J.R. Roberts
W. Ball
Animal Physiology, School of Rural Science and Agriculture
University of New England
Armidale, NSW
Australia
Diets based on wheat, barley or sorghum were fed to younger and older laying hens for a period of 12 weeks. Production and weekly egg mass were higher for the younger birds and feed intake and feed conversion efficiency were higher for the older hens, with no effect of diet. Egg shell quality and egg internal quality were better for the younger hens. The sorghum diet resulted in eggs with better shell quality but lighter shell colour and lower albumen quality. AME was higher for the older birds and differed among diets, with sorghum the highest and barley the lowest. Excreta moisture was higher for the wheat and barley diets than the sorghum diet, and higher for the older birds. The digesta viscosities of the jejunum and ileum were higher for the wheat and barley diets than for the sorghum diet and not different between the younger and older hens.
I. Introduction
In Australia, layer diets are usually based on wheat, sorghum, barley or a combination of these grains. Concern has been expressed about the use of barley and some wheats (e.g. new season wheats) in poultry diets, because the presence of non-starch polysaccharides (NSP) in these grains may result in anti-nutritive effects that appear to be caused by high viscosity of the contents of the digestive tract (Choct and Annison, 1992; Leeson and Summers, 2001). However, most of this research has been conducted with broilers and it is unclear to what extent the results can be extrapolated to laying hens. In addition, it is not clear whether the age of the hens has any influence on the response.
A previous study showed that increased digesta viscosity resulting from the inclusion of cereal rye in a wheat-based layer diet did not have any negative effects on bird performance (Roberts et al., 2003).
In the present study, diets based on wheat, barley or sorghum were fed to laying hens of two different ages and production, feed intake, feed conversion ratio, egg quality, apparent metabolisable energy (AME), digesta viscosity and excreta moisture measured.
II. Materials and methods
Diets based on wheat, barley or sorghum were formulated by a consultant nutritionist to typical Australian commercial standards. Diets were of equal energy levels, and very similar crude protein levels (wheat 165 g/kg; barley 177 g/kg, sorghum 165 g/kg) and were manufactured at the University of New England.
Each of these three diets was fed to 25 younger Isa Brown laying hens (26 weeks of age at the start of the experiment) and 25 older Isa Brown laying hens (78 weeks of age at the start of the experiment), a total of 6 experimental groups, housed in individual bird cages. The older birds had been moulted at 65 weeks of age.
The diets were fed for 12 weeks during which time production and egg weight of all eggs laid were measured daily, and feed intake was measured weekly. Egg mass and feed conversion ratios (feed consumed/egg mass) were calculated weekly. Eggs production was determined for all birds prior to the commencement of the experiment and then at 4-week intervals.
When birds were 39 and 91 weeks of age, apparent metabolisable energy (AME) was measured, in 10 birds from each of the 6 experimental groups, by the total collection procedure. At the end of the experiment, the birds used for the AME measurements were euthanased and the contents of the jejunum and ileum collected. The digesta from the jejunum and ileum were centrifuged at 15000 RPM for 15 min and the supernatant taken for measurement of digesta viscosity (Brookfield DVIII viscometer).
III. Results
Diet had no effect on body weight, production, weekly egg mass or feed conversion ratio (P>0.05). The older birds had significantly higher body weight than the younger birds throughout the experiment. For the 12 weeks of the experiment, production (P<0.01) and weekly egg mass (P=0.01) were significantly higher in the younger birds than the older birds and feed intake (P<0.01) and feed conversion ratio (P=0.03) were higher for the older birds (Table 1).
For all egg collections combined, there were significant differences in egg quality among the diets (Table 2). The sorghum diet resulted in lighter shell colour (younger birds) but higher breaking strength, shell weight, percentage shell and shell thickness (older birds) than the wheat and barley diets which were not significantly different from each other (P>0.05). For egg internal quality, albumen height and Haugh Units were highest for the wheat diet, and lowest for the sorghum diet, with barley intermediate. Egg internal quality and egg shell quality were better for the younger birds than for the older birds (Table 2), with shell colour being darker (based on reflectivity measurements) and breaking strength percentage shell, albumen height and Haugh Units being higher for the younger birds (P<0.01).
AME varied significantly among the diets (P<0.01), being highest for the sorghum diet, lowest for the barley diet, with the wheat diets intermediate (Table 3). There was also a significant main effect of bird age (P<0.01) on AME, with AME being higher in the older birds than the younger birds. There was a significant interaction between age and diet for AME. Excreta moisture measured during the AME determinations was higher for the older birds, as compared with the younger birds (P=0.02) and higher for the wheat and barley diets than for the sorghum diet (P<0.01).
Digesta viscosity was consistently higher (P<0.01) for the ileum than the jejunum. There were significant differences among the diets for digesta viscosity of both the jejunum (P<0.01) and the ileum (P<0.01) with digesta viscosity being similar for wheat and barley and higher for these two diets than for the sorghum diet (Table 4). However, there was no difference in digesta viscosity of either the jejunum or ileum between the older and younger hens. There was a significant inverse linear relationship between AME and digesta viscosity of both the jejunum (P<0.01) and ileum (P=0.01) for all diets combined. However, there was no significant relationship when each diet was considered separately.
Analysis of the three diets indicated that the levels of total NSP were similar for the wheat and sorghum diets (92.9 and 87.8 g/kg, respectively), with the barley diet being higher (135.7 g/kg). Insoluble NSP was also very similar for wheat and sorghum diets (83.7 and 83.6 g/kg, respectively), with barley being higher (112.6 g/kg). However, the levels of soluble NSP differed being 9.2, 23.1 and 4.3 g/kg for the wheat, barley and sorghum diets, respectively. Extract viscosities (centipoise) of the finished diets were: wheat 4.11, barley 2.89 and sorghum 2.46.
IV. Discussion and conclusions
Although the three diets differed in levels of non-starch polysaccharides, both the younger and older hens performed well on all diets. Although production was relatively high for the older birds, losses of eggs owing to poor shell quality resulted in a reduced egg mass. As would be expected, egg internal quality and egg shell quality were better for the younger birds. Although production, egg mass and feed conversion ratio did not differ among diets, egg shell quality was best for birds on the sorghum, particularly for the older birds. However, there were negative effects of the sorghum diet on shell colour in the younger birds and albumen quality in the older birds. It is not clear to what extent egg shell quality is correlated with the NSP levels in the diets because the wheat and barley diets differed in their levels of soluble, insoluble and total NSP but resulted in very similar egg quality. In addition, previous studies (Roberts et al., 2002, 2003) found differences in egg quality between diets based on two different wheats and also when 20% cereal rye was substituted for wheat in a wheat-based diet.
These findings suggest that adult laying hens cope well with a range of dietary ingredients, provided that the diets are properly formulated. However, the results provide more evidence that the grain on which a layer diet is based can affect egg shell quality and egg internal quality by mechanisms that are not fully understood at the present time.
V. Acknowledgements
This project was supported by a grant from the University of New England. The formulation of the diets by Mr. Rowley Horn of Rowley Horn Services is gratefully acknowledged. The authors thank Mr. David Curtis of Ridley AgriProducts, Tamworth, for assistance in sourcing feed ingredients.
References
Choct, M. and Annison, G. (1992). British Poultry Science 33: 821-834.
Leeson, S. and Summers, J.D. (2001). Scott's Nutrition of the Chicken. 4th Ed. University Books, Guelph, Canada.
Roberts, J.R., Ball, W. and Suawa, E. (2002). Proceedings of the Australian Poultry Science Symposium (R. Pym, Ed) 14: 137-140.
Roberts, J.R., Ball, W. and Suawa, E. (2003). Proceedings of the Australian Poultry Science Symposium (R. Pym, Ed) 15: 108-111.
From Proceedings of the "2004 Australian Poultry Science Symposium", New South Wales, Australia.
