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The influence of age and weaning on the structure of the gastrointestinal epithelium in Holstein bull calves
The objective of this study was to characterize how age and weaning influence structural adaptations of the gastrointestinal tract (GIT) in calves. Tissues from the GIT were taken from 21 Holstein bull calves that were randomly assigned to 1 of 3 treatments: pre-weaned calves sampled at d 16 (PRE; n = 7); weaned calves sampled at d 42 (WN; n = 7); and control calves sampled at d 42 (CON; n = 7). A step down weaning approach was used (from d 35 to d 42 of life), while CON calves were not weaned. Histological analysis was performed on the rumen, duodenum, jejunum, ileum, proximal and distal colon, and the cecum. Tissues were processed and fully imaged under 40x, and minimum of 10 images under 100x. Measurements were taken of rumen sloughing, papillae dimensions, crypt depth throughout the small intestines, mucosal width in the hindgut, and goblet cell counts in all intestinal compartments. Treatments were compared using the mixed procedure in the statistical analysis system. Weaning effects were most notable in the rumen and duodenum: rumen sloughing scores were highest (P < 0.01) in WN (2.64 ± 0.25) relative to CON (1.50 ± 0.25) and PRE (1.51 ± 0.25); duodenal villi length was longer (P = 0.02) in CON (356.5µm ± 32.67) than in WN (218.9µm ± 32.67). Crypt depths were consistently deeper (P < 0.01) for duodenum, jejunum, proximal and distal colon of PRE calves compared to CON and WN. Mucosa thickness in the hindgut compartments was greater (P < 0.01) in the PRE group. There were no treatment differences on goblet cell count except in the proximal colon, with PRE (0.08 ± 0.01) having less (P < 0.01) goblet cells in 100µm² than WN (0.15 ± 0.01) and CON (0.15 ± 0.01). These data suggest that during weaning there is significant structural alteration in the rumen and intestine. The most notable differences were detected in the rumen and the beginning of the small and large intestine. Future research is needed to assess the functional adaptation of the entire GIT, and how these adaptations may relate to calf health and performance.
Keywords:
GIT, weaning, histology