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The effects of ketosis, feed restriction, and an endotoxin challenge on circulating serotonin (5-HT) in lactating dairy cows
Circulating serotonin (5-HT) is thought to be associated with various metabolic disorders and hypocalcemia during the transition period. Objectives were to evaluate the effect of ketosis, feed restriction, or endotoxin challenge (models where energetic and calcium metabolism is markedly altered) in lactating cows on circulating 5-HT. Blood samples were obtained from three separate experiments and circulating BHBA, NEFA, and glucose were measured in all three experiments while ionized calcium was only measured in the endotoxin challenge. Data were analyzed using PROC MIXED and PROC CORR of SAS 9.4. In the ketosis study, blood samples from cows clinically diagnosed with ketosis (n=10) or classified as healthy (n=9) were obtained from a commercial dairy farm at d -7, 3, and 7 relative to calving (Abuajamieh et al., 2015 JDS. 98[2]:876). There was no effect of health status on circulating 5-HT. Circulating 5-HT was negatively correlated with NEFA (r= -0.47, P=0.04); however, no other relationships existed between 5-HT and the other metabolites. In the feed restriction experiment (Stoakes et al., 2015 JDS. 98[2]:274), mid-lactation cows were either fed ad libitum (n=3) or restricted to 20% of their ad libitum intake (n=5). There were no effects of feed restriction on circulating 5-HT, and energetic metabolites were not correlated with circulating 5-HT. In a model of endotoxemia (Stoakes et al., 2015 JDS. 98[2]:509), mid-lactation cows were either challenged with lipopolysaccharide (LPS; 1.5 µg/kg BW; n=6) or sterile saline (CON; n=6). LPS decreased blood ionized Ca++ (56%; P < 0.05), but had no effect on circulating 5-HT. No relationships existed between circulating 5-HT and energetic metabolites or ionized Ca++. In summary, ketosis, feed restriction, nor endotoxemia affected circulating 5-HT. Circulating 5-HT was moderately correlated with NEFA in the transition cow experiment, but no other relationships existed between 5-HT and energetic metabolites and calcium in these experimental conditions.
Keywords: feed restriction, ketosis, lipopolysaccharide, serotonin