Keep cows comfortable. Shade, water availability, air movement and sprinklers are key to cooling cows. By providing shade alone, cows have lower rectal temperature and respiration rates and can produce more milk. Shade does not influence air temperature, requiring producers in humid areas to provide additional methods of heat abatement. Several research studies have shown the combination of good ventilation, spray and fans to be most effective in free stall barns and along the feed bunk.
The holding pen is where cows experience the most heat stress, making sprinklers and fans especially worthwhile and effective3. To ensure highest milk quality, properly working sprinklers should wet the cow on her top and sides, leaving the udder dry. Dry cow and heifer housing also should be monitored as fetal development, milk production and fertility can be adversely affected by heat stress.
Focus on nutrition. Properly balanced rations provide adequate energy to reduce problems of herd health and reproduction associated with decreased DMI during heat stress. Feed ingredients given to buffer the rumen have been effective in lowering the incidence of acidosis, which is commonly seen during hot weather. Increasing ration energy density with additional grain or fat sources has been shown to be advantageous during summer months as well.
Preliminary research has shown fungal cultures can reduce body temperature and respiration rate, and beta-carotene has been successful in preliminary studies in increasing fertility and pregnancy rate in cows calving during the summer.
Heat detection aids. Summer weather makes a convincing argument to utilize detection aids, including HeatWatch®, tail chalk, tail patches and pedometers. Timed A.I. (TAI) is particularly useful to bypass the often nonexistent signs of estrus. There are several studies that have explored the use of additional hormones to make TAI more effective. For example, administering GnRH agonist or hCG (human chorionic gonadotrophin) on day five of the estrous cycle may reduce pregnancy loss during heat stress by stimulating ovulation and the formation of a CL. Additionally, their use results in higher plasma progesterone4.
Embryo Transfer. Several studies have demonstrated the effectiveness of ET to bypass embryo loss due to reduced oocyte maturation, fertilization and early embryonic death caused by exposure to heat stress5. Current research suggests fresh embryos are considerably more effective than frozen embryos or embryos flushed from heat-stressed cattle. The latter is lower due to fewer oocytes, lower fertilization rates and reduced embryo quality6. The high costs associated with ET and difficulty procuring quality, fresh embryos in a timely manner make it another area meriting continued research.
Room for improvement exists in managing reproduction during heat stress. Research shows promising alternatives to make a reproductive program even more successful in hot weather. It has been proven that with adequate, consistent cow cooling many reproductive issues can be diminished. Others can be managed and their negative impact reduced using heat detection aids, dietary supplements, embryo transfer, timed artificial insemination, or any combination thereof.