Heat Stress in Tunisia: Effects on dairy cows and potential means
Tunisia has a Mediterranean climate characterized by high ambient temperatures for a long period. Thus, one of the challenges to dairy producers is heat stress. The objectives of this work were to characterize the environmental conditions to which Holstein cows are exposed in Tunisia using the Temperature Humidity Index (THI), examine heat stress effects on lactating cows and to suggest potential management strategies that can be used to reduce such effects. THI values were calculated using a 10-year period average monthly temperature and relative humidity data from different weather stations. Milk production and its relationship with THI were than examined using the data of herds under the dairy herd recording programme. Reproductive indices were calculated using data from four selected herds and their relationships with corresponding THI values were examined. Results showed that summer heat stress prevails in Tunisia for four to five months going from May to September with THI values being greater than 72. The highest THI values were recorded for summer and early fall. Milk yield per cow dropped by about 10% between March and August. First conception (CRI1) and overall conception rates (CR) were lowest in the summer and highest in winter. Regression equations between THI and CRI1 and THI and CR had high R
2 values suggesting a strong relationship between heat stress and reproduction. Maintaining cow performance under hot conditions requires the adoption of environmental control techniques, appropriate feeding strategies, improved nutritional practices, and genetic improvement programs such as crossbreeding for enhanced heat tolerance.