Recommended duration for evaluating feed intake and validating the residual feed intake model in Brangus heifers
Type of DegreeMaster's Thesis
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In order to determine optimal measurement days, variables best describing variation for dry matter intake (DMI) and effect of residual feed intake (RFI) classification on reproductive and performance traits, RFI was predicted by measuring individual dry matter intake (DMI) and average daily gain (ADG) using 186 Brangus heifers from two southeastern farms over a 70 d test period during 2014 and 2015. Results from standard 70 d DMI intake trials were compared to shortened test length periods of 14, 28, 42 and 56 d by regressing 70 d values of RFI, ADG and DMI on each shortened test length. Test length to predict RFI can be shortened to 56 d without loss of prediction accuracy (R=0.93 (P < 0.0001), R2= 0.90, rp= 0.95 (P < 0.0001), and rs= 0.95 (P < 0.0001)). Including 70 d ultrasound 12th rib fat (UBF) in prediction of RFI, along with DMI and metabolic midweight, accounted for an additional 2% of model variation suggesting inclusion of UBF measurements is warranted. There were no significant differences for ADG, beginning or ending weight or age at first calving for heifers classified as efficient, average or inefficient based on RFI values. This suggests using RFI as a measure of efficiency will not affect other economically important traits. DMI was significantly different (P< 0.001) between RFI classifications. Significant feed cost savings ($63.91) were realized between efficient and inefficient RFI heifers. Shortening the measurement period by 14 d also could provide additional feed cost savings ($11.62/hd) and allow additional animals to be measured for DMI each year.