Objectives of this study were to examine the role of supplemental dietary fat and administration of bST initiated in early lactation on production responses, milk fatty acid composition, postpartum ovarian activity, and hepatic gene expression of dairy cows. Multiparous cows blocked by expected calving date and previous milk production were assigned randomly to one of four treatments in a 2 x 2 factorial arrangement of dietary fat enriched with omega-3 fatty acids (FA) and bST treatment. Administration of bST (POSILACRTM, 500 mg) was initiated at 12 DIM and continued at 10-d intervals through 70 DIM and at 14-d intervals thereafter. Feeding dietary fat was initiated at calving and dietary ratio of omega-6 to omega-3 FA varied by inclusion of whole sunflower seeds (10% dietary DM, omega-6/omega-3 FA ratio = 4.6) or a mixture of Alifet-High EnergyRTM and Alifet-Repro RTM (3.5 and 1.5% of dietary DM, omega-6/omega-3 FA = 2.6). Initiation of bST administration at 12 DIM increased milk, 3.5%-FCM, and 4.0%-SCM yields and plasma IGF-I. In addition, bST did not exacerbate the moment or magnitude of energy balance nadir but did prolong the postpartum delay in onset of tissue replenishment and partitioning of dietary FA into milk fat, and interacted with dietary fat to alter Delta9-desaturase index in the mammary gland. Feeding dietary fat enriched with omega-3 FA increased plasma IGF-I, decreased the impact of bST on overall energy balance, increased omega-3 FA in milk, and reduced the omega-6 to omega-3 FA ratio in milk. Results indicate diets enriched with omega-3 FA increased size of ovulatory follicles and corpus luteum development during the early luteal phase and that bST interacts with dietary omega-3 FA to increase the incidence of estrous cycles with 3-follicular waves. Our results suggest: IGFBP3 mRNA expression may be involved in molecular mechanisms that regulate the GH-IGF-I axis, administration of bST increased hepatic mRNA abundance of GH receptor, IGF-I, and IGFBP3 even when cows were in negative energy balance, and PPARalpha could mediate, at a molecular level, the interaction of bST and dietary fat on some productive and reproductive responses.Integration of metabolism and intake regulation: A review focusing on periparturient animals. J. Dairy Sci. 83:1573-1597 McBride, B. W., J. L. Burton, J. P. Gibson, J. H. Burton, and R. G. Eggert. 1990. Use of recombinant bovine somatotropin foranbsp;...
|Title||:||Dietary Fat and Bovine Somatotropin (bST) Initiated in Early Lactation in Dairy Cows|
|Publisher||:||ProQuest - 2006|