EVALUATION OF DIRECT AND MATERNAL (CO) VARIANCE COMPONENTS AND HERITABILITIES FOR SOME BODY WEIGHTS AND GROWTH TRAITS IN BARKI SHEEP

Abstract

ABSTRACTThe present study was conducted to investigate the importance of maternal effects on somebody weights and growth traits in Barki sheep. Body weight records and pedigree information of3189 lambs progenies of 186 sires were taken from the Barki sheep flock of the Desert ResearchCentre maintained at two research stations; Ras Elhekma (from 1963 to 1972) and Maryout (from1973 to 2004). The present study dealt with body weights at birth, BW, weaning, 120 days, WWand yearling, 360 days, YW as well as average daily gain from birth to weaning, DGBW and fromweaning to yearling, DGWY. (Co) variance components and the corresponding genetic parameterswere estimated by fitting a series of six animal models using the MTDFREML program. Thesemodels included the significant fixed effects together with the animal, sire and dam as randomeffects. Such models were fitted for each studied trait and differed in ignoring or including variousrandom effects. Log-likelihood ratio tests were conducted to determine the most suitable model forthe studied traits.Results indicated that the animal model which includes only direct genetic effect was the mostappropriate one. Direct heritability estimates ranged from 0.10 to 0.36 for BW, 0.13 to 0.30 for WW,0.07 to 0.23 for YW, 0.13 to 0.26 for DGBW and 0.08 to 0.10 for DGWY. The corresponding valuesfor maternal heritability ranged from 0.18 to 0.20, 0.12 to 0.19, 0.12 to 0.19, 0.10 to 0.17 and 0.01to 0.07, respectively. It is obvious that maternal influences were generally higher for BW, WW andYW than the respective direct ones. The direct and maternal environmental components tended toincrease as age advanced from birth to yearling. The correlation between direct and maternalgenetic effect ranged from 0.07 to 0.35 for the studied traits except for DGWY (-0.72). Althoughtotal direct components has a major contribution (82%) to the phenotypic variance, total maternalcomponents controls the remainder of about 20% and being relatively constant at that level to theyearling stage which imply the importance of maternal influences on growth traits of Barki sheep.The impact of maternal effects on BW appeared to be mainly genetic and tended to decline as ageadvanced. The current investigation advocates that selection process should account for both directand maternal genetic effects to increase the accuracy of genetic evaluation and enhance the geneticgain for growth traits in Barki sheep.