Metabolic Regulation in Danish Bull Calves and the Relationship to the Fertility of Their Female Offspring

The objective of this work was to estimate the genetic variation of free fatty acids (FFA), glucose, growth hormone (GH), and insulin in juvenile male dairy calves and to assess the relationships, if present, with the fertility of their female offspring. This study used data from 1,498 (269.5 d of age ± 11.1) male calves from a multiple ovulation and embryo transfer breeding scheme (data collected from 1997 to 2002). Calves were Danish Holstein (n = 1,047), Danish Jersey (n = 200), and Red Dane (n = 251), and were sampled following an overnight fast at approximately 9 mo of age. Plasma samples were assayed for basal FFA, glucose, GH, and insulin. Estimated breeding values of female fertility (high values indicating better fertility), based on progeny-test results for approximately 100 daughters per sire, were available for a subset (n = 810) of the male calves as adult sires. Data from Danish Holstein alone or Danish Holstein, Red Dane, and Danish Jersey combined (all breeds) were analyzed for each trait. In both data sets, the estimates of heritabilities of glucose (0.27 ± 0.06), FFA (0.11 ± 0.05), and insulin (0.21 ± 0.06) were moderate, and that of GH (0.09 ± 0.05) was low. Correlations of estimated breeding values for fertility traits with glucose and FFA breeding values were negative, indicating that male calves with high glucose or FFA had female offspring with reduced fertility. Selection for bull calves with lower concentrations of glucose and FFA following an overnight fast could result in female offspring with genetically better fertility. Glucose and FFA may therefore be of interest to enhance selection for improved female fertility, as a measurement in young bulls.