Is selecting dairy cows for fat and protein contents an opportunity to maintain yearly compact-calving systems?
2018
Bedere, Nicolas | Disenhaus, Catherine | Ducrocq, Vincent | Leurent-Colette, Ségolène | Delaby, Luc
This study aimed to explore the effect of alternative selection strategies based on milk fat and proteincontents instead of milk yield on reproduction of dairy cows. About 500 lactations were recorded, equallydistributed among breeds (Holstein: HO or Normande: NO) and genetic groups with similar geneticmerit for fat and protein yields and either high breeding values for milk yield (MILK) or fat and proteincontents (CONT). Milk progesterone monitoring enabled the study of the reproductive performance. Inboth 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-1in NO) than cows in MILK. Cows in CONT had an earlier resumption of luteal activity than cows inMILK (-6 d in HO, -4 d in NO). There was no difference in ovulation detection rates between geneticgroups. 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 andprotein contents may not be a good opportunity to improve reproduction.
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