PSII-23 Effect of Protein Supplementation Level and Degradability on N Balance in Steers Consuming Low-Quality Forage: Ii.Bos Taurus Indicus

Abstract

Abstract Low-quality forage lacks the nitrogen (N) necessary for optimal forage utilization and animal performance. Supplemental protein improves forage utilization by increasing ruminally available N and energy supply to the animal. Together these two are expected to increase N absorption and balance. Therefore, our objective was to determine the effect of ruminal degradability and level of protein supplementation on N balance in Bos taurus indicus steers. Accordingly, six ruminally cannulated Brahman steers (BW 369 ± 51 kg) were used in a 5 × 5 Latin square to evaluate the interaction between level and degradability of protein supplementation when consuming King Ranch Bluestem hay (3.5% CP, 71.0% NDF). Treatments were arranged as a 2 × 2 factorial with steers receiving protein supplements (43% CP) with two ruminal degradable protein levels; 35% RDP (35%; 58% corn gluten meal and 42% soybean hulls) and 70% RDP (70%; 100% soybean meal). Supplements were fed at two levels, providing 1.26 or 2.53 g of supplement/kg BW (LOW and HIGH). A control (CON) provided no supplement. Five, 14-d periods, consisted of 9 d adaptation and 4 d to measure intake, digestion, and N balance, and 1 d for ruminal fermentation. No degradability × level interactions were significant (P > 0.10) for any measures of N balance. Forage organic matter intake increased (P < 0.01) in response to supplementation, forage N intake tended to increase (P = 0.06). Supplemental N intake increased with increased supplementation, as designed, (P < 0.01) resulting in a significant increase in total N intake (P < 0.01). Degradability tended (P = 0.09) to affect supplement N intake with 70% RDP being greater than 35% RDP. Fecal N excretion increased 50% for LOW and 68% for HIGH (P < 0.01) compared with CON but did not differ (P = 0.24) between RDP levels. Urinary N excretion increased with increasing level (P < 0.01) and degradability (P < 0.01) of the protein supplement. Urinary N excretion increased 250% for the 70% HIGH supplement and 84% for the 35% HIGH supplement. Nitrogen absorption increased from -3.8 g N/d for unsupplemented steers to 38.8 and 48.8 g N/d for the 35% HIGH and 70% HIGH, respectfully (P < 0.01). Nitrogen retention increased (P = 0.03) with level of supplementation from -19.1 g N/d for unsupplemented steers to 10.6 and 9.7 g N/d for 35% HIGH and 70% HIGH, respectfully. Providing supplemental N to Bos taurus indicus increased N intake, excretion, absorption, and retention. Level of ruminal degradability did not affect the amount of N retained or absorbed suggesting that protein supplementation regardless of ruminal N degradability will improve N balance in Bos taurus indicus consuming low-quality forage.