Intake of nutrients (polyunsaturated fatty acids, tocols, and carotenes) and storage efficiency in different slow-growing chickens genotypes reared in extensive systems

Abstract

An extensive rearing system (ERS) for poultry requires an outdoor run, which enhances the foraging activity of chickens. Slow-growing (SG) strains are more adapted to ERS than fast-growing (FG); and generally, have higher levels of bioactive compounds in their meat. The aim of this paper was to assess the storage efficiency of n-3 and n-6 polyunsaturated fatty acids (PUFA), tocols and carotenes in the meat of seven commercial SG genotypes (SG1-7). One hundred SG chicks/strain of both sexes were included and their walking activity (High- or Low-W) was classified: SG1-4, HW comprised more than 10% of the time budget, and SG5-7, less than 10% (LW). Chickens were reared in pens (4 pens/strain) with indoor (0.10 m2/bird) and outdoor (4 m2/bird) areas, and they were fed the same diet ad libitum (starter feed for 1–21 d, grower feed from 22 d to slaughter at 81 d). The chickens were weighed weekly; feed consumption and grass intake were also estimated. At 81 days of age, 32 chickens/genotype were selected on the basis of the average weight (1:1, M:F) and slaughtered. The breast, thigh and drumstick meat were excised from 30 carcasses/genotype, sampled and stored at -20°C until analysis. Nutrients (e.g., n-3, n-6, carotenes and tocols) of feed, grass and meat were analyzed. The storage efficiency of nutrients was estimated as the ratio between the amount deposited in the body muscles (OUT) and the dietary intake (feed and grass, IN). The genotype affected chickens foraging behavior and the intake of nutrients. For SG1, SG2 and SG3, more than 50% of the intake of n-3 came from grass, whereas in the other genotypes, less than 20%. Accordingly, chickens that foraged more showed better meat nutritional profiles (less fat, more n-3 and antioxidants), which, in ERS, was ascribed to grass ingestion. However, the storage efficiency of nutrients into meat was inversely correlated with the grass intake: strains with higher grass intake (SG1, SG2, and SG3) had lower storage rates. Several hypotheses were proposed to explain these trends.

Performance, meat quality and blood parameters in four strains of organic broilers differ according to range use

“…Following similar trends, uric acid concentration, which acts as an antioxidant 35,36 , also decreased with range use in the strain S757N. Our observations are quite consistent with previous results that showed that locomotor activity (which is likely higher in HR chickens than in LR chickens) of Ross 308 broilers and other slow-growing strains are correlated to higher oxidative indicators and lower antioxidant concentration in the blood 11,18,37 . Therefore, range use seems to induce an imbalanced redox status in the JA757 strain, characterized by the highest growth rate among the studied strains.…”

“…Additionally, breast meat of HR was yellower than that of LR in both JA757 and dual-purpose strains. Increased yellowness has been reported in several other studies 10,27,28 and could be caused by the intake of fresh plants (e.g., grass or clover) containing carotenoids 11,29 . We can hypothesize that JA757 and dual-purpose highrangers dedicated a higher percentage of their time to foraging activities, and/or their metabolism is able to assimilate more pigments than other strains from the ingested plants, leading to a higher enrichment of their muscles in carotenoids.…”

“…Regarding blood lipids, it is worth noting that although no changes in FA concentration and pro le was observed between high-and lowrangers, n-6/n-3 ratio decreased with greater range use in S757N. It has been shown that pasture composition exhibits lower n-6/n-3 ratio and higher tocopherol concentration than diets classically provided to chickens 11,38 , which can explain changes in n-6/n-3 observed in the blood of S757N. In the White Bresse strain, an increase in total antioxidant status, triglyceride and n-6/n-3 ratio was observed in high-ranger chickens, which is di cult to explain.…”

“…However, when looking at the fatty acid composition, we showed a higher percentage of α-linolenic acid (C18:3 n-6) in the thigh muscle of HR compared to LR of the dual-purpose strain, without impact on the n-6/n-3 ratio. As α-linolenic acid is an omega 3 precursor, there could be a nutritional interest to its increase and, although the pasture fatty acids pro le was not investigated, we may hypothesize that α-linolenic acid increase could be due to higher grass ingestion 11 .…”

“…Free-range access can in uence chicken meat quality and composition but also blood physiological parameters due to animals' foraging and locomotor activities 10,11 , but results are sometimes inconsistent. The diversity of slow-growing genotypes studied, the varying level of free-range use and the lack of individual assessment of chickens' ranging behaviours may be the source of contradictory results.…”