Abstract :
Twelve mid-lactation Holstein cows were blocked according to milk production and assigned to diets containing +12, +54,or 64 meq [(Na++K+ )- C1- ]100-1 g diet dry matter (DM).The objective of this study was to examine diets having cation-anion balances spanning a range wider than had been examined previously.Diets were mixed to contain a 60:40 concentrate to corn silage ration (DM basis).treatment periods were 3 wk with th first 2 wk serving as an adaptation period.Feed intake,actual milk yield,milk fat fat yield,and 3.5,FCM increased as dietary cation-anion balance increased to +54 meq 100-1 g DM.Blood pH,PCO2 and HCO3 increased with increasing dietary cation-anion balance.Plasma Na+,K+,and Mg2+ levels were unaffected by the dietary treatment.Urinary pH was lower for cows fed the +12 diet than for those fed all other diets.Urinary Na+,K+ and C1-tended to reflect dietary concentration of these minerals.Cows fed the +12 diet excreted more C1 and Ca2+ in urine compared with those fed all other treatments.Ruminal pH was not affected by the dietaary treatment.Fermentation patterns were only slightly affected by the dietary cation-anion balance.The results suggest that dietary cation-anion balance may become a useful tool when examining the overall performance of lactaing dairy cattle.
