Feeding of white clover or red clover oestrogenic diets to wethers produced increases in teat length but did not affect the basal plasma luteinizing hormone levels or pituitary sensitivity to luteinizing hormone-releasing hormone.

Three experiments involving three early maincrop cultivars explored the effect of nitrogen fertilizer (0–301 kg N/ha) applied to seed potato crops on seed performance and the growth of the subsequent early ware crop.

The tuber N-content ranged from 1·1 g N/100 g dry matter (D.M.) to 1·6 g N/100 g D.M. for seed tubers obtained from crops grown at 0 and 201·301 kg N/ha. Seed of cv. Maris Peer from crops given 100 kg N/ha in 1969 produced ware yields 10% and 24% higher than those obtained from seed from crops given 0 and 201 kg N/ha. No effects of fertilizer applied to the seed crop on subsequent growth were observed in the other two experiments.

It is suggested that the effects of nitrogen fertilizer applied to the seed crop on subsequent growth other than that related to seed tuber size only arise as a result of effects on the maturity of the seed crop. Thus any observed effect is attributed to differences in the ‘physiological age’ of seed rather than to differences in seed tuber N-reserves.

The technique of regression on environmental index is used to examine the behaviour of varieties in monoculture and mixture. It is shown that, sometimes, single regressions for each variety do not provide an adequate explanation of the interactions between varieties and environments.

The reproductive performance of breeding and cyclic Welsh Mountain (WM) and Border Leicester (BL) ewes was compared in two contrasting photoperiodic environments during January 1971–April 1972. Treatment 1 consisted of natural daylength changes at latitude 51° 43’ N. There was no difference between the two breeds in onset of the breeding season, percentage exhibiting oestrus or percentage lambing. The breeding season of BL ewes terminated earlier (mean date, 31 January) than that of WM ewes (mean date, 9 March). The WM ewes had 8–12 oestrous periods and the BL ewes 7–11 oestrous periods. In treatment 2 a simulated equatorial photoperiod (13 h light: 11 h dark) was applied from January 1971 but was inadvertently interrupted by a short period of continuous light in June 1971. All WM ewes exhibited oestrus compared with 37·5% of BL ewes. The failure to show oestrus in the majority of BL ewes contributed to the marked difference between breeds in the percentage of ewes lambing: 88·9% in WM compared with 11·1% in BL ewes. In the cyclic subgroup, the WM ewes had 3–10 oestrous periods and the BL ewes, 2–7 oestrous periods.

It is concluded that the breeds showed a differential response to the two treatments and that Treatment 2 had a marked adverse effect on the reproductive potential of the Border Leicester ewes.