The Relation Between the Responses of Wool Growth and Body Weight to Changes in Feed Intake

Abstract

SummaryThe wool growth responses to changes in feed intake are related to the changes produced in body weight. The relation is expressed by the equation W = Ei-kG, where W = wool growth rate, i = feed intake rate, G = rate of body weight change, and E and k are constants. The ratio of E to k in sheep of different productive efficiency was found to be constant.Evidence is presented that this equation indicates a relation between wool growth and metabolic rate, both possibly being responses to changes in endocrine secretion. An alternative interpretation that the equation reflects the effect of body weight change on the supply of amino acids limiting wool growth is also discussed but is considered less likely to be true.The bearing of the results on the evaluation of feedstuffs for wool produc. tion and on the definition of individual productive efficiency is discussed.

The description and analysis of wool growth

“…In these experiments the constituents of the feed are sometimes held unchanged, in which case the intake can be regarded simply as gross energy intake (Ferguson 1962), while others seek to explore the effects of various constituents-for example, the protein fraction of the diet (Black et al 1973). The analysis of data carried out in order to relate wool growth to energy intake has usually only involved linear regression to test time-independent equations.…”

“…In this paper a more general approach is used to analyse the results reported by Ferguson (1962). The relationship between wool growth and intake in this approach is assumed to be time-dependent.…”

“…The results of the analysis indicate that there is a first order lag of c. 25 days between wool growth and intake. Evidence for the existence of a lag was presented by Sharkey and Hedding (1962), who also reanalysed the data of Ferguson (1962); however, the nature and duration of the lag was not derived. If there is a lag, then time-independent equations should prove inadequate in describing wool growth unless the sampling period is much greater than the lag involved.…”

“…The recursive technique offers significant advantages in the analysis of wool growth, since day length is known to have an important influence (Ferguson et al 1949), and other factors such as body weight change (Ferguson 1962) have also been suggested, while the functional form of the dependence of wool growth on these factors is not precisely known.…”

Growth patterns in sheep: wool growth during weight loss and subsequent compensatory growth

“…In addition, and contrary to the realimentation. views of Ferguson (1962), Black, Robards & Thomas (1973 suggested that the rate of body-MATERIALS AND METHODS weight change may influence WGR.…”