The substitute food of animal sourced foods for Vitamin A- crops biofortified foods

Vitamin A deficiency is common in poorer countries.It often causes night blindness, Xerophthalmia, keratomalacia, and even complete blindness(especially childhood) since Vitamin A has a major role in phototransduction. Vitamin A deficiency also contributes to maternal mortality and other poor outcomes in pregnancy and lactation.  

Animal sourced foods is a good source of Vitamin A ,but the are too expensive for poor rural people.Is there substitute food?Yeah!A research published in <Food and Nutrition Sciences> by Scientific Research Publishing claimed that crops biofortified with provitamin A offer a convenient and accessible source of vitamin A:

Crops biofortified with provitamin A offer a convenient and accessible source of vitamin A. The other micro-nutrient programs of fortification and supplementation require more expensive inputs. Biofortification programs have developed crops that are rich in provitamin A. These crops include: maize, golden rice, cassava and orange fleshed sweetpotato (OFSP). With exception of golden rice, the rest of the biofortified crops have received considerable acceptance among the communities. Both animal and human studies have shown that provitamin A from biofortified crops is highly bioavailable and have capacity to improve vitamin A status. After several years of research and promotion, it is time to fully commercialize provitamin A crops by encouraging farmers to start their large scale production and consumption.