Effects of form of the diet on anatomical, microbial, and fermentative development of the rumen of neonatal calves.

Eight neonatal, Holstein bull calves were paired by birth date and birth weight and randomly assigned to either a finely ground or unground control diet (chopped hay and rolled grain) to study the effects of the physical form of the diet on anatomical, microbial, and fermentative development of the rumen. The diets varied in particle size but were identical in composition (25% alfalfa hay and 75% grain mix). Calves were fed milk at 8% of birth weight daily until weaning. Feed intake was equalized for each pair of calves. Ruminal fluid samples were collected from ruminal cannulas to determine pH, fermentation products, and buffering capacity and to enumerate bacteria. Calves were slaughtered at 10 wk of age, and weights of the full and empty reticulorumen, abomasum, and omasum were recorded. Ruminal tissue samples were taken to assess papillary development by morphometric measurements. Calves had similar body weights at wk 10. Ruminal pH was affected by age and was lower for calves fed the ground diet. Total anaerobic bacterial counts were not affected by the physical form of the diet; however, calves fed the ground diet had lower numbers of cellulolytic bacteria and higher numbers of amylolytic bacteria than did calves fed the unground diet. Physical form of the diet did not affect the weights of the reticulorumen whether full or empty. However, calves fed the ground diet had heavier omasum weights, both full and empty. Physical form of the diet affected papillary size and shape but did not influence the muscle thickness of rumen. Results indicated that the physical form of the diet had a significant influence on the anatomical and microbial development of the forestomac and, therefore, might influence future performance.