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

ABSTRACT
The present study was conducted to investigate the importance of maternal effects on some
body weights and growth traits in Barki sheep. Body weight records and pedigree information of
3189 lambs progenies of 186 sires were taken from the Barki sheep flock of the Desert Research
Centre maintained at two research stations; Ras Elhekma (from 1963 to 1972) and Maryout (from
1973 to 2004). The present study dealt with body weights at birth, BW, weaning, 120 days, WW
and yearling, 360 days, YW as well as average daily gain from birth to weaning, DGBW and from
weaning to yearling, DGWY. (Co) variance components and the corresponding genetic parameters
were estimated by fitting a series of six animal models using the MTDFREML program. These
models included the significant fixed effects together with the animal, sire and dam as random
effects. Such models were fitted for each studied trait and differed in ignoring or including various
random effects. Log-likelihood ratio tests were conducted to determine the most suitable model for
the studied traits.
Results indicated that the animal model which includes only direct genetic effect was the most
appropriate 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 values
for 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 0.01
to 0.07, respectively. It is obvious that maternal influences were generally higher for BW, WW and
YW than the respective direct ones. The direct and maternal environmental components tended to
increase as age advanced from birth to yearling. The correlation between direct and maternal
genetic effect ranged from 0.07 to 0.35 for the studied traits except for DGWY (-0.72). Although
total direct components has a major contribution (82%) to the phenotypic variance, total maternal
components controls the remainder of about 20% and being relatively constant at that level to the
yearling 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 age
advanced. The current investigation advocates that selection process should account for both direct
and maternal genetic effects to increase the accuracy of genetic evaluation and enhance the genetic
gain for growth traits in Barki sheep.