Pregnant beef heifers categorized by residual feed intake measured in adolescence exhibit differential intake and feeding behaviors when fed a restricted diet

Abstract Text: Selection for residual feed intake (RFI) in cattle will bring about changes in metabolism and physiology that are not explicitly known. We appraised feed intake and feeding behaviour in heifers, characterized by a range of RFI, when fed two different planes of nutrition from day 30 to 150 of pregnancy. Sixty-nine purebred Angus heifers, with RFIf (RFI corrected for fat, ave=0.047, SD=0.7678) measured in adolescence, entered a GrowSafe® automated feed intake recording system after confirmation of pregnancy at 30-days post artificial insemination (AI). Heifers were divided randomly, yet equally in terms of RFIf, weight at start of test (SOT), and SOT rib and rump fat, into 2 diet-groups. Heifers received a ration formulated to allow gain of either 0.5 kg/d (L-diet), or 0.7 kg/d (H-diet). Rations were fed until 150 d of pregnancy, and were adjusted periodically to account for heifer and fetal growth plus decreasing fall temperatures. Heifer weight, as well as rib and rump fat were measured approximately once every 4 weeks, and individual feed intake and feeding behaviour was continuously measured by GrowSafe®. All weight and fat measurements, feed intake and behaviour were analyzed using PROC GLM in SAS 9.0, with RFIf, diet (H- or L-diet), RFIf*diet, and AI (1^st or 2^nd) included in the model. There were no significant differences due to RFIf, diet, or their interaction on SOT weight, or SOT rib and rump fat. By end of test (EOT), significant diet effects were seen upon EOT weight, both EOT rib and rump fat, and ADG during the feed trial (P<0.01), with heifers consuming H-diet displaying higher weights and fat measurements, but no effect of RFIf was detected. However, significant diet and RFIf effects were detected in average daily intake, feeding duration and head-down time (P<0.05), where heifers with lower RFIf ate less, had a lower average daily feeding duration and head-down time, than those with higher RFIf. Therefore, regardless of diet consumed and under limiting nutritional conditions, low RFIf pregnant heifers ate less, yet maintained the same growth and body condition when compared to high RFIf pregnant heifers. This result is important as RFIf is typically measured on virgin animals and under ad-libitum conditions. If selection for RFI is to become mainstream in the cattle industry, investigating the performance of high and low RFI animals in different nutritional environments and physiological conditions is important.

Keywords: Behavior, cattle, residual feed intake