Patterns of circulating serotonin (5-HT), calcium, and glucose in lactating Jersey and Holstein dairy cows
Dairy cows are challenged to maintain calcium (Ca) and glucose homeostasis during the transition period. Serotonin (5-HT) is a monoamine, which modulates Ca and glucose homeostasis in rodents. Serotonin was positively correlated with Ca and glucose status in dairy cows on d1 of lactation. However, the pattern of circulating concentrations of 5-HT over the course of a 305d lactation is unknown. In this longitudinal study, we examined the metabolite patterns of 5-HT, Ca, and glucose on two commercial dairy farms in southcentral, Wisconsin. Cows sampled on farm 1 were multiparous Jersey cows (n=30, avg lact=3.2), which calved within a 23d period and on farm 2 were multiparous Holstein cows (n=35, avg lact=2.8), which calved within a 20d period. Blood samples were collected daily during the transition period (d-5 through d10 relative to parturition) and on d30, 60, 90, 150, and 300. Data was analyzed using PROC MIXED and correlations were estimated using PROC CORR in SAS. Overall, there was a time effect (p<0.0001) and a farm and time interaction (p<0.0003). Near parturition, 5-HT decreased as compared to pre-partum by 57.8% (p<0.0001) and 29.6% (p=0.056) on farm 1 and farm 2, respectively. Transition period 5-HT nadir was observed at d2 on farm 1 (879 ± 215 ng/ml), and d1 on farm 2 (1064 ± 186 ng/ml). Serotonin was recovered to 1637 ± 211 ng/ml by d5 on farm 1, with a second decrease of 25.8% (p=0.11) on d7. Farm 2 showed a 5-HT recovery to 1577 ± 184 ng/ml by d5 and subsequent decrease of 34.7% (p=0.02) by d9. Furthermore, 5-HT increased markedly on both farms near peak lactation (d60, 90, 150) and decreased at d300. Calcium decreased compared to pre-partum levels by 35.3% (p<0.0001) and 10.9% (p<0.0001) on farm 1 and 2, respectively. Calcium nadir was observed at d1 on farm 1 (1.79 ± 0.06 mmol) and farm 2 (2.29 ± 0.06 mmol). Serotonin and Ca were positively correlated on farm 1 (r=0.24; p<0.0001) and farm 2 (r=0.15; p=0.0003). No significant correlation was detected between 5-HT and glucose. These results show that 5-HT concentrations change dynamically through the transition period and this change is positively correlated with circulating Ca patterns. Further research should be aimed at discerning how 5-HT affects Ca in different dairy breeds.
Keywords: calcium, serotonin, transition period