Effect of dexamethasone on milk yieldand composition in dairy cows

Abstract

Dexamethasone was injected in dairy cows in order to get a better insight into the effects of corticosteroids on milk secretion and composition. A single intramuscular dose of 40 mg dexamethasone caused a 45% reduction in milk yield after 24 h; full recovery took 5 d. The secretion of fat, casein and magnesium was not affected by the treatment. Consequently, the concentration of fat, total protein, total casein, magnesium and phosphorus increased then decreased in direct proportion to the changes in milk yield. The secretion of total protein, calcium and phosphorus decreased as a result of the treatment. The concentration of lactose and the monovalent ions (sodium, potassium, and chlorine) was unaffected, and as a result their secretion decreased and returned to pretreatment level in direct inverse proportion to the changes in milk yield. Whey protein secretion decreased for 48 h and was responsible for the decrease in total protein secretion for 48 h. The most profound effect of dexamethasone is the reduction in the secretion of the osmotic components. milk yield / dairy cows / stress / corticosteroids Rsum -Effet de la dexamthasone sur la production et la composition du lait chez les vaches laitires. La dexamthasone a t injecte des vaches laitires afin de mieux comprendre les effets des corticostrodes sur la scrtion et la composition du lait. Une dose unique intramusculaire de 40 mg de dexamthasone a rduit de 45 % la production de lait aprs 24 h ; le retour total la production antrieure a pris 5 jours. La scrtion des lipides, des casines et du magnsium n'a pas t affecte par le traitement. En consquence, la concentration des lipides, des protines totales, des casines totales, du magnsium et du phosphore a augment puis a diminu proportionnellement aux changements de production laitire. La scrtion des protines totales, du calcium et du phosphore a diminu la suite du traitement. La concentration du lactose et des ions monovalents (sodium, potassium et chlore) est reste inchange ; leur scrtion a diminu et est revenue au niveau initial dans une proportion inverse aux modifications de la production laitire. La scrtion des protines du lactoserum a diminu pendant 48 h et a t responsable de la diminution de la scrtion des protines totales