Iris Publishers- Open access Journal of Agriculture and Soil Science | Analysis of Growth Performance Data in Sidama Goats using Fixed and Random Regression Model

Authored by Kefelegn K

Most statistical approaches in experiments of feeding trial are based on the analysis of variance (ANOVA) and least square regressions. However, most of the time, the assumption that data are independent is violated since several measurements are taken on the same subject (repeated measures). In addition, the presence of intra- and interobservers variability can potentially obscure significant differences.
In this study, repeated records of body weight gains on goats were analyzed fitting fixed and random regression models. Up to eight ‘repeated records’ per goat, measured between 10th and 80th day of age post the time of initial body weight recording, were available for analysis.
The objectives of this study were to compare the growth curve of animals in different treatments and to evaluate the differences in body weight gains caused by different rations in the treatments and their implications on choosing a ration.
Results showed that a linear regression on age modelled changes in variation of body weight gain adequately. A ration with E. brucei leaf was found to provide goat with good body weight gain with a minimum cost of ration.
Based upon the species of farm animals, several traits such as milk yield, body weight gain, feed intake and longevity are used for selection of candidate animals as the genetic evaluation is practiced [1]. As mentioned by Meyer [2] growth of animals is a prime example of a trait measured repeatedly per individual along a continuous scale (time) which changes gradually and continually and can be modelled using random regressions [3]. In any meat producing goat industry, body weight and average daily gain are considered to be important components for market meat production. Random regression models have been utilized to describe a linear mixed model including appropriate covariates to model the effect of time on repeated records as fixed and random terms [4]. Using random regression models there is no need to correct towards certain landmark ages [3].
The objectives of this study were to compare the growth curve of animals in different treatments and to evaluate the differences in body weight gains caused by the different rations in the treatments and their implications on choosing a ration. This study was conducted at Dilla Agricultural, Technical, Vocational, Education and Training College, which is situated 365 km south of Addis Ababa, Ethiopia. The area lies at a latitude of 6° 27’ N and 38° 30’ E longitude with an altitude ranging from 1550- 1700 m.a.s.l. The mean annual temperature is 20.7° C and relative humidity ranging from 60-70%. The annual rainfall varies between 1100-1300mm.

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