Effects of protein supplementation and source in cow/calf systems and heifer development

Four experiments evaluated protein supplementation in cow/calf systems and heifer development diets. In the first experiment, cows grazed dormant Sandhills range and received either supplement or no supplement in late gestation and were fed hay or grazed subirrigated meadow after calving. Heifers from supplemented cows were heavier from weaning through three years of age, had greater pregnancy rates, and more calved during the initial 21 days of calving.; A subsequent experiment evaluated effects of protein supplementation of cows grazing dormant range or corn crop residue on cow and progeny performance. Cows that grazed corn stalks were heavier and had greater BCS before weaning and the subsequent breeding season, and had higher pregnancy rates than cows that grazed winter range. Cow BW and BCS prior to calving and breeding, and calf weaning BW was greater for calves from supplemented cows that grazed range. Final BW of steer progeny was heavier if dams grazed corn residue. Dam supplementation increased the proportion of steers grading USDA Choice. Heifer pre-breeding BW was greater for heifers from supplemented cows that grazed range than unsupplemented cows.; Additional experiments compared protein source during heifer development on reproductive performance. Heifers in the first experiment were fed dried distillers grains (DDG) as an energy source during development. The control supplement contained similar crude protein, energy, and lipid but differed in protein degradability. Growth, BCS, and age at puberty were similar between treatments. Heifers fed DDG had greater conception and pregnancy rates.; A final experiment evaluated the effects of feeding soybeans or DDG on reproductive characteristics of heifers. Pregnancy rate was unaffected by supplement, but heifers fed soybeans had greater dominant follicle diameter. Vascular Endothelial Growth Factor (VEGF) mRNA expression of the angiogenic isoform VEGF120 and the anti-angiogenic isoform VEGF164b were greater in granulosa cells from heifers fed DDG compared to heifers fed soybeans, expression of the dominant angiogenic isoform VEGF164 was not affected by treatment.; In summary, these experiments support a fetal programming effect of protein supplementation in cow/calf systems, increased fertility in heifers supplemented with DDG, and differential VEGF gene expression due to supplement.