Effect of different sources of specific variance on the biological prolificacy of the Karnobat Sheep breed

Genoveva Staykova, Margarit Iliev

Abstract: Subject of the study was a herd from the Karnobat Sheep breed, ownership of the Institute of Agriculture – Karnobat. The sheep were born during the period 2010–2015. The herd has been a nucleus for this breed. The reproductive ability of the breed and the year of birth and breeding line effects on it were studied. The rams used are from 3 breeding lines – number 013, 68 and 410. 903 observations of biological prolificacy from the first to the fifth lambing of ewes were recorded. The information was obtained from the Pedigree Books kept by the farm breeder. The data was obtained in conformity with the standard methods and guidelines in the Instruction Codex for Breeding for Preservation of the Local (Indigenous) Sheep Breeds in Bulgaria (2003). Analysis on variance was conducted on the basis of multi-factor linear models per each age. The assessments of heritability coefficients of biological prolificacy were established. The variations between levels of studied factors were established on the basis of the degree of distribution. It was established that lineage had significant effect on the phenotypic expression of the biological prolificacy in the Karnobat sheep breed at first lambing only. Year of birth significantly influenced the biological prolificacy at 3.5-, 4.5- and 6.5-years of age (P < 0.05). The highest prolificacy was at 4.5-years (1.295 lambs per ewe), followed by 5.5-
years (1.273 lambs per ewe) and 6.5-years (1.239 lambs per ewe). The average biological prolificacy
for the herd was 1.218 lambs per ewe. The coefficients of heritability of the biological prolificacy trait
were low and varied from h2 = 0.094 to h2 = 0.142. The analysis of the results indicated a tendency for
narrowing the genetic diversity in the population.

Keywords: biological prolificacy; breeding lines; heritability; Karnobat Sheep breed; year of birth

Date published: 2020-06-05