Genetic analysis of calving difficulty in South African Holstein cattle

Abstract

Calving difficulty is an economically important welfare-related trait in dairy cattle and, therefore, should be included in breeding objectives of South African Holstein dairy cattle. In South Africa, however, calving performance traits are not included in the national genetic evaluation programme. The present study was therefore carried out to estimate environmental and genetic influences on maternal calving difficulty in South African Holstein cattle, to develop models for genetic prediction of the trait. The final data set comprised of 14 250 calving records of 8 832 cows, from 14 herds, participating in the National Dairy Animal Recording and Improvement Scheme during the period 2009 to 2018. General Linear Models (GLM) technique was used to investigate environmental influences (SAS 2016) version 9.4. Sex of calf, parity, herd-year-season, and age of dam at calving had significant effects (P <0.05) on maternal calving difficulty. Variance components and for computing genetic parameters were estimated by the Restricted Maximum Likelihood (REML) approach using ASReml program., for variance component estimation, were included in the model. Estimates of maternal heritability effects from the linear animal model were 0.10±0.04, 0.04±0.09 and 0.12±0.10 for parities 1, 2 and 3, respectively. The estimate across all heritability were 0.04±0.04, with a repeatability model of 0.04±0.04 respectively. These estimates indicate low accuracy of selection for calving difficulty in the South African Holstein cattle population. However, these results provide the basis for computing estimated breeding values (EBVs), which will enable the reduction of calving difficulty in the South African Holstein cattle population; thus, genetic gain and performance improvement were slow.