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

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.

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.

Effect of grain processing on the performance of early-weaned lambs and kids

The effect of grain processing and form of the concentrate mixture were studied on early-weaned Chios lambs (42 days of age) and Damascus kids (56 days of age). Forty-five, 36, 33 and 33 animals were used in trials 1 (lambs), 2 (lambs), 3 (kids) and 4 (kids), respectively. Within trials animals were divided on the basis of live weight and age into three groups. Treatments (three forms of concentrate mixture) were randomly allocated to one of the three groups. The treatments were: whole cereal (WGP) grains mixed with pellets made from the other ingredients of the concentrate mixture; pelleted (P), where all ingredients were ground and pelleted in 5-mm cubes; rolled cereal grains (RGP), where cereal grains were rolled and then mixed with pellets (5-mm cubes) made from the other ingredients of the concentrate mixture. Cereal grains comprised 774 g/kg concentrate mixture. Fattening diets were based on ad libitum feeding of concentrates and a daily allowance of 01 kg per animal of long lucerne hay. Digestion coefficients, outflow rate of small particles from the rumen and rumen metabolites were measured using five animals per species per treatment.

There were no significant differences between diets for live-weight gain in lambs. On the other hand, kids on the P diet gained more weight and had better food to gain ratio than the other two diets. Feeding the P diet resulted in a significant decrease of acetate and butyrate molar proportion ( P < 0·001) and an increase (P < 0·001) of propionate molar proportion. Similarly, feeding the P diet resulted in a significant reduction in ruminal pH (P < 0·01) and NH,-N (P < 0·05) concentration. Outflow rate (% per h) of small particles from the rumen was lower from lambs and kids on the P diet (P < 0·001). There were no significant differences between species and/or among diets for apparent digestion coefficients and nitrogen balance.

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.

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.

Effects of limestone on starch digestion in Holstein steers

Eight calcitic and three dolomitic limestones were examined for particle size and reactivity with hydrochloric acid at pH 3.5 and 5.5. Reactivity was higher in calcitic than dolomitic limestone. Within calcitic limestones, reactivity was highly related to particle size. A highly reactive limestone was selected for use in two digestion trials with Holstein steers. In Trial 1, 4 steers (approximately 300 kg) were fed diets consisting of 40% corn silage and 60% concentrate (DM basis) with .62 or 2.34% limestone in a single reversal trial with 3-wk experimental periods. Added limestone affected only starch digestibility, which increased from 91.3 to 93.2%. Fecal pH increased from 5.7 to 6.4 by limestone addition. In trial 2, four rumen and duodenally cannulated steers (approximately 475 kg) were fed the same diets in the same design. Limestone addition increased fecal pH from 5.7 to 6.5. There were no effects of limestone on rumen or total tract digestion of starch or other nutrients. Limestone addition had no effect on rumen pH, buffering capacity, or VFA concentrations. Addition of a highly reactive limestone to diets containing high amounts of starch had little effect on starch digestion in either the rumen or lower gastrointestinal tract.