Estimation of genetic, heritability, and phenotypic trends for weight and wool traits in Rambouillet sheep

Abstract

Genetic and phenotypic trends give an indication of the progress of a breed over the years and help in understanding the effectiveness of selection. Therefore, a study was planned to estimate genetic, heritability and phenotypic trends for Rambouillet breed of sheep. Trends were estimated for birth weight, weaning weight, fibre diameter, greasy fleece weight at clip one and staple length on data collected from 1998 to 2008. Two yearly mean phenotypic values, heritability values, and mean breeding values for birth weight, weaning weight, fibre diameter, greasy fleece weight at clip one and staple length were estimated. These trends were determined as a linear regression coefficient of mean breeding values using BLUP (best linear unbiased prediction) for the animal’s year of birth and a trend line was generated separately for each trait. Trends for phenotypic values were positive for birth weight, staple length and greasy fleece weight whereas for weaning weight and fibre diameter, the trends were negative. The slopes for birth weight and weaning were found to be 0.040 ± 0.0525 and −0.07 ± 0.241 respectively. Slopes for fibre diameter, staple length and greasy fleece weight for first clip were -0.011 ± 0.01, 0.146 ± 0.041 and 0.052 ± 0.029 respectively. The slopes all traits were found to be insignificant except staple length. For heritability, the slopes of birth weight, weaning, fibre diameter, staple length and greasy fleece weight for first clip were 0.0005 ± 0.0048, 0.009 ± 0.0048 0.0058 ± 0.011, 0.0041 ± 0.003, and 0.0061 ± 0.0039 respectively. Trends obtained for breeding values were positive for birthweight, staple length and greasy fleece weight for first clip and negative for weaning weight and fibre diameter. All traits had an insignificant slope for breeding values. The slopes for breeding values for birth weight and weaning were 0.001 ± 0.0004 and −0.0025 ± 0.001 respectively. Slopes for fibre diameter, staple length and greasy fleece weight for first clip were −0.0002 ± 0.0002, 0.0002 ± 0.0001, 0.0001 ± 0.0002 respectively. It is concluded that an optimal selection strategy that considers both genetic merits and coancestry of mates (in order to avoid close breeding and inbreeding depression) should be adopted to sustain the sheep breeding programs in the State.