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Too Many Open Cows?

Livestock Update, December 2004

W. Dee Whittier, Ext. Veterinarian, VA-MD Regional College of Veterinary Medicine, VA Tech

As pregnancy checking has proceeded in spring-calving Virginia cow herds this summer and fall, it has become apparent that a greater number of non-pregnant cows are present in our herds than expected. Typical pregnancy rates in the mid-90's (92-98% of cows pregnant) are often being replaced by numbers in the 80's and some really problem herds have as many as one-half of cows being open.

Investigations into the causes of the pregnancy failure are ongoing but some important information is coming from veterinarians, extension agents and beef producers concerning this problem which will have a great impact on next year's profits.

Factors being investigated as the cause of reproductive failure can be grouped into the categories of nutrition, bull failure, grazing plant effects and disease.

Nutrition is typically the biggest variable that influences reproductive efficiently in a beef cattle herd. Two major nutritional challenges need to be overcome in order to get high pregnancy rates. First, cows need to have enough body condition at the time they calve to set the stage for early return to reproductive cycling following the calving. Secondly, cows need to be gaining weight during the breeding season. Using the 1-9 scale for scoring body condition (a visual estimate of the fat reserves a cow has), it has been documented that significant increases in the percentage of cows cycling soon after calving result when cows move up to a condition score of 6.

Body-condition influences on pregnancy rates in many cases may date back to well over a year ago. Virginia experienced one of the wettest seasons on record in the spring and summer of 2003. Hay making was either delayed until late in the summer or proceeded with extensive rain damage to hay. As cows were forced to eat this very poor quality hay in the winter of 2003-4, body condition scores plummeted. So severe were body condition losses that, in our practice at the College of Veterinary Medicine, we dealt with cows down from starvation in February and March of 2004. If the average spring-calving cow in Virginia started the grazing season with a body condition score one point lower than usual, I estimate an additional 5% of open cows would have resulted. This impact would have occurred despite an early spring that provided high quality grass to cows. My assessment is that, although we met the second nutritional challenge of gaining weight during the breeding season, we often started with cows that were too thin at calving time.

Bull failure is a constant and ongoing cause of reproductive failure in Virginia beef cattle operations. Breeding soundness examinations are recommended on bulls prior to beginning the breeding season to be assured that bulls are producing adequate amounts of high quality sperm cells. However, bulls that are producing quite enough sperm cells still fail to get cows pregnant if they do not deliver them. Significant numbers of bulls either have inadequate interest in breeding cows or have physical problems that prevent them from inseminating cows. Breeding success of bulls is best assessed by observing bulls to be sure that they show interest in, mount and successfully serve cows in heat.

Two important plants in Virginia pastures may have impacted success of breeding during him spring and summer of 2004. Fescue and its toxin are a constant threat to successful cattle reproduction in Virginia. It is widely known that Kentucky 31 fescue is heavily infected with an endophyte fungus. This fungus results in the production of a series of toxins that negatively affect cattle that graze the plant. One of the important things these toxins do is to change blood circulation so that cattle have a hard time getting rid of body heat. Cows and bulls that have high body temperatures because of fescue toxin are less fertile. In particular, if the cow's temperature is high in the first few days following breeding, the embryo dies and the cow comes back in heat at the expected time. This problem is so widespread that it has enforced a change to fall calving in much of the southern piedmont region of the state over the last few decades as fescue has become the predominant pasture grass. Of course, the infertility is an interaction with outside temperatures. Did an early warm spring get cows above the threshold temperature where embryos do not survive earlier than usual resulting in many open cows?

Clover, always thought of as blessing in pastures, may have been so abundant this year that it negatively affected pregnancy rates. It is documented that certain types of clover contain estrogen hormones that can influence reproduction. In general, the red and white clovers that are present in Virginia pastures are not thought to commonly have these estrogens in high enough levels to result in problems. However, clover amounts in pasture this year have been unprecedented perhaps contributing to the open cow problem.

The subject of diseases that impact reproduction is a large one. Diseases that have been thought to impact conception have included BVD virus, and the venereal diseases vibriosis and trichomoniasis. Because of our bull management approaches in Virginia there is little opportunity for venereal diseases to be a problem.

There are several diseases that result in abortion that may have an impact on the number of open cows seen. Abortions may go unnoticed or occur early enough that little is seen of the aborted fetus or placenta. We have historically considered leptospirosis to be an important cause of abortion in Virginia and recommended widespread use of leptospirosis vaccine to control this problem.

Newer research has indicated that our long-used 5-way Lepto vaccine does not protect against a strain of the disease causing organism commonly called "Lepto hardjo-bovis". A new vaccine has just come to the market for this strain of Lepto. There are many unanswered questions about this disease and its relatively expensive vaccine. How much infection with the disease do we have? The answer to this question is made more difficult by the rather high cost (around $500) of testing for the disease in a herd. Why would the levels of the disease have increased so rapidly to account for a sudden increase in open cows? Should vaccination programs be expanded to include the recommended two doses of this expensive vaccine without firm evidence that it is a problem in the herd? Time will be required to answer these questions.

Open cows result in large economic penalties to Virginia cattle producers. It would be very wise for all to consider their operations with regard to the above mentioned factors. Working with veterinarians, extension agents and other consultants to prevent recurrences of large percentages of open cows will pay dividends. High percentage calf crop is often the largest contributor to a profitable beef cattle operation.

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