Rightfully, a lot of focus is placed on the effect of heat stress on milk production and growth. However, one should not forget the severe impact heat stress may have on the reproduction of ruminants.

  1. Heat stress experienced by dry cows may result in a shorter gestation period and lighter calves at birth (Seyed Almoosavi et al., 2020).
  2. Immunoglobulins (IgG) and protein content of the colostrum was reduced when the dry cow experienced heat stress (Seyed Almoosavi et al., 2020).
  3. Dairy cows subjected to heat stress exhibit decreased Luteinizing hormone and estradiol levels, which are believed to contribute to seasonal dips infertility (Ross et al., 2017).
  4. Heat stress suppresses placental function, resulting in less oxygen and glucose flowing to the fetus (Brown et al., 1991).
  5. Heifers born from heat-stressed cows produced less milk (26.8 vs 31.9 kg) up to 35 weeks of their first lactation than heifers born from non-heat stress cows (Monteiro et al., 2016).
  6. Heat stress reduced lambs birth size from 4.6 kg to 3.1 kg (Brown et al., 1991).
  7. Supplementing Capsicum to ewes during breeding, gestation and lactation increased both birth and weaning weight of lambs (Block et al., 2007).
  8. Antioxidants, such as vitamin C and E, protect the body’s defence system against excessive production of free radicals during heat stress and can assist in stabilizing the animal’s health status (Al-Dawood, 2017).
  9. Proper assessment of heat stress and efficient cooling of dairy animals, irrespective of their stage of life on-farm, is an immediate strategy to reduce fertility declines (Sammad et al., 2019).
  10. Strategies to reduce fertility declines during heat stress include feeding care, reducing disease and mastitis rates, using semen from cooled bulls and timed artificial inseminations (Sammad et al., 2019).
  11. Providing sheep and goats access to shade improves weight gain, milk production and reproductive performance (Al-Dawood, 2017).
  12. Gonadotrophin-releasing hormone injection at days 6 and 12 post-AI is expected to increase the conception rate in hot weather (Sammad et al., 2019).


Although more challenging to measure the effect of heat stress on reproduction performance, management and feeding strategies should be put in place to reduce the impact of heat stress on the reproduction parameters of ruminants. Failing to do that may have long term consequences for the production animals.

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