Rumen development in the calf

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Abstract
Thirty Ayrshire bull calves were used in an experiment to study the effects of diets containing different proportions of concentrates to hay on rumen development at 12 wk. of age. In additon, 6 milk-fed calves were slaughtered at 3 wk. of age for comparison. Restriction of the maximum daily allowance of concentrates to the lower levels was accompanied by an increase in the voluntary intake of hay, but the performance of calves from 3 to 12 wk. of age was significantly better in calves given the high-concentrate diets. The weight of contents of the reticulo-rumen increased from 0. 7 kg at 3 wk. of age in the milk-fed calf to 7. 7 kg and 10.9 kg at 12 wk. in calves given the high-concentrate and high-roughage diets respectively. Between 68 and 79% of the total contents of the alimentary tract was contained in the reticulo-rumen of the ruminant calf. The weight of contents of the omasum was significantly greater in calves given 1. 36 kg concentrates/day than in those given either 0. 45 or 2. 27 kg concentrates/day. Equations were developed from the results by which the weight of contents of the various parts of the alimentary tract, and hence empty body weight in the live animal, can be determined from a knowledge of the live weight and daily consumption of concentrates and hay. Volume displacement of the reticulo-rumen tended to increase with increase in the proportion of hay in the diet. The volume displacement of the omasum increased in response to concentrate intake up to a maximum of 1. 36 kg/day and thereafter declined, but the nature of the diet had no significant effect on the volume displacement of the abomasum. Calves given the high-concentrate diets had a significantly greater weight of reticulo-rumen tissue at 12 wk. than those given the high-roughage diets. Whereas the thickness of the muscular wall of the rumen did not differ significantly between treatments, there was an increase in the length and density of papillas, particularly in the anterior dorsal and ventral sacs of the rumen, as the intake of concentrates was increased. The results show the marked relationship between the performance of the animal and an advanced stage of development of the rumen papillas.