The authors, writing in the Plant Biotechnology Journal, said trial work showed chickens fed a diet enriched with an engineered corn variety containing high levels of key carotenoids are healthy and accumulate more bioavailable carotenoids in peripheral tissues, muscle, skin and fat, and more retinol in the liver than birds raised on standard corn diets.
Carotenoids such as b-carotene, lycopene, zeaxanthin and lutein are health-promoting organic molecules that act as antioxidants and essential nutrients, said the authors.
The trial involved broilers being challenged with the protozoan parasite Eimeria tenella - those on the high-carotenoid diet grew normally, suffered only mild disease symptoms and had lower faecal oocyst counts than birds on the control diet, they concluded.
Biofortification of crops
The researchers said there has been substantial progress in the biofortification of staple crops with vitamins (Farré et al 2011), including rice producing high levels of beta-carotene (Paine et al 2005) and multivitamin corn simultaneously producing high levels of beta-carotene, zeaxanthin, lutein, lycopene, ascorbic acid and folate (Naqvi et al 2009).
“However, most early-stage research focuses on the accumulation of nutrients in planta and not on the fate of those nutrients after consumption, even though this is a key aspect of the metabolic process. It is important to recognize that the bioavailability of nutrients in staple crops provides a more accurate indicator of nutritional quality than the nutrient content alone,” said the team.
Plants and herbal products rich in carotenoids have recently been tested for their ability to prevent coccidiosis (Arczewska-Wlosek and Świątkiewicz, 2012) - a poultry disease caused by protozoan parasites of the genus Eimeria, which is currently controlled using drugs and vaccines.
Birds succumb to coccidiosis when they ingest sporulated oocysts, which are found in abundance on poultry farms. The authors said the development of alternative control measures to reduce the use of drugs would be beneficial, particularly if such measures could be administered in feed.
They thus evaluated commercial-type broilers fed on diets supplemented with four types of corn: the wild-type inbred M37W, which is essentially devoid of carotenoids and which was designated the control diet, its engineered derivative M37W-Ph3, high in levels of beta-carotene, lycopene, lutein and zeaxanthin, a standard commercial corn-based diet with color additives and the same standard corn-based diet without additives.
“We compared animals reared on these diets in terms of general health indicators, the accumulation of bioavailable carotenoids and their ability to withstand challenge with the commercially relevant protozoan parasite Eimeria tenella,” said the researchers.
The scientists said the high-carotenoid diet appeared to delay the E. tenella reproductive cycle. They also found such a diet seemed to promote resistance against oocysts, and the excretion of massive numbers of oocysts was attenuated or delayed.
Although liver and serum retinol levels were high in animals reared on the high-carotenoid diet, only traces of beta-carotene were found in the liver and breast muscle, noted the team.
“However, high levels of β-carotene and zeaxanthin oxidation products were present in blood, breast, thigh and shank skin and fat, indicating that the carotenoids were involved in antioxidant activity in these tissues, protecting the chickens from stress and maintaining the immune system.
These health-promoting effects included a reduction in the severity of coccidiosis symptoms concomitant with a delay in the parasite life cycle, reducing the oocyst load in the faeces.
Our results demonstrate that carotenoid-rich corn incorporated into commercial poultry diets can maintain poultry health and confer nutritional value to poultry products without the use of expensive feed additives such as canthaxanthin,” said the scientists.
They said the levels and composition of carotenoid supplements in commercial diets differ substantially from those delivered through the high-carotenoid corn in the study, and the supplements are less bioavailable than the intrinsic carotenoids delivered using the engineered corn variety.
“To achieve the same levels and composition, commercial diets would need to be supplemented with substantially higher amounts of these beneficial molecules, which is economically unfeasible. Thus, high-carotenoid corn offers an attractive replacement to the standard diet in a commercial setting,” concluded the team.
Source: Plant Biotechnology Journal
Published online ahead of print: DOI: 10.1111/pbi.12369
Title: Carotenoid-enriched transgenic corn delivers bioavailable carotenoids to poultry and protects them against coccidiosis
Authors: Nogareda C, Moreno JA, Angulo E, Sandmann G, Portero M, Capell T, Zhu C, Christou P