| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Cornell University,5, Ithaca, NY 14853-4801
Abstract
The objective was to study control of mature size by characterizing metacarpal growth plate closure in relation to relevant bone growth-regulating hormones in two breeds exhibiting distinct differences in mature frame size. Thirty-four Suffolk and 34 Dorset ram lambs were slaughtered in pairs within breed at birth, weaning and monthly intervals until 420 d and then bimonthly to 600 d. Plasma growth hormone was depressed to undetectable levels due to the high-energy, ad libitum-fed diet. Plasma insulin-like growth factor-I (IGF-I) rose over the growth period from 116 ng/ml (newborn Suffolk) to a high of 451 ng/ml (420-d Dorset); it appeared to peak at approximately 400 d and then declined to a stable level. Dorsets consistently exhibited higher IGF-I levels. The thyroid hormones exhibited no apparent age association. An age-associated rise was detected for testosterone, but not for estradiol. Mature metacarpal lengths were estimated to be 147.2 and 127.4 mm for Suffolks and Dorsets, respectively. Ninety-five percent of mature length was attained in Suffolks by 226 d and in Dorsets by 165 d. Growth plates, however, did not begin to appear closed until 390 d and closure was not complete in all animals until 480 d, suggesting that metacarpal growth rate was dissociated temporally from growth plate closure. Although growth plate closure likely is controlled by the endocrine system, there were no apparent relationships between circulating hormones and growth plate width, age at closure or zonal divisions within the growth plate, suggesting that the growth plate experiences a very different hormonal environment than what can be measured in the circulating blood.
1 The technical assistance of Nigel Firth, Debbie Ross, Madeline Seaman and Carol Smith and the services of the Cornell Teaching and Research Sheep unit staff are gratefully acknowledged. This work was supported in part by an NSF fellowship (AMO) and through Hatch Projects 426 and NE-148, USDA.
2 Address (July 1, 1989): Dept. of Anim. Sci., Univ. of California, Davis 95616.
3 Dept. of Pathol., College of Vet. Med.
4 To whom requests for reprints should be addressed (114 Morrison Hall, Cornell Univ., Ithaca, New York 14853-4801).
5 Dept. of Anim. Sci., College of Agric. and Life Sci.
This article has been cited by other articles:
|
|
 |
|
  L. B. Smith, M. R. Dally, R. D. Sainz, K. L. Rodrigue, and A. M. Oberbauer Enhanced skeletal growth of sheep heterozygous for an inactivated fibroblast growth factor receptor 3 J Anim Sci, November 1, 2006; 84(11): 2942 - 2949. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
