Genetic relationships of fertility traits with test‐day milk yield and fat‐to‐protein ratio in tropical smallholder dairy farms

Abstract

The test-day milk fat-to-protein ratio (TD-FPR) could serve as a measure of energy balance status and might be used as a criterion to improve metabolic stability and fertility through genetic selection. Therefore, genetic parameters for fertility traits, test-day milk yield (TD-MY) and TD-FPR, as well as, their relationships during different stages of lactation, were estimated on data collected from 25 968 primiparous Thai dairy crossbred cows. Gibbs sampling algorithms were implemented to obtain (co)variance components using both univariate linear and threshold animal models and bivariate linear-linear and linear-threshold animal models with random regression. Average TD-MY and TD-FPR were 12.60 and 1.15. Heritability estimates for TD-MY, TD-FPR and selected fertility traits ranged from 0.31 to 0.58, 0.17 to 0.19 and 0.02 to 0.05, respectively. Genetic correlations among TD-FPR and TD-MY, TD-FPR and fertility traits, and TD-MY and fertility traits ranged from 0.05 to -0.44, from -0.98 to 0.98 and -0.22 to 0.79, respectively. Selection for lower TD-FPR would decrease numbers of inseminations per conception and increase conception at first service and pregnancy within 90 days. In addition, cow selection based only on high milk production has strong effects to prolong days to first service, days open and calving interval.

Genetic associations between milk fat‐to‐protein ratio, milk production and fertility in the first two lactations of Thai Holsteins dairy cattle

“…The genetic correlations of MY within the first and second lactations were 0.65 to 1.00 (Fig. The estimates are similar to the results studied in Nordic Red cattle (Negussie et al 2013) and Thai Holstein (Buaban et al 2015b). 7b), respectively.…”

“…For MY, the heritability estimates ranged from 0.35 to 0.48, and from 0.36 to 0.55 in the first and second parities, respectively (Fig. The heritability estimates for MY in primiparous cows from our study was similar to Thai dairy cattle with ranges from 0.31 to 0.58 reported by Buaban et al (2015b). The estimates in multiparous cows were higher than primiparous with a similar curve shape.…”

“…Legendre polynomials of the second-and third-order were appropriate to describe random regression curves for FPR and MY, respectively (Buaban et al 2015b), which is descripted as: Legendre polynomials of the second-and third-order were appropriate to describe random regression curves for FPR and MY, respectively (Buaban et al 2015b), which is descripted as:…”

“…Milk fatto-protein ratio (FPR) has been suggested as a potential indicator of energy balance associated with several metabolic disorders and functional weakness in dairy cows. Increasing incidences of fertility problems, especially increases in days-open (DO), due to milk yield (MY) increases in Thai Holsteins, has been reported (Buaban et al 2015b). In the last decade, genetic selection in dairy cows has focused mainly on high production, whereas cows' health and fertility have provided more problems (Buttchereit et al 2010), resulting in increasing health costs and culling rates.…”

“…In fact, dairy production in Thailand has focused in the same direction as developed countries. In addition, Buaban et al (2015b) reported that genetic correlation between FPR and DO range from 0.53 to 0.67 in the early stage of lactation. The breeding objectives to incorporate DO or another fertility trait with MY in the selection index for Thai Holsteins have been proposed (Buaban et al 2015a).…”