Estimation of genetic and phenotypic trends for body weight traits of sheep in Guilan province of Iran

Abstract

The main objective of the present study was to estimate genetic and phenotypic trends for body weight traits in Guilan province sheep. Traits included were birth weight (BW, n=14,549), 3-month weight (3MW, n=13,109) and 6-month weight (6MW, n=10,141). Data and pedigree information used in this study were collected during 1994 to 2011 by the Agricultural Organization of Guilan province in Iran. Animal breeding values were predicted using univariate analysis based on animal model. The GLM procedure of SAS was used for determining the fixed effects which had significant influence on the traits under study. The Wombat software was employed to estimate the breeding values. The Best Liner Unbiased Predictions (BLUP) of breeding values were obtained, and genetic and phenotypic trends were estimated as the regression of the average predicted breeding and phenotypic values on birth year, respectively. Environmental trends were calculated as the difference between phenotypic and genetic trends. Direct genetic trends were positive and significant (P<0.0001) for BW, 3MW and 6MW and being 0.51±0.101, 5.56±1.21 and 18.46±2.24 g/year, respectively. Maternal genetic trends for BW, 3MW and 6MW were negative and significant (P<0.0001); these were -0.14±0.04, -1.42±0.31 and -5.48±0.67 g/year, respectively. Phenotypic trends for above mentioned traits were -40.21±1.02 (P<0.0001), -206.54±7.01 (P<0.0001) and 23.38±9.08 (P<0.05) g/year, respectively, with their environmental trends estimated to be -40.72±0.919, -212.1±5.8 and 4.92±6.84 g/year, respectively. The results showed increases in the average breeding values for body weight in Guilan province sheep during the years under study; therefore, improvement in body weight of Guilan province sheep seems feasible in selection programs.