Demographic and Endocrine Responses of Norway Rats to Antifertility Control

Abstract

The observation that Alpha-chlorhydrin (U-5897) specifically produces lesions in the caput epididymis of the Norway rat suggesting that it is a potential rat control agent has led to a study employing this agent in an effort to induce sterility among surviving male rats. Treatment of a land-fill open dump rat population after the onset of early spring breeding resulted in a 50% reduction of rat numbers according to both trapping success and food consumption estimates. The trapping success changed from 50% to less than 25% following U-5897 bait consumption. The fertility rate in the treated population remained equal to or lower than saturated-density land-fill populations and much lower than typical expanding pen populations. Pregnancy progression rates in the expanding pen populations went from 18% in early spring to 67% in the spring to 71% in the summer. The untreated saturated dump population went from 19% to 37% to 41% in the same time period while the U-5897-treated population was 18% to 37% to 32%. Aggression and male se condary sexual characteristics remained typical of expanding populations. The results of this study indicate that in saturated-density populations overdoses of U-5897 may be an effective rodenticide as well as an inhibitor of reproductive rebound.