An experiment was conducted using two batches of 40 purchased male Hereford x Friesian calves, reared conventionally with weaning after 5 weeks. Five diets were offered ad libitum for 9 weeks: a basic concentrate pellet A offered alone, or with additional chopped or long straw; a diet incorporating 35 g sodium bicarbonate per kg in the basic pellet; and a complete diet with the inclusion of 176g chopped straw (20 mm) per kg in the concentrate pellet.Concentrate intakes and live-weight gains tended to increase with voluntary intake of roughage and the inclusion of buffer in the diet; giving a complete diet, however, gave the best results, with total intake increased to 1 -6 of that for diet A and also significantly increased weight gains.Rumen acidity was decreased by roughage consumption or by buffer inclusion in the diet. Increasing roughage consumption tended to promote an increase in the molar proportions of acetic and butyric acids in the rumen liquor, and a decrease in the molar proportion of propionic acid.Results suggested that chopping the roughage into 20-mm lengths did not obviously alter the rumen-buffering characteristics of long roughage, provided that a greater quantity was included in chopped form.

Forty purchased male Hereford ♂ × Friesian ♀ calves (about 14 days old) were offered concentrate diets containing 0, 170, 230 or 320 g chopped (20 mm) straw per kg. Food intake and live-weight gains of calves were increased by the inclusion of straw, but the 320 g straw treatment tended to depress intake and gain. The optimum concentration of fibre for maximizing live-weight gains was 150 g trichloracetic acid fibre per kg of diet (220 g chopped straw per kg).