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Treating heifers with GnRH from 4 to 8 weeks of age advanced growth and the age at puberty

Lookup NU author(s): Dr Suzanne Madgwick, Dr Andrew Beard

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Abstract

In heifer calves, an early transient increase in circulating concentrations of LH is associated with early follicular development and is thought to regulate the timing of puberty. In an attempt to hasten the onset of sexual maturity, the early rise in LH concentration was advanced by injecting heifer calves with 120 ng/kg of GnRH (n = 6) twice daily from 4 to 8 weeks of age; control calves received saline (n = 6). Blood samples were collected every 15 min for 10 h at 4, 8, 14, 20, 26, 32, 38, 44 and 50 weeks of age. Treatment with GnRH increased mean circulating concentrations of LH at 8 weeks of age (P < 0.05), LH pulse frequency at 4 and 8 weeks of age (P < 0.05), and reduced the mean age at puberty by 6 weeks (56.8 ± 1.7 versus 62.8 ± 2.4 weeks of age, for GnRH treated and control calves, respectively; P = 0.04). Body weight gain was greater in GnRH-treated calves than control calves (P < 0.05), and the rate of weight gain was shown to be a significant covariate within age at puberty. In conclusion, we suggest that the timing of the early rise in LH concentrations is a critical signal involved in the timing of puberty in heifers. © 2004 Elsevier Inc. All rights reserved.

Publication metadata

Author(s): Madgwick S, Evans ACO, Beard AP

Publication type: Article

Publication status: Published

Journal: Theriogenology

Year: 2005

Volume: 63

Issue: 8

Pages: 2323-2333

ISSN (print): 0093-691X

ISSN (electronic): 1879-3231

Publisher: Elsevier Inc.

URL: http://dx.doi.org/10.1016/j.theriogenology.2004.10.011

DOI: 10.1016/j.theriogenology.2004.10.011

PubMed id: 15826693

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