A Chihuahuan Desert Brangus Breeding Program: Feed Efficiency, Metabolic Hormones, and Puberty in Heifers Sired by Bulls with Differing Expected Progeny Differences for Growth and Scrotal Circumference12

Our objectives were to evaluate growth, feed intake characteristics, metabolic hormones, and puberty in heifers from a Chihuahuan Desert Brangus breeding program. Heifers were of similar age and progeny of sires (n > 7 heifers per sire) with expected progeny difference [EPD (accuracy)] for yearling BW (kg) and scrotal circumference (cm) of 27.6 (0.54) and 0.1 (0.42) for a large growth-moderate scrotal circumference sire (LG-MSC), 16.4 (0.59) and 0.9 (0.47) for a moderate growth-large scrotal circumference sire (MG-LSC), and 17.8 (0.54) and 0.4 (0.37) for a sire with balanced EPD values (balanced). Heifers were trained to a Calan gate system (American Calan, Inc., Northwood, NH) for feed intake evaluation and were fed a diet of 11.6% CP and 79.4% TDN from 12.5 to 15.5 mo of age. Heifers from the balanced and LG-MSC sires had greater (P < 0.05) adjusted 205-d and 365-d BW than did heifers from the MG-LSC sire. Heifers from the balanced sire achieved puberty 1.6 mo earlier and at lesser (P < 0.05) BW than heifers from the MG-LSC or LG-MSC sires and consumed less (P < 0.05) feed. Residual feed intake was less (P < 0.05) in balanced and LG-MSC heifers than in MG-LSC heifers (−0.59 = −0.38 < 0.70 ± 0.3 kg/ d). Serum concentrations of insulin were less (P < 0.05) in heifers from a sire with balanced EPD relative to heifers from the MG-LSC sire (2.8 < 5.1 ± 0.7 ng/mL). This hormone concentration was also associated (r ≥ 0.45; P < 0.05) with age at puberty and concentrations of other metabolic hormones, particularly leptin. Results suggest that heifer progeny from a sire with balanced EPD for growth and scrotal circumference from a Chihuahuan Desert Brangus breeding program appear to have serum concentrations of insulin and feed intake characteristics more favorable for earlier puberty than heifers from a LG-MSC or MG-LSC sire.