A time series analysis of monthly Holstein milk yield and composition in a hot environment

This study aimed to evaluate the effects of thermal stress on milk yield and milk composition using the time series approach to forecast the trend of daily milk yield and milk components in Holstein cows in a hot-arid environment. Also, this study evaluated the effect of season on the microbiology of raw bulk Holstein cow milk. The obtained data comprised the average daily milk yield, composition, and bacterial counts from a single high-input dairy herd in northern Mexico, registered for seven consecutive years (2014-2020). The autoregressive integrated moving average (ARIMA) procedure showed a distinct pattern for the daily milk yield. A two-year forecasting showed 8.4 kg difference in daily milk yield between winter and summer months. The predicted future values based on past values showed that milk solids were highest in January (12.09 %; CI= 11.86-12.31 %) and the lowest in August (12.02; CI= 11.75-12.29). The mean predicted fat content was highest in January (3.60 %; CI= 3.48-3.71 %) and lowest in July (3.44%; CI= 3.29-3.59 %). Following the repeated observations, forecasting values for milk protein percentage were 3.22 % (CI=3.15-3.28 %) in January and 3.07 (CI=2.98-3.1) in April. The ARIMA method forecasted milk lactose as highest in January (4.87 %; CI=4.79-4.95) and lowest in June (4.77 %; 4.68-4.86 %). Standard plate count was higher (p<0.01) in autumn and winter than spring and summer. During winter, the average thermoduric count (TDC) in raw bulk milk was higher (12.5 +/- 2.01) compared with TDC in the spring (9.7 +/- 1.5; p<0.01). The somatic cell count did not differ between seasons. The coliform bacteria count was highest in autumn (77.8 +/- 28.3 cfu/mL; p<0.01) and lowest in spring (53.7 1.3 cfu/mL). It was concluded that hotter months diminished daily milk yield and its components. The ARIMA model can be used to accurately forecast daily milk yield and composition, which would allow to develop long-term strategies for managing milk production.