Impact of heat stress on the dairy cattle milk quality in two bioclimatic stages in Algeria

Karina Bachtarzi, Assia Allaoui, Lilia Belkacem and Mouni Saadoudi

Abstract: In recent years, global warming is a major concern for the agricultural sector. Heat stress impairs welfare and productive performance of dairy cattle .It negatively affects milk quality altering its nutritive value. This study aimed at assessing the impact of seasonal microclimatic conditions on milk quality of Holstein cows. The study was carried out in two dairy cattle farms located in eastern Algeria belonging to two different semi-arid and humid bio-climatic stages during the four seasons of the year 2021. Temperature and relative humidity were recorded and used to calculate the humidity index (THI), which was used as an indicator of the degree of heat stress. The relationship between the temperature-humidity index (THI) and the overall quality criteria of raw milk from Holstein cows was assessed by monitoring the physico-chemical and microbiological parameters of raw milk. The summer average THI values reached in the two regions exceeding 25°C and the 72 critical points for the Holstein breed thus demonstrate that the cows were exposed to heat stress with a summer average of 29.3°C and 75.8 for the semi-arid region and 26.33°C and 75.4 for the humid region. The analysis of variance showed that fat is significantly affected (p < 0.001) by heat stress. This is expressed by a drop in seasonal averages during the summer season (30.2±0.97 for region A and 29.9±0.49 for region B) as well as a highly significant negative correlation (p < 0.001, r = -0.823) between THI and fat for the humid region. Similarly, a highly significant seasonal effect was observed, characterized by a drop in the summer average protein levels (25.3 ± 2.12 for region A and 22.4 ± 1.82 for region B) with a negative correlation (p < 0008, r = – 0.723) for the semi-arid region. The analysis of the variance of the total flora showed a significant difference (p < 0.0005) between the two regions and highly significant difference (p < 0.0001) between the different seasons. Regarding total coliforms, the analysis of variance showed highly significant season effect in region B (p < 0.0004). It is therefore essential to adopt management strategies to reduce the negative consequences of heat stress in dairy cows and limit the economic losses for the dairy sector.

Keywords: dairy cattle; heat stress; milk composition; temperature-humidity Index

Date published: 2022-12-09