Stress and the breeding season

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Sometimes in the middle of A.I. season it seems as though we should be more worried about reducing stress on ourselves than our cow herd. From setting up breeding barns and portable pens to sorting cow/calf pairs into breeding groups and 11 p.m. requests to feed the breeding crew tomorrow when you are 50 miles from a grocery store (ladies you know what I am talking about!), breeding season can be a very stressful time for everyone involved. However, managing the stress of the cattle involved is much more critical to the successful outcome of pregnancies than one might think.

During the breeding season, cattle that are artificially inseminated (A.I.) are exposed to increased human interaction, which can dramatically increase stress levels, particularly for temperamental or excitable cattle.

Research has shown that cows with excitable temperaments have reduced reproductive efficiency compared to those that are considered calm. This can physiologically be explained by the stress response. Stress in cattle, as defined by Dr. Reinaldo Cooke from Oregon State University, is a reaction to internal and external factors that affect their well- being. When cattle become stressed, whether from human interaction, processing, or other environmental factors, the stress response is activated. While humans see altered behavior from cattle that are stressed, internally their body is experiencing changes as well, with the most notable being the alteration of hormone profiles with the release of cortisol, the “stress hormone”.

Research has proven that blood concentrations of cortisol are higher in stressed animals. The increase in cortisol is directly linked in alterations in cow herd fertility through the disruption of mechanism that regulates events such as ovulation, conception, and the establishment of pregnancy. One of the reasons for cortisol’s impact on reproduction is its negative correlation with luteinizing hormone (LH), which is a key player is follicle growth and regulator of ovulation. A study done by Echternkamp et al. showed that cows that were acclimated to processing and human interaction had decreased cortisol concentrations in their blood, and increase LH when being handled, whereas more temperamental cows had increased cortisol and decreased LH (Figure 1).

Figure 1: Relationship between cortisol and LH.

*Adopted from data from Echternkamp, S.E. 1984. Relationship between LH and cortisol in acutely stresses beef cows. Theriogenology 22:305-311.

Being aware of the affect that high stress environments have on cattle, whether it is due to their natural response as temperamental animals, or human induces from high stress handling practices, will help producers better manage their breeding seasons. Practices such as the use of a breeding barn and low-stress cattle handing will help in the management of stress on the females during breeding season.

Reference:

  • Echternkamp, S.E. 1984. Relationship between LH and cortisol in acutely stresses beef cows. Theriogenology 22:305-311.

Source: Kalyn Waters



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