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Effect of divergence in residual feed intake on feeding behavior, blood metabolic variables, and body composition traits in growing beef heifers

A. K. Kelly^*, M. McGee, D. H. Crews, Jr., A. G. Fahey^*, A.R. Wylie and D. A. Kenny^*

^* School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland , Teagasc, Grange Beef Research Centre, Dunsany, Co. Meath, Ireland , Department of Animal Sciences, Colorado State University, Fort Collins Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9 5PX, Northern Ireland

david.kenny{at}ucd.ie

Abstract

This study examined the relationship of feed efficiency and performance with feeding behavior, blood metabolic variables, and various body composition measurements in growing beef heifers. Individual DMI and growth were measured in yearling Limousin x Holstein-Friesian heifers (n = 86; initial BW = 191.8 (SD = 37) kg) fed a TMR diet comprising 70:30 concentrate:corn silage on a DM basis (ME 2.65 Mcal/kg DM; DM 580 g/kg) for 82 d. Meal duration (min/d) and meal frequency (events/d) were calculated for each animal on a daily basis using the Insentec computerized feeding system. Physical measurements as well as ultrasonic fat and muscle depths were recorded on 3 equally spaced occasions during the experimental period. Blood samples were collected by jugular venipuncture on 4 equally spaced occasions and analyzed for plasma concentrations of IGF-I, insulin, leptin, and various metabolites. Phenotypic residual feed intake (RFI) was calculated for all animals as the residuals from a multiple regression model regressing DMI on ADG and mid-test BW^0.75. Overall, ADG, DMI, feed:gain (F:G), and RFI were 1.51 (SD = 0.13), 6.74 (SD = 0.99), 4.48 (SD = 0.65) and 0.00 (SD = 0.48) kg/d, respectively. Residual feed intake was positively correlated with DMI (r = 0.47) and F:G (r = 0.46) but not with ADG or MBW. Moderate positive correlations ranging from 0.27 to 0.67 were estimated between ultrasonic measures of lumbar fat and accretion over the test period and DMI, FCR, and RFI. The inclusion of gain in lumbar fat to the base RFI model increased R² (0.77 vs. 0.80) of the variation in DMI not explained by MBW and ADG. The Pearson rank correlation between RFI and carcass-adjusted RFI (RFI_c) was high (r = 0.93). From the plasma analytes measured, NEFA (r = -0.23) and BHB (r = 0.39) concentration were correlated (P < 0.05) with RFI. Plasma glucose (r = -0.20), leptin (r = 0.48), glucose:insulin (r = -0.23), NEFA (r = -0.36) and BHB (r = 0.25) were associated (P < 0.05) with F:G. However, systemic IGF-I and insulin were unrelated (P < 0.05) to any measure of feed efficiency. The feeding behavior traits of eating rate, feeding events, and non-feeding events were positively correlated (P < 0.05) with RFI and RFI_c. This multifactorial study provides new information on some of the biological processes responsible for variation in feed efficiency in beef cattle.

Key Words: beef cattle • body composition • feeding behavior • feed efficiency • plasma analytes