Effects of exogenous recombinant bovine somatotropin (rbST) on mammary function in late lactating crossbred saanen goats

Abstract

The aim of this experiment was to evaluate the effects of rbST on milk production in late lactating crossbred Saanen goats. The mechanism by which rbST acts on mammary function including direct or indirect effects, an intra or extra mammary factors were carried out. Ten, multiparous, non-pregnant crossbred Saanen goats in late lactation, approximately 24 weeks postpartum were used in this study. The experimental goats were divided equally into control group injected with sesame oil as placebo and experimental group treated with rbST. The experimental goats received 250 mg of slow-released-formulation rbST by subcutaneous injection at the subscapular region. Seven days later, corresponding to the expected maximum response to each rbST were determined the mechanisms. The present study found that milk yield over the 4 weeks of this experiment increased 37% and the response to the second injection was greater than the first injection (+ 19%). Major milk constituent were no significant change. In contrast to the rbST treated goats, concentration of milk Na in the control goats were increased by the progress of lactation. After the 2[superscript nd] rbST administration, treated goats were decreased significantly of milk Na concentration and the ratio of milk Na/K also decreased significantly (P<0.05). The arterial plasma concentrations, A-V differences and mammary extraction ratio of precursors for milk synthesis were not statistical different. The plasma IGF-1 concentration was increased significantly after 2[superscript nd] rbST injection. Body fluid compartments for PV, ECW and TBW were significantly increased coincided with an increase in milk yield. The present results indicated that rbST affected the mammary function to increase milk yield in late lactating crossbred Saanen goats by involving the intra-mammary factors to maintenance of tissue integrity. Moreover, the rbST may mediate via IGF-1, mainly acts on extra-mammary factors involving body fluid regulations. The mechanism by which rbST could increase TBW and ECW to make up the largest portion of milk during milk synthesis.