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

Protein nutrition of growing cattle: food intake and growth responses to rumen degradable protein and undegradable protein

Groups of eight Friesian steers were given one of eight diets from 114 to 300 kg live weight. The iso-energetic diets were formulated to supply four levels of protein degradability within two concentrations of crude protein (CP), giving a range of rumen-degradable protein (RDP) and undegradable dietary protein (UDP) concentrations both above and below Agricultural Research Council (1980) recommendations. There were significant (P < 0·05), positive, linear responses of mean daily dry-matter (DM) intake (DMI) (g/kg M°75) to RDP concentration (g/kg DM) for both the low CP diets (DMI = -98·0 + 1·76 (RDP); P = 0·013) and the high CP diets (DMI = -157·5 + 218 (RDP; P = 0017). For the high CP diets, there was a significant (P = 0·045) positive, linear response of live-weight gain (LWG) (kg/day) to UDP concentration (LWG = 0·47 + 0·017 (UDP); P = 0·045). No such response was observed for the low CP diets, where the range of UDP concentrations supplied was smaller than expected. For both the low and high CP diets, LWG decreased as metabolizable energy, UDP and RDP intake increased. These negative responses to nutrient intake were reflected in a wide discrepancy between observed rates of gain and those predicted by current energy and protein nutrition systems. Interactions between food intake and digestive processes, which obstruct effective interpretation of these results, should form an explicit part of any revised protein nutrition scheme.

Studies on degradation and outflow rate of protein supplements in the rumen of dry and lactating Chios ewes and Damascus goats

Outflow rate of small particles from the rumen of dry and lactating Chios ewes and Damascus goats were measured in two separate trials using Cr-treated soya-bean meal (SBM). In another trial, the in situ degradation of fish meal (FM) and SBM in the rumen of Chios ewes and Damascus goats were measured. Outflow rate (per h) of small particles from the rumen of the two species was similar but higher outflow rates were observed in lactating than in dry animals (dry ewes 0·054, lactating ewes 0·086, dry goats 0·057, lactating goats 0·081). With the exception of dry-matter degradability of SBM at 6-h incubation periods there were no significant differences between ewes and goats in crude protein or dry-matter degradability of both supplements at all incubation intervals. Degradation measurements at various incubation periods and effective degradation values were different between supplements.

Factors affecting the outflow of protein supplements from the rumen. 2. The composition and particle size of the basal diet

Two experiments were conducted to investigate the effect of the composition and particle size of the basal diet on the outflow of chromium-treated fish meal from the rumen of lactating British Friesian dairy cows, using Cr-concentrations in faeces. A 4 × 4 Latin square design was used and the cows were fed at twice the estimated energy requirements for maintenance in two equal meals.

Fractional outflow rates per h were, 0·079, 0·088, 0·086 and 0·064 for the 1·00 hay: 0·00 concentrate, 0·75 hay: 0·25 concentrate, 0·50 hay: 0·50 concentrate and 0·25 hay: 0·75 concentrate respectively. The difference between 0·75 and 0·50 concentrate was significant (P < 0·05).

Grinding of long dried grass through 40 or 20 mm screens had no significant effect on the outflow of Cr-treated fish meal from the rumen, however fine grinding (5 mm) and pelleting significantly reduced the outflow from rumen (P < 0·05). Fractional outflow rates per h were 0·080, 0·086, 0·088 and 0·047 for the long, 40, 20 mm and the 5 mm and pelleted diets respectively.

Factors affecting the fractional outflow of protein supplements from the rumen 3. Effects of frequency of feeding, intake of water induced by the addition of sodium chloride, and the particle size of protein supplements

Four experiments were conducted with lactating dairy cows offered a hay and concentrate diet (0·5:0·5) to investigate the effects of (1) the frequency of feeding a completely mixed diet (experiment 1) compared with feeding the concentrate fraction and the roughage fraction separately (experiment 2), and (2) the addition of sodium chloride to a completely mixed diet (experiment 3), on the fractional rate of outflow (FRO) of chromium (Cr)-treated fish meal from the rumen, and on milk yield and composition. The cows were offered the diet at either twice the maintenance requirement (experiments 1 and 2), or 2-5 x maintenance (experiment 3) in a 4 x 4 Latin-square design. The effect of the particle size of the Cr-treated soya bean meal was investigated in experiment 4.

The frequency of feeding of the completely mixed diet had no significant effect on the rate of outflow of Cr-treated fish meal from the rumen, or on milk yield or composition. FRO per h were 0·070, 0·085, 0·079 and 0·086 when the diet was offered once, twice, four times or 12 times per day respectively. Increasing the frequency of feeding of the concentrate fraction of the diet had no significant effect on FRO. FRO per h were 0·073, 0·078, 0·081 and 0·081 when the concentrate fraction was offered once, twice, four times or 12 times per day respectively.

The addition of NaCl to the diet significantly increased water intake (P < 0·001), but had no significant effects on FRO or milk yield. FRO per h were 0·074, 0·075, 0·076 and 0080 when 50, 265, 529 or 794 g of NaCl were added into the diet respectively. The respective intakes of water were 66·6, 74·1, 88·4 and 101·6 kg/day.

The FRO per h of fine particles of Cr-treated soya bean meal was 0·085 and for coarse particles, 0·096. The difference was not significant.

The effect of increasing the proportion of barley straw in pelleted concentrate diets given to lambs on rumen outflow rate and degradation of protein supplements

Two experiments are described in which growing lambs were offered ad libitum two concentrate pelleted diets containing 60 (diet C) or 230 (diet D) g/kg barley straw.

In the first experiment, eight male and eight female lambs were used to determine the outflow rate from the rumen of chromium-mordanted fish meal and soya-bean meal, estimated from faecal marker excretion. Diet D promoted a higher rumen outflow rate (0·0769 per h) than diet C (0·0486 per h); no differences were found either between sexes or between Cr-mordanted protein supplements.

In the second experiment, the rumen degradation of fish meal, soya-bean meal, sunflower meal, pea seeds and sweet lupin seeds was studied by incubating the supplements in polyester bags in the rumens of four lambs, following a change-over design. Increasing the proportion of straw to 230 g/kg increased the rate of nitrogen disappearance from all vegetable supplements, the differences being significant only for pea seeds.

When degradation kinetics and outflow rates were considered together, effective nitrogen degradability of protein supplements was reduced by the increased proportion of dietary straw, indicating a greater influence of rumen outflow rate than of the increased rate of microbial degradation.

Responses of British Friesian steers with or without implants of oestradiol-17β to undegradable dietary protein

The ability of the protein nutrition scheme proposed by the Agricultural Research Council (ARC, 1980, 1984) to predict responses to protein supply was examined in two experiments. In experiment 1, groups of nine British Friesian steers implanted with oestradiol-17β and nine non-implanted steers were fed from 133 to 300 kg live weight on each of four all-concentrate diets (metabolizable energy (ME) = 12 MJ/kg dry matter (DM)) containing ratios of soya-bean meal and formaldehyde-treated soya-bean meal such that undegradable protein (UDP) concentration was 19, 25, 32 or 42 g/kg DM. Rumen degradable protein (RDP) concentration was relatively constant (111 to 116 g/kg DM). Implantation did not affect DM intake (DMI, g/kg M0·75). Both live-weight gain (LWG) and food conversion efficiency (FCE) (LWG/DMI) were greater (P < 0·05) for the implanted cattle (LWG = 1·41 (s.e. 0·04) kg/day; FCE = 0·24 (s.e. 0·02)) than for the non-implanted cattle (LWG = 1·23 (s.e. 0·05) kg/day; FCE = 0·22 (s.e. 0·02)). There were no dietary effects on either DMI or FCE. In the non-implanted steers, UDP did not affect LWG but, for the implanted steers, there were positive, linear responses in LWG to both UDP concentration (P = 0·048) and UDP intake (P = 0·026). In experiment 2, groups of eight implanted steers were fed from 132 to 300 kg live weight on each of six diets (ME = 12 MJ/kg DM, soya-bean meal and formaldehyde-treated soya-bean meal as chief protein sources) supplying 17, 26, 34, 39, 54 and 82 g UDP per kg DM and concentrations of RDP up to 1·5 times ARC recommendations. There was no effect of UDP on either DMI or FCE but positive, linear responses in LWG to both UDP concentration (P = 0·019) and UDP intake (P = 0·010). In both experiments, mean DMI exceeded that predicted by ARC (1980) (P < 0·05). LWG predicted by the ME system and the ARC protein scheme was not significantly different from observed LWG for non-implanted steers, but was an underestimate of observed LWG for implanted steers (P = 0·002 in experiment 1, P < 0·001 in experiment 2). Observed responses in LWG to UDP concentration were also poorly predicted (regressions of observed on predicted LWG: experiment 1, r2 = 0·12, residual s.d. = 0·126; experiment 2, r2 = 0·004, residual s.d. = 0·119). It was concluded that oestradiol-17p has significant effects on responses in LWG to UDP, which are not predicted by the current ARC (1980, 1984) protein nutrition scheme.

[Ruminal nitrogen metabolism in calves and sheep. 3. Effect of hay-concentrate ratio in calves]

During the milk feeding period (ca. 55th day of life) and 2 weeks after the milk feeding period (ca. 80th day of life) the influence of a hay quota in the ration (on DM basis) of 6, 10, 14 and 18% in the milk feeding period and of 16, 23, 31 and 37% in the period after milk feeding was tested as to ruminal N metabolization with calves supplied with duodenal re-entrant cannulae. The increase of the hay quota in the ration for ruminating calves reduced as a tendency duodenal NAN passage, its bacterial N-quota, post-ruminal NAN digestibility and, due to a worse utilization of available N for bacterial N-synthesis, bacterial N-synthesis rate. The apparent fermentation of organic matter was, as a tendency, increased with the growing hay quota in the ration.

Rumen protein degradation rates estimated by non-linear regression analysis of Michaelis-Menten in vitro data

An in vitro method applying Michaelis-Menten saturation kinetics was developed as an alternative approach for estimating protein degradation rates in the rumen. Non-linear regression (NLR) analysis of the integrated Michaelis-Menten equation yielded fractional degradation rates, kd, from direct estimates of the maximum velocity: Michaelis constant ratio (kd = Vmax:Km). Degradation rates obtained using data from a series of 2 h inhibitor in vitro incubations were respectively 0.989, 0.134, and 0.037/h for casein, solvent soya-bean meal (SSBM) and expeller soya-bean meal (ESBM). Degradation rates obtained from 2 h incubations had lower standard errors than those obtained using 1 h incubations; 2 h rates were not significantly different from 1 h rates, suggesting end-product inhibition was not significant at 2 h. The NLR Michaelis-Menten method was used to determine degradation rates for twelve protein sources: casein, bovine serum albumin, two samples of lucerne (Medicago sativa) hay, and four samples each of SSBM and ESBM. Statistical analysis of NLR results revealed significant differences among the twelve protein sources. Casein was degraded most rapidly (0.827/h), and the four ESBM samples most slowly (0.050-0.098/h). Degradation rate for serum albumin was 0.135/h; rates for SSBM and lucerne hays ranged from 0.160 to 0.208/h. Degradation rates estimated using the NLR method were more rapid than those obtained with a limited substrate approach; NLR rates were more consistent with in vivo estimates of rumen protein escape. Greater concentrations of slowly degraded proteins were needed with the NLR method to define curvilinearity of the degradation curve more accurately.

Digesta kinetics in sheep and cattle fed diets with different forage to concentrate ratios at high and low intakes

Effect of maintenance and ad libitum intakes on digesta kinetics was studied with six ruminally fistulated cows and six ruminally fistulated wethers to validate the use of sheep as a model of cattle. Complete diets were made up of ratios of alfalfa:cracked corn and soybean meal of 80:20, 55:45, and 30:70. The rate of passage of Cr-mordanted alfalfa and soybean meal in the reticulorumen was negatively related to percentage of concentrate in the diet in both species at low intakes. Passage values of particulate and liquid markers were faster at high than at low intakes in both species for all diets. Rumen liquid volume increased with intake only in the cows on the low and intermediate concentrate diets. No substantial differences were found in particulate passage values between sheep and cattle. However, liquid passage rates from the rumen and the differentials between liquid and particulate dilution rates were higher in cows than in sheep for all diets at both intakes. These results together with those for digestibility data reported in a previous communication suggest that caution should be exercised when extrapolating results from one species to the other.

Comparison of different methods of expressing dietary protein for lactating dairy cows

Data were from Holstein cows from 20 experiments at the University of Florida (1688 cow-period observations). Objectives were to compare milk responses to increasing dietary percent or daily intake of CP, estimated undegradable CP, and estimated metabolizable protein from Burroughs and Chalupa equations and to determine if higher producing cows (26.8 kg milk/d) responded differently to increasing dietary protein percent or intake than do lower producing cows (18.9 kg milk/d). The mathematical model included experiment, cow-within-experiment, period, body weight, and source of roughage. Intake of protein (kg/d) had a greater effect (cubic polynomial) on milk yield than protein percent of DM since CP, undegraded protein, Chalupa metabolizable protein, and Burroughs metabolizable protein intakes explained 17.2, 20.9, 23.5, and 24.1% of residual variation in milk yield compared with .6, 2.1, 1.7, and 2.1%, for percents of DM. High producing cows responded more to increasing protein intake than did low producing cows. Respective protein intake variables explained 20.6, 23.7, 30.5, and 31.2% of residual variation in milk yield in high production group compared with 17.2, 23.1, 20.6, and 20.6% in low production group.

Determination of protein degradation rates using a rumen in vitro system containing inhibitors of microbial nitrogen metabolism

1. A previously reported rumen in vitro system (Broderick, 1978) was modified to include chloramphenicol (CAP) with hydrazine sulphate (HS) to give quantitative recovery of protein breakdown products. Degradation rates were determined by regression v. time of log proportion remaining undegraded (computed by subtracting from added nitrogen the amount of N recovered as ammonia and amino acids). Concentrations of reagents giving optimal N recoveries and estimated degradation rates for casein and expeller soya-bean-meal (SBM) were: 1.0 mM-HS, 30 micrograms CAP/ml, 2.0 mM-mercaptoethanol, 3.3 mg maltose/ml, when protein was added at 0.125 mg N/ml. 2. Digestion of azo-casein and azo-albumin, solubilization of radioactivity from 14C-labelled casein, ovalbumin and bovine serum albumin (BSA), and hydrolysis of benzoyl-L-tyrosine p-nitroanilide and benzoyl-L-arginine p-nitroanilide were not significantly decreased by HS and CAP. This suggests that the inhibitors did not reduce microbial proteolysis. 3. Mean fractional degradation rates (/h) were: 0.395 casein, 0.135 BSA, 0.159 solvent-SBM, 0.045 expeller-SBM, 0.061 meat meal, 0.070 lucerne (Medicago sativa) hay. Extents of protein escape, estimated assuming rumen passage of 0.06/h, were 13, 28, 56 and 40% for casein, solvent-SBM, expeller-SBM and lucerne hay respectively. This method appears more reliable for assessing rumen degradability than buffer N solubility and protein digestibility with ficin protease. 4. Azo-dye treatment slowed the rate of casein degradation, measured by ammonia plus amino acid release, but did not alter digestion of BSA. 5. The validity of the inhibitor in vitro method for estimating protein degradability, as well as potential problems in its application, are discussed. The complete procedure may be limited to laboratories with automated analytical equipment, but a simplified version of the method may be more generally applicable.

Rumen degradation and fractional outflow rates of nitrogen supplements given to cattle eating sodium hydroxide-treated straw

1. Six rumen and abomasal cannulated heifers were used to study the effects of intake on the fractional outflow rates (FOR) of chromium-mordanted cotton-seed meal (Cr-CSM) and meat meal (Cr-MM), CrEDTA, ytterbium and lignin from the rumen. Values of FOR of Cr-CSM and Cr-MM were combined with values of nitrogen disappearance from the protein supplements, placed in porous synthetic (nylon) bags and incubated within the rumen (P), to calculate effective degradation (D) of CSM and MM when fed to heifers eating sodium hydroxide-treated straw. Also, N degradation in vivo (V) was measured as the difference between abomasal N flow and the sum of flows of microbial and endogenous N. 2. FOR were positively related to intake and differences between supplements were significant (P less than 0.01). FOR pertaining to high and low intakes respectively were 0.073 and 0.052 for Cr-CSM, 0.082 and 0.071 for Cr-MM, 0.030 and 0.023 for lignin, 0.082 and 0.073 for CrEDTA and 0.044 and 0.035 for Yb. 3. A rise of 28.8 and 13.4% in FOR of Cr-CSM and Cr-MM respectively, associated with an increase in intake from maintenance to 1.5 times maintenance, resulted in 10.7 and 2.2% reductions in D, 24 h after feeding, for CSM and MM respectively. 4. With the exception of CSM at the high intake, estimates of V were underestimated by D and were 8.6-25.0% greater than the D values when time of incubation (t) = infinity. The two techniques, however, ranked the degradation of the two supplements in the same order at both levels of intake. 5. Underestimation of V by D may be attributable to underestimation of P, overestimation of FOR (both resulting in underestimation of D) or overestimation of V due to biases associated with the estimation of this part of the comparison. The relative importance of these factors remains to be determined.