Significant differences in fertility between dairy cows selected for one QTL located on bovine chromosome 3 are not attributable to energy balance, although eating behaviour is affected.

Improvement of reproduction in dairy cows has become a major challenge in dairy production. We have recently shown that dairy cows carrying the 'fertil-' haplotype for one quantitative trait locus (QTL), affecting female fertility and located on the bovine chromosome 3, had a significantly lower conception rate after the first artificial insemination than cows carrying the 'fertil+' haplotype. The objective of this paper was to study other phenotypic modifications linked to this QTL. In the present study, 23 'fertil+' and 18 'fertil-' cows were characterized for live weight, milk production, food intake, eating behaviour and plasma metabolites. These parameters were measured during the first lactation, from calving to 40 weeks postpartum (wkpp). In the first 7 weeks of lactation, 'fertil+' primiparous cows had a significantly higher live BW and milk production than 'fertil-' cows. Dry matter intake tended to be slightly higher for 'fertil+' than for 'fertil-' primiparous cows in this period. However, energy balance was similar for the two haplotypes in the whole lactation, except in the first wkpp, and consequently, could not explain their different fertility. The major observation concerned the eating behaviour. 'Fertil+' primiparous cows had a significantly lower eating rate than 'fertil-' cows during the 40 weeks of lactation. In parallel, 'fertil+' cows spent significantly more time at the feeder for a similar number of visits than 'fertil-' cows. Furthermore, no differences in plasma concentrations of non-esterified fatty acids and insulin were observed between the two haplotypes. Plasma glucose was significantly lower in 'fertil+' than in 'fertil-' cows in the second wkpp. Taken together, our results show that 'fertil+' and 'fertil-' dairy cows, with different fertility, have also different eating behaviour without any variation in energy balance, except in the first week of lactation.