Abstract
The objective of the present study was to determine the effect of exogenous bovine somatotropin on the mammary function in late lactating crossbred Holstein cows. Twelve 87.5% late lactating Holstein cows, approximately 30 weeks postpartum, were divided into two groups of 6 animals each. Animals in the control group were given sodium bicarbonate buffer by subcutaneous injection, while animals in the treated group were given recombinant bovine somatotropin (bST) by subcutaneous injection with 500 mg of bST (14 day prolonged-release bST). After bST injection, milk yield significantly increased from the control level on day 8 to day 20 (p<0.05) with a concomitant increase in mammary blood flow (p<0.01). An increase in mammary blood flow in response to bST treatment was greater than an increase in milk production. An increased plasma concentration of IGF-I coincided with an increase in mammary blood flow in animals treated with bST. There were no significant changes in the concentration of arterial plasma glucose concentration, the arteriovenous concentration difference (A-V difference) and mammary extraction ratio while the mammary glucose uptake increased when compared to the control group. The concentration of arterial plasma triglyceride decreased throughout the experimental period in animals give bST. The plasma concentration of acetate, and the mammary uptake for acetate significantly increased (p<0.05) after bST treatment. The action of bST did not affect the plasma concentration, A-V difference and extraction ratio across the mammary gland for β-hydroxybutyrate. The concentrations of milk fat and lactose tended to increase during bST treatment. Milk protein concentration initially increased in the first few days and decreased after bST injection when compared to the pretreated period. The present results indicated that bST could affect the mammary function in late lactating cows by increase in milk yield involving changes in both extra-mammary and intra-mammary mechanisms. The exogenous bST exerted its galactopoietic action through an increase in circulating IGF-I of the late lactating Crossbred Holstein cattle. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 1 : 88-95)
Highlights
The problems for dairy farming in Thailand are the low milk production and short lactating period of indigenous dairy cattle
An increase in milk secretion in response to the treatment of bovine somatotropin requires partitioning of nutrients to accommodate an increase in the rate of milk synthesis by
The ratio of mammary blood flow to milk yield increased after bovine somatotropin (bST) treatment and it returned to pre-treated value on day 16
Summary
The problems for dairy farming in Thailand are the low milk production and short lactating period of indigenous dairy cattle. Many factors can affect milk production in crossbred dairy cattle such as a high environment temperature, a lower genetic potential of dairy cattle and an inadequate supply of forage during summer. These factors can affect the physiological signals received by the mammary gland. The lactating mammary gland receives signals from the rest of body in the forms of nutrients and hormones from blood to sustain milk synthesis. Growth hormone is a major galactopoietic factor during lactation, one of its key effects being greater utilization of nutrients for milk synthesis.
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