A field study on glucose, non-esterified fatty acids, beta-hydroxybutyrate and thyroid hormones in dairy cows during the breeding period in Fars province, Iran

It was hypothesized that under apparently good management practices in dairy farms, some cows may not be metabolically perfect during the breeding period and this may affect their performance. This study was conducted to assess probable metabolic drawbacks in mid-lactation dairy cows affecting their performance. Thirty-seven clinically healthy Holstein cows were assessed for plasma concentrations of glucose, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), thyroxin (T4), and tri-iodothyronine (T3) on days 60, 90 and 120 of lactation. The relationships of the measured analytes with some performance indices were also studied. Continuous declines in plasma glucose (within reference values; P<0.006), T4 (P<0.001) and T3 (0.003) were found during the study. Non-esterified fatty acids showed relatively high levels through the study with a rise at day 90 (P<0.041). Beta-hydroxybutyrate concentrations did not change significantly (P>0.05) but were higher than those reported by others in mid-lactation cows. By progress in lactation 27% of cows had glucose concentrations <2.5 mmol/L, 62% had NEFA concentrations >0.40 mmol/L and 13.5% had BHB levels above 1200 µmol/L, which are the threshold levels of peri- and post-parturient problems. Milk production had negative correlations with glucose and T4 while the correlation was positive with NEFA. The interval between calving to the 1st heat had positive correlations with BHB concentrations. The interval between calving and the 1st insemination was inversely correlated with glucose and positively correlated with NEFA levels. The changes of the studied analytes in mid-lactation cows resembled those that would happen during negative energy balance in early lactation cows and feed restriction in mid-lactation cows and may affect the general health and the performance of the cows.