EFFECTS OF FILL VOLUME OF DIETS ON DIGESTIVE-TRACT KINETICS AND FATTENING PATTERN OF GROWING HOLSTEIN-FRIESIAN BULL CALVES

Young Holstein-Friesian bull calves were tested in three trials for th eir performance and digestive tract kinetic responses to diets differi ng in their fill volume (FV) in the digestive tract. In Trial 1, a hig h ME (11.7 MJ/kg of DM) diet was compared with three medium ME (10.5 M J/kg of DM) diets, one of high FV and two of low FV. In Trial 2, two s ilages (wheat and sorghum), differing in FV, were compared with dr wit hout poultry Litter inclusion. Ah the diets in this trial had the same ME content of 10.5 MJ/kg of DM, Rate of gain, DM and ME intake, and d epot fat percentage at slaughter were recorded. In Trial 3, two diets (high and low FV) and the same ME content of 10.4 MJ/kg of DM were com pared in a short-term trial for digestive tract kinetics using a singl e dose of Cr-NDF and Co-EDTA as particulate and solute markers, respec tively. Calves in Trial 1 fed medium ME and Tow FV diets had higher (n ot significant) DMI than high ME calves but similar ADG, whereas mediu m ME and high FV calves had the lowest DMI (P <.1) and ADG (P <.05). L ow FV and medium ME calves were leaner (P <.05) at slaughter than the high ME calves and fatter (not significant) than the high FV and mediu m ME calves. In Trial 2, reduction of FV by silage replacement increas ed DMI (P <.01) and ADG (P <.05). Incorporation of poultry litter into the diets resulted in effects in the same direction (not significant) . Such a reduction caused increased (P <.01 for both silage end poultr y litter effects) deposition of cod fat in the carcass. Mean retention time estimations in Trial 3 indicated increased (P =.055) particle re tention time in the low FV calves, compared to the high FV calves. Thi s increase was due to a longer(P =.1) stay of particles in the lower p arts of the digestive tract, and not in the rumen. Lowering the FV of medium ME diets increased DMI of calves to support ADG equal to that o f a high ME diet, but with a lower fat accumulation.