Rickets is common in New Zealand lambs which are grazing on winter greenfeeds, the incidence being highest on cereal crops, lowest on brassicas, while ryegrasies appear to lie between these extremes in rachitogenic potency. The disease is more common in the milder seasons which favour good growth during late autumn find early winter. The presence of a rachitogenie substance in greenfeeds was first postulated by Fitch, and the results of subsequent work has not only confirmed his opinion but indicated that carotene, the main plant carotenoid precursor of vitamin A, is the main factor involved. The rachitogenic properties of vitamin A or its precursors have been described recently, and it is apparent that the higher the vitamin A uptake the greater will be the vitamin D requirement of the animal.
