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Phytoestrogens: Something to be Aware of, But Don't Overreact!

Posted: December 16, 2008

On occasion we receive inquires about the effect of phytoestrogens on reproductive performance of cattle. There have been a few reports from nutrition consultants and veterinarians working with well managed herds which experienced a sudden decline in reproductive performance for no obvious reason but when forages suspected to have high concentrations of phytoestrogens were removed from the ration performance improved. It is difficult to find well controlled studies which document how widespread this condition might be. However there are some good review articles describing the effect of phytoestrogens on sheep and cattle.

On occasion we receive inquires about the effect of phytoestrogens on reproductive performance of cattle. There have been a few reports from nutrition consultants and veterinarians working with well managed herds which experienced a sudden decline in reproductive performance for no obvious reason but when forages suspected to have high concentrations of phytoestrogens were removed from the ration performance improved. It is difficult to find well controlled studies which document how widespread this condition might be. However there are some good review articles describing the effect of phytoestrogens on sheep and cattle.

Three such articles are as follows:

  • Forage Plant Estrogens. A. L. Livingston, Journal of Toxicology and Environmental Health. 4: 301. 1978.
  • Toxicological Problems in Food Animals Affecting Reproduction. M. R. Putnam, Clinical Toxicology, In: Veterinary Clinics of North America: Food Animal Practice. 5: 325. 1989.
  • Detection of the Effects of Phytoestrogens on Sheep and Cattle. N. R. Adams, J. Animal Science. 73: 1509. 1995.

Here are some major points abstracted from these articles:

  • Phytoestrogens are a diverse group of naturally occurring non steroidal plant compounds that, because of their structural similarity with estradiol have the ability to cause estrogenic or/and antiestrogenic effects.
  • The major plants producing phytoestrogens that are of importance to animal agriculture are legumes, clovers (subterranean and red) and alfalfa. Selection and breeding of clovers has provided varieties low in phytoestrogens. Sheep are most sensitive to these substances. Alfalfa generally contains very minimal amounts of phytoestrogens. Aphids and fungi may induce production of these compounds. Several other factors affect the production of phytoestrogens. One study showed that field-curing hay reduced estrogenic activity somewhat while ensiling preserved the concentrations of these compounds.
  • The phytoestrogens of most concern are isoflavones and coumestans. Red clover silage with isoflavones and alfalfa containing coumestans has been reported to affect fertility in cattle. The research team of Alder and Trainin (1960) reported that feeding alfalfa with high levels of coumestans (> 25 μg equivalents of estradiol / lb. of feed) adversely affected performance. The symptoms of estrogenism included precocious mammary development and genital development in heifers, irregular estrus cycles, cystic ovaries, low conception rate in cows and even anestrus. They further reported reproductive perform- ance improved several months after removal of this specific feed source.
  • N. R. Adams (1989) reported the estrogenicity of coumestans and isoflavones are approxi- mately 1/1,000 and 1/ 10,000 compared to the activity of estradiol, respectively. However, there are no reports that phytoestrogens induce estrous behavior.
  • Laboratory analysis of the forages should be performed to document the levels of these compounds. My colleague, Dr.Van Saun, directed me to the Diagnostic Laboratory at North Dakota State for testing for phytoestro- gens. This laboratory also has an excellent mycotoxin screening test. Here is a link to the list of tests, scroll down to toxicology: www.vdl.ndsu.edu/vdl/FeeSchedule.aspx? f=services&sf=giv. Your nutritionist and veterinarian may know of other reputable testing laboratories.

There is a need for a comprehensive well-controlled study to document the prevalence of the problem. Frequently toxins and phytoestrogens are blamed for poor reproductive performance when management problems and herd health issues are the likely factors involved.

Before focusing attention on phytoestrogens or other toxins as the potential cause for lowered reproductive performance, it is important that a thorough review of herd reproductive management practices and herd health be performed.

Based upon that analysis, a list of bottlenecks likely restricting performance and an action plan to address those issues should be developed. If the management team and associated consultants feel that phytoestrogens or other toxins may be involved then appropriate testing should be performed.

Michael O’Connor, Dairy and Animal Science Extension