Abstract
The study objective was to evaluate dietary limestone buffer inclusion rates for impacting nutrient digestibility and excretion when growing dairy cattle are fed high distiller grains with solubles (DDGS) limit-fed ration. The hypothesis was that feeding more limestone buffer would offset a low rumen pH when feeding a high DDGS inclusion rate. Five ruminally cannulated Holstein and Brown Swiss steers were used in a crossover design having 2-wk periods to evaluate high and low buffer inclusion rates when limit-fed. Treatments were similar in ingredient composition being: 1) 40% DDGS at 0.80% high CaCO(3) buffer inclusion (HIGH) and 2) 40% DDGS with 0.25% low CaCO(3) buffer inclusion (LOW) with the remaining ration consisting of grass hay with minerals and vitamins. Rations were limit-fed at 2.50% of body weight (BW) using Calan feeding doors with steers being weighed every 2 wk with ration amounts adjusted accordingly. Rumen fluid was collected via the ruminal cannula at the start and end of each period for pH, ammonia-n, and volatile fatty acid (VFA)s. Fecal grab samples were collected at the end of each period for measurement of total-tract nutrient digestibility. There were no treatment-by-period interactions (P > 0.10) for any of the growth parameters measured. Gains in frame growth parameters were similar (P > 0.10) for steers fed both rations. BWs and gains were similar (P > 0.10) for steers fed both rations. Steers fed the LOW ration demonstrated a numeric improvement in average daily gain combined with a tendency (P < 0.06) for lower dry matter intake resulting in an improved (P < 0.01) feed efficiency (gain:feed) compared with steers fed the HIGH ration. Steers fed HIGH demonstrated greater (P < 0.01) ruminal ammonia-N and isovalerate concentrations compared with steers fed the LOW buffer ration. Steers fed both buffer inclusion rates were similar (P > 0.10) for ruminal pH and remaining VFAs concentrations. Steers fed both buffer inclusion rates were similar (P > 0.10) in DM and organic matter digestibilities. Limit-feeding a high DDGS inclusion rate ratio combined with a low buffer inclusion rate improved feed efficiency while maintaining growth performance. The study hypothesis was rejected in that feed efficiency can be enhanced when feeding a high DDGS ration by feeding a low calcium carbonate buffer.