Vitamin A nutrition of the equine: growth, serum biochemistry and hematology.

This experimental research study investigates the impact of varying levels of Vitamin A intake on the growth, serum biochemistry, and hematology of pony fillies. The study found that both deficiency and excessive intake of Vitamin A negatively affected growth and various blood and liver parameters. The study also suggests that the current recommendation for Vitamin A intake in young horses might be inadequate.

Methodology of the Study

• The study involved four dietary groups of pony fillies, which received different levels of Vitamin A over 40 weeks.
• The mildly deficient group received a diet low in carotene, a precursor of Vitamin A. Other groups received the same diet plus vitamin A propionate equivalent to 12 (control group), 1,200 (mildly intoxicated), or 12,000 (severely intoxicated) microgram retinol/kg body weight/day.

Findings of the Study

• The group that received a mildly deficient diet experienced impaired growth and hematopoiesis (the production of blood cell components). Serum concentrations of iron, albumin, and cholesterol decreased in this group prior to the depletion of liver Vitamin A.
• Both mildly and severely intoxicated groups showed depressed growth. The severely intoxicated group became debilitated and died within 40 weeks, with reduced serum concentrations of iron, albumin, and cholesterol.
• The study also found significant associations between dietary vitamin A and vitamin A concentrations in plasma, liver, and kidney. There was also a connection between plasma vitamin A concentrations and liver and kidney vitamin A levels.

Implications of the Study

• The research suggests increases in retinyl ester, a biomarker of Vitamin A levels, occur due to excessive dietary Vitamin A, before clinical signs appear, and might reflect kidney vitamin A levels.
• According to the data, optimal vitamin A intake for maximal growth averaged 1.4 times the current National Research Council recommendation. For liver secreted serum constituents, 5.4 times more was optimal, and for red blood cell criteria, 10 times more was optimal.
• This suggests that the recommended intake of 12 microgram/kg for weanling horses could be less than optimal, and that hematology and serum biochemistry could be more sensitive markers of vitamin A nutrition status than growth measurements.