Effect of low-frequency oscillations on blood cortisol concentration and milk quality in dairy cows

Abstract

Previous investigations have evaluated the impact of low-frequency oscillations on udder function, milk composition, and welfare of dairy cows during milking [1]. We hypothesised that the organism of the cow may respond to a low-frequency oscillation device as an external stressor. In cattle, cortisol produced under stress conditions has been associated with reduced reproductive performance, lowered milk production, and suppression of the immune system [2, 3]. Stress also influences milk composition, decreasing fat and protein content while increasing somatic cell count, which reflects poorer milk quality [4, 5]. The objective of this study was to investigate the impact of low-frequency oscillations on cows’ stress level and milk composition. In the first trial, healthy cows were assigned into two groups of 20 cows using the principle of analogy. In the experimental group, low-frequency oscillations were applied to the udder during morning milking [1]. Blood samples were collected from the tail vein right after morning milking to determine cortisol concentration (ELISA). In the second trial, cows were divided into two groups of 10 cows and observed for two weeks. In the experimental group, conventional milking was carried out during the first week, while in the second week, udder stimulation with low-frequency oscillations was applied during each milking. The control group underwent conventional milking throughout both weeks. Daily milk yield was recorded, and at the end of each week, milk samples were collected to determine fat, protein, lactose, and urea content, as well as somatic cell count (SCC). For statistical evaluation, t test analysis was used to compare cortisol, milk yield, and milk quality parameters. In the first trial, the cortisol concentration in the blood of cows in the experimental group was 2.81 ng/mL lower (P = 0.2102) than in the control group, indicating that low-frequency oscillations did not induce stress during milking. In the second trial, application of low-frequency oscillations in the experimental group during the second week resulted in an average daily increase of 0.99l of milk per cow (P = 0.1475) compared with the first week, when no oscillations were applied. In the control group, the increase between weeks was only 0.26 L of milk per cow (P = 0.9245). These differences were not statistically significant. Analysis of milk quality parameters showed that in the experimental group, the milk fat content was 0.58% higher in the second week compared to the first week (P = 0.038). Other milk quality indicators (protein, lactose, urea, SCC) did not differ significantly between weeks in either group. In conclusion, low-frequency oscillations applied to cows during milking did not induce stress. Moreover, they tended to increase milk yield and improve milk quality indicators.