Quantity of digesta in the reticulo-rumen of cows differing in susceptibility to bloat

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Abstract
In five experiments, one hay diet and eight pasture diets were offered to cows of either high (HS) or low (LS) susceptibility to bloat. Four or five cows of each susceptibility were used in each experiment; one of the five experiments involved lactating cows offered pasture to appetite and the remainder involved non-lactating cows offered diets at maintenance feeding level for 2 h each day. The quantity of digesta in the reticulo-rumen was estimated at intervals before and after feeding, by removal of digesta through a fistula in the dorsal rumen of each cow. On three of the seven pasture diets offered to non-lactating cows, LS cows had less digesta in the reticulo-rumen before feeding than HS cows. Increasing or decreasing the quantity of digesta in the reticulo-rumen after feeding correspondingly increased or decreased both the quantity of digesta subsequently lost and the quantity remaining 21 h after feeding, for both HS and LS cows. The net loss of fluid from the reticulorumen during feeding was lower and that after feeding was higher for LS than for HS cows. Lactating HS and LS cows offered pasture ad libitum did not differ in their intakes of dry matter (DM) and water or in the quantities of fluid and DM in the reticulo-rumen. HS and LS cows did not differ in the capacity of the reticulo-rumen. The rumen fluid dilution rate, estimated using Cr EDTA, was similar for both susceptibility groups in two experiments and higher for LS than HS cows in one experiment. The weight of digesta as a percentage of reticulo-rumen capacity was lower for LS cows than for HS cows in all experiments.