Effects of supplemental zinc on the rumen fermentation, nutrients digestibility, milk yield and composition of dairy cows

Abstract

Three experiments were conducted to investigate effects of supplemental zinc on protein degradation, rumen fermentation characteristics and lactation performance of dairy cows. Experiment 1 was designed to investigate effects of different type and particle size of zinc supplementation on in situ nutrient degradation. In DM degradation, zinc supplementation decreased potentially degradable fraction (P<0.01). In addition, the potentially degradable fraction and effective degradability (ED) were decreased by particle size (P<0.01 and P<0.001, respectively). While, in CP degradation, zinc supplementation did not affect immediately and potentially degradable fractions, degradable rate per hour of fraction and ED, but particle size influenced ED (P<0.01). Therefore, larger particle size beneficially decreased protein degradation in the rumen, but the effect of zinc was not clear for ruminal protein degradation. In experiment 2, zinc was mixed with heat treated soybean meal and Aspergillus oryzae. Therefore, three treatments were used, which were soybean meal as a control, zinc with heat treated soybean meal (Zn-SBM), and zinc with heat treated soybean meal and Aspergillus oryzae, to assay in vitro fermentation. Generally, the medium pH was higher in control and Zn-SBM compared with ZnAo-SBM during the incubation. Until 16 h, gas production was highest in ZnAo-SBM among the treatments. However there was no significantly different among the treatments from 24 to 48 h. The NH3-N concentration was not affected by treatments, except for 8 and 16 h. On 8 and 16 h, NH3-N concentration was lowest in ZnAo-SBM among the treatments (P<0.01). There was a tendency of decreased DM and CP degradation in ZnAo-SBM compared with other treatments during the incubation.