Master of Science (MS)


Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type



Breeding beef heifers to produce calves at 2 years of age could be a profitable management decision. The current practices have proved inefficient, which has justified further research in the area. The objective of this study was to examine the effects of repeated progestogen priming on the attainment of puberty by prepubertal heifers, to evaluate the potential additive effect of progestogen priming plus sodium monensin on the attainment of puberty by prepubertal heifers, to examine subsequent reproductive performance, including the response to synchronization of the estrous cycle, first-service pregnancy rates and overall pregnancy rates and to examine the effects of repeated progestogen priming on follicular dynamics of prepubertal beef heifers. Data were collected and analyzed for birth weight, adjusted weaning weight, postweaning gain/loss in weight and daily gain throughout the experiment. Also the average frame score, average breeding weight, average breeding body condition score, average change in body condition score, average number of animals that showed estrus behavior prior to the breeding season, average number of animals that responded to synchronization, average number of corpora lutea formed during the treatment periods, reproductive tract score at breeding as well as the change in reproductive tract score, follicle populations, change in ovary scores throughout the experiment, pregnancy percentage and the average fetal age at pregnancy determination were evaluated. In this study, treatment groups fed sodium monensin (Rumensin and MGA+Rumensin groups) had significant (P<0.05) advancements in fertility and maturational status when compared with Control animals. The MGA group did excel in follicle development when compared with the Control group, but more heifers became pregnant from artificial insemination combined with natural mating in the Rumensin groups than in the Control group. In conclusion, these experiments provide evidence for the positive effect of sodium monensin on puberty attainment and increased overall pregnancy rates when using artificial insemination in conjunction with natural mating. However, the additive effect of melengestrol acetate, if any, is yet to be defined.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Robert A. Godke