Genetic parameters of milk fatty acid profile in sheep: comparison between gas chromatographic measurements and Fourier-transform IR spectroscopy predictions

Abstract

Fatty acid (FA) composition is a key component of sheep milk nutritional quality. However, breeding for FA composition in dairy sheep is hampered by the logistic and phenotyping costs. This study was aimed at estimating genetic parameters for sheep milk FA and to test the feasibility of their routine measurement by using Fourier-transform IR (FTIR) spectroscopy. Milk FA composition of 989 Sarda ewes farmed in 48 flocks was measured by gas chromatography (FAGC). Moreover, FTIR spectrum was collected for each sample, and it was used to predict FA composition (FAFTIR) by partial least squares regression: 700 ewes were used for estimating model parameters, whereas the remaining 289 animals were used to validate the model. One hundred replicates were performed by randomly assigning animals to estimation and validation data set, respectively. Variance components for both measured and predicted traits were estimated with an animal model that included the fixed effects of parity, days in milking interval, lambing month, province, altitude of flock location, the random effects of flock-test-date and animal genetic additive. Genetic correlations among FAGC, and between corresponding FAGC and FAFTIR were estimated by bivariate analysis. Coefficients of determination between FAGC and FAFTIR ranged from moderate (about 0.50 for odd- and branched-chain FA) to high (about 0.90 for de novo FA) values. Low-to-moderate heritabilities were observed for individual FA (ranging from 0.01 to 0.47). The largest value was observed for GC measured C16:0. Low-to-moderate heritabilities were estimated for FA groups. In most of cases, heritabilites were slightly larger for FAGC than FAFTIR. Estimates of genetic correlations among FAGC showed a large variability in magnitude and sign. The genetic correlation between FAFTIR and FAGC was higher than 60% for all investigated traits. Results of the present study confirm the existence of genetic variability of the FA composition in sheep and suggest the feasibility of using FAFTIR as proxies for these traits in large scale breeding programs.

Genomic selection of milk fatty acid composition in Sarda dairy sheep: Effect of different phenotypes and relationship matrices on heritability and breeding value accuracy

“…Heritability estimates based on pedigree models were consistent with a previous work carried out on a similar data set (Correddu et al, 2018), whereas genomicbased h 2 were higher and lower than pedigree based on SFA (<C14) and UFA, respectively. A large variation among different FA was observed, regardless of the considered approach or the phenotype used, in agreement with previous studies (Sánchez et al, 2010;Boichard et al, 2014).…”

“…Good prediction accuracies of milk FA based on FTIR spectrum have been reported for dairy cattle (Arnould and Soyeurt, 2009;De Marchi et al, 2011). Similar results, even though with a certain degree of variability and in a limited number of studies, have been reported for dairy sheep (Ferrand-Calmels et al, 2014;Caredda et al, 2016;Correddu et al, 2018). Fatty acid predicted by FTIR exhibited genetic variation both in dairy cattle (e.g., Soyeurt et al, 2007;Bastin et al, 2013;Narayana et al, 2017) and sheep (Sánchez et al, 2010;Boichard et al, 2014).…”

“…Fatty acid predicted by FTIR exhibited genetic variation both in dairy cattle (e.g., Soyeurt et al, 2007;Bastin et al, 2013;Narayana et al, 2017) and sheep (Sánchez et al, 2010;Boichard et al, 2014). Moreover, genetic correlations ranging from 60 to 99% between FTIR-predicted and GC-measured milk FA have been reported both in cattle (Bonfatti et al, 2017) and sheep (Correddu et al, 2018).…”

“…One hundred replicates randomly assigning animals to the 2 data sets were performed. Details for GC analysis are reported in the work of Correddu et al (2018).…”

“…Ruminant dairy products are among the most important sources of CLA in human diets (Nudda et al, 2014). Although animal feeding is considered the most important factor affecting milk fatty acid (FA) composition (Cabiddu et al, 2005;Sánchez et al, 2010), genetic variation for these traits has been reported in cattle (Stoop et al, 2008;Pegolo et al, 2016) and sheep (Sánchez et al, 2010;Correddu et al, 2018), suggesting the possibility for a genetic improvement.…”