Processing, mixing, and particle size reduction of forages for dairy cattle

Adequate forage amounts in both physical and chemical forms are necessary f or proper ruminal function in dairy cows. Under conditions in which total a mounts of forage or particle size of the forage are reduced, cows spend les s time ruminating and have a decreased amount of buoyant digesta in the rum en. These factors reduce saliva production and allow ruminal pH to fall, de pressing activity of cellulolytic bacteria and causing a prolonged period o f low ruminal pH. Insufficient particle size of the diet decreases the rumi nal acetate-to-propionate ratio and reduces ruminal pH. The mean particle s ize of the diet, the variation in particle size, and the amount of chemical fiber (i.e., NDF or ADF) are all nutritionally important for dairy cows. D efining amounts and physical characteristics of fiber is important in balan cing dairy cattle diets. Because particle size plays such an important role in digestion and animal performance, it must be an important consideration from harvest through feeding. Forages should not be reduced in particle si ze beyond what is necessary to achieve minimal storage losses and what can be accommodated by existing equipment. Forage and total mixed ration (TMR) particle sizes are potentially reduced in size by all phases of harvesting, storing, taking out of storage, mixing, and delivery of feed to the dairy cow. Mixing feed causes a reduction in size of all feed particles and is di rectly related to TMR mixing time; field studies show that the longest part icles (> 27 mm) may be reduced in size by 50%. Forage and TMR particle size as fed to the cows should be periodically monitored to maintain adequate n utrition for the dairy cow.