Production Pointers: Reproduction

August 3, 2009

Reproduction efficiency feeling the heat?

The anxiety about reproductive performance rises with the temperature. Heat stress can greatly affect the ability to get a cow pregnant, making summer breeding progress difficult for producers.(1) But, by understanding the effects of heat stress and ways to combat the challenges, producers can regain profits that might otherwise be lost.

“Higher temperatures usually mean decreased conception rates among dairy herds(1),” said Dr. Tom Van Dyke, manager, Merial Veterinary Services. “Producers need to battle heat stress for a number of reasons, but the effects hot weather can have on fertility may be one of the most important.”

In a study, ovulation failure was 3.9 times higher in cows inseminated during warm months (May to September) than in cool months (October to April).(1) These inefficiencies occur when an animal is exposed to a high temperature-humidity index (THI).(1) THI combines ambient temperature and relative humidity in an index to measure the heat’s impact on an animal.(1) A high THI can cause cows to have interruptions in their estrous cycles resulting in failed ovulations.(2) In addition, heat stress reduces growth of the dominant follicle in the ovaries and causes incomplete dominance, which leads to an increased growth of inferior follicles.(3)

“The good news for producers is that a gonadotropin-releasing hormone (GnRH) can be used to treat a leading cause of reproductive failure — ovarian follicular cysts,”(4) Dr. Van Dyke said. “GnRH helps clear the ovary of cysts that form from old follicles so new ones can take their place.(4) This activates the process leading to estrus.”(4)

Ovarian cysts cause reproductive problems in all weather types, but as a GnRH treats this disease, it can help induce ovulation during times when breeding is most difficult — like during the heat of summer.

“When treating this fundamental source of reproductive failure, a GnRH causes the release of both luteinizing hormone (LH) and, to a lesser extent, follicle stimulation hormone (FSH), which leads to ovulation,”(4) Dr. Van Dyke said. “Ovulation clears out the problem cyst and helps keep cows calving on a schedule that is profitable and convenient for producers.”

Along with administering a GnRH to keep ovaries healthy and cows calving, Dr. Van Dyke recommends other common practices to help raise conception rates during the summer months.

“Proper ventilation, cooling systems and hydration are obvious concepts to remember when helping cows avoid heat stress,” Dr. Van Dyke said. “Keeping cows cool can influence a major source of their health and productivity — feed intake.”

Cows tend to consume less feed when heat stressed,(2) which can set off a chain reaction of negative effects. Consuming less feed results in less milk production and less energy. Less energy means cows move around less, making it more difficult for producers to detect cows in heat when breeding. Overall, keeping cows cool is important to more than just reproduction.(2)

Dr. Van Dyke adds that using a trusted and leading GnRH gives producers a tool to help keep cows reproductively healthy in all weather conditions. Along with fundamental nutrition and cooling techniques, a GnRH can be the boost a dairy herd needs to beat the summer heat.

“Although there may be a number of factors contributing to lower conception rates, there are ways to reduce the reproductive loss resulting from heat stress,” Dr. Van Dyke said. “Profits and reproduction go hand in hand, and a better summer breeding program can mean certain returns in an uncertain economic time.”

(1) Science Daily. Heat stress influences low conception of dairy herds. September 7, 2007.

(2) NCSU Dairy Extension News. Summer 2005. North Carolina Cooperative Extension Service.

(3) Al-Katanani YM, Et al. Effect of season and exposure to heat stress on oocyte competence in holstein cows. J Dairy Sci 2002;85:390-396.

(4) Martinez MF, Mapletoft RJ, Kastelic JP, Carruthers T.The effects of 3 gonadorelin products on luteinizing hormone release, ovulation and follicular wave emergence in cattle. Can Vet J 2003;44:125-131.

Source: Merial. Visit

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Ordering from the menu of dairy breeding programs

During the past 30 years, a number of factors have contributed to the modern dairy cow showing decreased signs of estrus (“heat”). It has become harder to accurately identify cows to breed and, therefore, also harder to achieve pregnancy.

Not surprisingly, various breeding programs have developed over this time period to help address this concern. Many of these programs are referred to as “synch” programs because they enable producers to synchronize the ovulations of the cows, making timed-artificial insemination (AI) breedings possible. The plethora of options available may result in producers finding themselves feeling like everything but the kitchen “synch” has been thrown at them.

“The menu of program options can be very confusing and encourages the idea that the newest, latest synch will be the best program yet. This may not be the case for that dairy and a change may actually result in poorer reproductive efficiency. Neither is it true that any one ‘cookie cutter’ approach will work predictably on every dairy,” said Gavin Staley, DVM, DiplACT, Senior Fresh Cow Reproductive Manager, Pfizer Animal Health. The most important decision to make is which program can be reliably and reasonably implemented, within the existing constraints of dairy management, with outstanding compliance, again and again and again.

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