Title page for ETD etd-07292005-151652


Type of Document Master's Thesis
Author Getzewich, Karen Elizabeth
Author's Email Address kgetzewi@vt.edu
URN etd-07292005-151652
Title Hormonal regulation of the onset of puberty in purebred and crossbred Holstein and Jersey heifers.
Degree Master of Science
Department Dairy Science
Advisory Committee
Advisor Name Title
Nebel, Raymond L. Committee Chair
Akers, Robert Michael Committee Member
Cassell, Bennet G. Committee Member
Keywords
  • GnRH
  • Crossbreeding
  • Holstein X Jersey
  • Puberty
Date of Defense 2005-07-19
Availability unrestricted
Abstract
The objective of this study was to determine the onset of puberty by using progesterone profiles and anterior pituitary gonadotropin releasing hormone (GnRH) challenges in purebred and crossbred Holstein and Jersey heifers. In experiment 1, fifty prepubertal heifers by four sire - dam classifications (18 HH, 11 JJ, 10 JH, and 11 HJ) were used. The HH heifers attained puberty at an older age than the HJ, JH or JJ heifers, and these three classifications were not different from each other. There were significant differences in weight and wither height at puberty and average daily weight gain (ADWG) between all four sire - dam classifications. Season of birth had a significant effect on age and weight at puberty. In experiment 2, four prepubertal heifers from each sire - dam classification in experiment 1 were used at 3, 6, 9 and 12 mo of age to determine the effects of administering 200 μg GnRH on LH secretion. The effects of breed, age at challenge, and their interaction were only significant for time to LH peak. In conclusion, age at puberty in crossbred Holstein X Jersey heifers is regulated by breed and season of birth, and further research with larger sample sizes is needed to establish the relationship of pituitary maturation and the capacity to secrete LH in response to GnRH stimulation as related to onset of puberty in purebred and crossbred dairy heifers.
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