J. R. Roberts, W. Ball and E. Suawa
School of Rural Science and Agriculture,
University of New England, Armidale, Australia
In Trial 1, 4 enzymes were added to wheat-based layer diets and fed to Isa Brown laying hens from 25 weeks of age. In Trial 2 (50 to 65 weeks of age), all diets were based on wheat or wheat containing 20% cereal rye. Egg quality, apparent metabolisable energy (AME) and excreta moisture were measured every 5 weeks. The AME of the diets was similar for the diets in both trials. Excreta moisture was not affected by enzymes in either trial. Egg quality varied with hen age and was significantly better for normal wheat than pinched wheat and for wheat + rye versus wheat. There were some effects of enzymes on egg quality. Production was not affected by type of diet or enzymes in either trial. Digesta viscosity was not affected by the addition of enzymes but was greater when rye was added.
Introduction
Enzymes are added to commercial layer diets to increase the digestibility of feed ingredients, reduce the incidence of wet droppings resulting from non-starch polysaccharides in the diets (Acamovic, 2001) and to increase the availability of feed microingredients which influence egg shell quality (Hurwitz, 1987). A recent study showed that addition of commercial enzyme preparations improved eggshell quality in wheat-and barley-based layer diets but that there were some negative effects on shell colour and Haugh Units (Roberts and Choct, 1999; Roberts et al., 1999). In Australia, wheat is a common ingredient in layer diets. However, the quality and composition of Australian wheats are variable (Choct and Hughes, 1996). The present study was therefore conducted to investigate the effect of dietary enzymes and wheat quality on egg and eggshell quality in Isa Brown laying hens.
Material and Methods
For Trial 1, two basal diets were formulated to standard commercial specifications, each containing 670 g/kg of either "normal" wheat or "pinched" wheat (water-stressed prior to harvest). The other ingredients were identical in the two diets.
The basal diets were each used to prepare five experimental diets by adding one of four commercial feed enzyme preparations according to the manufacturers' instructions; a control diet of each wheat type (no enzyme added), Biofeed Wheat (175 g/tonne), Avizyme 1302 (265 g/tonne), Roxazyme G2 granular (100 g/tonne), or Kemzyme W dry (600 g/tonne).
For Trial 2, all diets were based on "pinched" wheat and, for the birds that had previously received the "normal" wheat, 20% of the pinched wheat was substituted with cereal rye.
In Trial 1, the diets were fed from 25 to 50 weeks of age to 760 Isa Brown laying hens which were maintained, three to a cage, in a commercial poultry house at the University of New England "Laureldale" Poultry Farm. The different treatment groups were randomised to avoid effects due to position in the poultry house.
Trial 2 was conducted on the same birds at 50-65 weeks of age. Egg and eggshell quality were assessed at 27 and 30 weeks of age, then at 5 weekly intervals. At each age, 300 eggs were collected, 30 from each of the ten treatment groups. Egg and eggshell quality analyses were completed within 24 hours of the eggs being laid. Measurements taken to assess eggshell quality were egg weight, shell reflectivity (an indication of the colour of the egg shell), egg shell breaking strength (measured by quasi-static compression), deformation (the distance that the egg shell is depressed by the shell breaking strength machine before the shell cracks) and shell weight (Technical Services and Supplies, U.K.). The percentage shell was calculated as the ratio of shell weight to egg weight, expressed as a percentage. The internal quality of the eggs was assessed as albumen height and Haugh Units as well as yolk colour. Apparent metabolisable energy (AME) and excreta moisture were measured every five weeks from 30 to 65 weeks of age. AME was determined by the conventional total collection procedure.
Birds had received the experimental diets for at least five weeks prior to the AME assays, which were conducted over 4 days. Feed intake was measured and all excreta collected daily. Excreta were dried in a fan-forced oven at 80ºC for 36 hours and excreta from each replicate were pooled over the collection period for the determination of gross energy (GE).
AME of diets was calculated as:
At the end of Trial 2, digesta were collected from 5 birds from each diet, centrifuged and the viscosity of the supernatant determined using a Brookfield DVIII Model viscometer. Data were analysed by ANOVA with bird age, wheat type and enzyme treatment as independent variables. Differences between means were assessed by Fisher's (Protected) Least Significance Difference test. Significance was assumed at P<0.05.
Results and discussion
Contrary to expectation, on analysis the two wheats used in Trial 1 were found to be similar for total, soluble and insoluble non-starch polysaccharides. Protein analysis of both wheats and the control diets prepared from them showed that the crude protein level was higher for pinched wheat (178 g/kg in the wheat, 228 g/kg in the final diet) than for normal wheat (149 g/kg in the wheat, 185 g/kg in the final diet). However, the average AME of the two diets from 30 to 50 and 50-65 weeks of age was similar. AME increased to 40 weeks of age (p<0.0001) and remained relatively constant (Table 1).
Feed intake and excreta moisture of birds on the two wheat diets in Trial 1 and the wheat and wheat + rye in Trial 2 were also similar, as was production. The addition of commercial enzyme preparations had no significant effect on AME, excreta moisture or production in either trial (data not shown).
At the end of Trial 2, digesta viscosity was significantly higher for the wheat + rye diet than for the wheat diet in both the jejunum (wheat 1.95 cP, wheat + rye 3.19 cP) and the ileum (wheat 3.57 cP, wheat + rye 8.88 cP) but was not affected by the addition of commercial enzyme preparations.
Egg and eggshell quality, in general, deteriorated with the age of the hens (data not shown). Egg weight and shell weight increased although the increase in shell weight was not proportional to that of egg weight, resulting in a reduction in the percentage shell. Shell thickness decreased from 27 to 35 weeks of age and then increased. Haugh Units deteriorated with increasing hen age, and yolk colour increased overall. The age-related changes in egg and eggshell quality are similar to those reported previously.
In Trial 1, eggs laid by birds receiving diets based on normal wheat had greater shell breaking strength, Haugh Units, percentage shell, shell weight and shell thickness, and darker shell colour than those given pinched wheat (Table 2).
For Trial 2, pinched wheat containing 20% cereal rye resulted in better egg quality than the diet containing only pinched wheat (Table 3).
The type of grain on which diets are based therefore appears to have had direct effects on egg quality.
Enzyme type and/or inclusion had significant effects on shell breaking strength, shell reflectivity, yolk colour, percentage shell and shell thickness in Trial 1 and shell colour and albumen quality in Trial 2 (Table 4). Shell breaking strength was lower on diets with Biofeed Wheat or Avizyme than for the control, Roxazyme and Kemzyme. Shell reflectivity was slightly but significantly higher for diets with Roxazyme or Kemzyme. Percentage shell and shell thickness were highest for Kemzyme whereas yolk colour varied, being highest for the control and lowest for Avizyme.
The improved shell breaking strength observed in a previous study in eggs from birds given enzymes (Roberts and Choct, 1999; Roberts et al., 1999) was not found in the present study. This may be due to differences in feed ingredients used in the two experiments. However, the decrease in shell colour in response to dietary enzyme inclusion was consistent across the two studies.
Percentage shell and shell thickness were improved only by Kemzyme in Trial 1. However, Kemzyme had negative effects on shell colour and albumen quality during Trial 2. Yolk colour was slightly lower than the control for all diets containing enzymes in Trial 1. However, all treatment groups had yolk colour at very acceptable levels. In conclusion, both type of wheat and the addition of commercial feed enzyme preparations had effects on egg and eggshell quality.
Acknowledgements
The support of the Egg Program of the Australian Rural Industries Research and Development Corporation (now the Research and Development of Australian Egg Corporation Limited) for this study is gratefully acknowledged. We thank Ridley AgriProducts, Tamworth, Australia for formulation and manufacture of the diets, the enzyme companies for their cooperation in this study, and colleagues and staff of the University of New England for advice and assistance.
References
Acamovic, T. 2001. Commercial application of enzyme technology for poultry production. Worlds Poult. Sci. J. 57: 225-242.
Choct, M., and B. Hughes. 1996. The nutritive value of Australian wheats for poultry: Results of a 3-year survey. Proceedings of the Queensland Poultry Science Symposium 5: 6.1-6.6.
Hurwitz, S. 1987. Effect of nutrition on egg quality. In: Egg quality – current problems and recent advances. pp. 235-254. Ed. R.G. Wells and C.G. Belyavin, Butterworths, London.
Roberts, J.R., and M. Choct. 1999. The use of commercial enzymes and egg and eggshell quality in four strains of laying hens. Proceedings of the VIII European Symposium on the Quality of Eggs and Egg Products, Bologna, Italy: 113-118.
Roberts, J.R., M. Choct and W. Ball. 1999. Effect of different commercial enzymes on egg and egg shell quality in four strains of laying hens. Proceedings of the Australian Poultry Science Symposium, Ed. D.J. Farrell. 11: 139-142.
From Proceedings of the "XVI European Symposium on the Quality of Poultry Meat" and the "X European Symposium on the Quality of Eggs and Egg Products", Saint-Brieuc Ploufragan, France.
