PS-5 In Vitro NDF Digestibility and In Vitro Dry Matter Digestibility and Disappearance Are Similar Between Beef Heifers Differing in Feed Efficiency

Abstract

Abstract Feed efficiency is a critical component of improving beef production. Previous research has indicated that differences among lowly and highly feed efficient animals may be the result of differences in digestibility through the gastrointestinal tract. The objective of this study was to evaluate differences in neutral detergent fiber (NDF) and in vitro dry matter digestibility (IVDMD) in the rumen and cecum over time. To determine feed efficient animals to utilize, 134 yearling heifers were individually fed ad libitum for 84 days using a Calan Broadbent Feeding system (Northwood, NH, USA). Heifers were fed a total mixed ration containing 86% ground brome hay, 10% wet distillers grains with solubles, and 4% mineral supplement. Heifers were stratified by body weight and at the end of the feeding period, and sixteen heifers with the least and greatest average daily gain (ADG) were chosen for sampling. Low ADG heifers (n = 8) gained 0.5 ± 0.6 kg/d and high ADG heifers (n = 8) gained 0.85 ± 1.0 kg/d. Rumen content and cecal content were collected from heifers and incubated to determine in vitro NDF and IVDMD over 0, 6, 12, 24, 36, and 48 hours. Samples were incubated in triplicate in individual conicals utilizing the Tilly and Terry method. After incubation, samples were freeze-dried. After freeze-drying, 0.3g of sample was added to F57 fiber bags for determination of NDF disappearance using the ANKOM 200 fiber analysis system. Samples were grouped by site and time of incubation to avoid errors between samples. Data were analyzed using the MIXED procedure of SAS, with fixed effects of treatment (efficiency), collection site (rumen or cecum), incubation time, and interactions. Significance was determined at P ≤ 0.05 and tendencies at 0.05 ≤ P ≤ 0.10. There was a significant effect of site (P < 0.0001), and incubation time (P < 0.0001), as well as a site × incubation interaction (P = 0.01) for NDF disappearance. Treatment did not impact NDF disappearance (P = 0.53), and site × treatment was not significant (P = 0.26), however a tendency for a treatment × incubation time was observed (P = 0.08). In vitro dry matter digestibility was significantly affected by time of incubation (P < 0.0001), site × incubation (P = 0.01), and site × treatment (P = 0.03). Treatment did not affect IVDMD (P = 0.87), nor did site of sampling site (P = 0.64), and a treatment × incubation effect was not observed (P = 0.14). In conclusion, the efficiency of cattle was determined to not play a role in NDF disappearance or in vitro dry matter digestibility. These data indicate that additional factors, including forage type, microbial communities, and host genetics, play a larger role in influencing differences in forage digestibility.