[Roles and mechanisms of action of somatotropin (growth hormone) in lactating ruminants].
In 18 short-term trials from the literature using dairy cows, somatotropin resulted in increased milk yield (+4.0 kg/d), increased fat, lactose and protein secretions, decreased dry matter intake (-0.5 kg/d) and decreased calculated energy balance (-4.2 Mcal/d). Milk composition was also changed (fat, + 1.9 g/kg; protein, - 1.4 g/kg, and lactose, + 0.6 g/kg), due to the fact that treated cows were often in negative energy balance. In 15 long term trials, somatotropin resulted in increased milk yield (+ 5.7 kg/d) and increased dry matter intake (+ 1.2 kg/d), whereas calculated energy balance decreased (- 2.2 Mcal/d). In 4 trials, digestive efficiency did not seem to be altered by somatotropin. In two long-term trials, body lipids (as estimated by deuterium marked water space) were about 40 kg lower in treated cows, probably reflecting a lower lipid deposition, owing to their lowered energy balance. Current hypothesis on mechanisms of action of somatotropin or somatomedins are discussed, concerning mammary tissue (secretory cell number or metabolic activity), as well as teleophoretic adaptations that alter nutrient partitioning between mammary, liver, muscle and adipose tissues, by way of modifications of tissue responsiveness to homeostatic insulin or adrenergic regulations. Somatotropin could indirectly stimulate metabolic activity in mammary cells. Simultaneously, it could decrease adipose tissue lipogenesis and increase fatty acid mobilization and oxidation in other tissues, thus allowing decreased glucose and amino acid oxidations that insure adequate nutrient supply to the mammary gland.
Chilliard
Y
Y
Laboratoire de la Lactation, I.N.R.A., Ceyrat, France.
D000818:Animals; D002417:Cattle; D005260:Female; D005947:Glucose / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology* / Q000502:physiology; D007774:Lactation / Q000187:drug effects*; D050356:Lipid Metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects; D011247:Pregnancy
D013006:Growth Hormone; D005947:Glucose
Rôles et mécanismes d'action de la somatotropine (hormone de croissance) chez le ruminant en lactation.