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Zearalenone's (ZEN) effects can impair reproduction and cause spontaneous abortions, resulting in enormous economic losses to dairy producers. Here's how to recognize--and treat--the effects of ZEN in dairy cattle.
When addressing mycotoxins on dairy farms it is common to focus on the direct losses in production and health status. With Zearalenone (ZEN), the worries are different: Since it has a very similar structure to estrogen, ZEN can bind to the receptors located in distinct areas of the body, such as the uterus, mammary gland, hypothalamus and pituitary gland and cause delays in reproduction, spontaneous abortions and other reproductive challenges.
Before discussing the impact of ZEN, it’s important to understand how estrogen works in a cow’s body. During the estrous cycle of a cow, estrogen concentration remains stable and low until the heat, or estrus, where it increases abruptly. Estrogen prepares the reproductive organs of the cow for breeding. It also influences behavior that encourages mating. A normal estrus lasts one day (plus or minus), and once it has passed, the concentration of estrogen reduces again (Figure 1, adapted from Senger (2003).
Figure 1. Hormonal fluctuations along the estrus cycle
When ZEN is ingested and reaches the rumen, a sort of transformation of the molecule can occur. Compared to swine or poultry, ruminants are considered more resistant to mycotoxins since the microbiota that inhabits the rumen is supposed to act as a first line of defense against toxins. However, in the case of ZEN, this metabolization 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). Although most of the ZEN stays unaltered, the biggest portion of what gets degraded becomes α-ZEL (figure 1, Gruber-Dorninger, submitted manuscript) and the estrogenicity is increased. Thus, one can say that if the feed is contaminated, the passage through the rumen will make ZEN either remain as estrogenic or get worse, but not less harmful.
Figure 2. In vivo degradation of Zearalenone in rumen cannulated dairy cows (Gruber-Dorninger et al., submitted manuscript)
A recent case in a farm attended by Dr. Marios Christoforou in Cyprus
Size of herd: 170 milking cows, Holstein breed
During winter some symptoms started to be observed in some of the cows, such as:
Dr. Christoforou did the pregnancy checks 30 days after insemination via embryonic test and an additional check with ultrasound. He found that an important number of cows had aborted and had cystic ovaries (>20 mm diameter). He indicated that finding ovarian cysts during winter in Cyprus is rare as it tends to be influenced by heat stress. He started suspecting ZEN contamination, so he followed the following steps:
In this case the problem was more severe due to the concentration of ZEN in the feed, but in some cases the effects, although less dramatic, can still impact the reproduction of cows.
When ZEN binds to the estrogen receptors in different tissues, endocrine disruption takes place. This is why typical behavior of heat can happen even if a cow is not in real estrus, for instance when pregnant. Some of the most important negative effects of ZEN are the following:
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).
Considering the economics of cow reproduction, ZEN can negatively impact a dairy farm if not addressed properly. A deactivation strategy for this particular mycotoxin is necessary in order to ensure an adequate hormonal balance and successful reproduction.
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15 January 2021
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