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.

The effect of T-strain infectious bronchitis virus on early lay pullets that had received different first vaccinations, and their third vaccination at either 14 or 18 weeks, was examined. For the whole flock there was an immediate decline in egg internal quality after challenge with the virus. Shell quality also declined as evidenced by both objective measurement and visual assessment. There were no major effects due to the strain of vaccine that the birds received at day old, although there were some effects of vaccine protocol. The revaccination of birds at 5% lay (18 weeks old) resulted in an increased decline in egg quality measurements when they were challenged with T-strain. This flock is continuing to be monitored to assess long-term effects.

Measurements of infectious bronchitis virus (IBV) antibody titres by IDEXX IBV antibody ELISA were compared with the results of agar-gel precipitation (AGP) and serum neutralisation (SN) tests. The percentage of samples testing positive by AGP and SN increased as the ELISA IBV antibody titre increased. Although it is not clear at what antibody titre level birds are protected against intercurrent infection, a mean IBV antibody titre measured by IDEXX ELISA of 439 correlated with a high level of protection against exposure to T-strain IBV. A comparison of two different IBV antibody ELISA kits showed a significant linear correlation although individual samples did not always correlate closely.

Problems with egg quality have resulted in large economic losses to the egg industry. Studies have been conducted to provide realistic commercial guidelines on the internal and shell quality of the eggs, for the Australian Egg Industry. Eggs were obtained from commercial operations, both from flocks that were followed throughout their laying life (longitudinal studies'), and also from flocks that were sampled at that were age one and across a range of ages of flocks (cross-sectional studies'). A total of almost 25,000 eggs were used. Eggs were analysed individually for internal quality and egg shell quality as soon as possible after collection using specialized equipment from Technical Services and Supply, U.K. The data collected indicate that there is considerable variation among flocks in egg and egg shell quality measurements, although there is little difference among the three main brown egg layer strains currently used in Australia (Isa Brown, HyLirie Brown, HiSex Brown). However, consistent findings in relation to bird age were: an increase in egg weight and shell weight up to 45 and 40 weeks of age, respectively, after which these weights remained relatively constant. Shell colour, shell breaking strength, deformation, percentage shell, albumen height and Haugh Units all declined with hen age. Eggs lost weight during storage and this was influenced by storage time, temperature and humidity. Haugh Units also deteriorated during storage and this effect was accentuated at higher storage temperature but was not greatly influenced by humidity.

Different vaccination protocols with two vaccine strains (VicS and A3) for infectious bronchitis (IB) virus were administered to Isa Brown laying hens during rearing and half the birds were revaccinated regularly during lay. At 57 wks of age, half of the birds were placed into an induced moult for a period of 5 weeks (moulted prior to revaccination), all birds were then revaccinated for IB and the other half of the birds moulted (moulted following revaccination). Production was lower in the birds that were revaccinated regularly during lay and the control (no vaccination until 14 weeks) and VicS eyedrop groups. Egg shell quality was better in the birds that were revaccinated prior to moult. Excreta moisture following revaccination was higher in the birds that had been revaccinated regularly during lay and in birds that were moulted after revaccination.

Four different commercial enzyme products were added to either a standard commercial wheat-based layer diet or the same diet with 20% of the wheat substituted with cereal rye. Diets were fed to Isa Brown laying hens from 50 to 65 weeks of age. Measurements of egg and egg shell quality, apparent metabolisable energy and excreta moisture were conducted at five-weekly intervals. Digesta viscosity was measured at the end of the trial. The AME of the diets was similar and relatively stable. Excreta moisture was not affected by the addition of feed enzymes. Egg and egg shell quality varied significantly as the birds grew older and was significantly better for the wheat+rye diet as compared with the wheat diet. There were few effects of enzymes on egg and egg shell quality except that Kemzyme resulted in lower albumen quality and lighter shell colour. Production was not affected by type of diet but the Roxazyme treatment had the highest production. Both type of diet and the addition of enzymes affected egg and egg shell quality.

Different vaccination protocols for infectious bronchitis virus (IBV) were administered to ISA Brown laying hens during rearing and half the birds were revaccinated regularly during lay. At 57 wks of age, half of the birds were placed into an induced moult (moulted prior to revaccination), all birds were then revaccinated for IB and the other half of the birds moulted (moulted following revaccination). Production and egg quality were lower in the birds that were revaccinated regularly during lay, especially from 18 to 56 weeks. IB antibody titres increased at 6 and 16 weeks, then decreased and remained relatively constant from 27 to 77 weeks, increasing markedly following exposure to T-strain IBV. Egg shell quality was better in the birds that were revaccinated prior to moult. There appears to be little advantage, and some disadvantage, of regular revaccination during lay, provided that the birds have been effectively vaccinated during rearing.

In Trial 1, four different commercial enzyme products were added to standard commercial layer diets, based on two different types of wheat, "normal" wheat and "pinched" wheat. Diets were fed to Isa Brown laying hens from twenty-five weeks of age. In Trial 2 (50 to 65 weeks of age), all diets were based on pinched wheat or pinched wheat containing 20% cereal rye. Measurements of egg and egg shell quality were conducted at five-weekly intervals. Apparent metabolisable energy and excreta moisture were measured every 5 weeks from 30 to 65 weeks of age. The AME of the diets was similar for the two types of diet in both trials. AME increased to 40 weeks of age, remained relatively stable and then decreased slightly. Excreta moisture was not affected by enzymes in either trial. Egg and egg shell quality varied significantly as the birds grew older and was significantly better for normal wheat than pinched wheat and for wheat+rye versus wheat. Shell breaking strength was slightly lower for Biofeed Wheat and Avizyme, shell reflectivity was higher for Roxazyme and Kemzyme, and percentage shell and shell thickness was higher for Kemzyme. Yolk colour showed minor variation among the enzyme treatment groups. Production was not affected by type of diet or enzymes in either trial. Both type of grain and the addition of enzymes have the potential to affect egg and egg shell quality.

The eggshell quality of vaccinated hens challenged with infectious bronchitis (IB) virus in-lay at 41 weeks of age was found to decline. These effects were observed in hens vaccinated only during the growth phase and not revaccinated during the lay period. T strain virus was found to have a more prolonged impact while the antigenically-different Nl/88 strain produced a greater decrease in egg quality parameters. There was an unexpected increase in internal quality of the virus-exposed groups during the challenge period. While the genetic strain of the hen had no significant effects on the response to challenge in terms of egg quality, there were inherent strain differences in egg quality unrelated to the challenge and these are briefly discussed.