Is selecting dairy cows for fat and protein contents an opportunity to maintain yearly compact-calving systems?

This study aimed to explore the effect of alternative selection strategies based on milk fat and protein contents instead of milk yield on reproduction of dairy cows. About 500 lactations were recorded, equally distributed among breeds (Holstein: HO or Normande: NO) and genetic groups with similar genetic merit for fat and protein yields and either high breeding values for milk yield (MILK) or fat and protein contents (CONT). Milk progesterone monitoring enabled the study of the reproductive performance. In both breeds, cows in CONT produced less milk (-763 kg in HO, -649 kg in NO), with higher fat content (+4.1 g kg-1 in HO and +3.9 g kg-1 in NO) and higher protein content (+1.6 g kg-1 in HO, +2.0 g kg-1 in NO) than cows in MILK. Cows in CONT had an earlier resumption of luteal activity than cows in MILK (-6 d in HO, -4 d in NO). There was no difference in ovulation detection rates between genetic groups. No difference in fertility performance was observed between genetic groups in NO. However, HO in CONT had a lower re-calving rate than in MILK (48 vs 55%). Selecting dairy cows for fat and protein contents may not be a good opportunity to improve reproduction.