Santas and Duhram Reds
Well-known member
Summer is a great time for a vacation but it is not a good time for cattle breeding. There are physiological reasons for not breeding, or not expecting bulls to breed your females during summer. Other than just being too darn hot, fertility is lower during the summer as compared to fall, winter, and spring. This lowered fertility is called the "summer breeding slump" and it affects all livestock producers (beef, dairy and swine) by reducing conception rate and reproductive efficiency. Summer heat stress due to elevated environmental temperature and humidity can affect fertility of both cows and bulls, but increased summer temperature extended over several weeks predominantly causes lower libido, lower semen quality and quantity, and extends the time required for recovery of normal levels of semen production. Most southern bull studs collecting semen for AI begin to reduce their collection schedule by mid-June.
Cows and heifers produce healthy oocytes (eggs) at normal body temperature (101ºF) whereas bull sperm production is optimized at 96ºF, 5º to 6ºF below normal body temperature. Thus, ovaries reside inside the body cavity and testicles do not. However, increased body temperature can negatively affect the expression of estrus, fertilization rate, uterine environment and the ability to develop a viable embryo, and may affect oocyte quality during the maturation process, which occurs over the 60 days prior to ovulation.
Bulls possess remarkable anatomical structures to assist with testicle temperature regulation including: muscles, nerves, sweat glands, a modified circulatory system, and the ability to pant. These tools are designed to keep testicles warmer or cooler than the environment. It is much easier to keep testicles warm than cool. On a cold day the bull simply uses muscles to raise the testicles close to the body and wrinkle the scrotum to decease surface area. In summertime the process is essentially reversed to dissipate and avoid heat. In addition, a modified circulatory structure that sits atop each testicle (pampiniform plexus) cools the blood coming from the body and warms the blood returning from each testicle. This system works similar to the radiator in your truck.
Bos indicus and American Breeds of cattle are highly adapted to hot and humid environments due to less body heat production, greater skin surface area, and more and larger sweat glands that are closer to the skin surface (Anim. Reprod. Sci., 82-83:349-360, 2004). But when it comes to bull reproductive anatomy, all breeds of cattle are very similar; thus even Brahman influenced cattle can experience the "summer slump" albeit less pronounced as compared to non-Brahman influenced cattle. Researchers have evaluated heat stress and semen production in dairy bulls by covering the scrotum with a sock and insulating material for 48 hours (J. Dairy Sci. 74:3827-3825, 1991). Semen was collected every 3 days before and after heat stress treatment. After day 9, semen quality began to decline and was at lowest quality 18 days after heat stress. Semen quality (morphology and motility) was below normal for 40 days after the heat stress event. Similar results were reported in a Brazilian study (Anim. Reprod. Sci., 79:1-15, 2003) that evaluated semen quality in Nelore and Charbray bulls after a 4-day scrotal insulation treatment [both breed types were equally affected]. These results indicate that even a short-term heat stress has long-term consequences. This is because it takes 63 days to produce a sperm cell and an additional 14 days for final maturation and transport to the storage site. Increased testicular temperature affects sperm in the mid to latter stages of development and thus lower quality ejaculates take time to appear and will persist because sperm production is a continual process. Managing heat stress includes avoid breeding June 1 to October 1, and providing access to shade and water at all times (20 gal. per 1000 lb. animal per day). Providing adequate fly control may be important as cattle may avoid shade as a means of avoiding flies. Enjoy the rest of your summer.
Author: Randy L. Stanko, Ph.D., Texas A&M University-Kingsville
Cows and heifers produce healthy oocytes (eggs) at normal body temperature (101ºF) whereas bull sperm production is optimized at 96ºF, 5º to 6ºF below normal body temperature. Thus, ovaries reside inside the body cavity and testicles do not. However, increased body temperature can negatively affect the expression of estrus, fertilization rate, uterine environment and the ability to develop a viable embryo, and may affect oocyte quality during the maturation process, which occurs over the 60 days prior to ovulation.
Bulls possess remarkable anatomical structures to assist with testicle temperature regulation including: muscles, nerves, sweat glands, a modified circulatory system, and the ability to pant. These tools are designed to keep testicles warmer or cooler than the environment. It is much easier to keep testicles warm than cool. On a cold day the bull simply uses muscles to raise the testicles close to the body and wrinkle the scrotum to decease surface area. In summertime the process is essentially reversed to dissipate and avoid heat. In addition, a modified circulatory structure that sits atop each testicle (pampiniform plexus) cools the blood coming from the body and warms the blood returning from each testicle. This system works similar to the radiator in your truck.
Bos indicus and American Breeds of cattle are highly adapted to hot and humid environments due to less body heat production, greater skin surface area, and more and larger sweat glands that are closer to the skin surface (Anim. Reprod. Sci., 82-83:349-360, 2004). But when it comes to bull reproductive anatomy, all breeds of cattle are very similar; thus even Brahman influenced cattle can experience the "summer slump" albeit less pronounced as compared to non-Brahman influenced cattle. Researchers have evaluated heat stress and semen production in dairy bulls by covering the scrotum with a sock and insulating material for 48 hours (J. Dairy Sci. 74:3827-3825, 1991). Semen was collected every 3 days before and after heat stress treatment. After day 9, semen quality began to decline and was at lowest quality 18 days after heat stress. Semen quality (morphology and motility) was below normal for 40 days after the heat stress event. Similar results were reported in a Brazilian study (Anim. Reprod. Sci., 79:1-15, 2003) that evaluated semen quality in Nelore and Charbray bulls after a 4-day scrotal insulation treatment [both breed types were equally affected]. These results indicate that even a short-term heat stress has long-term consequences. This is because it takes 63 days to produce a sperm cell and an additional 14 days for final maturation and transport to the storage site. Increased testicular temperature affects sperm in the mid to latter stages of development and thus lower quality ejaculates take time to appear and will persist because sperm production is a continual process. Managing heat stress includes avoid breeding June 1 to October 1, and providing access to shade and water at all times (20 gal. per 1000 lb. animal per day). Providing adequate fly control may be important as cattle may avoid shade as a means of avoiding flies. Enjoy the rest of your summer.
Author: Randy L. Stanko, Ph.D., Texas A&M University-Kingsville
