Factors affecting the voluntary intake of food by cows. 5. The relationship between the voluntary intake of food, the amount of digesta in the reticulo-rumen and the rate of disappearance of digesta from the alimentary tract with diets of hay, dried grass or concentrates

Freer, M.; Campling, R.C.

Brit Jour Nutr 17(1): 79-88

1963


Accession: 014045413

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Abstract
The relationship between the voluntary intake of food, the amount of digesta in the reticulo-rumen and the rate of disappearance of digesta from the alimentary tract with diets of hay, dried grass or concentrates was examined in a Latin square design with 3 adult non-lactating cows. The mean voluntary intakes of food offered ad lib. for 5 h/day were 20.9 lb hay, 28.2 lb dried grass and 18.8 lb concentrates. The intakes of hay and dried grass were directly related to the digestibility of the foods in the whole alimentary tract and in the reticulo-rumen alone and inversely related to the mean retention time of residues in the alimentary tract. The amount of digesta in the reticulo-rumen immediately after feeding was about the same with diets of hay as it was with diets of dried grass and was consequently much less with the diet of dried grass immediately before the next meal. With the feeding regime used in our experiments it is suggested that with different roughages having a mean daily rate of disappearance from the reticulo-rumen greater than about 18 lb dry matter, eating ceased when the reticulo-rumen contained the same amount of digesta, about 35 lb dry matter for our cows, a limit possibly set by the capacity of the organ. With roughages having a slower rate of disappearance it appears that eating ceased when the reticulo-rumen contained less digesta, the amount present being that which would be reduced to about 19 lb dry matter immediately before the next meal. The voluntary intake of concentrates was not related in the same way to the digestibility of the food or its mean time of retention in the alimentary tract. The amount of digesta in the reticulo-rumen did not approach the amount found with the other foods, either before or after eating. It is suggested that the concentration of products of digestion of the concentrates may have limited their intake. The pH of rumen digesta fell to about 4.6 within 1 or 2 h of the beginning of feeding and remained at this level for from 3 to 6 h. Individual differences in voluntary intake of concentrates were similar to individual differences between cows in the intake of the 2 roughages. Although there was little difference between cows in overall digestibility of the concentrates there were wide differences in the proportion of the disappearance by digestion which occurred in the reticulo-rumen and this was directly related to the mean retention time of food in that organ. In all cows cotton threads suspended in the rumen were not reduced in weight with a diet of concentrates, but when hay was given they disappeared within 5 days at a rate typical of a hay diet.