PSI-8 Evaluating the Effects of Individual Eating Rates of Feedlot Heifers on Ruminal Fermentation Using an Ex vivo Model

Abstract

Abstract The objective was to determine if the eating rate of individual feedlot heifers affects ruminal fermentation using an ex vivo model. Differences in eating rate could affect ruminal fermentation and predispose an animal to be susceptible to metabolic disorders. From a contemporary group of Simmental × Angus heifers (n = 90; BW = 323 kg), 14 heifers were selected for divergent individual eating rates. During the initial 30 d on the finishing diet, a GrowSafe feed intake system was used to identify the heifers with the 7 fastest (7.60 kg DM / h; 9.25 kg DMI in 1.2 h) and 7 slowest (1.38 kg DM / h; 9.24 kg DMI in 6.7 h) eating rates. Prior to feeding, rumen fluid was collected via esophageal tubing 1 d after intake evaluation period. Each rumen fluid sample was mixed with McDougall’s buffer and a common feed substrate (similar to finishing diet). Then the samples were incubated for 24 and 48 h. In vitro dry matter disappearance (IVDMD), pH, volatile fatty acids (VFA), and ammonia were measured following incubation. The MIXED procedure of SAS 9.4 was used for statistical analysis. No eating rate by incubation time interactions (P ≥ 0.11) were observed. Although heifer eating rate did not affect (P = 0.65) IVDMD, values were greater (P < 0.01) at 48 h compared with 24 h. While time affected pH as it decreased (P < 0.01) from 24 to 48 h, heifer eating rate did not affect (P = 0.84) pH. Eating rate had no effect (P ≥ 0.10) on ammonia, total VFA, and molar proportions of acetate, propionate, isobutyrate, butyrate, valerate, and isovalerate at 24 h. Overall, the results indicated individual eating rates of feedlot heifers did not affect ruminal fermentation using an ex vivo model.