Metabolic response to exercise in the lactating ewe

Abstract

Proc. Amt. Sot. Anim. Prod. 1994 Vol. 20 METABOLIC RESPONSE TO EXERCISE IN THE LACTATING EWE G. ANIMUT, K.D. CHANDLER and G.H. MCDOWELL School of Agriculture, La Trobe University, Bundoora, Vic. 3083 Substrate supply to the mammary gland depends on arterial concentrations of metabolites and blood flow, both of which might be affected by exercise. Although the lactational performance following exercise in dairy cows has been studied (Lamb et al. 198l), there is limited knowledge on the effect of exercise on mammary metabolism. This study was conducted to examine metabolic adaptations in the mammary gland during moderate exercise. Nine lactating ewes were kept in metabolism cages and fed to meet requirments for liveweight and milk production (see McDowell et al. 1987). Blood flow probes (Transonics Inc. Ithaca, NY) were fitted around an external pudendal artery in each ewe under general anaesthesia. The ewes were exercised on a moving belt treadmill at a speed of 0.7 m/second and inclination of 9' for 1 hour. Three sets of arterial and mammary venous blood samples were drawn simultaneously via indwelling catheters inserted into the femoral artery and an external pudendal vein at intervals of 10 minutes while the ewes were at rest and further 3 sets were collected at intervals of 20 minutes during exercise. Blood plasma was assayed for metabolites using standard techniques (McDowell et al. 1987). Mammary uptakes were calculated as the product of arteriovenous differences (A-V) and blood flow. Table 1. Arterial plasma concentrations, arteriovenous differences (A-V) and mammary uptakes of glucose (mmol/L or pmol/minute), alpha amino-nitrogen (o-amino N; mg/lOO mL or mg/minute), acetate (mmol/L or pmollminute) and non-esterified fatty acids (NEFA; PmollL or pmollminute) and as well as mammary blood flow (mL/minute) during rest and exercise Arterial plasma concentrations of glucose, a-amino N and non-esterified fatty acids (NEFA) significantly increased in response to exercise and a small insignificant decrease was observed for acetate. These changes were accompanied by increases of 25%, 21%, 376% and a fall of 19% in the mean mammary A-V for glucose, a-amino N, NEFA and acetate respectively. The mammary uptakes of olucose and a-amino N were unaffected by exercise because reduced blood flow was offset by a greater L-V. However, the marked increase in A-V for NEFA and lower A-V for acetate resulted in an increased uptake for NEFA and reduced uptake for acetate during exercise. Exercise was accompanied by marked changes in mammary metabolism. The changes in acetate and eland may have implications for milk lipid biosynthesis. NEFA fluxes across the mammary a LAMB, R.C., ANDERSON, M. J. and WALTERS, J.L. (19Sl). J. Dairy Sci. 64: 2017-24. MCDOWELL, G-H., GOODEN, J.M., LEENANURUKSA, D., JOIS, M. and ENGLISH, A.W. (1987). Aust. J Biol. Sci. 40: 295306. 404