Seasonal semen quality of a local and commercial taurine cattle breeds, raised in a subtropical climate: Relationship between external morphology of the animals and climate.

Livestock production is considered an important factor influencing global warming; however, climate change has also been considered one of the major factors affecting livestock production and reproduction. The present study was carried out in the Southern region of Brazil and aimed to assess the seasonal influence of climatic factors and external morphology of the animals on the semen quality. Three ejaculates were obtained from each bull (Crioulo Lageano and Angus) in summer and winter seasons. Motile cells, sperm vigor, sperm concentration, sperm membrane status, and sperm abnormalities were analyzed in fresh and post-thawed semen. In addition, the sperm kinetics using CASA was assessed on post-thawed semen. Environmental data such as air temperature (AT), relative humidity (RH), mean radiant temperature (MRT) and temperature-humidity index (THI) were measured. Furthermore, body and testicular metrics, as well as hair coat characteristics, were recorded in each season on all bulls. Environmental traits differed significantly between seasons. Results of the PLS regression and Spearman's correlations confirmed a negative relationship between climatic variables and sperm traits in both seasons. Semen quality between breeds and seasons was similar, satisfactory, and heat stress was not sufficient to impair spermatozoa viability. External morphological traits were considered non-important in the final model. The findings of this study suggest that AT, MRT, and THI were the most important factors that could affect seminal characteristics of bulls raised in a subtropical climate.