Evaluation of selection program by assessing the genetic diversity and inbreeding effects on Nellore sheep growth...

The main objectives of the present study are to assess the genetic diversity, population structure and also to appraise the efficiency of ongoing selective breeding program in the closed nucleus herd of Nellore sheep through pedigree analysis.

Information utilized in the study was collected from the pedigree records of Livestock Research Station, Palamaner during the period from1989 to 2016. Genealogical parameters like generation interval, pedigree completeness, inbreeding level, average relatedness among the animals and genetic conservation index were estimated based on gene origin probabilities. Lambs born during 2012 and 2016 were considered as reference population. Two animal models either with either the use of F_i or∆F_ias linear co-variable were evaluated to know the effects of inbreeding on the growth traits of Nellore sheep.

Average generation interval and realized effective population size for the reference cohort were estimated as 3.38±0.10and 91.56±1.58, respectively and the average inbreeding coefficient for reference population was 3.32%. Similarly, the effective number of founders, ancestors and founder genome equivalent of the reference population were observed as 47, 37 and 22.48, respectively. Fifty per cent of the genetic variability was explained by 14 influential ancestors in the reference cohort. The ratio fe/fa obtained in the study was 1.21, which is an indicator of any bottlenecks in the population. The number of equivalent generations obtained in the study was 4.23 and this estimate suggested the fair depth of the pedigree.

Study suggested that the population had decent levels of genetic diversity and non-significant influence of inbreeding coefficient on growth traits of Nellore lambs. However, little portion of genetic diversity lost due to disproportionate contribution of founders and bottlenecks. Hence, breeding strategies which improve the genetic gain, widens the selection process and with optimum levels of inbreeding are recommended in the herd.