EFFECTS OF POSTWEANING DIET AN AGE AND WEIGHT AT PUBERTY AND MILK-PRODUCTION OF HEIFERS

One hundred 7-mo-old spring-born beef heifers (215 kg) were used to ev aluate effects of level of supplementation and short-term concentrate feeding on age and weight at puberty and milk production. In each of t wo winters,heifers were individually fed .9 kg/d of a 40% CP supplemen t (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 .9 kg/d of SBM until February, and then fed a high-concentrate diet (NE(g) = 1.31 Mca l/kg) in drylot to weigh the same as HIGH-20 heifers on May 1, the beg inning 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 < .01) than those of LOW-20 heifers (289 kg), which were heavier (P < .01) than SBM-fed heifers (278 kg). Pubertal weight was similar for SBM, LOW-20, and DRYLOT (290, 296, and 297 kg, respectively) and heav iest for HIGH-20 heifers (P < .01, 325 kg). DRYLOT heifers reached pub erty at 29 d younger (P < .05) than heifers on the other treatments. P ercentage of heifers puberal on May 1 were 0, 9, 13, and 72 for SBM, L OW-20, HIGH-20, and DRYLOT heifers, respectively. Pregnancy rates were significantly lower for SBM (67%) than for LOW-20, HIGH-20, and DRYLO T (94, 94, and 86%, respectively). Milk production after first parturi tion 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 weigh t and condition score are not affected.