Impact of three THI levels on somatic cell count, milk yield and composition of multiparous Holstein cows in a subtropical region.

In Egypt, cow's milk represents 52.11% of the total milk production. Climatic condition is mainly expected to impact the welfare and productive performance of livestock animals. Thus, we aimed to explore the impact of temperature-humidity index (THI) on somatic cell count (SCC), milk production and composition on daily milk test records (33600) of Holstein cows under subtropical Egyptian conditions with different levels of THI. Our results revealed that daily milk yield and composition (fat%, protein %, yielded fat, yielded protein and the percentage of lactose) were higher in low THI (31.91kg, 3.91%, 3.22%, 418kg, 349kg and 4.20%, respectively) when compared with high THI. SCC significantly increased 36% from low to high THI. In addition to, it was increased with advanced parities 231.11% from 2nd to 7th parities. At high THI level, SCC was negatively correlated with total MY (r=-0.12P<0.05), 305 MY (r=-0.16P<0.05), protein % (r=-0.15P<0.01), fat% (r=-0.14P<0.01) and lactose % (r=-0.26P<0.01). The current study concluded that dairy cows performance was better in most of the investigated parameters at low THI than those in high THI. Thus, indicating a detrimental effect of THI on both welfare and economic return.