Effects of trace elements supplementation in commercially reared dairy cows of different lactation in relation to mineral metabolism

An on-farm trial was conducted with crossbred cows of 2nd and 3rd lactation to study the effects of supplemental Cu, Mn and Zn on utilization efficiency of major (Ca and P) and trace (Cu, Fe, Mn and Zn) elements. The animals received 3 treatments in a switchover fashion to receive Cu, Mn and Zn at approximately 120% (T-1), 100% (T-2) and 140% (T-3) of the respective planes of requirement (NRC 1989). Intakes of Ca, P and Fe were above the level of requirements in all the treatment groups irrespective of lactation number due perhaps to the fairly high concentrations of these elements in diet. Apparent absorption (%) of Cu, Mn and Zn were higher (P < 0.01) in T-2 where the intake was minimum (P < 0.01). Though intakes of these trace elements were higher (P < 0.01) in T-3 the respective apparent absorption did not vary much between T-1 and T-3. The pattern of absorption, however, remained unaffected with the lactation number. Plasma concentrations of both major (Ca and P) and trace (Cu, Fe, Mn and Zn) elements were not affected by treatment or by lactation number and no interaction could be observed between them. Plasma concentrations of all these minerals were above the respective minimum critical levels. Milk mineral concentrations were also within the normal ranges of variation with little effects of either treatments or lactation numbers. It was concluded that there is need to optimize the dietary levels of various major and trace elements in order to maximize their efficiency of utilization in lactating cows.