Effects of concurrent selection for residual feed intake and average daily gain on fertility and longevity in black Angus beef females

Abstract Text:

During an individually-fed feed efficiency test, traits including ADG, DMI, G:F, residual feed intake (RFI), and residual gain (RG) are evaluated.  Almost invariably, ADG and RFI are the only traits in this list that are not correlated. Previous data would suggest that RFI does not affect fertility; however, a selection index that incorporates RFI and improves fertility has not been well defined.  Thus, the objective was to determine if concurrent selection for RFI and ADG may identify beef heifers that have improved fertility and longevity in the beef herd.  Yearling feed efficiency testing and subsequent production data were collected on 540 purebred, Black Angus heifers from 14 contemporary groups over 6 yr.  These data were unbiased in that heifers were retained based on fertility, irrespective of feed efficiency performance indicators.  Cattle that were both above contemporary group average for ADG as well as below contemporary group average for RFI were categorized as PASS, and all other heifers were categorized as FAIL.  The MIXED and GLIMMIX procedures of SAS were used to analyze continuous and binary variables, respectively.  The model included heifer category as the main effect and included contemporary group as a random effect. Across the dataset, ADG and RFI were not correlated (P = 0.64).  Yearling pregnancy rates did not differ (P = 0.14) between PASS (87.2%) and FAIL (82.3%), nor did the proportion of heifers that became pregnant in the first 21 d of the breeding season (P = 0.69).  Pregnancy rate as a 2-yr-old tended to be greater (P = 0.07) in PASS (85.7%) compared to FAIL (75%).  Moreover, the proportion of females that remained in the herd at 3, 4, and 5 yr or age was greater (P ≤ 0.05) in PASS than FAIL.  It should be noted that PASS did not differ from FAIL for phenotypic birth BW, weaning BW, yearling BW, or yearling height (P ≥ 0.53).  Furthermore, nonparent EPDs for calving ease maternal, scrotal circumference, milk, and ribeye area did not differ between PASS and FAIL (P = 0.42).  However, PASS tended to have a greater nonparent marbling EPD than FAIL (0.409 vs. 0.375, respectively).  These data indicate that dual selection for ADG and RFI may identify beef heifers that have improved fertility and longevity without impacting growth and maternal EPDs.               

Keywords: feed efficiency, fertility, residual feed intake