Estimation of Heritability and Genetic Correlations for the Major Fatty Acids in Bovine Milk

Abstract

The current cattle selection program for dairy cattle in the Walloon region of Belgium does not consider the relative content of the different fatty acids (FA) in milk. However, interest by the local dairy industry in differentiated milk products is increasing. Therefore, farmers may be interested in selecting their animals based on the fat composition. The aim of this study was to evaluate the feasibility of genetic selection to improve the nutritional quality of bovine milk fat. The heritabilities and correlations among milk yield, fat, protein, and major FA contents in milk were estimated. Heritabilities for FA in milk and fat ranged from 5 to 38%. The genetic correlations estimated among FA reflected the common origin of several groups of FA. Given these results, an index including FA contents with the similar metabolic process of production in the mammary gland could be used, for example, to increase the monounsaturated and conjugated fatty acids in milk. Moreover, the genetic correlations between the percentage of fat and the content of C14:0, C12:0, C16:0, and C18:0 in fat were −0.06, 0.55, 0.60, and 0.84, respectively. This result demonstrates that an increase in fat content is not directly correlated with undesirable changes in FA profile in milk for human health. Based on the obtained genetic parameters, a future selection program to improve the FA composition of milk fat could be initiated.

Genetic variability of milk fatty acids

“…All of these studies confirmed the existence of the genetic variability of the FA concentrations in bovine milk and fat, sug-gesting a potential future animal selection. Results obtained by Soyeurt et al (2007a) and Bobe et al (2008) and presented in Table 2 suggest that the concentrations of FAs in milk (expressed as g 100g -1 of milk and g L -1 of milk) are generally more heritable than the concentrations of FAs in milk fat (expressed as g 100g -1 of fat and %wt). Renner and Kosmack (1974a) also observed this trend.…”

“…Further, this model permits to take into account the performances of ancestors, descendants and collateral relatives, and thus improves the accuracy of the estimation. More recent studies, such as Soyeurt et al (2007a and2008b), Stoop et al (2008) and Bobe et al (2008), used an animal model to estimate the genetic parameters of FAs.…”

“…The estimation of the genetic parameters needs a large amount of data, hence Soyeurt et al (2006a) proposed to use mid-infrared spectrometry to predict the FA concentrations directly in bovine milk. Thanks to the large data set including the spectral data and, thus, the FA concentrations estimated by applying the developed calibration equations on these collected spectra, Soyeurt et al (2007a) estimated the genetic parameters of FAs by using a multi-trait test-day animal mixed model. A total of 7700 milk samples were collected in 25 herds between April 2005 and May 2006, and analysed by mid-infrared spectrometry.…”

“…All this suggests that in the near future a larger number of labs could predict the FA concentrations needed for a selection program. Thanks to a larger data set, a test-day animal mixed model could be used to describe the variability of FAs, as done by Soyeurt et al (2007aSoyeurt et al ( , 2007bSoyeurt et al ( , 2008b. The use of this type of model presents some advantages, such as a more efficient use of the collected data, a genetic model that accounts better for the biology of dairy cows, a better accounting for short-term environmental effects at each test-day milk recording, and finally, more accurate estimations of cow indices (Schaeffer et al 2000;Mayeres et al 2004;Muir et al 2007).…”

“…The answer to this question is not easy. The genetic correlations among some FAs are high (Soyeurt et al 2007a;Stoop et al 2008). This relationship is explained by the similarities in their metabolic production processes.…”