The relationship between residual feed intake and feeding behavior in growing heifers
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The objective of this study was to determine if feeding behavior traits are correlated with performance and feed efficiency traits in growing heifers. Individual dry matter intake (DMI) was measured in Brangus heifers (n = 115) fed a roughage-based diet (ME = 2.1 Mcal/kg) for 70 d using Calan gate feeders (6 heifers/pen). Residual feed intake (RFI) was computed as the residuals from linear regression of DMI on mid-test BW0.75 and average daily gain (ADG). Heifers with the highest (n = 18) and lowest (n = 18) RFI were identified for feeding behavior measurements. During days 28 through 56 of the 70-d feeding trial, continuous video recordings were obtained for all heifers. Video images of two sets of four 24-h periods, two weeks apart, were analyzed for the focal animals. All occurrences of feeding were timed and counted per day, and the eight 24-h periods averaged to derive the overall feeding event (FE) and meal duration and frequency for each focal heifer. Total feeding event duration was defined as the total min per day the animals head was down in the feed bunk. A meal included all visits an animal made to the feed bunk that were separated by less than 5 min. The mean RFI values for the low and high RFI heifers were (mean SE) - 1.03 and 1.00 0.03 kg/d, respectively. Low RFI heifers consumed 21.9% less (P < 0.0001) DMI, but had similar BW and ADG compared to high RFI heifers. Heifers with low RFI spent more time (P < 0.0001) eating (152 vs 124 4.26 min/d) at a lower eating rate (62.8 vs 99.6 3.28 g/min), but had similar FE frequencies compared to high RFI heifers. Feeding event duration was negatively correlated with RFI while FE frequency and FE eating rate were positively correlated with RFI. However, meal duration and frequency were not correlated with RFI. Therefore, measuring FE characteristics could prove more useful than analyzing meals when trying to predict RFI. Additionally, eating rate appeared to be more closely related to RFI than any of the other feeding behavior traits measured.
