Low Dairy Cow Conception Rate? Consider Zearalenone's Role

Degradation in the rumen... is it for good or for bad?

When zearalenone is ingested and reaches the rumen, microbes can transform the molecule but this change does not result in an actual detoxification. The two main resulting molecules of this metabolic process are α-zearalenol (α-ZEL) and β-zearalenol (β-ZEL) which can be 60 or 0.2 times as estrogenic (respectively), with the biggest portion becomes α-ZEL (figure 2, Gruber-Dorninger et al., 2021). This means that zearalenone’s estrogenicity is heavily increased, resulting on even bigger hormonal unbalances in animals.

Figure 3. Changes in concentration of main reproductive hormones when two different zearalenone treatments were fed to Holstein dairy cows.

The first clear effect of a change on zearalenone contamination in the diet is that all the concentrations of hormones in blood (such as estrogen, progesterone, luteinizing hormone, T3, T4 and prolactin) were affected significantly by the treatment. The cow has a normal level of estrogen that would naturally increase only right before estrus. If zearalenone is on circulation binding with receptors of estrogen, this alters the natural concentration of other hormones. This hormonal imbalance can result in unsuccessful reproduction, lack of response to hormonal treatments for artificial insemination, as well as false heats.

Increased risk of miscarriage

The increase of zearalenone in the diet resulted in a reduction of progesterone, also known as the “pregnancy hormone” because it ensures the physiological conditions are right to keep the embryo. In Figure 1 it can be observed how estrogen and progesterone regulate each other, when estrogen is high, progesterone is lower, and the opposite.  Thus, having any increase of zearalenone, which will behave like estrogen, can result in the decrease of progesterone levels, thereby losing the conditions to keep the embryo and increasing the likelihood of a spontaneous abortion.

Figure 4. Graphic comparison between a normal ovary with successful ovulation with a polycystic ovary without possibility to ovulate.

Economic impact

Any sort of delay in the reproduction of dairy cows is a great economic concern. According to different authors (De Vries, 2006; Eicker & Fetrow, 2003; Hovingh, 2009), the cost of a cow spontaneously aborting can be 550-1200 USD, and every extra open day costs 5.20-6 USD (Cabrera, 2014). Additionally, breeding problems are one of the top reasons for cow replacement. A cow that takes longer to become pregnant has a 75% higher possibility of being culled (Cabrera, 2014).

Conclusion

When addressing poor reproductive efficiency in a dairy farm, it is essential to ensure that mycotoxins are not the limiting factor to reach reproductive potential. Once this burden has been removed, other strategies to promote successful reproduction can be implemented.

Considering the economics of cow reproduction, zearalenone can represent relevant losses if not addressed properly. A deactivation strategy for zearalenone is necessary in order to ensure an adequate hormonal balance and successful reproduction.