Abstract
Using a retrospective evaluation of feed efficiency, 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 crossbreeding program utilizing a five-breed diallel mating scheme using Angus, Brahman, Hereford, Holstein and Jersey breeds. At approximately 6 months of age, pre-pubertal heifers were individually penned and received ad libitum access to a balanced diet. Individual feed intake and body weight data were collected at 28-day intervals for 84 days prior to puberty and for 90 days after puberty. The diet was changed at puberty to provide a lower energy density. Considering all females as cohorts, RFI was calculated for each heifer for each period using separate models for the pre- and post-pubertal periods. A moderate, positive Pearson correlation (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 order 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.
Highlights
Feed provided to cattle represents a significant portion of the cost of producing beef [1]
The Beef Improvement Federation (BIF) has developed guidelines to standardize the methodology for residual feed intake (RFI) evaluation [2]
body weight (BW) and average daily feed intake (ADFI) were greater for the post-pubertal period than for the pre-pubertal period
Summary
Feed provided to cattle represents a significant portion of the cost of producing beef [1]. Selection strategies for improving feed efficiency have been shifting away from the conventionally used feed:gain ratio (FG) and are incorporating residual feed intake (RFI) as an indicator of feed efficiency in beef cattle. Many variables can influence the outcome of an RFI evaluation; many of these factors can be controlled (i.e. test duration, type and amount of diet provided, selection of cohorts of animals, etc.). The Beef Improvement Federation (BIF) has developed guidelines to standardize the methodology for RFI evaluation [2]. It is recommended that cattle be at least 240 days of age and not differ by more than 60 days of age at the beginning of an RFI feeding trial [2]. Cattle may be of similar chronological age, they may differ in physiological maturity since an important biological phenomenon (puberty) may occur during this time in bulls and heifers
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