HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Staniar, W. B. Articles by Harris, P. A. Search for Related Content PubMed PubMed Citation Articles by Staniar, W. B. Articles by Harris, P. A.

Growth rate consists of baseline and systematic deviation components in Thoroughbreds

W. B. Staniar^*,2, D. S. Kronfeld^*, K. H. Treiber^*, R. K. Splan^* and P. A. Harris

^* Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306 and and Equine Studies Group, Waltham Centre for Pet Nutrition, Melton Mowbray, United Kingdom

² Correspondence: Middleburg Agricultural Research and Extension Center, 5527 Sullivans Mill Rd., Middleburg, VA 20117 (phone: 540-687-3521; fax: 540-687-5362; e-mail: wstaniar{at}vt.edu).

Abstract

The objective of this study was to establish a procedure for differentiating a baseline curve from a systematic deviation in weight-age data, and hence to develop a physiological growth model for the Thoroughbred. A total of 2,698 records for 175 foals was obtained during a period of 8 yr (1994 to 2001). Weight-age data were fit with a sigmoid growth equation, W = A(1 + be^-kt)^M, where W is BW at age t, A is the asymptotic value of W, b is a scaling parameter that defines the degree of maturity at t = 0, k is a rate constant, and M defines the point of inflection in the sigmoid curve in relation to age. Short-term systematic deviations in the weight-age data were identified by a goodness-of-fit procedure and illustrated in three-dimensional contour plots of the sigmoid equation parameters as they changed upon removal of selected subsets of the data. Based on features of the contour plots, a negative deviation between 210 and 420 d of age was set aside, with the remaining data establishing the baseline data set. The sigmoid growth equation was fit to the baseline data set using a nonlinear mixed model with repeated measures, and indicated a mature weight of 542 ± 6.2 kg reached at 7 yr. The systematic deviation identified in this weight-age data set is present in other published Thoroughbred growth data and is likely to result in erroneous parameter estimates if not set aside before fitting sigmoid growth equations to the thus-modified weight-age data set. The techniques developed in this study enable identification of short-term systematic deviations in weight-age data and define a realistic baseline growth curve. Differentiation of these two components enables the development of a physiological model of growth that distinguishes between baseline growth and environmental influences, represented respectively, by the baseline curve and the systematic deviation.

Key Words: Growth • Physiological Model • Sigmoid Function • Thoroughbred

This article has been cited by other articles:

				J. L. Lusk Association of single nucleotide polymorphisms in the leptin gene with body weight and backfat growth curve parameters for beef cattle J Anim Sci, August 1, 2007; 85(8): 1865 - 1872. [Abstract] [Full Text] [PDF]