Influence of the level of daily milk yield on some blood biochemical parameters in dairy cows reared under the same temperature and humidity conditions

Rumyana Ivanova, Hristo Hristev and Zhivka Gerovska

Abstract: The present study examines the relationship between the milk productivity and some biochemical parameters in dairy cows of the Holstein cattle breed reared under the same temperature-humidity conditions. The tests were performed in the course of one year in three cattle-breeding farms with a different capacity. The farms are located in the central part of Southern Bulgaria, in the region around Plovdiv. The region itself is characterized by a temperate continental climate with high temperatures during the summer and moderately cold ones during the winter. The conditions in the cow-rearing premises of the three farms examined ranged from mild to moderate heat stress zone during the summer and partially – during the spring. Based on the daily milk yield and THI (by classes) values reported, a model for assessment of their effect on the biochemical indicators of the cows: protein and energy metabolism, enzymes, liver markers and cortisol was applied. The highest glucose levels were reported for the cows with an average daily milk yield between 30 and 40 kg (p < 0.001), and the lowest- for the highly productive animals (≤ 40 kg) – 2.46 mmol/L which is even below the reference value for the breed (2.50 – 4.16 mmol/L). With the THI values increase, the glucose levels of the cows from all daily milk yield level groups decreased and this dependence is high (p < 0.001). The protein levels were the lowest in the cows with the lowest milk yield (up to 30 kg per day)- with approximately 7.5% when compared with the other two milk yield groups. The blood urea levels increase was more considerable in the cows with higher daily milk yield from 30 to 40 kg and over 40 kg- from 3.25 mmol/L, and 3.33 mmol/L to 7.72 mmol/L, and 7.62 mmol/L respectively. The creatinine LS means of the cows from all productivity groups increased with the increase of the THI values (p < 0.001) with the elevation being more significant in the cows with higher daily milk yield (p < 0.001). The cholesterol levels increased along with the milk yield (p < 0.001) but a considerable decrease in this parameter was reported for the cows of the three milk yield groups (p < 0.001) upon increase in the THI values over 80. The LS means of the two transaminases in the cows blood were in an inverse correlation with their daily milk yield. The cows with lower milk yield of up to 30 kg had lower ASAT levels (92 U/L) and higher ALAT levels (23.38 U/L) when compared with the cows with high daily milk yield – 106.6 U/L and 19.74 U/L respectively. The present study displays a significant increase in the two enzymes activity upon increase of the THI values: ASAT – p < 0.001 and ALAT – p < 0.01. A high significance (p < 0.001) was ascertained in the related effect of the daily milk yield and the cortisol levels.

Keywords: dairy cows, THI, daily milk yield, protein and energy metabolism, ASAT, ALAT, cortisol

Date published: 2022-11-02