Efecto del manejo del pastoreo en el comportamiento y en la performance productiva de vacas lecheras de alta producción en un sistema mixto de alimentación

A study was conducted to evaluate the effect of two contrasting defoliation intensities on a second-year Festuca arundinacea pasture on the behavior, forage and total dry matter intake, and milk production of dairy cows. Two post-grazing heights were applied: 12-15 cm (treatment TL) and 5-7 cm (treatment TT). Grazing was initiated when the pasture reached 18-20 cm in height and/or three leaves per tiller. Thirty-two autumn-calving Holstein cows were used, grouped based on calving date (3/4/2023 ± 14,5 days), previous milk yield, body weight (665 ± 12,9 kg), body condition score (BCS; 3,3 ± 0,04), and number of lactations, and randomly assigned to the treatments. After the morning milking, the cows had access to the pasture, and after the evening milking, they were housed in a compost barn until the next milking. Grazing and rumination times, as well as the number and duration of grazing sessions, were recorded automatically. Forage intake were estimated through energy balance, and milk production was measured daily. Response variables were analyzed using PROC GLIMMIX in SAS. Grazing time was not affected by treatment (298 ± 8,6 minutes). The reduction in post-grazing height increased the duration of the first grazing session (174 vs. 139 ± 8,5 minutes). The number of grazing sessions was higher in TL at the midpoint of the occupation period, while TT did not alter the number of sessions during the occupation period. Forage intake was higher in TL (12,0 vs. 9,1 kg DM/cow/day), which explained the higher dry matter intake (25,6 vs. 22,4 kg DM/cow/day). Milk production during the general evaluation period and the specific measurement period was higher in TL than TT (38,9 vs. 36,2 ± 0,54 and 37,3 vs. 33,2 ± 1,02 kg/cow/day). Fat and total solids concentrations did not differ between treatments, while protein and lactose concentrations showed a significant treatment by month interaction. The BCS at the end of the experiment was higher in TL than in TT (3,3 vs. 3,1). TL achieved higher milk production and BCS, which was explained by higher pasture intake through changes in ingestive behavior.