Adaptive Responses of Thyroid Hormones, Insulin, and Glucose during Pregnancy and Lactation in Dairy Cows

SIMPLE SUMMARY: The effects of different stages of pregnancy and lactation on thyroid, insulin, and glucose responses in 30 dairy cows from different breeds were studied. Thyroxine (T(4)) and insulin were higher at the end of pregnancy than at >60–120 d or in nonpregnant cows. Along the lactation phase, T(4) initially decreased, reaching the lowest values at >60–120 d, and then increased until the end of lactation. Glucose showed the highest concentrations during the first 120 days of lactation, and the lowest values at the end. The monitoring of thyroid hormones, insulin, and glucose changes represents an important tool to evaluate the anabolic and/or catabolic adaptation in response to functional periods in dairy cows, which can potentially predispose the cows to an excessive negative energy balance and related metabolic issues. ABSTRACT: The study examined the effects of different stages of pregnancy and lactation on thyroid, insulin, and glucose responses in dairy cows. In the present study, 30 dairy cows (10 Holstein, 10 Simmental, and 10 Brown) at 30 ± 20 d of lactation were randomly selected and blood samples were collected once every 60 d for one year to measure circulating thyroid stimulating hormone (TSH), total and free triiodothyronines (T(3), fT(3)) and thyroxines (T(4), fT(4)), insulin, and glucose. Pregnant cows showed higher T(4) (p = 0.010) and insulin (p = 0.046) concentrations at >180 d than at >60–120 d of pregnancy and in nonpregnant cows. Along the lactation phase, circulating T(4) concentrations showed a biphasic trend, decreasing from 0–60 d to >60–120 d phase, which showed the lowest values, and then increasing until the end of lactation (>300 d) (p = 0.016). Glucose showed the highest concentrations at the start of lactation (0–120 days) and the lowest values at the end (p = 0.008). The monitoring of thyroid hormones, insulin, and glucose changes represents an important tool to evaluate the anabolic and/or catabolic adaptation in response to functional periods in dairy cows, which can potentially predispose the cows to an excessive negative energy balance and related metabolic issues.