Postpartum Changes in Hormones and Metabolites During Early Lactation in Summer and Winter Calving Holstein Cows.

Abstract

Changes in metabolites and metabolic hormones during the first 12 weeks postpartum in both summer and winter were analyzed on a total of 18 lactating, Holstein cows (summer, n=11; winter, n=7). The summer trial covered the months of August through October. The winter trial began in November and lasted through early February. Maximum and minimum temperature and humidity values were recorded daily. Blood was sampled in serum, fluoride and heparin tubes from the coccygeal vein once a week beginning at day of calving for 12 weeks. Concentrations of progesterone, cortisol, thyroxine, leptin, NEFA, cholesterol and insulin were analyzed from serum samples. The metabolites glucose, PUN and &#946;-HBA were analyzed with plasma collected from fluoride and heparin containing tubes. No significant seasonal differences were found between summer and winter calving groups for P4, T4, glucose, insulin, PUN and NEFA. However, leptin (P < 0.01), cholesterol (CHL) (P < 0.0001) and &#946;-HBA (P < 0.0001) had significant seasonal differences between the two calving groups. The mild heat stress during the early part of the summer trial may not have been severe enough to detect significant changes in serum T4 or the animals had become acclimated to these temperatures. Summer calving cows may have experienced a drop in feed intake at calving (not measured) enough to increase their plasma ketone bodies (&#946;-HBA), but not enough to dramatically reduce circulating levels of glucose and insulin.