Effect of duration of restricted-feeding on nutrient excretion, animal performance, and carcass characteristics of Holstein × Zebu finishing steers

Restricted-feeding may be a useful management tool available to reduce environmental impact in feedlots. Therefore, the objectives of the present study were to determine the effects of the duration of restricted-feeding on nitrogen (N) and phosphorus (P) excretion, growth performance and carcass characteristics of finishing steers. Twenty-five Holstein × Zebu steers (average initial bodyweight (BW) = 319 ± 16.2 kg; age = 19 ± 1 months) were used. Five steers were slaughtered to provide baseline empty BW (EBW) and empty body composition at Day 0. The remaining steers were randomly allotted to four groups of five steers, which were restricted to 85% ad libitum feed intake for either 0 (R0), 28 (R28), 42 (R42) or 84 (R84) days of an 84-day finishing period. All steers were fed a diet of 40% corn silage and 60% concentrate (DM basis) for 84 days. Total excretion of faeces and urine were collected during two periods: Days 25 to 27 (period 1) and Days 73 to 75 (period 2). The DM intake, average daily gain (ADG) and gain-to-feed ratio (G:F) were evaluated in three blocks, Days 0 to 28, Days 28 to 42 and Days 42 to 84. As expected, DM, N and P intakes were greater (P < 0.05) for R0 steers than R28, R42 and R84 steers when steers in R28, R42 and R84 treatments were restricted. When transitioned to ad libitum feeding, R28 and R42 steers had similar (P > 0.05) DM, N and P intakes compared with R0 steers. Faecal N and urinary P excretions did not differ (P ≥ 0.40) among restricted and ad libitum-fed steers in either period evaluated. However, greater (P < 0.05) faecal P excretions were observed in steers fed ad libitum intake in period 2 (R0). Phosphorus retention in period 2, and whole-body N retention were greatest (P < 0.05) in steers fed R28 and least (P < 0.05) in steers fed R84, steers fed R0 and steers fed R42 were intermediate and not different (P > 0.05). Final BW, overall ADG, G:F and carcass characteristics were not affected (P ≥ 0.11) by treatments. Restricted-feeding Holstein × Zebu steers to 85% of ad libitum intake for 84 days in the feedlot reduced DM intake and P excretion, without impairing steer growth performance or carcass characteristics. Nevertheless, it is important to highlight that the small sample size was one limitation of this present experiment.

Effects of carbohydrate and nitrogen supplementation on fermentation of cheatgrass () in a dual-flow continuous culture system

Cheatgrass (CG; ), an introduced winter annual grass, is an aggressive invader of the sagebrush community in the Western United States. Because of its greater flammability, mature CG constitutes a fire hazard leading to repeated wildfires. One fuel-reduction strategy is livestock grazing. The objective of this study was to evaluate the effects of urea, molasses, or a combination of urea and molasses supplementation of a CG-based diet on digestibility, microbial fermentation, bacterial protein synthesis, and nutrient flow using a dual-flow continuous culture system. Eight fermenters were used in a replicate 4 × 4 Latin square design with four 10-d experimental periods. Experimental treatments (DM basis) were 1) forage only (CON), 2) CG plus urea alone (URE; 1.36% urea), 3) CG plus molasses alone (MOL; 15.9% molasses), and 4) CG plus urea and molasses combined (URE+MOL; 1.28% urea plus 19.3% molasses). Each fermenter was fed 72 g/d of DM, and data were analyzed using the GLIMMIX procedure of SAS (SAS Inst. Inc., Cary, NC). The true digestibilities of NDF and ADF were not affected by diets ( > 0.05). Molasses-containing diets had greater true digestibility of OM ( = 0.02). However, true digestibility of CP was increased when molasses was fed alone ( < 0.01). Molasses-containing diets had lower pH ( < 0.01) and greater VFA concentrations ( < 0.01) compared to those of the other diets. The URE+MOL diet resulted in a greater VFA concentration ( < 0.01). Propionate concentration increased ( < 0.01), whereas acetate concentration decreased ( < 0.01) when molasses alone or in combination with urea was added to the diets. Supplying molasses alone resulted in greater ( = 0.03) total branched-chain VFA compared to the other diets. The concentration of NH-N and total N flow increased ( < 0.01) in response to urea supplementation and was greater ( < 0.01) when urea alone was supplemented in the diet. On the other hand, molasses-supplemented diets yielded more non-ammonia N ( < 0.01) and bacterial N ( = 0.04). Supplementation had no effect ( = 0.83) on bacterial efficiency. Results from this study indicate that the addition of urea and molasses in a CG-based diet could improve nutrient supply to animals, notably VFA supply and microbial N supply; however, in the levels tested in this study, it did not improve CG utilization as assessed by NDF digestion.

Effects of replacing soybean meal with canola meal differing in rumen-undegradable protein content on ruminal fermentation and gas production kinetics using 2 in vitro systems

Previous research indicated that there were significant differences in rumen-undegradable protein (RUP) among canola meals (CM), which could influence the nutritional value of CM. The objectives of this study were to (1) evaluate the effects of feeding CM with different RUP contents on ruminal fermentation, nutrient digestion, and microbial growth using a dual-flow continuous culture system (experiment 1) and (2) evaluate ruminal gas production kinetics, in vitro organic matter (OM) digestibility, and methane (CH4) production of soybean meal (SBM) and CM with low or high RUP in the diet or as a sole ingredient using a gas production system (experiments 2 and 3). In experiment 1, diets were randomly assigned to 6 fermentors in a replicated 3 × 3 Latin square. The only ingredient that differed among diets was the protein supplement. The treatments were (1) solvent-extracted SBM, (2) low-RUP solvent-extracted CM (38% RUP as a percentage of crude protein), and (3) high-RUP solvent-extracted CM (50% RUP). Diets were prepared as 3 concentrate mixtures that were combined with 25% orchardgrass hay and 15% wheat straw (dry matter basis). Experiments 2 and 3 had the same design with 24 bottles incubated 3 times for 48 h each. During the 48-h incubation, the cumulative pressure was recorded to determine gas production kinetics, in vitro OM digestibility, and CH4 production. In experiment 1, N flow (g/d), efficiency of N use, efficiency of bacterial N synthesis, total volatile fatty acids (mM), and molar proportion of acetate, propionate, and isobutyrate were not affected by treatments. There were tendencies for a decrease in ruminal NH3-N and an increase in molar proportion of butyrate for the SBM diet compared with both CM diets. The molar proportion of valerate was greater in both CM diets, whereas the molar proportion of isovalerate and total branched-chain volatile fatty acids was lower for the CM diets compared with the SBM diet. In experiments 2 and 3, the SBM diet had a greater gas pool size than both CM diets. The SBM diet increased in vitro OM digestibility; however, it also tended to increase CH4 production (mM and g/kg of DM) compared with both CM diets. Based on the results of this study, CM with RUP varying from 38 to 50% of crude protein does not affect ruminal fermentation, nutrient digestion, and microbial growth when CM is included at up to 34% of the diet.