LAUSR

The objective of this study was to investigate rumen fermentation, apparent digestibility of nutri - ents, and morphology of ruminal und intestinal mucosa in two cattle breeds of different metabolic type. From each breed six purebred German Holstein (H) bulls representing the secretion type and six Charolais (CH) bulls representing the accretion type were raised and fattened under identical conditions with semi ad libitum feeding of a high energy diet. The animals were used for a digestion trial started at nine months of age and animals were slaughtered at 18 months of age. Body weight (668 vs. 764 kg, P = 0.011), body weight gain (1 223 vs. 1 385 g/day, P = 0.043), and body protein gain (93 vs. 128 g/day, P = 0.001) were lower in H compared to CH bulls. Protein expense per kg protein accretion was higher in H bulls (13.8 vs. 10.2, P = 0.001). No significant differences were found in concentration and pattern of ruminal short chain fatty acid and in apparent digestibility of organic matter, crude fibre, and N-free extracts. There were no significant differencs in all morphometric traits of rumen mucosa between both cattle breeds. Compared to H, the villi of CH bulls were higher in duodenum (586 vs. 495 µm, P = 0.001) and proximal jejunum (598 vs. 518µm, P < 0.001), the crypt were deeper in duodenum (295 vs. 358, P < 0.001) and proximal jejunum (292 vs. 344 µm, P = 0.020). In contrast, the villi in ileum were higher in H (522 vs. 471 µm, P = 0.006). The weight of total small intestine, as percentage of total body weight, was 1.1 in H and 0.8 in CH (P = 0.002). The utilization of food crude protein was positively related to the duodenal ( P = 0.001) and proximal jejunal villus height ( P = 0.003) and to the duodenal crypt depth ( P < 0.001) and negatively related to weight of small intestine ( P = 0.004). It is concluded, that the higher growth potential and feed efficiency in CH bulls compared to H bulls is not caused by differences in digestion processes, but in size of small intestine, and morphology of small intestinal mucosa. Obviously the duodenum and proximal jejunum of CH bulls adapt to increase the absorptive surface due to the increase in nutrient demand.