Thundathil, JacobKastelic, JohnDance, Alysha2016-06-142016-06-1420162016http://hdl.handle.net/11023/3054Holstein bull calves often reach AI centers in suboptimal body condition. Early-life nutrition is reported to increase reproductive performance in beef bulls. The general aim of this thesis was to determine effects of early-life nutrition on reproductive performance of Holstein bulls. We hypothesized that Holstein bull calves on high-nutrition diets during early-life will have larger testes, greater sperm production, and be younger at puberty than those on low-nutrition diets. We determined that bulls fed the high-nutrition diet from 2 to 31 wk were younger at puberty, had larger testes and had higher concentrations of circulating IGF-I than low-nutrition bulls. Furthermore, early-life nutritional modulation did not alter semen quality. The high-nutrition bulls had more proliferating and differentiating Sertoli cells earlier in life than low-nutrition bulls and IGF-I promoted proliferation of bovine Sertoli cells in culture. Overall we demonstrated that IGF-I has important roles in bovine reproduction and we identified key periods during bull development where it appeared that nutritional modulation affected testes development. Therefore, nutritional modulation can be recommended as a management tool to improve reproductive potential of AI bulls. In addition, we inferred that nutritional modulation may serve as a model for studying mechanisms controlling reproductive development in bulls.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.Veterinary ScienceVeterinary ScienceBovineNutritionPubertyMale reproductiondoctoral thesis10.11575/PRISM/27153