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 influenc e of trace mineral (TM) supplementation on growth and bone mineral con tent in young growing horses from 340 to 452 d of age. In each experim ent the yearlings were assigned at random within breed and sex outcome groups to one of three treatments. Horses were fed assigned concentra tes individually to appetite for two 1.5-h feeding periods daily and g roup-fed Coastal bermudagrass (Cynodon dactylon) hay in drylot paddock s at a rate of 1.0 kg/100 kg BW daily. In Exp. 1, the concentrates wer e 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 supplement ation had no effect on growth and development of the yearlings in eith er experiment. Weight gains equaled or exceeded gains specified as rap id (NRC, 1989) for yearlings of the age and expected mature weight use d in these two experiments. No gross skeletal abnormalities were detec ted. Bone mineral deposition was increased by supplementation of the d iet with a complete TM premix (P < .05). The addition of copper or cop per plus zinc to the diets of yearling horses did not increase bone mi neral deposition (P > .10). Results suggest that other trace minerals (Fe, Mn, Co, or I) are critical for bone mineralization.