title: 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.
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 (UIP) supplementation on intake, digestion, microbial efficiency, in situ disappearance, and plasma hormones and metabolites in steers fed low-quality grass hay. The steers were offered chopped (10.2 cm in length) grass hay (6.0% CP) ad libitum and 1 of 4 supplements. Supplemental treatments (1,040 g of DM daily), offered daily at 0800, were control (no supplement) or low, medium, or high levels of UIP (the supplements provided 8.3, 203.8, and 422.2 g of UIP/ d, respectively). The supplements were formulated to provide similar amounts of degradable intake protein (22%) and energy (1.77 Mcal of 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 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, or total ruminal 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 supplementation with medium and high compared with low UIP. Daily plasma insulin concentrations were increased (P = 0.004) in protein-supplemented steers compared with controls 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 controls and increased (P < 0.02) for intensive and daily sampling, 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. An increasing level of UIP increases urea N and baseline plasma insulin concentrations in steers fed low-quality hay.
authors.affiliation: Department of Animal and Range Sciences, North Dakota State University, Fargo 58105, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Reed
authors.forename: M R
authors.initials: MR
authors.lastname: O'Neil
authors.forename: G P
authors.initials: GP
authors.lastname: Lardy
authors.forename: K A
authors.initials: KA
authors.lastname: Vonnahme
authors.forename: L P
authors.initials: LP
authors.lastname: Reynolds
authors.forename: J S
authors.initials: JS
authors.lastname: Caton
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000382:microbiology / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D004044:Dietary Proteins / Q000378:metabolism*; D019587:Dietary Supplements; D004063:Digestion / Q000502:physiology*; D005247:Feeding Behavior; D007328:Insulin / Q000097:blood; D008297:Male; D012417:Rumen / Q000378:metabolism / Q000382:microbiology
chemical_list: D004044:Dietary Proteins; D007328:Insulin