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Effect of estrus activity when evaluating feed efficiency in heifers
The objective of this trial was to evaluate the impact estrus activity has on feed efficiency measurements. Virgin, yearling, Angus and Sim-Angus heifers from six weaning contemporary groups numbering 169 total head were placed into a 70 day feed intake trial as described by the Beef Improvement Federation guidelines. All heifers received Kamar estrus detection patches at the start of the trial to assist in estrus detection. Daily, individual animal feed dry matter intake was measured and estrus activity was monitored. At the end of the trial the number of estrous cycles along with the calculated residual feed intake (RFI) and residual gain (RG) were evaluated for each animal using SAS proc mixed procedure. Heifers that did not show any estrus activity, those that appeared to undergo puberty and display their first estrous cycle and those that showed consistent estrous cycles were compared. Those animals that appeared to undergo puberty and display their first estrous cycle while on test showed poorer RFI (P<.11) and RG (P<.05) when compared to those that did not cycle. When compared with those that consistently cycled the same pattern continued with RFI (P<.03) and RG (P<.02). The animals that cycled consistently and those that did not show any estrus activity did not appear to differ with RFI (P<.34) and RG (P<.34).
Keywords: RFI Estrus Heifers