Estimation of (co)variance components, genetic parameters, and genetic trends of growth traits in community-based breeding programs of Bonga sheep

Community-based sheep breeding programs (CBBPs) have been adopted strategically to improve Bonga
sheep, the most popular sheep breed in Ethiopia. The present study was undertaken to estimate genetic
parameters and genetic trends for growth traits and inbreeding levels in each Bonga sheep CBBP. Data
pertaining to growth traits, spanning a period of seven years (2012–2017), were collected from 14
Bonga sheep CBBPs. Data were analyzed using the General Linear Model procedure of SAS to study the
performance of the breed over the years. The genetic parameters were estimated by univariate and multivariate animal model using restricted maximum likelihood method of WOMBAT software. The genetic
trends were estimated by the regression of the average breeding values of the animals on the year of
birth. The overall least square means ± SE of BW (kg) were 3.10 ± 0.010, 16.1 ± 0.07, 24.7 ± 0.20,
30.4 ± 0.40 and 34.0 ± 0.84 for birth weight (BWT), weaning weight (WWT), six-month weight
(SMWT), nine-month weight (NMWT) and yearling weight (YWT), respectively. Direct heritability estimates from selected models were 0.56 ± 0.030, 0.36 ± 0.030, 0.22 ± 0.040, 0.17 ± 0.070 and 0.13 ± 0.150
for BWT, WWT, SMWT, NMWT and YWT, respectively. Six-month weight was the selection trait and presented positive trends for 10 CBBPs, and negative trends for four CBBPs. Moderate to high heritability
estimates and positive genetic trends indicated scope for further improvement of BW. Additionally, the
positive and high correlation between BW traits indicated that selection for just one trait would also
improve the other traits through correlated responses