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Research article2020Peer reviewedOpen access

Heat stress and bull fertility

Morrell, Jane M.

Abstract

Since bull fertility may be adversely affected by hot humid conditions, the current increase in global temperature is of concern for future livestock production. Heat stress occurs when the body's normal physiological mechanisms to regulate body temperature cannot cope with external conditions. The testes and scrotum have their own complex regulatory mechanisms to protect developing sperm during their most vulnerable stages, but even these may be overwhelmed by unfavourable external conditions. The effects of mild, moderate and severe heat stress are somewhat different, with cattle exposed to mild and moderate heat stress apparently showing an adverse effect on fertility, whereas cattle in very hot, humid climates almost continuously may not exhibit any difference in sperm quality throughout the year. This apparent paradox may be due to differences in the cattle populations being studied, since they could differ in breed, age, purpose (beef versus dairy), or even in the methods used to assess sperm quality. The adverse effects on fertility may occur through the effects of reactive oxygen species on sperm DNA, or through perturbation of the production of antioxidants that usually protect sperm from oxidative attack. These effects can be mitigated to some extent by choosing breed and age of bulls with care, and adopting breeding strategies that avoid semen collection or ejaculation at the most adverse times of year. Husbandry measures such as controlled ventilation, misting, provision of shade or cool surfaces for lying down, could aid temperature regulation. Avoiding heat stress during late pregnancy aids calf growth in early life; careful feeding regimens for young bull calves create good conditions for sperm quality after puberty. Bull fertility is too important to be left to chance. Breeds should be chosen according to climate conditions and the purpose of livestock production. (C) 2020 Elsevier Inc. All rights reserved.

Keywords

Thermal humidity index; Spermatogenesis; Scrotum; Testicular heat regulation; Sperm quality; Sperm morphology

Published in

Theriogenology
2020, volume: 153, pages: 62-67
Publisher: ELSEVIER SCIENCE INC

SLU Authors

UKÄ Subject classification

Animal and Dairy Science

Publication identifier

  • DOI: https://doi.org/10.1016/j.theriogenology.2020.05.014

Permanent link to this page (URI)

https://res.slu.se/id/publ/106782