Insufficient data are available to support estimates of the maximum dietary tolerance of vitamin B6 for cats. It is suggested, primarily from dog and rat data, that dietary levels of more than 1,000 times the nutritional requirements are needed to produce signs of toxicity in these species (NRC, 1987).
Dogs given oral doses of 20 mg of pyridoxine per kg (9.1 mg per lb) of body weight reported no signs of toxicity (Unna and Antopol, 1940). Higher doses of the vitamin have been found to produce signs of toxicity. Phillips et al. (1978) reported that ataxia, muscle weakness, and loss of balance developed between 40 and 75 days in dogs that received 200 mg of pyridoxine per kg (90.9 mg per lb) of body weight. Histological examination of the tissues revealed bilateral loss of myelin and axons in the dorsal funiculi and loss of myelin in individual fibers of the dorsal nerve roots. A lesser amount of pathological damage was observed in dogs receiving 50 mg per kg (22.7 mg per lb) of body weight daily. Dogs fed daily doses of 250 mg per kg (113.6 mg per lb) began to develop incoordination and ataxia within the first week of treatment.
Krinke et al. (1980) administered daily oral doses of 300 mg of pyridoxine per kg (136.4 mg per lb) of body weight to pairs of 7- to 11-month-old beagle dogs for 78 days. Treated dogs developed a swaying gait and became unable to walk. It was concluded that excess vitamin B6 produced a toxic, peripheral, sensory neuronopathy involving degeneration of the dorsal root ganglia, gasserian ganglia, and sensory nerve fibers.