Skeletal development in growing ponies fed high-energy diets and differing nutrient, calorie ratios

Abstract

Skeletal development was examined in weanling pony foals fed either (1) a control diet of 100% NRC requirement for energy and all other nutrients (n=6); (2) a high-energy diet containing 138% of NRC recommended level of energy and 100% of all other nutrients (n=5); or (3) a high-energy diet with 138% NRC recommended level of energy and all other nutrients at a nutrient:calorie ratio similar to diet 1 (n=5). Ponies were fed assigned diets for 190 d, during which time growth measurements and blood samples were taken at 28-d intervals. A 4-d digestion trial was conducted after d 190, and subsequently three foals per treatment were sacrificed for determination of bone characteristics. No skeletal disorders were observed in any foal on any treatment. Ponies on treatment 3 had higher (P <.05) in ponies fed treatments 3 (45.3%) and 2 (41.6%) than treatment 1 (21.5%). Serum mineral concentrations were similar across treatments. Thyroxine values at d 180 were higher (P<.06) in foals on treatments 1 and 3 than those on treatment 2 at 1.5 to 6 h after feeding, and mean triiodothyronine was numerically higher in treatments 2 and 3 than 1. There were no significant treatment effects on metacarpal weight, length, width or specific gravity, nor was there any effect on ether extract or ash content of bones, or P, Mg, Cu or Zn content of bone ash. However, Ca content of the bone ash was greater (P<.05) in treatments 2 (35.4%) and 3 (35.2%) than in treatment 1 (34.4%). There were no significant treatment effects on length of the resting, proliferative/maturation, or hypertrophied zones of growth plates of selected long bones. Mineral metabolism, serum minerals and serum thyroid hormone concentrations were not adversely affected in pony foals fed high-energy diets compared to controls. Feeding high-energy diets did not produce detrimental effects on skeletal development as measured by physical, chemical or histological characteristics of bone.