Feeding strategies during fresh cow period in pasture-based dairy systems: Metabolic adaptation to lactation and resumption of ovarian cyclicity in primiparous and multiparous cows.

The study aimed to determine whether confinement with TMR during the first 21 DIM, followed by grazing supplemented with partial mixed ration (PMR), alleviates negative energy balance, enhancing productive performance and accelerating the resumption of ovarian cyclicity in primiparous and multiparous dairy cows, relative to a control group managed on grazing supplemented with PMR after calving. Following calving, 16 primiparous and 24 multiparous Holstein dairy cows were blocked and randomly distributed into 2 treatments: one included grazing plus supplementation with PMR after calving (T0), while the other one involved confinement with TMR ad libitum during the first 21 DIM and the same feeding management of T0 from d 22 onwards until 60 DIM (T21). Primiparous cows showed no significant differences between treatments in milk production. However, T21 primiparous cows displayed lower nonesterified fatty acids (NEFA), greater glucose, and greater insulin and IGF-1 concentrations compared with T0 primiparous cows during the 21 DIM of the feeding management. In contrast, multiparous T21 cows achieved greater milk production during the first 21 DIM, with no differences in NEFA and BHB levels but greater insulin and IGF-I concentrations than multiparous T0 cows. Both parity groups in T21 underwent an extra metabolic adaptation following the management change at 22 DIM, increasing NEFA and BHB concentrations and decreasing milk production during this period. Despite the improved endocrine-metabolic profile observed in T21 during the first days postpartum, no differences were found in the resumption of ovarian cyclicity, which was shorter in multiparous than primiparous cows. Untargeted metabolomics supported evidence that primiparous cows grazing from calving had greater lipid and muscle mobilization than other groups, reflected by lower glucose and greater creatinine, dimethylglycine, and formate. Strategic feeding management during the fresh cow period affects the metabolic adaptation to lactation, but milk production responses were observed only in multiparous cows, reflecting parity-specific homeorhetic priorities.