Michael E. Peterson,     Albany, Oregon

Reproductive Toxicity

Sexually intact dogs and cats constitute a small percentage of patients in the average veterinary practice. Clinical focus on reproduction in small companion animals is a relatively new field, limited to breeding primarily purebred dogs and cats. Clients concerned about a reproductive disorder in their animals generally seek reproductive workups when the animals fail to conceive. Early ultrasonographic or hormonal diagnosis of pregnancy (within the first half of gestation) is of greatest benefit when dams fail to produce offspring from a breeding. The ability to distinguish between the failure to conceive and failure to carry a pregnancy to term defines the problem and correctly directs the workup between the dam, the sire, and the breeding management.

The differential diagnosis of a reproductive toxicity usually does not result until a specific problem is identified as the source of the infertility. At this point, the effect of exposure is apparent (e.g., ovulation failure as in the case of methanol exposure), but the underlying cause may never be known. In addition, some toxic effects may not become apparent until the next generation, as is the case of male offspring with decreased testosterone levels and low sperm counts whose dams were exposed to lindane while pregnant or lactating. Specific treatments for reproductive toxicities are limited to a number of conditions. For example, recovery of spermatogenesis after cyclophosphamide exposure may be improved with GnRH treatment.

Reproductive problems in kennels or catteries in which multiple animals are housed are presented less commonly but are easier to work up with an epidemiologic approach. Diagnosing reproductive intoxications depends on a thorough history, physical examination, and appropriate laboratory testing. The history should include family reproductive history as well as past and current feeding and husbandry practices (Box 223-1). Industrial hygienists may be useful in site visits because these professionals are experienced in assessing sick building syndrome and workplace exposures to toxins. Assessing any exposure requires more than finding a suspect xenobiotic (Box 223-2). The Environmental Protection Agency (EPA) currently is assessing 87,000 compounds for their impact on the endocrine system. Issues relative to the total dose received, route of exposure, and length of exposure to a possible reproductive toxicant or teratogen are important in determining if the cause is sufficient to result in the particular disorder diagnosed. The level, timing, and nature of the exposure are paramount in assessing the possible reproductive risk to either the male or female breeding animal. It is not enough to determine exposure alone. In the case of the bitch or queen, was exposure preconception or postconception?

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