Effects of postweaning diet on age and weight at puberty and milk production of heifers

One hundred 7-mo-old spring-born beef heifers (215 kg) were used to evaluate effects of level of supplementation and short-term concentrate feeding on age and weight at puberty and milk production. In each of two winters, heifers were individually fed 0.9 kg/d of a 40% CP supplement (SBM) or 1.8 or 2.7 kg/d of a 20% CP supplement (LOW-20 or HIGH-20, respectively) while grazing dormant native pastures or 0.9 kg/d of SBM until February, and then fed a high-concentrate diet (NEg = 1.31 Mcal/kg) in drylot to weigh the same as HIGH-20 heifers on May 1, the beginning of the breeding season. Weights on May 1 were similar for HIGH-20 and DRYLOT heifers (320 and 314 kg, respectively) and were heavier (P 0.01) than those of LOW-20 heifers (289 kg), which were heavier (P 0.01) than SBM-fed heifers (278 kg). Pubertal weight was similar for SBM, LOW-20, and DRYLOT (290, 296, and 297kg, respectively) and heaviest for HIGH-20 heifers (P 0.01, 325 kg). DRYLOT heifers reached puberty at 29 d younger (P 0.05) than heifers on the other treatments. Percentage of heifers puberal on May 1 were 0, 9, 13, and 72 for SBM, LOW-20, HIGH-20, and DRYLOT heifers, respectively. Pregnancy rates were significantly lower for SBM (67%) than for LOW-20, HIGH-20, and DRYLOT (94, 94, and 86%, respectively). Milk production after first parturition was similar for all treatments. Age and weight at puberty may be altered by short-term feeding of high-concentrate diets. The amount of supplemental energy may affect pregnancy rates even though body weight and condition score are not affected