Development of Replacement Heifers Using Programmed Feeding1

This experiment was conducted to determine the effects of diet and pattern of gain on reproductive performance. On November 24, 80 spring-born Angus- and Brangus-sired heifers (BW = 230 ± 23 kg) were allotted by breed and BW to one of four treatments (two replicates per treatment). Heifers were program-fed to gain 0.68 kg/d until April 14 (134 d, MODERATE), grazed wheat (cv. Hickory, Triticum aestivum L.) and ryegrass (cv. Marshall, Lolium multiflorum Lam.) interseeded into bermudagrass pasture (GRAZED), or were program-fed to gain 0.23 kg/d until February 4 (71 d) and then program-fed to gain 0.91 kg/ d (63 d, SLOW-FAST) or grazed wheat and ryegrass pastures (SLOW-GRAZED). On February 4, MODERATE heifers were heavier (P<0.05) than heifers on other treatments, but BW did not differ on April 8 (P=0.46). At the end of breeding, GRAZED heifers were heavier (P<0.05) than MODERATE and SLOW-FAST heifers; SLOW-GRAZED heifers were intermediate. Over the dry-lot feeding period, the MODERATE heifers consumed more (P=0.04) feed than SLOW-FAST heifers, but feed efficiency did not differ (P=0.57). Age and BW at puberty did not differ (P>0.70) among treatments. Pregnancy rate tended to be less (P=0.16), conception date was later (P<0.05), and serum urea N (SUN) tended to be greater (P=0.14) for GRAZED and SLOW-GRAZED heifers than for MODERATE and SLOW-FAST heifers. Program feeding can be a valuable tool for developing replacement heifers as long as BW goals pre-breeding are reached. Grazing heifers on cool-season annuals during breeding may impair reproduction as a result of the high forage N concentrations, causing reduced fertility.