Two flocks of 42 multiparous (M) and 27 primiparous (P) Nilotic ewes (Southern Sudan) were used in an experiment conducted at the Animal Production Research Centre, Khartoum N., Sudan, to study the effect of age and diet on reproductive performance. Each age group (M and P) was subdivided into two diet groups, fed either a sorghum (So) or a molasses (Mo)-based diet. The two diets were approximately isoenergetic (12·2 and 11·4 MJ ME/kg DM for So and Mo diets, respectively) and isonitrogenous (217 g CP/kg). These diets were formulated from sorghum and groundnut cake or molasses and urea as main sources of energy and protein, respectively. Each of the four diet groups of ewes was further divided into 6 subgroups (replicates) of similar body weights housed and fed together for two successive gestation periods. The results showed that the diet treatments had no significant effect on age and weights at first oestrous (210, 238 days and 22, 20 kg) and at first lambing (407, 418 days and 30, 28 kg) of the PSo and PMo groups, respectively. Age of the ewes and the diet treatments had no significant effects (P>0·05) on feed intake, conception weight, litter size, lamb birth weight, gestation period, postpartum anoestrous period, lambing interval, sex ratio of offspring as well as conception, fertility, abortion and lambing proportions. Primiparous ewes (P) had significantly (P<0·05) higher pre-weaning lamb mortality proportion, whereas the sorghum-based diet groups had higher (P<0·05) gestation body gain and lambing weights.

It was concluded that Nilotic ewes, compared with the other African sheep breeds reviewed, reach sexual maturity at an earlier age and are highly prolific due to their short postpartum anoestrous period. The results also highlight the importance of molasses and urea as efficient and good substitutes for sorghum grains and oil cakes, respectively, in the diets of ewes.