Seasonal variations in the composition of Holstein cow’s milk and temperature–humidity index relationship

What is it about?

The increasing concern with the thermal comfort of agricultural animals is justifiable not only for countries occupying tropical zones, but also for nations in temperate zones where high ambient temperatures are becoming an issue. In our recent studies we studied and described the temperature humidity index (THI) dynamics over the Mediterranean basin for the period 1971–2050. In this study we demonstrated a gradual increase of both annual and seasonal THI during the period under investigation and a strong heterogeneity of the Mediterranean area. In particular, the analysis indicated that Spain, southern France and Italy should be expected to undergo the highest THI increase, which in the last decade under study (2041–2050) will range between 3 and 4 units. However, only during summer months the area presents characteristics indicating risk of heat stress for farm animals. In this regard, scenario maps relative to the summer season suggests an enlargement of the areas in the basin where summer THI values will likely cause thermal discomfort in farm animals. The study indicated that the Mediterranean basin is likely to undergo THI changes, which may aggravate the consequences of hot weather on animal welfare, performances, health and survival. At a World level, animal production has to increase in the next decades to satisfy the growing need. We have to expect that the livestock systems (based on grazing, the mixed farming systems or industrialized system) will be more and more negatively affected by climate changes (namely global warming). Other than the production also quality of animal products are strongly and negatively affected by hot environment. This is more important for high quality products like PDO cheeses and than for many European excellences.

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Why is it important?

The retrospective study of the annual, seasonal and monthly variations in bulk milk composition demonstrates a significant association with climatic conditions. High somatic cells count (SCC) and total bacterial count (TBC) values and lower FA% and PR% values were recorded during the summer months, in correspondence with an increase in THI. Moreover, THI break points for milk SCC, TBC, fat and proteins were established. The model indicated a positive relationship and significant change in the slope at 57.3 and 72.8 maximum THI for SCC and TBC respectively, and demonstrated a negative correlation between THI and FA% and PR% and provided break points in the pattern at 50.2 and 65.2 maximum THI respectively. The study indicates the presence of critical climatic thresholds for bulk tank milk composition, and demonstrated different sensitivity of milk characteristics to adverse environmental conditions. Such indications could facilitate the adoption of heat management strategies, which may ensure the health and production of dairy cows and limit related economic losses. Those actions are of particular meaning in European countries where milk is largely used for producing high quality cheeses.

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