Infusion of a 5-hydroxy-L-tryptophan (5-HTP) to late-lactation cows impacts circulating calcium and glucose concentrations
Supplementation of 5-hydroxy-L-tryptophan (5-HTP) improved calcium (Ca) and glucose status in lactating rodents, and serotonin was shown to be an indicator of positive Ca and glucose status in lactating dairy cows. Here, we examined the effect of intravenous infusion of 5-HTP on circulating Ca and glucose concentrations. Using a 4x4 latin square design, multiparous Holstein cows (avg. lactation=3; avg. DIM=333 d) were infused with a sterile saline control (CON) or one of 3 doses of 5-HTP (TRT; 0.5, 1.0 and 1.5 mg/kg). Infusion periods were 4d, with a 5d washout between periods. Cows were infused at a constant rate for 1h, and blood samples were collected at 0 (pre-infusion), and 5, 10, 30, 60, 90 and 120 min post-infusion. Heart rate (HR), respiration rate (RR) and rectal temperature (TEMP) were recorded every 15 min during infusion, and 15 min post-infusion, milk yield (MY) was recorded daily, and manure score (0-4, MS) and frequency were recorded during infusions. Data were analyzed using PROC MIXED in SAS. HR, RR, TEMP and MY, were not different between CON and TRT at any dose (P>0.05) and MS was affected by TRT (P=0.013). The MS was similar between CON and 0.5 mg/kg TRT, but different between CON and 1.0 and 1.5 mg/kg TRT (0.44 vs. 1.69 and 2.06 ± 0.33, respectively). Serum Ca and plasma glucose concentrations were measured and area under the curve (AUC) was calculated using the trapezoidal model. For Ca, all 5-HTP doses significantly decreased AUC compared to CON (P<0.001), decreasing the first 30 min post-infusion, increasing and reaching initial Ca concentrations 120 m post-infusion. Mean Ca was greater for CON compared to all TRT doses (1.70 vs. 1.56, 1.60 and 1.59 ± 0.05 mM, respectively) and the same was observed for minimum Ca. Glucose AUC was greater for 1.0 and 1.5 mg/kg TRT compared to CON and 0.5 mg/kg TRT (P=0.02). Mean glucose was greater for 1.0 mg/kg TRT compared to CON and 0.5 mg/kg TRT only at 90 m post-infusion (P<0.04). These results demonstrate that 5-HTP stimulates a decrease in circulating Ca, and only the two higher doses of 5-HTP increased circulating glucose. In conclusion, 5-HTP differentially affects circulating Ca and glucose concentrations in dairy cattle, suggesting significant impacts on Ca and glucose metabolism during lactation.
5-Hydroxytryptophan, calcium, glucose