Metabolic Trajectory and Metabolic Robustness Assessment of Grazing Dairy Cows Through an Integrative Approach

This study explored the effect of dairy genotypes and feeding strategies on the metabolic trajectory and robustness of grazing dairy cows. The individual metabolic trajectory was determined as the temporal profile of the norm of a vector (P_v, Perturbation vector) that integrates the concentrations of blood plasma metabolites and hormones. Two datasets were used. Dataset 1 comprised North American (NAH, n = 20) and New Zealand (NZH, n = 20) Holstein cows under two feeding strategies (restricted grazing activity, P30, vs. maximised grazing activity, PMAX) that were sampled at -45, 21, 100 and 180 days in milk (DIM). Dataset 2 comprised Holstein (HF, n = 14) and Normande (NR, n = 13) cows monthly sampled between -15 and 336 DIM. For Dataset 2, P_v results were individually fitted to the 1st harmonic model and the metabolic robustness was characterised for each cow based on the response amplitude (maximal P_v), time of recovery after calving, and average and maximal recovery velocities. In Dataset 1, cows showed a high perturbation state (high P_v) between -45 and 21 DIM that decreased at 100 DIM for all cows. However, later during mid lactation, P_v increased in PMAX at 180 DIM in particular for NZH-PMAX cows, which had a higher metabolic perturbation than their NZH-P30 counterparts. In Dataset 2, the metabolic trajectory was also characterised by high perturbation state at the onset of lactation in all cows, but it decreased earlier for NR than HF cows. The NR cows appeared to have a better metabolic robustness than the HF cows as the former had an earlier recovery time after calving, and tended to have a greater recovery velocity.