Heritabilities of measured and mid-infrared predicted milk fat globule size, milk fat and protein percentages, and their genetic correlations

Abstract

The objective of this study was to estimate the heritability of milk fat globule (MFG) size and mid-infrared (MIR) predicted MFG size in Holstein cattle. The genetic correlations between measured and predicted MFG size with milk fat and protein percentage were also investigated. Average MFG size was measured in 1,583 milk samples taken from 254 Holstein cows from 29 herds across Canada. Size was expressed as volume moment mean (D[4,3]) and surface moment mean (D[3,2]). Analyzed milk samples also had average MFG size predicted from their MIR spectral records. Fat and protein percentages were obtained for all test-day milk samples in the cow's lactation. Univariate and bivariate repeatability animal models were used to estimate heritability and genetic correlations. Moderate heritabilities of 0.364 and 0.466 were found for D[4,3] and D[3,2], respectively, and a strong genetic correlation was found between the 2 traits (0.98). The heritabilities for the MIR-predicted MFG size were lower than those estimated for the measured MFG size at 0.300 for predicted D[4,3] and 0.239 for predicted D[3,2]. The genetic correlation between measured and predicted D[4,3] was 0.685; the correlation was slightly higher between measured and predicted D[3,2] at 0.764, likely due to the better prediction accuracy of D[3,2]. Milk fat percentage had moderate genetic correlations with both D[4,3] and D[3,2] (0.538 and 0.681, respectively). The genetic correlation between predicted MFG size and fat percentage was much stronger (greater than 0.97 for both predicted D[4,3] and D[3,2]). The stronger correlation suggests a limitation for the use of the predicted values of MFG size as indicator traits for true average MFG size in milk in selection programs. Larger samples sizes are required to provide better evidence of the estimated genetic parameters. A genetic component appears to exist for the average MFG size in bovine milk, and the variation could be exploited in selection programs.

Estimation of genetic parameters for mid-infrared–predicted lactoferrin and milk fat globule size in Holstein cattle

“…The average genetic correlation between MFGS MIR and fat percentage in this study (0.53) was found to be more similar to the average correlation between D[4,3] and fat percentage (0.54) than the correlation between MIR-predicted D[4,3] and fat percentage (0.97) reported previously by Fleming et al (2017b). Additionally, standard deviations estimated for the correlations of MFGS MIR with fat percentage and other milk components were significantly lower in this study than the ones reported previously by Fleming et al (2017b), who used records from 254 cows in 29 herds. Therefore, one could speculate that the prediction equation generated by Fleming et .…”

“…The average heritability throughout lactation for MFGS MIR from the 2 multivariate analyses is shown in Table 2 and was estimated at 0.46. This estimated value was higher than the value estimated in a previous study by Fleming et al (2017b), in which the mean estimated heritability for MIR-predicted volume moment mean (D[4,3]) was 0.30 (SE = 0.17). Fleming et al (2017b) analyzed only a subset of the records used in the present study, which may explain the variation in estimates.…”

“…This estimated value was higher than the value estimated in a previous study by Fleming et al (2017b), in which the mean estimated heritability for MIR-predicted volume moment mean (D[4,3]) was 0.30 (SE = 0.17). Fleming et al (2017b) analyzed only a subset of the records used in the present study, which may explain the variation in estimates. Average heritability direct measures of MFGS were investigated in a limited number of studies using different methodologies and numbers of records.…”

“…Another gene, LASS2, has an active effect on MFGM synthesis, with the peak of expression on d 60 postpartum in the bovine mammary gland (Bionaz and Loor, 2008). Taking all this informa-tion together supports the heritability estimate found for MFGS MIR in this study; however, the complete genetic architecture of MFGS still needs to be studied further, as discussed in Fleming et al (2017b).…”

“…Routine determination of MFG size (MFGS) and LF is currently not feasible due to the analytical time, cost, and complexity of the requirement of fresh milk for MFGS measurements (Fleming et al, 2017b). Midinfrared spectroscopy, however, has been recognized as a powerful tool for phenotyping traditional and novel traits at a low cost on a large scale through regular milk recording (de Roos et al, 2007;Rutten et al, 2009;Bonfatti et al, 2011;McParland et al, 2011;De Marchi et al, 2014).…”