Will Cows Get Pregnant In The Coming Breeding Season?

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The winter of 2010 has broken a number of records. Beef cows on most farms have probably been affected to a significant degree by the winter. The seventy days of snow cover that we experienced in Blacksburg have altered cow diets for the worse while unusually cold temperatures and wind chills have markedly increased nutrient requirements.

A review of what research and experience has taught us about reproductive performance helps us predict and hopefully take steps to remedy the effects of this situation on the upcoming breeding season. Otherwise open cows and later calves may have a profound effect on future profits.

The number of cows that get pregnant during a calving season is a function of three major factors:

1. The number of cows that are cycling (coming into heat) at any point in the breeding season.
2. The fertility of the cows, that is, the likelihood that they get pregnant each time they come into heat.
3. The fertility of the male, whether in the form of a bull breeding or an artificial insemination.

Years of research have helped to show the major factors that influence each of these main items. Here are the generally agreed on contributors:

Estrous cycling:

* Days since calving
* Body condition score at calving
* The nursing of the calf
* Exposure to a bull
* Age of the cow
* The influence of hormones

Cow conception rates:
* Days since calving
* Whether cows are gaining or losing weight
* Heat stress, especially as influenced by fescue grazing

Bull fertility:
* Normal sperm cells
* Scrotal circumference
* Libido
* Body condition
* Age and dominance

So what’s different this season than most years? Cows lost more weight in the winter and therefore calving at lower body condition scores than usual. That means that they will tend to be slower to cycle than usual. If the average cow begins cycling twenty-one days later that results in about 15% more open cows in a 65-day breeding season.

A wise producer can use the other knowledge we have of the factors that determine outcomes of beef reproduction to overcome this drawback. Here are some procedures that can be done to increase the odds that cows will become pregnant efficiently.

1. Do everything possible to get cows in a gaining situation as early in the spring as possible. Judicious use of fertilizer on some pastures might pay premiums in pregnant cows.
2. Don’t stop feeding cows until there is plenty of grass to meet nutritional needs.
3. Take extra care of young and old cows.
4. Consider the use of teaser bulls with cows before actual breeding begins. Bull exposure has been shown to start cows cycling as much as thirty days earlier.
5. Removing calves from cows for 48 hours at the beginning of the calving season or as part of a synchronization program has been documented to increase the number of their dams that begin cycling.
6. If you are doing synchronization for artificial insemination, consider using a system that adds progesterone in the program as progesterone treatment has been shown to increase the number of cows that are cycling.
7. Manage pastures and grazing to minimize the effects of fescue toxicity. Take steps now to get clover into pastures and manage grazing so that cows are not eating headed out fescue while being bred.
8. Perform Bull Breeding Soundness examinations on all bulls before the breeding season. Then watch bulls carefully during the season to be sure they are performing well.

Having a successful breeding season this year will require that typical management be improved in many operations. Utilizing some of the above special techniques, even if they are not necessary in most breeding situations, may pay real dividends this season.

Source: Dr. W. Dee Whittier, Extension Veterinarian, Cattle, VA-MD Regional College of Veterinary Medicine, VA Tech



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