Investigation of the Effects of Oat and Barley Feeding on Performance and Some Lipid Parameters in Table Ducks

: The effects of barley and oat feeding in table duck were investigated. During a 49-day growing period a corn-based diet was supplemented by 45% barley and 45% oats (isonitrogenously and iso-energetically), respectively. Daily feed intake, FCR-, and weight gain were measured. Abdominal fat, liver, and gizzard weights were determined and dry matter, protein, fat content and fatty acid composition of femoro-tibial muscles and liver fat were measured on the 35 th , 42 nd and 49 th days of age. Feeding 45% barley caused a decrease of growth rate (p ≤ 0.05) during the first 4 weeks, which was followed by a rapid, compensatory growth from the 6 th week of age (p ≤ 0.05). Both barley and oat supplementation increased protein (p ≤ 0.05), while decreasing fat (p ≤ 0.05) and dry matter (p ≤ 0.05) content of the liver. Feeding of 45% oats in the diet decreased the monounsaturated fatty acid (p ≤ 0,05) and increased the n-6 (p ≤ 0,05), n-3 (p ≤ 0,05) and total polyunsaturated (p ≤ 0,05) fatty acid content of the intramuscular fat owing to the high proportion of soluble non-starch polysaccharides (NSP) in the diet. This might be explained by the more pronounced decrease in digestibility of saturated than unsaturated fatty acids in birds fed a soluble NSP-enriched diet. This result might be caused by the “cage effect” of soluble NSP trapping the bile salts which are more important for the absorption of saturated than polyunsaturated fatty acids.


INTRODUCTION
Fatty acid composition of animal tissues depends on different factors such as species, breed, sex, diet and feeding regime. Changes in fatty acid composition have an effect on the quality of meat (Cho et al., 2005). Polyunsaturated fatty acids in the diet are considered as essential dietary lipids in humans and have an important role in prevention of cardiovascular disease (Khanal, 2004).
Non-starch polysaccharides (NSP) have anti-nutritive properties in monogastric animals, e.g. ducks  because soluble viscous NSP is associated with an increase in digesta viscosity (Dusel et al., 1997), and for that reason may reduce the connection between nutrients (e.g. fat) and digestive enzymes (e.g. lipase) and the transport of substrates to the epithelial surface. Alternatively,  found that the antinutritive effect was attributable to a specific interaction, called "cage effect", rather than the viscosity of soluble NSP. Viscous soluble NSPs have a "matrix" molecular structure and are able to entrap bile salts within the gastrointestinal tract (Ebihara and Schneeman, 1989) which could be the reason for reduced solubilization of fat components and decreased lipid absorption (Smits and Annison, 1996). Choct et al. (1996) reported that digestibility of fatty acids was reduced by feeding of a NSP-enriched diet, but the effect was more severe on saturated than on unsaturated fatty acids in broiler chickens. Our research group also found a reduction in digestibility of crude fat when feeding a soluble NSPenriched diet to waterfowl (Vetési et al., 1997a).
The β-glucan content of barley is considered the most important anti-nutritive, soluble and viscous NSP of that cereal. The effect might be increased in the presence of arabinoxylans (Jeroch et al., 1992;, especially during the first weeks of life. Recently oats and oat products have become of research interest because of their role in improving carbohydrate metabolism (Bach Knudsen et al., 1990) and reducing cholesterol level (Chen and Anderson, 1986) due to their soluble and/or insoluble NSP content. Oats, and especially oat bran, are rich in soluble dietary fiber (NSP plus lignin) in the form of mixed linked β (1-3; 1-4)-D-glucan, which is an easily fermentable energy source for microflora in the large intestine of the pig (Bach Knudsen et al., 1993). The other main soluble NSP in oats are arabinoxylans, which are primarily responsible for butyrate production in the large intestine (Bach Knudsen et al., 1993), and it was also reported that addition of oat bran to the diet decreased the digestibilities of energy, protein and fat in the terminal ileum of pigs.
The main objectives of the present study were to investigate the effects of soluble NSP-enriched oat and barley on lipid metabolism, especially the fatty acid profile of the femoro-tibial muscles and liver, in table ducks.

Animals, diets and performance traits
In these experiments K94-breed ducks (Szarvas, Hungary) were used with a sex ratio of 1:1 and 50 birds in each group which were grown following procedures for standard Peking-type duck technology. The ducks were reared under floor management on wheat straw. Light was provided continously in a temperature-controlled room with stock numbers of 1.6 per square meter during the first 2 weeks of age. From the 3 rd week of age birds could use a separated, open-air, concrete-based paddock and flume all day. Feed and water were available ad libitum. 25 male and 25 female ducklings were grown in one block together and fed pelleted starter diet to the 14 th day of age and finisher diet from the 15 th to the 49 th day of age.
Treatment groups (50 birds/group) were as follows: i) control (corn based diet) ii) 45% barley in the diet (isoenergetic and isonitrogenous composition based on AME n and nitrogen content) iii) 25% oats in starter and 45% oats in finisher diet (isoenergetic and isonitrogenous composition based on AME n and nitrogen content).
The reduced oat level in the starter diet was applied to avoid digestion problems in young ducks because of extremely high fiber content.
The composition and calculated nutrient content of the diets are shown in Table 1. Daily feed intake and individual live weight in each week were measured during the experiment. Abdominal fat weight, liver and gizzard weight were determined on the 35 th , 42 nd and 49 th days of age, respectively. Ten randomly selected birds from each group (50 birds/group) were slaughtered by cervical dislocation, bled and dissected. Sexes were separated by individual badges (worn on bird wings) installed after post-hatch sex identification. Grill weight (carcass: without alimentary tract, heart, abdominal fat, legs from tarsus and neck) was determined on the 49 th day of age only. Muscles adhering to the femur and tibia (without the skin and subcutaneous fat) and the liver were dissected from each bird, homogenized and deep frozen until chemical analyses.

Chemical analyses
Chemical composition of feed, muscle and liver : Dry matter, crude protein and crude fat content of feed, femorotibial (FT) muscles and liver were determined according to Hungarian National Standard Methods (Hungarian Feed Codex, 2000).

Statistical analysis
All results were calculated as the means ± SEM of measurements. Statistical analysis was performed by SPSS 14.0 for Windows (ANOVA and Duncan Range Post Hoc test).

Performance traits
Depressed weight gain was found during the first 5 weeks using 45% barley in the diet compared to the control birds, however a significant increase (p<0.01) was observed during the last two weeks. Due to that rapid growth the terminal live weight was similar to the control group. A slight increase was found in feed intake and cumulative feed conversion ratio (FCR) of the barley-fed group as compared to the control (Table 2). Similar slaughter weight, higher feed intake and cumulative FCR values were observed in ducks fed the oat-based diet to those in the control group (Table 2). Treatment, sex and age did not have any significant effect on the relative liver weight (p>0.05; Table 3).
Abdominal fat content increased with age in both sexes and each treatment group, but fat deposition was the most intensive during the last week, between the 42 nd and 49 th days of age (p<0.001 male, p<0.01 female in control group) Higher weight of abdominal fat pad was observed in the case of female ducks as compared to males on the 35 th , 42 nd and 49 th days of age in each group.
Proportion of abdominal fat in the carcass of ducks fed the oat-based diet decreased from the 35 th day of age in both sexes as compared to the control (p<0.01 female; p<0.05 male) while a slight (not significant) increase was observed in the group fed 45% barley (Table 3).
Grill weight was the same in each group on the 49 th day of age (Table 3).

Chemical composition of muscle and liver
Femoro-tibial muscles : Dry matter and fat content of FT muscles decreased with age, while protein content increased between the 35 th and 42 nd day of age in each group. Later, between the 42 nd and 49 th day of age, age had no effect on chemical composition of the FT muscles. Significant differences or trends in chemical composition of FT muscles among the treatments were not observed (Table  4).
Liver : Fat content of liver was decreased with age between the 35 th and 42 nd day of age in the groups fed oatand barley-based diets. During that period protein content increased, while dry matter content was slightly lower in the oat-fed group. Age-dependent increase in the crude protein and decrease in the dry matter content was found in the barley-fed group one week later (42 to 49 days of age).
Significantly lower fat (p<0.05 barley and oat male; p<0.01 barley female; p<0.001 oat male), and higher crude protein (p<0.01) and lower dry matter (p<0.05) content were found in oat-and barley-fed groups as compared to the control on the 49 th day of age.

Fatty acid composition
Fatty acid composition of the FT muscles and liver is presented in Table 5 and 6. The results showed that the applied treatments (45% barley and 45% oat in the diet) had more significant effect on the fatty acid composition of liver than of muscles.
Femorotibial muscles : MUFA content was lower (p<0.05) in males, while total n-6 (p<0.01) and n-3 fatty acids (p<0.001) as well as total PUFA content of FT muscle were higher (p<0.01 male; p<0.05 female), on the oat-based diet on the 49 th day of age. The barley-based diet did not have a significant effect on the fatty acid composition in muscle lipids (Table 5).
Liver : Feeding oat-based diet caused significantly lower MUFA content (p<0.01 male; p<0.001 female), and higher total n-6 (p<0.01 male; p<0.001 female), total n-3 (p<0.001), and PUFA content (p<0.01 male; p<0.001 female) of liver compared to the control on the 42 nd and 49 th days of age. Similar results were found on the 49 th day in the 45% barley-fed group (Table 6).

Performance traits
Feeding 45% barley in an isoenergetic and isonitrogenous diet caused decreased growth rate and increased FCR in young ducks during the first 5 weeks of age. Owing to the higher amount of entirely undigestible fiber (ADL-content of control: 9.1 g kg -1 , 45% barley: 13.9 g kg -1 in starter diet), insoluble fiber with poor digestibility (ADF-content of control: 45.3 g kg -1 , 45% barley: 56.3 g kg -1 in starter diet) and presumably non-or poorly digestible soluble fiber (soluble NSP-content of control: 16.8 g kg -1 , 45% barley: 36.6 g kg -1 in starter diet), this feeding regime can be considered as nutrient restriction even in the case of higher feed consumption (exceeding amount of non-or poorly digestible fiber reduces digestibility of the other nutrients, as protein and fat). It was followed by more rapid, compensatory growth, a finding which is supported by the results of Vetési et al. (1997b) in table ducks, and in broiler chickens by Wiseman (1988). The first weeks can be considered as an adaptation period for intestinal microorganisms, when a proliferated microbial population can produce adequate amounts of β-glucanase for enzymatic degradation of the fiber components (Jeroch    , 1995). Contrary to the effect of the barleybased diet, growth depression was not found as an effect of feeding the oat-based diet which is similar to the previous finding of Vetési et al. (1998). A possible explanation might be that the oat-based starter diet contained less soluble NSP compared to the barley-based starter diet (soluble NSPcontent of 45% barley: 36.6 g kg -1 and 25% oat: 24.2 g kg -1 in starter diet). The 45% oats in the diet resulted in higher FCR than the control diet, which may be considered as an anti-nutritive effect owing to the high proportion of non-or poorly digestible non-soluble fiber components (25% oat-ADF: 71.6 g kg -1 and ADL: 14.9 g kg -1 in starter diet, 45% oat-ADF: 90.6 g kg -1 and ADL: 18.9 g kg -1 in finisher diet).

Organ weight
Feeding barley-based diet slightly improved the abdominal fat deposition, but did not affect the relative weight of liver, gizzard and grill carcass. Wiseman (1988) also observed that compensatory growth is associated primarily with fat deposition in broiler chickens. Mollison et al. (1984) found that early dietary fat restriction caused an increase in abdominal adipose tissue weight at 7 weeks in broiler chickens. Fat deficiency at a young age may also account for the increase of abdominal fat deposition in the present study since a soluble NSP-enriched diet (and higher consumption rate) can trap the bile acids and reduce fat digestibility.
The oat-based diet caused slightly lower abdominal fat content as compared to control birds and the difference was more pronounced in male ducks, because of the lack of compensatory growth. The high dietary fiber content (25% oat: 182.4 g kg -1 in starter diet, 45% oat: 217.4 g kg -1 in finisher diet) of the diet improved the weight of gizzard since it may stimulate the function of this organ as also found by Vetési and Bokori (1990) in geese which consumed green alfalfa as compared to a cereal grain-based diet.

Organ composition
The barley-based diet did not have any marked effect on chemical and fatty acid composition of femoro-tibial muscles. However, the oat-based diet decreased the MUFA and increased n-6 and n-3 PUFA content of the intramuscular fat. The barley-and oat-based diets significantly modified the liver fatty acid composition. Previously it was found (Bartov, 1992) that size, fat content and fatty acid composition of the liver responded to feed withdrawal, while there were no changes in concentration or fatty acid composition of fat in breast and thigh muscles (Hulan et al., 1989). These results also suggest that the liver is a more sensitive indicator of changes in lipid metabolism than muscle. In present study 45% barley and 45% oats in the diet increased protein while decreasing fat and dry matter content of liver. The quantitative changes in the chemical composition, namely decreased fat content, of liver caused by barley-and oat-based diets occurred simultaneously with the qualitative changes in fatty acid composition during the last three weeks of the experiment. Contrary to the decrease in the fat and MUFA content of the liver, the barley-and oat-based diets caused an increase in total n-6 fatty acids and total n-3 fatty acid content. These changes cannot be explained by the differences in fatty acid composition of the diets, since the barley-and oat-based diet contained slightly more SAT, MUFA, total n-3 fatty acids and less or similar total n-6 fatty acids and PUFA than the control (Table 1). It may be explained by the results of Choct et al. (1996) who reported more pronounced decrease in the digestibility of saturated than unsaturated fatty acids of birds fed an increasing amount of soluble NSP in the diet. That result might be caused by the "cage effect" of soluble NSP trapping the bile salts which are more important for the absorption of saturated fatty acids than PUFA. Reduction of fat and increase of PUFA, mainly n-3 fatty acid, content in meat is a focus of research. However, although poultry meat contains low fat and a high amount of unsaturated fatty acids, further modification would be advantageous. Most of the vegetable oils increase the linoleic acid content of poultry meat without negative effect on its flavour, but they usually do not increase its EPA and DHA level (Hawrysh et al., 1980;Salmon et al., 1981;Chanmugam et al., 1992). In our study oats have increased n-6 and n-3 content of the femoro-tibial muscles and liver fat.
Lipid peroxidation is considered to be an important factor in affecting flavor, stability and nutritive value of poultry meat. There is a positive correlation between oxidative stability of poultry meat and dietary PUFA levels (Manilla, 1999). Lopez-Bote et al. (1998) reported that an oat-based diet enhanced oxidative stability of chicken meat, so they suggest oats as a natural antioxidant.
Owing to its positive effect on lipid composition of table duck meat, liver and antioxidant activity, an oat-based diet would be a possible way of improving waterfowl meat quality.

CONCLUSIONS
Barley and oats modify the lipid metabolism, since barley improved the abdominal fat deposition while oats reduced weight of abdominal fat pad in ducklings.
Barley and oats as a high proportion of the diet (45% in finisher diet) modified the chemical composition of liver but did not have an effect on muscle composition. An oatbased diet decreased MUFA and increased n-6, n-3 PUFA content of the intramuscular fat, and significantly modified the liver fatty acid composition.
In summary, oat-based diet would be a possible way to improve waterfowl meat quality owing to the proven positive effect of oats on lipid composition of table duck meat and liver.