Trace mineral supplementation of yearling horses.

Thirty-three Thoroughbred and Quarter Horse yearlings were used in two experiments (18 in Exp. 1 and 15 in Exp. 2) to determine the influence of trace mineral (TM) supplementation on growth and bone mineral content in young growing horses from 340 to 452 d of age. In each experiment the yearlings were assigned at random within breed and sex outcome groups to one of three treatments. Horses were fed assigned concentrates individually to appetite for two 1.5-h feeding periods, daily and group-fed Coastal bermudagrass (Cynodon dactylon) hay in drylot paddocks at a rate of 1.0 kg/100 kg BW daily. In Exp. 1, the concentrates were A) basal, B) basal + complete TM premix, and C) basal + Cu. In Exp. 2, the concentrates were D) basal, E) basal + complete TM premix, and F) basal + Cu + Zn. The basal diet in both experiments provided Cu and Zn intakes below NRC (1989) recommendations. Trace mineral supplementation had no effect on growth and development of the yearlings in either experiment. Weight gains equaled or exceeded gains specified as rapid (NRC, 1989) for yearlings of the age and expected mature weight used in these two experiments. No gross skeletal abnormalities were detected. Bone mineral deposition was increased by supplementation of the diet with a complete TM premix (P < .05). The addition of copper or copper plus zinc to the diets of yearling horses did not increase bone mineral deposition (P > .10). Results suggest that other trace minerals (Fe, Mn, Co, or I) are critical for bone mineralization.