To investigate the suitability of using high levels of British (high glucosinolate) rapeseed meal (RSM), 80 adult Suffolk-Mule ewes of mean live-weight 64.8 kg (s.e. 0.5) were divided into four balanced groups. Three of the groups were allocated to a concentrate diet containing 20% RSM as the major protein supplement: extracted (B), expeller (C) and extruded (D). The control group (A) was given a diet containing 16.5% soyabean meal (SBM) as the only protein supplement. The remainder of these pelleted diets consisted of barley, molassine meal, oat husks, minerals and vitamins. All four diets contained similar levels of protein and energy.

The ewes were fed 0.7 kg/day during maintenance, 1 kg/day durino mating and increasing amounts from late pregnancy up to a maximum of 2.5 kg/day during lactation. Barley straw was available ad libitum. The ewes were weighed twice monthly. Jugular blood samples were taken monthly for thyroxine (T4) and thiocyanate (-SCN) analyses of plasma, also every five days during mating and the first two months of pregnancy for profiles of progesterone in plasma. The ewes were exposed to raddled entire rams for six weeks during November and December.