RESUMO
Hypocalcemia is a metabolic disorder that affects dairy cows during the transition from pregnancy to lactation. Twelve multiparous Holstein cows and twelve multiparous Jersey cows were intravenously infused daily for approximately 7 days prepartum with either saline or 1.0mg/kg bodyweight of the immediate precursor to serotonin synthesis, 5hydroxy-l-tryptophan (5-HTP). On infusion days, blood was collected before, after, and at 2, 4, and 8h postinfusion. Blood and urine were collected daily before the infusion period, for 14 days postpartum and on day 30 postpartum. Milk was collected daily during the postpartum period. Feed intake and milk yield were unaffected by 5-HTP infusion postpartum. Cows infused with 5-HTP had elevated circulating serotonin concentrations prepartum. Infusion with 5-HTP induced a transient hypocalcemia in Jersey cows prepartum, but not in any other treatment. Holstein cows infused with saline had the highest milk calcium on the day of and day after parturition. Postpartum, circulating total calcium tended to be elevated, and urine deoxypyridinoline (DPD) concentrations were elevated in Holstein cows infused with 5-HTP. Overall, Jerseys had higher urine DPD concentrations postpartum when compared with Holsteins. Taken together, these data warrant further investigation of the potential therapeutic benefit of 5-HTP administration prepartum for prevention of hypocalcemia. Further research should focus on delineation of mechanisms associated with 5-HTP infusion that control calcium homeostasis during the peripartum period in Holstein and Jersey cows.