A meta-analysis of heritability estimates for milk fatty acids and their genetic relationship with milk production traits in dairy cows using a random-effects model

Abstract

It is necessary to have valid estimates of genetic parameters for economically important traits in the breeding programs of animals. During the past years, estimates of genetic parameters have been reported for different groups of fatty acids in dairy cows. However, these estimates have been obtained from studies based on different cow populations. This has resulted in substantial variability among heritability and genetic correlation estimates. Thus, this study aimed to conduct a meta-analysis based on a random-effects model to combine different published heritability estimates for milk fatty acids and their genetic correlations with milk production traits in dairy cows. In total, 272 heritability and 141 genetic correlation estimates from 20 peer-reviewed articles published in five different scientific journals between 2007 and 2020 were used in the present study. Chi-square (Q) test and the I2 statistic were determined to measure heterogeneity of genetic parameter estimates. Also, Egger's linear regression asymmetry was used to examine the presence of publication bias. The weighted coefficients of variation for the milk fatty acids varied from 1.35 to 26.05. The heritability estimates for the group and individual fatty acids ranged from 0.092 to 0.428, and from 0.109 to 0.421, respectively. Based on the values of the I2 index, negligible heterogeneity was observed for the heritability estimates of polyunsaturated fatty acids, short-, medium- and long-chain fatty acids expressed in g/ 100 g of milk fat, but the other group fatty acids experienced a moderate to considerable heterogeneities. In general, all group fatty acids had positive and high genetic correlations with fat and protein percentages of milk, negative and low to medium genetic correlations with milk and protein yields, positive and low to medium genetic correlations with fat yield, and positively low and near to zero correlations with somatic cell score. Except for genetic correlations between group fatty acids with SCS, other correlations were significant (P<0.05). The values of the I2 index indicated the negligible heterogeneity for the genetic correlations between group fatty acids with protein yield, fat and protein percentages of milk, but the heterogeneity for the genetic correlations between group fatty acids with milk and fat yields would be moderate, and considerable heterogeneities were observed between group fatty acids and somatic cell score. The mean estimates of genetic parameters reported in this meta-analysis study are surely suitable to use in breeding programs when reliable estimates are not accessible for milk fatty acids in dairy cow populations.