Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 12, 2012
Publication Date: January 27, 2012
Repository URL: http://handle.nal.usda.gov/10113/56292
Citation: Sawyer, J.E., Mulliniks, J.T., Waterman, R.C., Petersen, M.K. 2012. Influence of protein type and level on nitrogen and forage utilization in cows consuming low-quality forage. Journal of Animal Science 90(7):2324-2330. Interpretive Summary: This study explored the link between the amount of supplemental protein fed to range cows and the efficiency of utilization to promote ruminal function when consuming dormant forages. The results showed that 40 g/d of crude protein from a high bypass protein supplement can replace 160 g/d of crude protein of a lower bypass protein supplement while maintaining ruminal function. Feed supplemental protein sources greater in ruminal bypass may improve crude protein utilization efficiency when fed at low amounts by minimizing nitrogen losses due to ruminal and metabolic inefficiencies while maintaining feed fiber digestibility. The results indicate that providing small quantities of protein supplements to cattle consuming dormant forages has the potential to bring out a greater improvement in roughage fiber digestibility per unit of protein fed improving overall supplement utilization efficiency. Because only minimal amounts of crude protein (~ 40 g/d) were needed to improve fiber digestion, it is plausible that protein supplements high in ruminal bypass protein could be added to a self fed salt and mineral program to allow for less labor when feeding to support maintenance of beef cows grazing dormant rangeland in extensive environments and to enhance roughage fiber digestibility.
Technical Abstract: Minimal quantities of ruminally degradable protein from supplements may improve supplement utilization efficiency of ruminants grazing dormant forages. In Exp. 1, N retention, ruminal NH3, serum urea N, and NDF digestibility was evaluated for 12 ruminally cannulated cows in an incomplete Latin Square design with 3 periods of 42 d each. Cows were fed weeping lovegrass hay (4.1% CP, 75% NDF, OM basis) at 1.3 % BW/d and offered 1 of 3 sources of CP (urea, UREA; cottonseed meal, CSM; or 50% blood meal, 50% feather meal combination, BFM) fed to supply 0, 40, 80, or 160 g/d of CP. Beginning on d 22 of supplementation, ruminal contents and serum samples were collected at -2, 0, 3, 6, 9, 12, 18, 24, 30, 36, and 48 h relative to the morning offering of hay. On d 24, feces and urine were collected for 72 h. In Exp. 2, four ruminally cannulated steers were used in a replicated 4 × 4 Latin Square to evaluate utilization of supplements differing in quantity and ruminal CP degradability. Steers were fed 6.8 kg/d chopped sudangrass hay (3.7% CP, 74% NDF on OM basis) and supplemented with 56 g/d of a salt mineral mix (CON); CON + 28 g/d blood meal + 28 g/d feather meal (BFM); CON + 98 g/d CSM (LCS); or CON + 392 g/d CSM (HCS). Treatments provided 0, 40, 40, or 160 g/d of CP for CON, BFM, LCS, and HCS; respectively. In Exp. 1, N utilization and total tract NDF digestibility were not affected by protein sources or levels (P > 0.18). Ruminal NH3 concentrations exhibited a quadratic response over time for UREA (P < 0.05) and was greater with increasing levels of UREA (P < 0.05); whereas BFM or CSM did not differ (P > 0.05) by level or across time. In Exp. 2, supplementation had a tendency (P = 0.09) to increase DM disappearance. Supplementation also increased (P < 0.01) serum glucose concentrations; however, no difference (P > 0.28) was found between supplements. Serum urea N and ruminal NH3 concentrations were increased (P < 0.01) in steers fed HCS. Feeding low quantities of a high-RUP supplement maintained rumen function without negatively affecting DM or NDF digestibility of a low-quality forage diet.