INFLUENCE OF PREGNANCY AND LACTATION ON GLUCOSE METABOLISM OF NUBIAN GOATS

Abstract

Two in vivo metabolic challenges were conducted to assess the changes in glucose metabolism during three intervals prepartum (-6, -4, -2 weeks) and three postpartum (+2, +4, +6 weeks) in six multiparous pregnant Nubian goats. Challenges consisted of intravenous administration of 1) glucose (62.5 g/goat) and 2) L-epinephrine (0.7 mg/kg body weight). Blood samples were collected via jugular cannula from 30 min pre-injection (basal concentrations) to four hours post-injection. Response variables for glucose challenge were glucose concentration at zero time (to) glucose disappearance rate (t½), insulin and NEFA concentrations; for the epinephrine challenge glucose, NEFA and insulin integrated responses were determined through the four hours of sampling. Data were analyzed according to a repeated-measures design. Dry matter intakes (1.8±0.07 kg/d) were not different throughout the study (P>0.1). Average milk production (649±69 g/d) was not different among periods (P>0.1). Basal glucose and insulin concentrations were not different (P>0.1) between pregnancy and lactation, with means (± standard error) of 77.9±3.7mg/dl, and 0.264±.034ng/dl, respectively. Basal NEFA concentrations were greater (P<0.001) during weeks 2 and 4 postpartum (0.40±0.2 and 0.57±0.3 mmol/l) and lowest during prepartum periods. Responses to glucose challenge did not differ throughout periods evaluated, with means for to of 289±17 mg/dl (P>0.1) and for t½ of 31±15 min (P>0.1). Insulin responses were similar for all periods (63.3±8.2 ngml-1min) (P>0.1). The epinephrine challenge resulted in similar changes in glucose and insulin integrated responses throughout the periods evaluated (P>0.1), with corresponding means for glucose of 3886.5±318 mgml-1min, and 21.6±7.7 ngml-1min, but elicited a significant (P<0.001) increase in plasma NEFA concentrations during weeks 2 and 4 postpartum (1.24±0.6 and 1.40±0.3 nmol.l-1min), but not during the prepartum periods. Metabolic responses of dairy goats to exogenous glucose and epinephrine markedly influenced by physiological stage, mainly with onset of lactation.