammonia tended to be maintained at higher levels throughout the day by the fish-meal supplement.

Intake, digestion, gastro-intestinal transit time and nitrogen balance in working oxen: studies in Costa Rica and Nepal

Experiments were carried out in Nepal and Costa Rica to compare voluntary dry-matter intake (DMI) by oxen of diets based on poor quality hay (Costa Rica) and rice straw (Nepal) supplemented with different levels of concentrate foods when the animals were working and not working. Values for the apparent digestibility of the diets, rates of passage of solid and liquid phases ofdigesta and nitrogen balance are also reported.

Amounts of work calculated to raise daily energy expenditure to 1·3 to 1·6 × maintenance were associated with the following effects. (1) A depression of proportionately 0·11 and 0·14 in the DMI of oxen given a diet based on rice straw plus 18 and 27 g/kg live weight of concentrate respectively during work. No depression of DMI was seen with the hay diets which had slightly higher metabolizable energy but less nitrogen than the rice straw diets. (2) An increase in intake in the weeks following work on both the hay and rice straw diets. (3) Variable effects on apparent digestibility of food probably related more to the changes in DMI. (4) A tendency for gastro-intestinal mean retention time to be increased in working weeks particularly on the more fibrous diets.

The effect of altering the hormone status of ewes on the outflow rate of protein supplements from the rumen and so on protein degradability

Four experiments were carried out on individually penned Finn Dorset and Suffolk × Finn Dorset ewes receiving complete diets of milled hay and concentrates and rationed at various levels below voluntary intake. In the first experiment, 20 non-pregnant non-lactating ewes were each given daily 1·6 kg food and injected intramuscularly with either isotonic saline (control), progesterone plus oestrogen (20 mg + 80 ng per 24 h) to mimic hormone status in pregnancy, bromocriptine (1 mg per 12 h) to suppress plasma prolactin, or thyrotrophin releasing factor (TRF) to elevate plasma concentrations of prolactin and the iodothyronines. Fractional outflow rates of chromium-mordanted fish meal from the rumen were estimated from the rate of excretion of chromium in faeces and were proportionately 0·25 higher for ewes given TRF than for controls (P < 0·025). None of the other treatments had a significant effect on outflow rate.

In experiment 2, fractional outflow rates from the rumen were determined during July (long daylength) and again during December (short daylength) in 12 ewes that had their seasonal pattern of plasma prolactin modified by removal of their anterior cervical sympathetic ganglia. Another 12 sham-operated ewes were used as controls. Neither the seasonal changes in prolactin nor their modification by cervical ganglionectomy significantly affected outflow rate.

Twelve non-pregnant non-lactating ewes were used in the third experiment to test the effects of mid-winter shearing (mean ambient temperature −4°C) on fractional outflow rates from the rumen and on the plasma concentrations of prolactin, thyroxine (T4) and cortisol. Shearing caused a drop in plasma prolactin, gave proportional increases (P < 0·05) of 0·47 and 0·16 in T4 and cortisol respectively and gave a 0·12 increase (P < 0·01) in the outflow rate of chromium-mordanted fish meal from the rumen. The increases in T4, and outflow rate were sustained for at least 2 weeks.

For experiment 4, 22 ewes each suckling two lambs were used in three trials to see if variation between ewes in milk production and in lamb growth rate was correlated with variation in outflow rate from the rumen. The only significant correlation (r = 0·68, P < 0·01) was between outflow rate and lamb growth rate for the eight ewes in trial 1. The results of all four experiments are discussed in relation to the mechanisms by which non-dietary factors, via their effect on the rate of outflow of digesta from the rumen, may alter the quantity of protein reaching the abomasum and the likely significance of this alteration on animal performance.