Influence of amount and frequency of protein supplementation to ruminants consuming low-quality cool-season forages: efficiency of nitrogen utilization in lambs and performance of gestating beef cows

Authors: CAPPELLOZZA, BRUNO - Eastern Oregon Agricultural Research; BOHNERT, DAVID - Eastern Oregon Agricultural Research; REIS, MARIA - Eastern Oregon Agricultural Research; VAN EMON, MEGAN - Montana State University; SCHAUER, CHRISTOPHER - North Dakota State University; Falck, Stephanie; COOKE, REINALDO - Texas A&M University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2021
Publication Date: 4/19/2021
Citation: Cappellozza, B.I., Bohnert, D.W., Reis, M.M., Van Emon, M.L., Schauer, C.S., Falck, S.J., Cooke, R.F. 2021. Influence of amount and frequency of protein supplementation to ruminants consuming low-quality cool-season forages: efficiency of nitrogen utilization in lambs and performance of gestating beef cows. Journal of Animal Science. 99(6):1-10. https://doi.org/10.1093/jas/skab122.
DOI: https://doi.org/10.1093/jas/skab122

Interpretive Summary: Protein supplementation of ruminants consuming low-quality forage can be expensive with costs associated with the labor and purchase of the protein supplement. Infrequent supplementation is a practice that can be used to reduce the labor and other costs associated with delivery of supplement as part of a nutritional management plan, thereby improving the economics of protein supplementation for ruminant livestock producers. No data is available related to evaluating the quantity of supplement provided at extended supplementation intervals (> 7 days) on efficiency of nitrogen (protein) use and performance of ruminants. We conducted 2 studies, the first a nitrogen balance study using 7 western white face wethers in an incomplete 4 x 7 incomplete Latin square design, and the second a randomized complete block using 84 late-gestation beef cows, to evaluate 2 levels of supplementation (100% of requirements and 50% of requirements) and 3 supplementation frequencies (daily, once every 5 days, and once every 10 days) with a non-supplemented control. When evaluating supplementation frequencies greater than 5 d, reducing the amount of a CP supplement provided by half maintained adequate N status of wethers, improved pre-calving BCS change, and alleviated BCS losses often observed in post-partum animals. Winter feed costs are one of the largest costs for producers of ruminant livestock in the Intermountain West. Supplementation strategies, such as infrequent supplementation and reducing the quantity of supplement necessary to meet management objectives, that reduce the time, labor, supplement costs provide livestock producers with a tool to reduce these feed costs and improve their overall costs of production.

Technical Abstract: We evaluated the influence of amount and crude protein (CP) supplementation frequency (SF) on nitrogen (N) use by wethers and the performance of late-gestation beef cows. In exp. 1, seven Western whiteface wethers (31.8 ± 1.4 kg) were used in an incomplete 7 × 4 Latin square to evaluate intake and N use. Wethers received one of the seven treatments in a 2 × 3 factorial design containing two levels of supplemental soybean meal offered at a rate of 100% (F) or 50% (H; 50% of F) of the estimated CP requirement daily, once every 5, or once every 10 d, plus a non-supplemented control (CON). Low-quality cool-season forage (4.9 % CP; dry matter [DM] basis) was provided daily for ad libitum intake. Experimental periods lasted 30 d. In exp. 2, 84 Angus × Hereford cows (560 ± 35 kg) were stratified by age, body condition score (BCS), and expected calving date and allocated to 1 of the 21 feedlot pens (three pens per treatment). Pens were randomly assigned to receive the same treatments as in exp. 1 and cows had free access to low-quality cool-season forage (2.9% CP; DM basis). Cow body weight (BW) and BCS were measured every 14 d until calving and within 24 h after calving. In exp. 1, supplementation did not alter total DM and organic matter (OM) intake (P = 0.26), but both parameters linearly decreased as SF decreased (P = 0.02). Supplementation increased DM, OM, and neutral detergent fiber (NDF) digestibility (P = 0.02). Additionally, F feeding linearly increased DM, OM, and NDF digestibility as SF decreased (P = 0.04). Digestibility of N, N balance, and digested N retained were greater with supplementation (P < 0.01), and N digestibility linearly increased as SF decreased (P = 0.01). Mean plasma urea-N concentration was not only greater (P < 0.01) for supplemented vs. CON wethers but also greater (P = 0.03) for F vs. H. In exp. 2, pre-calving BCS change was greater (P = 0.03) for supplemented cows. A linear effect of SF × supplementation rate for pre-calving BCS change was noted (P = 0.05), as F-supplemented cows lost more BCS compared with H as SF decreased. When considering supplementation intervals greater than 5 d, reducing the quantity of supplement provided, compared with daily supplementation, may be a feasible management strategy to maintain acceptable nutrient use and animal performance while reducing supplement and labor costs.