Effects of a direct-fed microbial on digestive-tract morphology of Holstein bull calves and performance and carcass characteristics of Holstein steers1

Two experiments were conducted to evaluate the effects of live cultures of Lactobacillus acidophilus and Propionibacterium freudenreichii on digestivetract morphology of neonatal-transition Holstein bull calves and performance and carcass characteristics of calf-fed Holstein steers. In Exp. 1, forty-three 1-d-old Holstein bull calves (42 kg of BW) were supplemented with a direct-fed microbial (DFM) consisting of L. acidophilus and P. freudenreichii. Treatments consisted of a control (n = 21) and a treatment (n = 22) of direct-fed microbial (5 × 108 cfu) supplemented daily in a commercial milk replacer. At the conclusion of the milk-feeding stage (weaning), 11 calves from each treatment group were slaughtered at the University of Arizona Meats Laboratory for gastrointestinal-tract collection. The remaining calves were abruptly weaned and moved to concrete-floor pens for 14 d before slaughter (DFM treatments were mixed in the diet). Samples of the rumen and ileum were collected at the time of slaughter and examined for gastrointestinal-tract morphology. Before weaning, average ileal height, crypt depth, and total height (villus + crypt) were greater in DFM treatment (P < 0.03) compared with controls. After weaning, average ruminal papillae width was greater (P < 0.01) in calves receiving DFM versus controls. In Exp. 2, calves were fed control (no DFM) or 1 × 105 or 1 × 106 L. acidophilus strain NP 51 plus 1 × 109 P. freudenreichii strain NP24 from 1 to 3 d of age (d 0 of experiment) through finishing (average 462 d of age). No differences were noted in intake or G:F during the preweaning period. During the growing period, there were no statistical differences in BW, ADG, feed intake, or G:F. Average daily gain showed a trend for being greater (quadratic; P < 0.07) for Holstein steers receiving 1 × 105 L. acidophilus versus control steers and steers receiving 1 × 106 L. acidophilus during the finishing period. No differences (P > 0.10) were noted in daily intake or G:F between treatments during the finishing period. Overall, steers fed 1 × 105 L. acidophilus had no difference in final BW and ADG versus steers fed the control diet.