The Role of Nutrition and Administration of Estrogen in Holstein Calf Growth, Development, and Adenogenesis
Raising replacement heifers consumes a large portion of dairy and beef producers' income. An ultimate goal of producers is to decrease inputs and maximize outputs to produce fertile replacement heifers. Manipulating early postnatal growth and development through diet enables this practice to be successful. Puberty is greatly influenced by body weight (BW). Once heifers reach puberty, they become fertile and can achieve their reproductive potential. Growth can easily be influenced during the preweaning phase of development. Offering calves a higher plane of nutrition through milk diets prior to weaning hastens development and can lead to an earlier age at the onset of puberty. The objective of the first study was to understand how plane of nutrition influences BW, bone mineralization, and organ growth during the preweaning phase of development in Holstein calves. Calves offered a higher plane of nutrition experienced greater BW gains, increased bone mineralization, and accelerated organ growth. The second study evaluated plane of nutrition on reproductive development, specifically adenogenesis in Holstein heifer calves. Adenogenesis, or the development of uterine glands, is initiated in the early postnatal period. It involves rapid endometrial epithelial cell proliferation, germinal bud formation, invasion into the stroma, and extensive branching and coiling. Little is known about how nutrition impacts adenogenesis in ungulates, however, this study provided validation that it does drive gland formation. Additionally, this study assessed the influence of exogenous estradiol on reproductive development and adenogenesis when given after the completion of adenogenesis. We can confirm that exogenous estradiol given after the completion of adenogenesis does not alter the outcomes of gland formation. The beneficial effects of feeding a higher plane of nutrition to calves prior to weaning on bone mineral density, organ growth, and adenogenesis may provide new possibilities for understanding the impacts of early nutrition on calf immune responses and productive lifespan of the cow. Collectively, these studies emphasize the importance of nutrition during preweaning growth and development of Holstein calves.