Using a retrospective evaluation of feed effi- ciency, this study investigated the effects of physiological age on residual feed intake (RFI) in growing heifers. Data were collected during 1973 and 1974 at the McGrego...Using a retrospective evaluation of feed effi- ciency, this study investigated the effects of physiological age on residual feed intake (RFI) in growing heifers. Data were collected during 1973 and 1974 at the McGregor location of the Texas Agricultural Experiment Station. Heifers (n = 77) were obtained from a large crossbreed- ing program utilizing a five-breed diallel mating scheme using Angus, Brahman, Hereford, Hol- stein and Jersey breeds. At approximately 6 months of age, pre-pubertal heifers were indi- vidually penned and received ad libitum access to a balanced diet. Individual feed intake and body weight data were collected at 28-day in- tervals for 84 days prior to puberty and for 90 days after puberty. The diet was changed at puberty to provide a lower energy density. Con- sidering all females as cohorts, RFI was calcu- lated for each heifer for each period using separate models for the pre- and post-pubertal periods. A moderate, positive Pearson correla- tion (r = 0.48;P < 0.001) was detected between pre- and post-pubertal RFI. Furthermore, heifer RFI rank was compared between the pre- and post-pubertal periods using Spearman rank or- der correlation and a similar correlation (r = 0.46;P < 0.001) was revealed. This suggests that RFI determined during the pre-pubertal period may only be a moderate predictor of post-pubertal RFI. As a result, physiological age should be considered when evaluating cattle for feed efficiency using RFI.展开更多
文摘Using a retrospective evaluation of feed effi- ciency, this study investigated the effects of physiological age on residual feed intake (RFI) in growing heifers. Data were collected during 1973 and 1974 at the McGregor location of the Texas Agricultural Experiment Station. Heifers (n = 77) were obtained from a large crossbreed- ing program utilizing a five-breed diallel mating scheme using Angus, Brahman, Hereford, Hol- stein and Jersey breeds. At approximately 6 months of age, pre-pubertal heifers were indi- vidually penned and received ad libitum access to a balanced diet. Individual feed intake and body weight data were collected at 28-day in- tervals for 84 days prior to puberty and for 90 days after puberty. The diet was changed at puberty to provide a lower energy density. Con- sidering all females as cohorts, RFI was calcu- lated for each heifer for each period using separate models for the pre- and post-pubertal periods. A moderate, positive Pearson correla- tion (r = 0.48;P < 0.001) was detected between pre- and post-pubertal RFI. Furthermore, heifer RFI rank was compared between the pre- and post-pubertal periods using Spearman rank or- der correlation and a similar correlation (r = 0.46;P < 0.001) was revealed. This suggests that RFI determined during the pre-pubertal period may only be a moderate predictor of post-pubertal RFI. As a result, physiological age should be considered when evaluating cattle for feed efficiency using RFI.
