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.

Twelve newborn Holstein bull calves were used to evaluate the effects of dietary abrasiveness, determined by a new method, on ruminal development. Calves were blocked by age and body weight and were assigned to one of three different diets. Each diet had the same ingredients but different particle sizes, which resulted in different abrasive values. No differences were detected in molar percentages of volatile fatty acids in ruminal fluid or in plasma concentrations of urea, glucose, or beta-hydroxybutyrate. The pH of ruminal fluid was lower for calves fed the fine and intermediate diets than for those fed the coarse diet. Digesta-free weights of the stomach and stomach compartments were similar among calves fed the three diets, except that omasum weights were heavier for calves fed the fine diet. Length of the ruminal papillae increased as the abrasive value of the diet decreased. Measurements of ruminal tissue layers from the ventral floor of the cranial sac were not different among diets, but the keratin portion represented more of the epithelial layer for calves fed the diet with the lowest abrasive value, thus decreasing the percentage of metabolically active tissue for those calves.

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A total of 240 weanling pigs (22 d of age and 5.3 kg average BW) were used to determine the effects of particle size of corn and two sorghum hybrids on diet processing, growth performance, apparent digestibility of nutrients, and morphology of the stomach and intestines in weanling pigs. Treatments were corn, hard endosperm sorghum, and soft endosperm sorghum milled to particle sizes (geometric mean) of 900, 700, 500, and 300 microns, in a 3 x 4 factorial arrangement. All diets were pelleted and the pigs were allowed to consume feed and water on an ad libitum basis. As particle size was reduced, production rate (tons/hour) decreased and energy required to mill (kilowatt hours/ton) increased. Corn required more energy to mill and had a lower production rate than the sorghums. For d 0 to 14, ADG and gain/feed increased linearly (P < .009 and P < .002, respectively) as particle size was decreased to 300 microns. However, there was a grain source x particle size interaction; pigs fed corn responded to particle size reduction more than pigs fed the sorghums (P < .04). For d 0 to 35, pigs fed diets with corn grew 23% faster and were 6% more efficient (P < .001) than pigs fed diets with sorghum. Gain/feed responded quadratically to reduction of particle size (P < .01), with maximum gain/feed at 500 microns for all grains. Lowest cost of gain (including milling and ingredient costs) was achieved at 500 to 700 microns for corn and 500 microns for the hard and soft sorghums. These data suggest that response to reducing particle size is greatest during the first 2 wk postweaning and that optimal particle size for corn and sorghums increases with age of nursery pigs.

Three experiments were conducted to determine the effects of enzyme supplementation and particle size of wheat-based diets on growth performance and nutrient digestibility in nursery and finishing pigs. In Exp. 1, 180 weaned pigs (5.7 kg and 21 d of age) were fed diets in a 35-d growth assay without or with a Trichoderma longibrachiatium enzyme product (4,000 units of xylanase activity per gram of product) and with wheat ground to mean particle sizes of 1,300, 600, or 400 microm. Enzyme supplementation had no effect on ADG or gain/feed (P > 0.32), but there was a trend (P < 0.10) for greater digestibility of DM (d 6) in enzyme-supplemented diets. A particle size of 600 microm supported the greatest overall gain/feed (quadratic effect, P < 0.01). An interaction of enzyme supplementation with particle size occurred; gain/feed was improved (P < 0.01) with enzyme supplementation at the coarse (1,300 microm) particle size but not when the wheat was ground to 600 or 400 microm. In Exp. 2, 160 finishing pigs (67 kg) were fed a diet without or with the same enzyme used in Exp. 1 and wheat ground to 1,300 or 600 microm. No interactions occurred between enzyme supplementation and particle size of the wheat (P > 0.15). However, there were trends for greater gain/feed (P < 0.10) during the 67- to 93-kg phase of the experiment and for greater digestibility of DM (P < 0.10) and N (P < 0.07) with enzyme supplementation. When particle size was reduced from 1,300 to 600 microm, gain/feed was improved (P < 0.03) for the 93- to 114-kg phase of the growth assay, and digestibilities of DM (P < 0.02) and N (P < 0.04) were greater. In Exp. 3, 160 finishing pigs (63 kg) were given diets without or with the enzyme product and wheat ground to 600 or 400 microm. Enzyme supplementation improved ADG (P < 0.04) in the 90- to 115-kg phase but otherwise did not affect growth performance, carcass measurements, or stomach lesions. A particle size of 400 microm increased overall gain/feed (P < 0.04), digestibilities of DM and N (P < 0.01), and development of stomach lesions (P < 0.01). In conclusion, pigs did not benefit consistently from enzyme supplementation. However, wheat particle sizes of 600 and 400 microm supported the best overall performance in nursery and finishing pigs, respectively.