Influence of amount and frequency of protein supplementation to steers consuming low-quality, cool-season forage: intake, nutrient digestibility, and ruminal fermentation

Authors: CAPPELLOZZA, BRUNO - Eastern Oregon Agricultural Research; BOHNERT, DAVID - Eastern Oregon Agricultural Research; REIS, MARIA - Eastern Oregon Agricultural Research; SWANSON, KENDALL - 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: 4/8/2021
Publication Date: 4/13/2021
Citation: Cappellozza, B.I., Bohnert, D.W., Reis, M.M., Swanson, K.C., Falck, S.J., Cooke, R.F. 2021. Influence of amount and frequency of protein supplementation to steers consuming low-quality, cool-season forage: intake, nutrient digestibility, and ruminal fermentation. Journal of Animal Science. 99(6):1-12. https://doi.org/10.1093/jas/skab112.
DOI: https://doi.org/10.1093/jas/skab112

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 forage intake, nutrient digestibility, and ruminal fermentation by beef cattle. We conducted a digestion and ruminal fermentation study using 7 ruminally fistulated steers in an incomplete 4 x 7 incomplete Latin square design evaluating 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 supplementation intervals are greater than 5 d, our data suggest that reducing the overall quantity of supplemental N provided at each supplementation event to = 0.6 g/kg BW is a management strategy that will maintain acceptable levels of DMI, nutrient digestibility, and ruminal fermentation while reducing supplementation costs. 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: This experiment evaluated the influence of protein supplementation frequency (SF) and amount offered on intake, nutrient digestibility, and ruminal fermentation by rumen-fistulated beef steers consuming low-quality [2.9% crude protein (CP); dry matter (DM) basis], cool-season forage. Seven Angus × Hereford steers (300 ± 27 kg) fitted with ruminal cannulas were randomly assigned to 1 of 7 treatments in an incomplete 7 × 4 Latin square. Treatments, in a 2 × 3 factorial design plus a non-supplemented control (CON), consisted of 2 levels of supplemental soybean meal, 100% (F) or 50% (H) of the estimated rumen-degradable protein requirement, provided daily (D), once every 5 d (5D), or once every 10 d (10D). Experimental periods were 30 d and dry matter intake (DMI) was measured from days 19 to 28. On days 21 (all supplements provided) and 30 (only daily supplements provided; day immediately prior to supplementation for 5D and 10D treatments) ruminal fluid was collected for ruminal pH, ammonia-N (NH3), volatile fatty acids (VFA), and determination of ruminal fermentation variables. Forage and total DM, organic matter (OM), and nitrogen (N) intake increased with supplementation (P = 0.04).However, a linear effect of SF × amount of supplement interaction was observed for forage and total DM, OM, and N intake (P = 0.04), with each variable decreasing as SF decreased, but the decrease being greater with F vs. H. Apparent total tract DM, OM, and neutral detergent fiber digestibility was not affected by supplementation or amount of supplement provided (P = 0.10). In contrast, N digestibility increased with supplementation and for F vs. H (P < 0.01). Digestibility of DM, OM, and N increased linearly as SF decreased (P = 0.03). When all supplements were provided, ruminal NH3, total VFA, and molar proportions of all individual VFA increased with supplementation (P = 0.04), whereas acetate:propionate ratio decreased (P < 0.01). When only daily supplements were provided, none of the aforementioned fermentation parameters were affected (P = 0.09). In summary, reducing the amount of supplemental CP provided to ruminants consuming low-quality forages, when supplementation intervals are >5 d, can be a management tool to maintain acceptable levels of DMI, nutrient digestibility, and ruminal fermentation while reducing supplementation cost.