The cow for the system: limiting milk yield and body condition loss to ensure reproduction on time

To study reproductive performances of Holstein and Normande cows managed under a compact calving system (3 months), 2 contrasted grazing-based feeding systems (FS) are used since 2006 in a trial at the INRA farm of Le Pin-au-Haras. The High FS enables cows to produce more milk (MY) while limiting their body condition loss whereas the Low FS limits MY while inducing a large body condition loss throughout lactation (High vs Low: +2,355 kg MY for Holstein, +1,402 kg MY for Normande and +0.40 body condition score in both breeds, P<0.001). It was possible to study the different steps of the reproductive process by combining milk progesterone information (sampled 3 times a week) with intensive oestrous behaviour recording and pregnancy diagnosis (using ultrasonography). Cyclicity of dairy cows was not affected by FS. Normande cows had an earlier resumption of ovarian activity (28.0 vs 31.5 d) and a higher proportion of normal cyclicity patterns than Holstein cows (+22 points, P<0.001). Estruses were more intense in the Low FS than in the High one (+13 points standing to be mounted, P<0.001). For Holstein cows, fertility problems were different in each FS: in the Low FS a higher proportion of inseminations were not-fertilizing or resulted in early embryo mortality (+14 points, P<0.05) whereas in the High FS a higher proportion of inseminations resulted in late embryo mortality (+9 points, P<0.05). Finally, Normande had a higher re-calving rate than Holstein (+19 points, P<0.001), and the High FS tended to be positively associated with re-calving rate (+6 points, P<0.10). The Low FS was very restrictive in nutrients. By limiting their MY to this nutritive constraint Normande do not experience too severe negative energy balance while Holstein tried to maintain the highest MY possible. This resulted in preserved reproduction for Normande cows, and thus animals more robust to compact calving and grazing-based dairy systems.