Vet Column 4-19-10 | TheFencePost.com
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Vet Column 4-19-10

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

How soon after breeding can one haul cows or heifers to avoid negatively impacting pregnancy rates? It is a frequent question and many times, producers have to move their animals unavoidably. Minimizing stress is standard practice when managing cattle, and it includes transport stress. To further evaluate the effect of transport stress after mating beef cows and heifers, a recent study by investigators from the United States Department of Agriculture and Montana State University examined a potential management tool to reduce the effect of transport stress on pregnancy rates.

Previous studies have determined that fertilization occurs in 90 to 100 percent of beef cows that are bred by natural service or artificial insemination. Conception rates to a single service, however, are generally less than 70 percent, indicating that embryonic loss occurs in 20 to 30 percent of cows. Scientists have shown that the majority of early embryonic loss occurs because the embryo fails to produce sufficient hormone to initiate maternal recognition of pregnancy approximately 14 days after breeding.

So what’s happening at 14 days after breeding in the cow or heifer that makes this a critical time? The heat cycle length in cattle is approximately 21 days. At or near 14 days, if mated during the preceding heat, the cow or heifer either recognizes the pregnancy that might be occurring, or begins to get ready for the next heat which would occur at or near seven days later. To facilitate getting ready for the next heat, cows or heifers would normally secrete a hormone referred to as prostaglandin. A common trade name for prostaglandin is Lutalyse. If prostaglandin is secreted, the next heat cycle will likely occur. If it is not secreted, then likely a pregnancy will become established.

Flunixin meglumine (one trade name is Banamine) is a potent nonsteroidal, anti-inflammatory agent that inhibits, or greatly reduces, the production of prostaglandin. Previous studies have demonstrated as much as a 10 percent increase in pregnancy rates in cows receiving flunixin meglumine at day 14 after mating. Other studies have shown no difference in pregnancy rates when both transported and nontransported cows received flunixin meglumine at day 14 following mating.

Approximately 1,468 predominantly Angus heifers and 1,040 Angus and composite cows were divided into three experiments in this study. All were administered flunixin meglumine intramuscularly at 13 days following insemination.

Results from this study found that pregnancy rates to artificial insemination were reduced among heifers receiving the flunixin meglumine (66 percent) compared with control heifers (72 percent). Among suckled beef cows, pregnancy rates to artificial insemination did not differ between the flunixin meglumine treated cows (57 percent) and control cows (59 percent). When comparing beef heifers and suckled beef cows from one location, pregnancy rates to artificial insemination were not different between those cows receiving flunixin meglumine (45 percent) and control cows (42 percent) or beef heifers receiving flunixin meglumine (56 percent) and control beef heifers (55 percent).

Conclusions from this study indicate that administering flunixin meglumine intramuscularly at the label dose on day 13 following artificial insemination did not improve pregnancy establishment in beef cows and heifers. What is perhaps most important is to recognize that the effects of handling on beef cows and beef heifers around day 14 following mating may decrease pregnancy establishment.


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