The
              Report

No 75: Factors Affecting Egg and Egg Shell Quality in Laying Hens


The full report
This is a summary of the RIRDC full report (UNE-43A) titled "Factors affecting Egg and Egg Shell Quality in Laying Hens" by Juliet R.Roberts (with Alison Leary). A copy of this full report ($10) is available from Dr Irene Gorman on phone 02 9570 9222, Email ireneg@rirdc.gov.au 

The Australian consumer expects and demands high standards for all food products,including eggs and egg products.

Most eggs in Australia are sold as shell eggs and they must reach the market place in a condition which is acceptable to the consumer.Problems with the quality of eggs and egg products have the potential to cause health risks and undermine the confidence of consumers in the quality and safety of the product.

Losses to the Australian Egg Industry as the result of problems with egg and egg shell quality have been estimated to be in excess of ten million dollars annually.

Even a small percentage improvement in the overall quality of eggs and egg shells could result in significant savings to the industry in an increasingly competitive environment.

The internal quality of eggs and the quality of the egg shells are influenced by many factors.

These include bird strain,bird age,nutrition, disease,management practices,water quality, housing conditions,temperature,disturbance or stress.Sometimes,a number of these factors will interact to cause a problem.Because of these interactions,the causes of egg and egg shell quality problems are often difficult to diagnose.

The following research was conducted at the Armidale campus of the University of New England and documents a range of factors which influence egg and egg shell quality.

The Investigation

An aim of these investigations was to provide scientifically-documented evidence of factors influencing egg and egg shell quality.

The Infectious Bronchitis Virus

This experiment was conducted to assess the effect of exposure of hens to different strains of infectious bronchitis virus (IBV)on egg and egg shell quality.The birds had been vaccinated previously,according to standard commercial practice.Therefore,the experiment simulated an intercurrent infection in the field situation.

Challenge with IBV of previously vaccinated laying hens produced relatively small changes in egg shell quality,although there were changes in the appearance of the eggs,including changes such as an increased number of “pimpled ” eggs and lighter coloured shells.The types of changes in egg shell appearance were related to the strain of IBV with which then hens were challenged.

These findings emphasise the importance of appropriate vaccination programs in protecting hens against intercurrent infections.

Moulting

The management practice of "forced" or "induced" moulting has been shown to improve eggshell quality and egg production in an ageing flock.In this experiment,moulting was induced according to the Australian Model Code of

Practice for Welfare of Domestic Poultry (1995) and resulted in a reduction in egg production within 48 hours.All birds had gone out of lay within 8 days and did not resume production until 2-3 weeks later.Egg shell quality was examined in three strains of layer,one imported (Isa Brown)and two Australian (Hy-Line Tint and SIRO-CB),prior to the induced moult,during the moult (as birds were going out of production), and at intervals after the birds resumed production.Figure 1 shows the percentage production of eggs throughout the moult period. Figure 2 shows the increase in egg weight during the initial stages of the post-moult period.

Following the moult,egg specific gravity,shell weight,shell thickness and percentage shell were either the same as they had been prior to the moult,or had improved,for all three strains. Egg shell breaking strength was improved in all strains as the result of the induced moult (Figure 3).However,the greatest improvements in egg shell quality were seen in the Australian strains. Strain,Age,Calcium Source and Housing

Two major experiments were conducted to compare the imported strains,Isa Brown, Hy-Line Brown,Lohmann Brown,(and,in the second experiment,the Tegel Hi-sex)with the Australian strains Hy-Line (SIRO)CB and Tegel SB2.

The first of these experiments also studied the effect of calcium source and found that,although particulate calcium (oyster shell or limestone chips)resulted in a slight improvement in egg shell quality,there was reduced production and required additional labour.

The second of these experiments investigated the effect of housing,with Shed 1 receiving more natural light and fitted with 5-bird cages and Shed 2 being darker and fitted with 3-bird cages.


 
 
Key:Period during moult (figures 1,2 and 3).1 -Seven days prior to moult;2 -Eight days as birds go out of production; 3-Two weeks after birds come back into production;4 -Seven weeks after birds come back into production;5 -Eleven weeks after birds come back into production.

These studies confirmed previously reported findings that there are strain differences in both internal quality and egg shell quality in laying hens.The imported strains had heavier and thicker shells than did the Australian strains.

However,because the eggs of the imported strains also tended to be larger,there were no significant differences among strains in the shell weight :egg weight ratio.

These studies also confirm previously reported findings that aspects of egg and egg shell quality deteriorate as the hens age (Figures 4-9).All strains showed a reduction in internal quality, as evidence by the Haugh units,as the hens grew older (Figure 7).Egg shell quality also declined with age with reductions in egg specific gravity,shell breaking strength,shell weight,shell thickness and shell weight :egg weight ratio.The experiment on the effect of housing showed that these types of housing conditions had little effect on egg and egg shell quality.However,the 5-bird cages in the shed receiving more natural light resulted in the production of eggs which were slightly lighter in colour (Figure 9).Egg and egg shell quality also varied among strains.

Heat Stress

One known cause of egg shell quality problems which occurs commonly in Australia is high ambient temperature causing heat stress.In the present study,five strains of laying hen were subjected to heat stress that was sufficient to induce intermittent panting and postural changes such as holding the wings out from the sides of the body.

Feed intake was significantly depressed during heat stress as shown in Figure 10 and egg weight was reduced (Figure 11).The heat stress was also sufficient to cause a reduction in egg shell quality.Although the present study utilised only small numbers of birds from each strain,some strain differences were found in the effect of heat stress on egg and egg shell quality.


 

Relocation Stress*

Relocation stress is known to have effects on the visual appearance of eggs produced,by increasing the incidence of calcium coated and body checked (misshapen) eggs.The aim was to investigate the effect of different types of relocation and housing environments on egg and egg shell quality and to investigate whether the hen will tend to become used to repeated relocation.

The results indicate that even simple relocations into a slightly changed environment can have negative effects on both the egg and egg shell quality.More major types of relocation,such as movement from one type of housing to a completely new housing environment,can produce severe visual and structural defects of the egg (Figure 12).These results suggest that relocation of any type,once laying hens are in lay,will have a negative economic effect due to reduced egg shell quality causing a downgrading of the eggs produced.

*Part of the PhD project of Ms Alison Leary Dietary

Manipulations – Linoleic Acid**

Linoleic acid (LA)is an essential fatty acid, which means it cannot be produced by the hen and so it must be consumed in the diet.This study aimed to investigate if reducing dietary LA in both Australian and imported strains of laying hen will effectively reduce egg size.The effect on egg and egg shell quality was also studied. The Australian strains used were the Hy-Line CB and the Tegel SB2 and the imported strains were the Isa Brown,Lohmann Brown,Hy-Line Brown and Hisex Brown.

The results show the effects of dietary LA are strain dependent with respect to egg weight.The strains in which egg weight responded most to varying levels of LA were the Hy-Line Brown (higher levels of LA produced larger eggs and lower levels produced smaller eggs)and the Hy-Line CB (lower LA caused smaller eggs). The Isa Brown hens did not respond to changes in dietary LA.There appears to be no consistent improvement in egg shell quality in any of the strains of laying hen examined as a result of either increasing or decreasing dietary LA.

Effect of Dietary Ingredients/ Enzymes

It is common knowledge within the egg industry that some cereal grains contribute to wet droppings problems in laying hens.However, whether or not these cereals affect egg shell quality is not clear,despite claims that problems with egg shell quality in broiler breeders result from the use of rations based on certain grains.

This experiment measured egg and egg shell quality in laying hens which were receiving diets based on different cereal grains.

Layer rations were formulated based on a range of cereal grains:sorghum,triticale,barley or wheat and compared with a standard commercial layer ration.The results indicate that the type of cereal grain on which a layer ration is based can affect egg shell quality.This is demon- strated by the shell breaking strength which was greatest for the sorghum diet while the weakest shells occurred on the barley diet,as seen in Figure 13.Egg weight was also affected and was highest for the wheat diet and lowest for the triticale with the other diets producing interme- diate sized eggs (Figure.14).


During the second part of this experiment the effect of including chloride or magnesium at two and three times the normal level was investi- gated.No deleterious effects on egg and egg shell quality were observed from levels of chloride and magnesium in layer rations at two and three times the recommended levels of inclusion.

The third section of the experiment looked at the use of four commercial feed enzymes in diets based on different cereal grains.This study dem- onstrated improvements in egg shell quality as the result of adding commercial enzyme prep- arations to either barley-based or wheat-based layer diets.However,the enzymes caused a small reduction in the colour of the egg shells and a reduction in the albumen quality.Minor effects on yolk colour were also observed for some enzymes.Figure 15 shows the improvement in shell strength when commercial enzymes are added to a barley-based diet.However,as seen in Figure 16,shell colour was slightly lighter when enzymes were used.

Other RIRDC egg reports: