Effect of a synthetic corticoid on milk yield and composition and on blood metabolites and hormones in dairy cows.

Twenty-five dairy cows were assigned randomly by breed to flumethasone treatment (10 mug/day, 13 cows) or placebo control (12 cows) from 4 to 44 wk of lactation. Lactation means and trends with stage of lactation were treatment responses. Mean milk yields of cows supplemented with flumethasone were not significantly different from controls. Mean metabolite (glucose, nonesterified fatty acids, and total esterified fatty acids) and hormone concentrations (corticoids, insulin, and prolactin) of blood plasma and their trends throughout lactation were unaffected by supplementation. Data were pooled to determine effects of stage of lactation, temperature, pregnancy, and month on these variables. Changes during lactation were systematic for feed intake, body weight, milk yield, milk components except somatic cells, blood metabolites, and prolactin. At environmental temperatures above 18 C, effects were consistently negative for milk yield and composition, but only above 26 C for feed intake. Prolactin of plasma increased with increasing temperature to 18.2 C and then decreased. No other plasma metabolite or hormone was affected by days pregnant, age, or temperature. Months affected feed intake, milk yield, milk fat percentages, all blood metabolites, and prolactin. Prolactin concentrations increased as daylight hours increased. Our inability to augment established lactation by feeding a supplement of synthetic glucocorticoid to lactating cows is consistent with the view that a lack of avialable corticoids does not limit persistency of lactation in the cow.