Trade-off between animal resilience and energy use in grazing cows of two Holstein strains

A trade-off between animal resilience (Res) and feed efficiency has been evoked in dairy cows, limiting the genetic progress if both traits are not considered together. New Zealand Holstein (NZH) has a greater energy and feed efficiency than the North American Holstein strain (NAH) under grazing conditions, and a greater adaptive capacity also for NZH than has been suggested, but no quantitative comparison is reported yet. The Res of multiparous 39 cows was estimated as the log-transformed variance (LnVar) of the daily deviation from the modelled lactation curve between 10 and 200 DIM. Based on hierarchical cluster analysis of LnVar and regardless of the strain, the cows were grouped into 2 groups of Res: low (Low-Res, n=25, 14 NAH + 11 NZH) and high (High-Res, n=14, 6 NAH + 8 NZH). The LnVar, and productive (persistence, milk peak yield, 200 DIM accumulated milk yield) and energy use traits [residual heat production, (RHP), energy efficiency (EF = milk retained energy/metabolizable energy intake), measured at 180 DIM] were analysed by t-test comparing Low- and High-Res groups. The LnVar was similar (P=0.28) between Holstein strains. High-Res had a lower LnVar (1.09 vs 1.88±0.09, mean ± SEM; P<0.01), greater milk persistency (+23%; P=0.03) but similar milk peak (32.1 vs 33.3±1.78 kg/d, P=0.49), and 200 DIM-accumulated milk yield (5,443 vs 5,557±288 kg, P=0.67) than Low-Res cows. Both RHP and EF did not differ between Low- and High-Res. While LnVar and RHP were not correlated, LnVar and EF tended to be negatively correlated (r=-0.26, P=0.09) suggesting that greater EF is associated to lower animal Res. Our results indicate that High-Res individuals can be found in both Holstein strains under grazing conditions, and that increased Res would be associated with decreased EF. Further studies are warranted to confirm these preliminary results.