PSXIII-22 Effects of Isoacids on Rumen Ph, Microbial Protein and in Situ Dry Matter Disappearance in Beef Heifers Fed Growing Diet

Abstract

Abstract The objective of this study was to evaluate effects of feeding supplemental isoacids in a growing diet on parameters of rumen fermentation and in situ DM disappearance. Eight mature ruminally cannulated beef heifers (Angus crossbred; mean BW 618 ± 31 kg) were used in a replicated 4 x 4 Latin square design. Heifers were housed in individual pens and fed the following treatment diets: no supplemental isoacids (ISO) in the basal diet (Control); 7.2 g of 2-methylbutyric acid· animal-1· day-1 (ISO1); 7.2 g of 2-methylbutyric + 7.2 g isobutyric acids· animal-1· day-1 (ISO2); and 7.2 g 2-methylbutyric + 7.2 g isobutyric + 7.2 g isovaleric acid· animal-1· day-1 (ISO3). Basal diet consisted of (DM basis) 26.9% wheat hay, 35.5% steam flaked corn, 22.6% wet corn gluten feed, 12.3% DDG, and 2.7% mineral/vitamin supplement. Each experimental period lasted 28 d, with 21 d for diet adaptation and 7 d for data and sample collection. On day 1 of each sampling period ruminal fluid was collected 2 hours before and 1, 3, 7 and 10 hours after morning feeding. The pH of ruminal contents was immediately measured with an electrode pH meter. Urine samples (approximately 200 mL) were collected on day 2 of each sampling period 4 h after the feeding and filtered to remove particles. Urine was analyzed for creatinine, uric acid, and allantoin. Bags were placed into rumen for 72, 48, 36, 24, 12, 8, 4 and 0 hours and all bags were removed at same time on the end of incubation (hour 0), rinsed with tap water and dried at 55°C. Data were analyzed using the MIXED procedure of SAS. A contrast was observed (P = 0.029) for overall rumen pH between control versus isoacid treatments (6.44 vs 6.31). Uric acid, allantoin, total purines and intestinal flow of microbial nitrogen were not affected by treatments (P ≥ 0.10) with overall means of 10.47, 328.80, 339.27 mmol/d and 246.64 g N/d, respectively. Overall, no effects were observed for in situ dry matter disappearance (P ≥ 0.10). However, at hour 4 differences between ISO2 and ISO3 (P = 0.02; 44.89% vs 38.45%) and ISO2 and ISO4 (P = 0.05; 44.89% vs 39.75%) were observed. No effects of in situ DM disappearance was observed (P ≥ 0.10). Supplementing beef heifers with isoacids may reduce rumen pH as a result of increased ruminal volatile fatty acid production; however, supplemental ISO in this study did not affect microbial nitrogen synthesis or dry matter in situ disappearance. Further analyses are currently in progress.