Interrelationships Between Behavioural and Physiological Responses and Milk Production in Dairy Cows

Dairy cattle are particularly susceptible to welfare challenges that can negatively impact their behaviour, physiological responses, milk yield, and overall health. These challenges include rough handling by unfamiliar people, extreme climatic conditions, inconsistent feeding, regrouping, and transportation. This pilot study investigated the interrelationships between behavioural and physiological responses and milk production of dairy cows reared in a smallholder stall housing system, restricting cow movement to standing and lying down in the Rajshahi district of Bangladesh. Fifty cows were observed, with all cows assessed over two days. Video recordings were made using a smartphone during the morning milking routine, focusing on specific behaviours: ear position (upright, forward, backward, downward), sniffing, stepping, and tail movement. Observations were conducted during the first two minutes after the start of the milking process manually. Physiological responses recorded included rectal temperature, vaginal temperature, and heart rate. Productivity outcomes include body condition score (BCS), milk yield per milking, daily milk yield, and milking frequency. Environmental data were collected to calculate the Temperature-Humidity Index (THI), which averaged 84.5 (±1.78 SD), exceeding the thermal comfort zone for dairy cattle (THI < 72). Statistical analyses comprised principal component analysis (PCA) to determine the most descriptive variables. Pearson correlation assesses the direction and strength of relationships between variables, and simple linear regression to evaluate milk production variables using all other variables as predictors. Results showed that cows displaying an upright ear position during milking had a positive relation with average daily milk yields (r = 0.456, p = 0.001). Milk yield was negatively correlated with THI (r = −0.331, p = 0.02), forward ear position (r = −0.356, p = 0.01), kicking (r = −0.531, p < 0.001), and sniffing behaviour during milking (r = −0.511, p < 0.001). The daily milk yields were positively correlated with body condition scores of milking cows (r = 0.661, p < 0.001). Rectal and vaginal temperatures were positively associated with each other (r = 0.777, p < 0.001). Similarly, rectal temperature and heart rate were positively associated with each other (r = 0.511, p < 0.001). Therefore, ear position, kicking, and sniffing behaviour during milking were used to assess emotional states, with forward ears associated with signs of stress. Healthy cows with higher body condition scores (BCS) produced more milk, requiring farmers to milk them more than twice a day. This pilot study highlights key behaviour and physiological responses relevant to stress and milk production, and thus overall welfare. For greater generalisability, future research should incorporate larger sample sizes and repeated environmental assessments over extended periods.