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Studies of the Effects of Dietary NaF on Dairy Cows

I. The Physiological Effects and the Developmental Symptoms of Fluorosis¹

Department of Biochemistry, University of Wisconsin, Madison

The effects of dietary increments of fluorine fed as the soluble NaF salt to young adequately nurtured dairy cows for a period of 5 years and through 5 lactations have been studied. The data obtained permit the classification of the evidence into three categories in relation to fluorine ingestion, and subsequent development of fluorine toxicosis.

1. This study indicates that there was no direct relationship between over-grown hooves, dew claws, or diarrhea in stall-fed dairy cows and the ingesting of as much as 50 p.p.m. of fluorine in the ration. Neither was there any interference with conception, gestation and parturition. There was a measurable fluorine transfer across the placental membranes and secretion of minute quantities of fluorine in the milk of NaF-fed cows.

2. The earliest observable measures of increased fluorine ingested by young cows were the physiologic effects upon the teeth and elevated concentrations of fluorine present in urine and rib bone biopsy samples. These data also indicate that the control-cow urine averaged under 5 p.p.m. and rib bone under 600 p.p.m. of fluorine.

3. After the early evidence of increased fluorine ingestion, no other untoward effects were observed except a steady rise in bone fluorine concentration until after a considerable period of time had elapsed. Depending upon intake level, and the duration or time interval, the latent period was followed by positive evidence of developing fluorosis. These were, in close sequence: a refusal of fluorine-supplemented feeds, accompanied by excessive loss in body weight and stiffness in the legs with lameness as the result thereof. These effects were severe enough to debilitate the animal within several weeks at sustained high intake levels.

The symptoms just enumerated were observed in two out of three animals fed 50 p.p.m. of fluorine during the third year on experiment. They were also observed in two out of three animals fed 50 p.p.m. fluorine with extra calcium and beginning in two out of 4 animals fed 40 p.p.m. during the 5th year. The inclusion of added calcium in the ration increased the tolerance of these cows to fluroine. Other criteria observed were fluorine concentrations in excess of 6,000 p.p.m. in rib biopsy and in urine levels above 30 p.p.m. Concurrently, teeth classifications were 5A or higher. From these results it would appear that lactating dairy cows tolerate 30 p.p.m. of fluorine fed as NaF with comparative safety, that 40 p.p.m. is near marginal tolerance level and 50 p.p.m. causes the development of fluorosis within three to 5 years.

² Present address: Virginia Polytechnic Institute, Blacksburg, Virginia.

Manuscript received 18 April 1957.