20 Carotenoids in Aviculture
519
22.2 (18.8–27.9) (Middendorf et al. 1980). In this experiment, statistically significant differences among samples within and among generic sources were obtained.
Furthermore, xanthophyll (lutein + zeaxanthin) concentrations in different feed vary
substantially (mg/kg): lucerne meal (40–260), grass meal (140–500), yellow maize
(8–40), plate maize (10–50) and maize gluten meal (60–360) (Belyavin and Marangos
1989).
The main dietary sources of carotenoids in poultry nutrition are maize, maize
products, lucerne, alfalfa meal (organic egg production) and commercial concentrated forms including marigold and paprika (Nys 2000). Most of the mentioned
feedstuffs provide mainly lutein and zeaxanthin plus β-carotene (alfalfa meal) and
β-cryptoxanthin (maize and maize gluten). Our data indicate that a major difference
between the American maize-based diet for breeders and the European wheat-barley
based diet is in the level of carotenoids (lutein + zeaxanthin), which is more than
twice higher in the maize-based diet (Surai and Sparks 2001). This difference is due
to a low carotenoid content of wheat and barley although both feeds contain lutein
and zeaxanthin as major carotenoids. The main factors affecting carotenoid transfer
to the egg yolk are shown in Table 20.1.
After ingestion of feed, carotenoids are released from the matrix by digestive
enzymes. The liberated carotenoid compounds together with other feed lipids are
emulsified in the presence of bile salts to form oil droplets. Carotenoids can be
spontaneously transferred from lipid droplets to mixed micelles. Because of their
large size, the droplets are not able to gain proximity to the absorptive surfaces of
the small intestine for carotenoid transfer to enterocytes (Combs 1996).
Instead, as a result of lipase action, the droplets are degraded to form mixed
micelles. The hydrophobic cores of the micelles contain non-polar, nonamphiphilic
lipids, such as cholesterol and oxycarotenoids, which partition between the oil and
micellar phases. Carotenoid absorption from the intestinal tract is associated with
the same intraluminal, membrane and intracellular events as have been described
for dietary lipids (Krogdahl 1985) although some specific features relating to the
site of absorption of various carotenoids in birds have been described (Tyczkowski
and Hamilton 1986b). This process includes emulsification, solubilisation, diffusion
across the unstirred water layer, permeation through the membrane of the enterocytes,
incorporation into lipoprotein particles and release into the circulation via lymphatic
pathways in mammals (Cohn 1997), or the portal system in birds. Carotenoid absorption is a very delicate and sensitive process and an impairment of any of these stages
can decrease carotenoid assimilation from the diet. In birds, lipid digestion starts in
the gizzard where bile salts and pancreatic lipases are responsible for about 30%
of dietary triglyceride hydrolysis (Sklan et al. 1978). Emulsification of dietary fat is
accelerated greatly as the chyme moves into the small intestine and is mixed with bile
and pancreatic secretion. The jejunum is the major site of lipid absorption in birds,
although some absorption occurs in the ileum (Hurwitz et al. 1973). It has been shown
that lutein is absorbed in the duodenum and jejunum (Hamilton 1992) but absorption
of zeacarotene takes place mainly in the ileum (Tyczkowski and Hamilton 1986a, b).
Carotenoid absorption takes place by unsaturable, passive diffusion down a concentration gradient similar to other nonpolar lipids (Hamilton 1992), although some
519
22.2 (18.8–27.9) (Middendorf et al. 1980). In this experiment, statistically significant differences among samples within and among generic sources were obtained.
Furthermore, xanthophyll (lutein + zeaxanthin) concentrations in different feed vary
substantially (mg/kg): lucerne meal (40–260), grass meal (140–500), yellow maize
(8–40), plate maize (10–50) and maize gluten meal (60–360) (Belyavin and Marangos
1989).
The main dietary sources of carotenoids in poultry nutrition are maize, maize
products, lucerne, alfalfa meal (organic egg production) and commercial concentrated forms including marigold and paprika (Nys 2000). Most of the mentioned
feedstuffs provide mainly lutein and zeaxanthin plus β-carotene (alfalfa meal) and
β-cryptoxanthin (maize and maize gluten). Our data indicate that a major difference
between the American maize-based diet for breeders and the European wheat-barley
based diet is in the level of carotenoids (lutein + zeaxanthin), which is more than
twice higher in the maize-based diet (Surai and Sparks 2001). This difference is due
to a low carotenoid content of wheat and barley although both feeds contain lutein
and zeaxanthin as major carotenoids. The main factors affecting carotenoid transfer
to the egg yolk are shown in Table 20.1.
After ingestion of feed, carotenoids are released from the matrix by digestive
enzymes. The liberated carotenoid compounds together with other feed lipids are
emulsified in the presence of bile salts to form oil droplets. Carotenoids can be
spontaneously transferred from lipid droplets to mixed micelles. Because of their
large size, the droplets are not able to gain proximity to the absorptive surfaces of
the small intestine for carotenoid transfer to enterocytes (Combs 1996).
Instead, as a result of lipase action, the droplets are degraded to form mixed
micelles. The hydrophobic cores of the micelles contain non-polar, nonamphiphilic
lipids, such as cholesterol and oxycarotenoids, which partition between the oil and
micellar phases. Carotenoid absorption from the intestinal tract is associated with
the same intraluminal, membrane and intracellular events as have been described
for dietary lipids (Krogdahl 1985) although some specific features relating to the
site of absorption of various carotenoids in birds have been described (Tyczkowski
and Hamilton 1986b). This process includes emulsification, solubilisation, diffusion
across the unstirred water layer, permeation through the membrane of the enterocytes,
incorporation into lipoprotein particles and release into the circulation via lymphatic
pathways in mammals (Cohn 1997), or the portal system in birds. Carotenoid absorption is a very delicate and sensitive process and an impairment of any of these stages
can decrease carotenoid assimilation from the diet. In birds, lipid digestion starts in
the gizzard where bile salts and pancreatic lipases are responsible for about 30%
of dietary triglyceride hydrolysis (Sklan et al. 1978). Emulsification of dietary fat is
accelerated greatly as the chyme moves into the small intestine and is mixed with bile
and pancreatic secretion. The jejunum is the major site of lipid absorption in birds,
although some absorption occurs in the ileum (Hurwitz et al. 1973). It has been shown
that lutein is absorbed in the duodenum and jejunum (Hamilton 1992) but absorption
of zeacarotene takes place mainly in the ileum (Tyczkowski and Hamilton 1986a, b).
Carotenoid absorption takes place by unsaturable, passive diffusion down a concentration gradient similar to other nonpolar lipids (Hamilton 1992), although some