Bioclimatic thermal stress indices and their relationships with andrological characteristics in hair rams

Authors: MOLINA, JULIO - Universidade Federal De Sergipe; SANTOS DA SILVA, REBECA - Universidade Federal De Sergipe; BIDEGAIN, FABIANA ALMEIDA - Universidade Federal De Sergipe; SOUZA, YÂNCA BIZERRA - Embrapa; Purdy, Phil; Blackburn, Harvey; AZEVEDO, HYMERSON COSTA - Embrapa

Submitted to: International Journal of Biometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2023
Publication Date: 12/1/2023
Citation: Molina, J.C., Santos da Silva, R., Bidegain, F., Souza, Y., Purdy, P.H., Blackburn, H.D., Azevedo, H. 2023. Bioclimatic thermal stress indices and their relationships with andrological characteristics in hair rams. International Journal of Biometeorology. 68:253-261. https://doi.org/10.1007/s00484-023-02587-0.
DOI: https://doi.org/10.1007/s00484-023-02587-0

Interpretive Summary: This study evaluated how climate affects sperm production and quality in rams in Northeast Brazil. Over a year ram semen quality was monitored and bioclimatic indices (temperature and humidity index, equivalent temperature index, black globe temperature and humidity index, and thermal comfort index) were used as predictors of reproductive performance. Sperm motility parameters were depressed in the dry season of the year compared to the rainy and rainy to dry transition seasons. The black globe temperature and humidity index and thermal comfort index values demonstrated antagonistic relationships with most parameters and specifically affected the type of motility, velocity, and quantity of sperm in motion in a sample, meaning that sperm quality declined as the environmental temperature and humidity increased. Use of these indices should help producers determine more optimal breeding seasons for their sheep and therefore increase the productivity and profitability of their flocks.

Technical Abstract: This study evaluated relationships among reproductive parameters and bioclimatic indices: temperature and humidity index (THI), equivalent temperature index (ETI), black globe temperature and humidity index (BGTHI), and thermal comfort index (TCI), during spermatogenesis phase referring to 45 days (SP-45) and sperm transit phase through the epididymis referring to 15 days (STP-15) that preceded the reproductive assessments (ReA). Such information is useful in determining breeding season in Northeast Brazil. Santa Inês rams (n = 25) underwent two reproductive assessments in three periods of the year (D-P = dry; R-P = rainy and RD-P = rainy/dry transition), and the bioclimatic indices were calculated at the corresponding SP-45 and STP-15 prior to each ReA which included the evaluation of ejaculated semen. Sperm kinetic parameters in D-P were depressed compared to R-P and RD-P (P < 0.05). The index values showed an antagonistic correlation with most parameters and regression showed that the BGTHI and the TCI had a negative association with the progressive motility, curvilinear, straight line, and average path velocities, and a positive association with slow sperm in the ejaculate in SP-45 and STP-15 (P < 0.01). Semen quality kinetics is affected throughout the year, it is impaired in D-P and better in R-P and RD-P. The BGTHI and TCI measured in the sperm production phase classified the environment more coherently and presented better association with the behavior of sperm kinetics.