Fleece measurements were made in a closed flock of Oxford Down sheep being maintained by random mating. The original 20 ewes were sampled in 1970 and another 20 of the 30 ewes were sampled in 1980. Staple length, mean fibre diameter and secondary/primary follicle ratio were similar at the two sampling times. There were more inactive follicles in 1980 and more follicles with multiple fibres, but the differences were not significant. The appearance of some medullation and pigmentation in 1980 could have an environmental rather than a genetic cause. Follicles intermediate between primaries and secondaries were observed, and in all fibres the bilateral structure was clearly visible.

Computer simulation was used to study the effect of assortative mating in tandem selection. Selection was applied alternatively for each of two traits of equal economic importance, the mating being assortative for the trait not subjected to selection. Two heritabilities (0·2, 0·4), two selection intensities (20/40, 20]100) and three additive genetic correlations (0·50, 0, —0·50) were considered. Assortative mating gives a response which is 1·03 to 1·10 times that achieved when random mating is employed.

Individual and group-penning, and entire male and female sexes were investigated in a factorial design. The size of group was five pigs. The diets were given to a scale based on live weight.

Individual penning gave significantly faster gains than group penning (679 v. 653 g/day, P < 0·01) but the improvement in food conversion ratio was not significant. Loin sample joints from individually-penned pigs had less lean and significantly more fat than did those from group-penned pigs. The faster growth rate and greater fatness of the individually-penned pigs indicated that more energy was retained by these animals and it was concluded that the greater retention of energy derived primarily from an apparently reduced metabolic heat production. The associated increase in initial growth rate was accentuated by the nature of the feeding scale.

There was some indication that boars did not grow as well as gilts in individual pens. Boars grew faster than gilts and converted food more efficiently to live-weight gain especially above 50 kg. They had lower killing-out yields and less fat than gilts.

The effect of frequency of feeding on the efficiency of utilization of L-lysine hydrochloride supplements was studied in 30- to 60-kg pigs. The feeding regimes were: (A) once daily, (B) twice daily, (C) four times daily between 08.30 and 20.30 h, (D) four times daily at 6-h intervals. The response criterion was urinary-nitrogen (N) excretion during 5-day periods. Linear improvements in N utilization were seen in response to lysine supplementation: (a) of a mineralized barley diet (4·0 g lysine per kg to levels of 5·0 and 6·0 g/kg (trial 1)), and (b) of a barley-soya diet (5·5 g lysine per kg to levels of 6·8 and 8·1 g/kg (trial 2)). In both trials the efficiency of N use averaged over the three diets was significantly poorer with once-daily feeding than for the other three treatments, which did not differ significantly from each other.