Endocrine and metabolic status of commercial dairy goats during the transition period

摘要

The aim of this study was to evaluate temporalvariations in circulating levels of selected hormonesand metabolites in commercial dairy goats during thetransition period. Blood samples from 940 goats werecollected weekly, from −3 to 3 wk relative to delivery,to measure the effects of level of milk production, paritynumber, and litter size on concentrations of glucose,β-hydroxybutyrate (BHB), fatty acids, and plasma ureanitrogen (PUN). A subset of 80 goats [40 low-yielding(LY, < 1.8 L/d) and 40 high-yielding goats (HY, >3.7 L/d)] were selected from the study populationto measure the effects of level of milk production onplasma concentration of insulin, prolactin, and growthhormone. Average (±SD) milk yield (from 3 to 30 din milk), body weight, and body condition score forthe study population were 2.4 ± 0.78 L/d, 70 ± 16.0kg, and 2.5 ± 0.28 units, respectively. Milk yield wasmoderately correlated with parity number (r = 0.49)but had weak correlation with litter size (r = 0.14). Inmultiparous but not in primiparous goats, antepartumconcentrations of fatty acids and BHB increased withincreasing litter size. Concentrations of fatty acids,BHB, and PUN were consistently lower in primiparousgoats compared with those in second or greater parity.Postpartum, HY goats had higher ratios of glucose,fatty acids, and BHB to insulin than did LY goats,which might explain the greater mobilization of bodytissues and enhanced milk production observed in thisgroup. Collectively, our results indicate that increasedmilk yield has the most significant influence on themagnitude of body tissue mobilization. Our resultsalso show that goats of higher parity display higherlevels of lipid mobilization, and that both pregnancyand lactation are less able to elicit lipomobilization inprimiparous compared with multiparous goats.