Evaluation of the productive and reproductive performance of Holstein dairy cows reared in a warm Tunisian (Mediterranean) climate

This work consists in studying the productive and reproductive performance of Holstein dairy cows (n=77) reared in an intensive production system in a Mediterranean climate, as well as the factors of their variations. Meteorological data collected between 2017 and 2020 for the region of Beja, North-West of Tunisia, revealed that the average monthly values ​​of ambient temperature (Ta), relative humidity (HR) and temperature-humidity index (THI), are respectively 19.97 ±1.24°C, 73.69±3.42%, and 66±1.74. During the 3 years of study, the cows were exposed to a hot summer season which began in Jun (THI= 76) and persisted until September (THI =77). On average, milk production at 305 days of lactation, milk fat (MG) and protein (MP) content, as well as somatic cell count (SCC) were respectively 5782 ± 358 Kg, 3.36 ± 1.65%, 3.12 ± 0.42% and 489 ± 305 x 103 cells/ml. Several factors significantly (P < 0.05) affect milk production. Indeed, the highest milk production is observed during the year 2020. When the THI increases, the drop of milk production is greater (-0.18kg/d, per THI point). Multiparous cows produce more milk than primiparous cows, with higher yields at peak lactation (30.0 kg/d) and a lower persistence coefficient (95.6%). Cows calved in winter produced more milk (+22%; P