Two experiments were conducted with three types of polyethylene particles to establish their retention time in castrated male cattle (steers) offered diets which contained predominantly cereals ad libitum. The particles were (1) ‘Ruff Tabs’, a corrugated particle of dimension 1·27 × 0·63 × 0·95 cm3 and subsequently referred to as RT and (2) and (3) plain plastic rods of 1·27 cm length and 0·32 cm (BP) or 0·63 cm (RBP) diameter.

In the first experiment with steers weighing 170 or 260 kg, 1 kg of RT particles were excreted in the faeces at a similar rate by the steers of different weights whereas BP particles passed out in the faeces more slowly in the lighter steer.

In the second experiment 30 steers weighing 440 kg were slaughtered at 7, 14, 28 and 42 days after dosing with 1 kg of BP, RT or RBP. The recovery of RT was significantly lower (P < 0·05) than that of BP 7 days after dosing and this difference was also found at 14 and 28 days. RBP behaved like BP up to 14 days but thereafter the rate of passage of RBP was faster than tha t of BP and recovery from the rumen approached that of RT.

Experiments were carried out to determine the effects of giving 1·36 kg of ‘RuffTabs’, polythene particles of dimension 1·27 × 0·63 × 0·95 cm3 (RT) to castrated male cattle (steers) given an all-concentrate diet, on the outflow of fluid from the rumen, on rumination and on the molar proportions of volatile fatty acids produced in the rumen.

RT reduced the flow of fluid from the rumen of steers, given a restricted amount of an all-concentrate diet, from 4·65 to 2·75% rumen volume/hr. RT had no effect on the total time spent daily in ruminating and eating. The molar proportions of volatile fatty acids were unaffected by RT in steers which were given the diet ad libitum but when RT was given to steers offered a restricted allowance of feed there was a highly significant (P < 0·001) reduction in acetic and an increase in butyric, valeric and caproic acids.

The feed intake of the steers was unaffected by RT.