Liver vitamin A slow release syndrome in cattle with a multiple nutrient imbalance.

Data on liver vitamin A concentrations in malnourished, debilitated, down cattle in tropical, northern Australia support the hypothesis that 12% annual cattle mortality was due, in part, to a slow release of liver vitamin A. High Ca and low Zn levels in the legume forage apparently contributed to the slow release. The cattle showed marked sensitivity to sunlight and exhibited problems of sight. The malnourished yearling steers averaged 183.3 micrograms vitamin A/g wet liver vs 152.3 micrograms for steers slaughtered off good green wet season forage. Indications of a slow release of liver vitamin A were that: (1) only 4 to 7 micrograms vitamin A/g liver were in the alcohol fraction or release form; (2) after adjustments for decreases in liver and blood volume in starving animals, blood vitamin A was lowered to 18 micrograms/100 ml, which was low in relation to the adjusted liver vitamin A level of 91.7 micrograms/g, and (3) after adjustments, the liver had released only 1,667 units of vitamin A/day in the dry season, or about 1/4 of maintenance needs. The cattle were grazing a legume forage pasture containing 7.1% protein and no measurable carotene. The forage was deficient in Zn (25 ppm), which would slow the release of liver vitamin A. High Ca levels in the legume forage (.4 to .54%) in combination with low P levels (.11 to .18%) would further aggravate the low Zn level.