Rumen development in the calf

Abstract

1. Twenty-four Ayrshire bull calves were reared on either high-concentrate or high-roughage diets to study the effect of diet on the subsequent ability of the calf to digest either concentrates or hay when given alone. The rearing diets were known to produce different types of rumen development. 2. Although there were significant differences between the apparent digestibility coefficients of the high-concentrate and high-roughage rearing diets and between concentrates and hay when given alone, the subsequent ability of the calf to digest either concentrates or hay was unaffected by the type of diet given during the rearing period to 13 weeks of age. 3. The amount of nitrogen retained was significantly greater in calves reared on the high-concentrate diet than in those given the high-roughage diet, but similar amounts of N were retained/100 g gain in body-weight in both groups. After the change in diet, the amount of N retained was significantly greater in calves given concentrates after a rearing diet high in concentrates than in those given concentrates after a rearing diet high in roughage, although in both groups 32% of the N intake was retained. Four of the six calves given hay after a rearing diet high in concentrates were in negative N balance, but only one calf lost weight. Only 19% of the N intake was retained in calves given hay after being reared on a high-roughage diet. 4. The concentration of total volatile fatty acids (VFA) in the rumen contents rose to reach peak levels at about 3 h after food was offered; the concentration then declined. VFA concentrations tended to be higher in calves given the rearing diet high in concentrates than in those given the one high in roughage, and differences reached significance when the diet was changed to one of all concentrates or all hay, with no obvious carry-over effect of the rearing diet. The proportion of propionic, butyric and higher acids tended to be greater in calves given high levels of concentrates than in those given high levels of hay and also tended to rise, irrespective of diet, as the concentration of total VFA rose. 5. A change of diet at 14 weeks from one high in concentrates to one consisting entirely of hay resulted in a significant decline in the viable counts of streptococci, lactobacilli and coliform organisms in the rumen liquor at 16 weeks. The numbers of bacteria were unaffected by the other dietary changes. 6. The concentration of total VFA in plasma of peripheral blood tended to be higher in calves given the high-roughage or all-hay diets. A fall in the concentration of plasma VFA occurred when calves were changed from a high-roughage diet to an all-concentrate diet and a rise in concentration was observed when an all-hay diet replaced one containing a high proportion of concentrates. 7. During the initial rearing period the mean blood plasma glucose concentration was 92.8 mg/100 ml in calves given the high-concentrate diet, a value significantly higher than the mean value of 64.5 mg/100 ml found in calves given the high-roughage diet. The concentra- tion of plasma glucose rose to 89.8 mg/100 ml in calves changed from the high-roughage diet to concentrates and declined to 81.7 mg/100 ml in calves that were given hay in place of the high-concentrate diet. 8. The weight of contents of the reticulo-nunen and omasum and the volume displacement of these organs were significantly greater in calves given hay as the sole diet during the last 3 weeks of life than in those given concentrates during this period. The weight of tissue forming the reticulo-rumen was significantly greater in calves given the all- concentrate diet during the last 3 weeks of life than in those given only hay during this period. It was apparent that the rumen papillas developed rapidly in those calves given concentrates as the sole diet for a period of 3 weeks after a rearing diet high in roughage, whereas there was a marked retrogression of papillas when concentrates were withdrawn from the diet. 9. It is concluded that the ruminant calf adapts readily to marked dietary changes, with the result that differences in the size and structure of the ruminant stomach, which have been shown to occur when different types of diet are given, have no permanent effect on the ability of the calf to digest diets of concentrates or hay.