The Relationships Between Milk Production and Some Blood Metabolites and Their Effects on Returning to Estrus in Lactating Holstein Dairy Cows

In this study, the relationships and correlations between milk production and some blood metabolites related to energy and protein balance and their effects were investigated on returning to estrus after AI in lactating Holstein dairy cows. Blood and milk samples were collected from sixty lactating Holstein dairy cows based on their reproductive status in 13-17 d post AI. BUN, MUN, glucose, triglyceride, cholesterol and BHBA were measured by enzymatic colorimetric method and blood progesterone concentration was measured by ELISA method. Between 18-25 d post AI, 27 cows returned to estrus (RE group), but 33 cows did not (NRE group). In RE group, there were significant correlations between DIM and Monthly Milk yield Record (MMR) (p 0.05), BUN (p 0.01) and glucose (p 0.01). Furthermore, MMR was correlated with BUN (p 0.05), MUN (p 0.05), glucose (p 0.05) and cholesterol (p 0.05). In addition, BUN in this group was correlated with MUN (p 0.01) and glucose (p 0.05) and the correlation between glucose and BHBA (p 0.05) was significant. In NRE group, there were significant correlations between DIM and MMR (p 0.01) and between MMR and glucose (p 0.05). Also parity was correlated with glucose (p 0.05). BUN and MUN concentrations correlation was also significant (p 0.05). Except progesterone concentrations (p 0.01), there was not any difference between the mean of the two groups variables. In conclusion, the result of this study suggested that in animals returned to estrus after AI and failed to continue pregnancy, there were significant correlations between milk yield and some blood metabolites (BUN, MUN, glucose, triglyceride, cholesterol and BHBA) related to physiological imbalance. In animals that continued pregnancy and did not return to estrus, there was not any significant interpreted correlation between the variables. Therefore, despite adverse effect of negative energy balance on physiological imbalance and blood metabolites, progesterone concentration had the key role in stability of the pregnancy.