Effect of graded levels of iron, zinc, and copper supplementation in diets with low-phytate or normal barley on growth performance, bone characteristics, hematocrit volume, and zinc and copper balance of young swine

Fifty crossbred barrows with an aver- age initial age of 31 d and BW of 9.94 kg were used in a 28-d experiment to evaluate the effect of a low-phytic acid (LPA) barley mutant (M) M955, a near-isogenic progeny of the normal barley (NB) cultivar Harrington with about 90% less phytate than NB, to increase the utilization of Fe, Zn, and Cu compared with diets con- taining NB. The response criteria were growth perfor- mance, hematocrit volume, metacarpal bone charac- teristics, and the apparent absorption, retention, and excretion of Zn and Cu. The 2 barley cultivars (NB and M955) and the 5 trace mineral (TM) treatment concentrations of Fe and Zn (0, 25, 50, 75, and 100% of the requirement as FeSO4 and ZnSO4) and Cu (0, 40, 80, 120, and 160% of the requirement as CuSO4) made 10 treatments in a factorial arrangement. Available P was equalized at 0.33% in all diets by adding monoso- dium phosphate to the basal diet containing NB, and all diets contained 0.65% Ca. Diets were adequate in all other nutrients. Barley and soybean meal were the only sources of phytate in the practical diets that also contained spray-dried whey. The barrows were fed the diets to appetite in meal form twice daily in individual metabolism crates. There were no barley cultivar × TM treatment interactions, and there were no differ- ences between the NB and M955 barley cultivars for any of the response criteria measured. However, for the TM treatments, there were linear increases (P ≤ 0.05) in ADFI, ADG, hematocrit volume, metacarpal bone breaking strength and ash weight, and the apparent absorption, retention, and excretion (mg/d) of Zn and Cu. In conclusion, the LPA barley had no effect on the response criteria in this experiment, apparently be- cause of the small increase in the availability of the en- dogenous trace minerals in the practical diets contain- ing M955 compared with NB. However, increasing the supplementation of Fe and Zn from 0 to 100% (160% for Cu) of the requirement resulted in linear increases in growth performance, hematocrit volume, metacarpal bone strength and ash weight, and the apparent ab- sorption, retention, and excretion of Zn and Cu. There- fore, these results indicate that the inorganic trace min- eral supplementation of practical diets for young pigs should not be less than the National Research Council requirements for swine.