Morphological and functional development of the rumen in the calf: Influence of the time of weaning 1. Morphological development of rumen mucosa

The objective of this study was to determine whether the nutritional regime n of rearing calves would influence the morphometric and histological devel opment of rumen mucosa. Twelve male Holstein calves 7 d of age were assigne d to three groups of 4 animals each: milk group (I), early weaned (6 weeks) group (II) and late weaned (9 weeks) group (III). All animals received add itional solid feed. Animals of group I were slaughtered after 6 weeks of ag e, whereas those in groups II and III were slaughtered after 9 weeks of age . At slaughter, the ruminal digesta amounted to 2035 g (milk group), 3092 g (late weaned group) and 5374 g (early weaned group). The differences in th e ruminal molar percentage of SCFA were not significant. There was a trend for lower pH and higher SCFA concentrations in the order late weaned, early weaned and milk Fed animals (pH: 6.4, 6.6 and 6.7, respectively; SCFA: 96, 87 and 77 mmol/l, respectively). The mean length (1.07 mm in milk group. 1 .45 mm in late weaned group and 1.87 mm in early weaned group), width (0.43 , 0.58 and 0.71 mm, respectively) and surface of papillae (190, 232 and 241 mm(2)/cm(2) mucosa, respectively) increased with both the age of the anima ls and the elevated intake of solid feed, whereas the number of papillae (2 10, 140 and 92 per cm(2) mucosa, respectively) decreased. In both milk-fed groups type A and B corneal cells were present in the Stratum corneum, wher eas in the earlier weaned calves type C-cells could be also seen. These fin dings indicate a more advanced stage of development of the rumen epithelium in the earlier weaned calves fed higher amounts of concentrate and hay.