Increasing blood 5-hydroxy-L-tryptophan concentration for prevention of periparturient hypocalcemia in dairy cows

Abstract Text:

Hypocalcemia in dairy cows is caused by the sudden increase in demand for Ca²⁺ by the mammary gland for milk production after partum and simultaneously the limited ability of Ca²⁺ to be mobilized from bone in a timely manner. Serotonin (5-HT) is a key factor which mediates Ca²⁺ mobilization from bones. Therefore, we hypothesized that administration of 5-hydroxy-L-Tryptophan (5-HTP), a 5-HT precursor, would increase 5-HT concentration in blood, and in turn induce Ca²⁺ mobilization from bone. In this study, 20 Holstein dairy cows were randomly assigned to two experimental groups. Ten animals received a daily i.v. infusion of one liter of 0.9% NaCl (control; C). The other 10 animals received one liter of 0.9% NaCl containing 1 mg of 5-HTP/kg BW daily (5-HTP group). Infusions were performed beginning on day 10 before estimated parturition. Infusions were conducted until the day of parturition, resulting in at least 4 days of infusion. Until parturition, blood samples were collected every morning before the infusions, and after parturition daily until day 7, and on day 30. Milk yield was recorded during this period. No differences between groups were observed for blood glucose, Mg²⁺, beta-hydroxybutyrate, and non-esterified fatty acid concentrations. Serum 5-HT concentration was increased until day 5 after partum in the 5-HTP group compared to the C group. Colostrum 5-HT concentrations were higher in the 5-HTP group than in the controls (37.10±3.12 vs. 25.02±2.75 nM; P<0.05), but differences were undetectable in milk 7 days after partum (13.43±1.12 vs. 14.63±1.13 nM; P>0.05). Serum total Ca²⁺ concentrations decreased in both groups around parturition (P<0.05), however, 5-HTP group had higher blood Ca²⁺ concentrations than controls on day 1 (1.93±0.06 vs. 1.62±0.09 mM) and day 2 (2.07 ± 0.04 vs. 1.83±0.07 mM), respectively (P<0.05). Additionally, colostrum yield (first milking) was lower in the 5-HTP group compared to the C group (5.63±0.34 vs. 8.56±0.47 kg; P<0.05), but no differences in colostrum IgG concentration were detected (68.41±5.20 vs. 60.70±10.27 mg/mL; P>0.05). Milk yield did not differ between groups during the rest of the experiment. In conclusion, 5-HTP infusions increased blood 5-HT concentration. Moreover, 5-HTP can reduce the decline in blood Ca²⁺ concentration around parturition, and hence may influence the occurrence of clinical or subclinical hypocalcemia. Finally, 5-HTP reduced colostrum production, without affecting IgG concentrations, suggesting the mass of IgG available from colostrum may be sufficient to fulfill the needs of the offspring.

Keywords: dairy, hypocalcemia, serotonin