Heat stress and sperm production in the domestic cat

This study aimed to assess 1) the effect of high environmental temperatures on sperm production and 2) the effectiveness of a temperature-humidity index (THI) to predict the degree of thermal stress in a cat model. Semen collection was performed by electroejaculation for 18 mo in 20 tomcats maintained under controlled photoperiod. Still, temperature and humidity were not experimentally manipulated to describe the effect of natural climate conditions on seminal samples. Ejaculates (n = 512) were then grouped according to temperature records of the sampling day and compared by temperature and THI index. Significant lower sperm parameters and increase sperm tail abnormalities were observed during warm environments (temperature and THI). Concentration and total sperm count were the most affected parameters. Environmental temperatures of 28.5 °C with 54% relative humidity (THI = 77.07) and 27.9 °C with 66% humidity (THI = 77.84) were upper thresholds of moderate thermal stress. Moreover, days with relative humidity near 90% led to severe thermal stress with temperatures as low as 26.6 °C (THI = 78.88). The current study demonstrates the detrimental effect of high environmental temperatures on sperm quality in the domestic cat. This effect is observed at lower temperatures when high relative humidity is present. In this sense, the THI was a reliable predictor of the magnitude of thermal stress experienced by cats. Thus, cats from reproductive programs should be maintained under controlled photoperiod cycles with temperatures around 20 °C and humidity around 70% to avoid semen detrimental effects.