Observations were made over four breeding seasons to determine the effect of excessive intake of fluorine in the drinking water on the breeding efficiency of cattle.
Fifty Afrikaner heifers, maintained under ordinary ranching conditions, were divided into five groups which received 5, 8 and 12 ppm fluorine respectively in the drinking water.
They were tested daily for oestrus during the breeding season (September to May) and those showing heat were served.
The two criteria for judging breeding performance were calving percentage and the number of services per conception.
In the first season reproduction was normal in every respect in all groups, but in the next season there was a noteworthy increase in post-calving anoestrus in the groups receiving 8 and 12 ppm fluorine. The third season revealed an appreciable decline in fertility, notably in the animals receiving over 5 ppm fluorine. The fourth season was characterized by a marked drop in breeding efficiency as judged by calving rate and services per conception in all groups. This was mostt pronounced in the groups receiving 8 and 12 ppm.
The addition of defluorinated superphosphate to the drinking water did not diminish the harmful effect of fluorine on reproduction, but, on the contrary, appeared to aggravate it.
The adverse influence of excessive fluorine on reproduction was manifested before the animals revealed any evidence of impairment of general health, such as loss of condition and inappetence.
It is concluded that for normal reproduction the fluorine content of drinking water should be under 5 ppm.
The possibility that excessive intake of fluorine may inhibit thyroxine output, thus interfering with the normal secretion of gonadotrophins and giving rise to the functional disturbances observed in the ovaries, is discussed.