Relationship between Breeding Value for Milk Yield and Change in Concentration of Metabolites during Fasting at Five Months of Age

Abstract

The rate of improvement of milk production will be accelerated, if the characters related tc milk production or indicator trait can be measured in calves or young bulls. Many report: suggested the relationship between genetic ability for milk production and changes of blood metabolite concentrations in a response to fasting. In this study, we examined the relationships between breeding value for milk yield and the changes in metabolites concentration during 24 and 48 hours of fasting. Sixteen female Holstein calves at five months of age were fasted for 48 hours. Relationships between breeding value for milk yield and the changes in metabolites concentrations were analyzed by regression analysis using four types of covariates; first degree of one metabolite (equation 1), second degree of one metabolite (equation 2), first degree of two metabolites (equation 3) and second degree of two metabolites (equation 4). Measurements of the change in metabolite concentration obtained at 24 hours of fasting were more suitable than those at 48 hours of fasting as indicator traits for milk yield, because the values of R² at 24 hours of fasting were larger than those at 48 hours of fasting in all equations. The regression equations by equation 1 at 24 hours of fasting were obtained by using urea nitrogen (BUN) (R²=0.14) and triglyceride (TG) (R²=0.23, P<0.1). The quadratic regression equations by equation 2 at 24 hours of fasting gives was obtained by using glucose (Glu) (R²=0.27). These results indicated Glu, BUN and TG at 24 hours of fasting are useful indicator traits to estimate the breeding value for milk yield. BUN and TG linearly and Glu quadratically related with breeding value for milk yield. The linear regression equation from BUN and TG at 24 hours of fasting by equation 3 was significant (R²=0.43, P<0.05). The quadratic regression equation from BUN and TG by equation 4 was also significant (R²=0.61, P<0.05). The R² value from Glu and BUN by equation 4 was not significant but showed high multiple regression coefficient (R²=0.51, P<0.1). As the R² obtained from the equation 3 and equation4 showed high values than those from the equation 1 and equation 2, the usefulness of metabolite enhanced by utilizing two metabolites together as the indicator for estimating breeding value for milk yield.