Abstract
Abstract. Weight (kg)-age (days) data of 524 Horro sheep of Ethiopia were fitted to a Brody function to estimate parameters of growth curve and their genetic and phenotypic parameters. Genetic and phenotypic relationships were also estimated between growth curve parameters and weight at birth (BW), weaning (WW) six-month (WT6) and yearling (YW). For ewes Pearson correlations were also calculated between growth curve parameters and ewe productivity over first to fourth parities. Least squares means of growth curve parameters A (asymptotic mature weight, kg), B (proportion of mature weight attained after birth) and K (the rate of maturity, kg gain kg-1 body weight) were 37.6, 0.88, and 0.27∙10-2, respectively. Heritability estimates were 0.29, 0.18 and 0.14 for A, B, and K, respectively. Genetic correlations between A and B, A and K, and B and K were 0.39, −0.07, and 0.25 respectively. Genetic correlations of A and K with BW, WW, WT6, and YW were 0.27 and −0.13, 0.34 and 0.37, 0.44 and 0.61, and 0.67 and 0.66, respectively. The growth curve parameters have small but positive (r=0.05 to 0.28) relationship with indicators of lifetime productivity. Medium heritability estimates of A and K indicate that progress in improving these traits can be made through selection. WT6 and YW have medium genetic correlations with the growth curve parameters and these may allow the use of these weights as indirect early selection criteria for optimum growth curve.
Highlights
Sheep production in Ethiopia is characterized by smallholder farming
Growth rate is related to rate of maturing and mature weight and these latter traits have been suggested to have relationship with other female lifetime productivity parameters in goats (PALA et al 2005)
Growth curve parameters provide potentially useful criteria for altering the relationship between body weight and age through selection (KACHMAN and GIANOLA 1984) and an optimum growth curve can be obtained by selection for desired values of growth curve parameters (BATHAEI and LEROY 1998)
Summary
Sheep production in Ethiopia is characterized by smallholder farming. Sale of lambs provides a considerable part of the income of farmers. Growth rate is related to rate of maturing and mature weight and these latter traits have been suggested to have relationship with other female lifetime productivity parameters in goats (PALA et al 2005). Existence of optimum size to improve productivity has been suggested for sheep (BEDIER et al 1992, KESBI et al 2008). Because of this rate of gain and mature weight need to be considered in selection programs. Fast early growth on the part of the slaughter generation and smaller mature size (though smaller income in culled ewe value) on the part of the reproducing female are desirable traits. Growth curve parameters provide potentially useful criteria for altering the relationship between body weight and age through selection (KACHMAN and GIANOLA 1984) and an optimum growth curve can be obtained by selection for desired values of growth curve parameters (BATHAEI and LEROY 1998)
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