Effect of undegradable intake protein supplementation on intake, digestion, microbial efficiency, in situ disappearance, and plasma hormones and metabolites in steers fed low-quality grass hay

¹ Department of Animal and Range Sciences, North Dakota State University, Fargo, 58105

^* To whom correspondence should be addressed. E-mail: joel.caton{at}ndsu.edu.

	Abstract

Four ruminally and duodenally cannulated beef steers (492 ± 30 kg) were used in a 4 x 4 Latin square design to evaluate the effect of undegradable intake protein supplementation (UIP) on intake, digestion, microbial efficiency, in situ disappearance, and plasma hormones and metabolites in steers fed low-quality grass hay. Steers were offered chopped (10.2 cm) grass hay (6.0% CP) ad libitum and 1 of 4 supplements. Supplemental treatments (1,040 g DM daily), offered at 0800, were control (no supplement), low, medium, and high levels of UIP (supplements provided 8.3, 203.8, and 422.2 g of UIP/d, respectively). Supplements were formulated to provide similar degradable intake protein (DIP, 22%) and energy (1.77 Mcal NE_m/kg). Blood samples were taken at -2, -0.5, 1, 2, 4, 8, 12, and 24 h after supplementation on d 1 (intensive sampling) and at -0.5 h before supplementation on d 2, 3, 4, and 5 (daily sampling) of each collection period. Contrasts comparing control vs. low, medium, and high; low vs. medium and high; and medium vs. high levels of UIP were conducted. Apparent and true ruminal OM and nitrogen (N) digestion increased (P < 0.03) in steers fed supplemental protein compared with controls, but there were no differences (P > 0.26) among supplemental protein treatments. There were no differences (P > 0.11) among treatments for NDF or ADF digestion, total VFA, or microbial protein synthesis. Ruminal pH was not different (P = 0.32) between control and protein supplemented treatments; however, ruminal pH was greater (P = 0.02) for medium and high UIP compared with low UIP supplementation. Daily plasma insulin concentrations were increased (P = 0.004) in protein supplemented steers compared with control and were reduced (P = 0.003) in steers fed low UIP compared with steers fed greater levels of UIP. Intensive and daily plasma urea N concentrations were increased (P < 0.01) in protein supplemented steers compared with control and increased (P < 0.02) for intensive and daily, respectively) in steers supplemented with medium and high UIP compared with low UIP. Supplemental protein increased apparent and true ruminal OM and N digestion, and medium and high levels of UIP increased ruminal pH compared with the low level. Increasing level of UIP increases urea N and baseline plasma insulin concentrations in steers fed low-quality hay.

Key Words: digestion, forage, insulin, protein supplementation, steers