بررسي پارامترهاي صفات رشد براي برخي از نژادهاي گوسفند ايراني

Review of growth traits parameters for some Iranian breeds of sheep

In this study 137 published estimations of growth traits from 126875 lambs for 13 breeds in 35 studies during 1980 to 2004 were reviewed to determine factors affecting the estimates, and to make recommendations regarding appropriate mean values. Weighted least-squares analyses were performed with 2 factors (breed and method of estimation) fitted for each parameterʹs trait. The weighted least square means of performances and direct heritabilities were as, 4.3 kg and 0.16 for birth weight, 23.7 kg and 0.16 for weaning weight, 31.4 kg and 0.19 for weight of 6 months, 39.2 kg and 0.25 for yearling weight and 206 gr and 0.12 for average daily gain from birth to weaning. The maternal effects (maternal heritability and proportion of maternal permanent environment variance to phenotypic variance) accounted for significant part of variation in growth traits and which were reduced with increasing age of lamb. The effect of breed was significant on weighted means of traits and heritabilities (p< 0.05). The effect of estimation method was significant (p< 0.05) alone on weighted mean of heritabilities for birth and yearling weights. The results of this study showed that weighted means of growth traits heritabilities to weaning was less than moderate, while for post weaning was more than moderate. Thus, the weighted means for heritabilities presented in this paper are recommended for use when reliable estimates are not available.