Effects of feeding level, milking frequency, and single injection of cabergoline on blood metabolites, hormones, and minerals around dry-off in dairy cows

This study aimed to investigate the effect of the dif-ferent dry-off strategies based on reducing feeding level (normal vs. reduced energy density), reducing milking frequency (twice vs. once daily), and administration of a dopamine agonist after last milking (i.e. saline vs. cabergoline injection) on blood metabolites, hormones, and minerals around dry-off. In this experiment, 119 Holstein dairy cows were used in a 2 x 2 x 2 factorial arrangement. In the last week before dry-off, cows were allocated to 1 of the 4 possible dry-off strategies based on feeding level and milking frequency. Within 3 h after last milking, cows were injected with either saline or a D2 dopamine agonist (cabergoline; Velactis, Ceva Sante Animale, Libourne, France; labeled for use only with abrupt dry-off, e.g., no preceding reduction in feeding level or milking frequency before last milking). After dry-off, all cows were fed the same dry cow diet and data collection continued for a week. Blood samples were collected from the coccygeal vein on d -9, -6, -5, -2, 1, 2, 5, and 7 relative to dry-off. Addition-ally, blood was sampled at 0, 3, and 6 h relative to injection of either cabergoline or saline, equivalent to d 0.125, 0.250, and 0.375 relative to last milking (dry -off). The reduced feeding level before dry-off caused reduced glucose and insulin concentrations as well as increased free fatty acid concentrations, particularly when reduced feeding level was combined with milking the cows 2x daily. The intramuscular injection of ca -b ergoline caused the expected reduction in circulating prolactin concentrations. In addition, dopamine-agonist cabergoline induced an atypical simultaneous patternof plasma metabolites (i.e., increased glucose and free fatty acid concentrations), hormones (i.e., reduced insulin and increased cortisol concentrations), and min-erals (i.e., reduced calcium concentration), indicating that normal metabolic and mineral homeostatic regula-tions were hindered after the injection of ergot alkaloid cabergoline. In conclusion, reducing milking frequency seems the best management strategy to reduce milk production at dry-off among those tested in this study.

Automated summary

This study aimed to investigate the effect of different dry-off strategies on blood metabolites, hormones, and minerals. It was found that reducing feeding level and milking frequency can decrease glucose and insulin concentrations while increasing free fatty acid concentrations in dairy cows. The injection of dopamine agonist cabergoline can reduce prolactin concentration and cause abnormal changes in plasma metabolites, hormones, and minerals.