| Background: |
Recent developments in the Australian
poultry industry include the introduction of overseas strains of layer,
the move to de-regulation and unrestricted trading between states and improvements
in welfare standards for poultry. Compared with local strains of bird,
the "imported" strains are generally more docile, lay much larger eggs,
convert feed to eggs more efficiently and tend to be less resistant to
disease organisms occurring in the Australian environment. It is therefore
probable that different management standards and strategies are needed.
Although breeding company recommended dietary specifications are higher
than for local strains, these standards have been questioned. The increasing
use of imported strains has caused surpluses of very large eggs in many
areas, resulting in a need for the development of feeding and management
strategies to overcome this problem. With reduced prices for the largest
grades of eggs, the viability of keeping flocks for a second production
cycle has been put in doubt, though modified husbandry techniques for moulted
birds might improve this prospect. The kinds of rearing techniques advocated
in the past for local strains have also tended to result in an increase
in average egg weight, and some of these techniques are now ethically unacceptable.
Different rearing methods may therefore be appropriate not only for imported
strains but for the industry in general. |
Outcomes |
It was found that average egg
weight was markedly reduced and egg numbers were increased by the combined
use of feeding and lighting techniques in the rearing period designed to
hasten maturity. Conversely, egg weight tended to be increased at the expense
of egg number when maturity was delayed. Feeding techniques alone during
rearing, conducted within ethically acceptable limits, were not consistently
efficient at controlling egg weight. High dietary protein concentrations
were found to increase egg weight of most strains, particularly in the
first laying cycle, and usually resulted in higher financial margins than
low specification diets in the first laying cycle and substantially lower
margins in the second laying cycle. High dietary linoleic acid concentrations
also tended to increase egg size, but the effect was greater in the second
laying cycle than in the first. For all strains of bird under most egg
price structures, increasing the dietary linoleic acid reduced the daily
average financial margin. The effects of protein and linoleic acid on egg
weight were usually additive. Under most egg price structures the financial
margin of the Isabrown strain was higher with a high (approximately 180g/kg)
protein diet than with a lower protein diet but the financial margin of
other strains was not clearly affected by protein level. Following an induced
moult, birds given a high protein, high linoleic acid diet for a 23-day
period returned to lay more rapidly and with larger eggs than those given
a lower specification diet. In one trial, in which a proportion of the
flock suffered a production setback due to AE, the affected birds were
not rehabilitated by either of two moulting treatments. Control birds that
were unaffected by AE responded positively to these treatments. A diet
of high nutrient density greatly improved the rate of lay, egg weight,
egg shell quality and bodyweight of the AE-affected birds, as compared
to a low-medium density diet. |
| Implications |
The results of the rearing experiments
indicate that lighting programs are an indispensable component of rearing
management. Nutritional manipulations alone, conducted in an ethically
acceptable manner, are probably insufficient to ensure maximum returns
over a full production cycle. A step-up lighting program together with
a high specification grower diet increases total egg number and reduces
mean egg weight in the first laying cycle. This may be economically advantageous
for imported large-egg strains of layer.
Under most market conditions, the profitability of imported
large-egg strains of layer may be improved by feeding a diet with a high
protein content in the first laying cycle, a medium/low protein content
in the second cycle and low linoleic acid content throughout lay. Other
strains may not need a high protein diet in the first cycle. The rapidly
increasing use of imported strains is profoundly altering the relative
proportions of different egg grades produced on farms. Producers will be
able to apply the findings of this project according to the strain of bird
used and with a view to meeting changes in consumer demand for different
egg grades so as to maximise returns. However, management techniques such
as those studied here provide only limited means of aligning the grade-mix
produced on a farm with the saleable grade-mix.
Birds that have suffered a severe set-back causing loss
of bodyweight and production appear to require a high quality diet to assist
recovery and are unlikely to be rejuvenated by induced moulting. |
| Publications: |
Robinson, D. (1996). Imported
stock performance – meeting grade mix requirements. 1996 Poultry Information
Exchange, pp 15-21.
Robinson, D. (1996). Early performance of imported and
local laying strains after advancing or delaying maturity. In an Eggshell,
No. 2: 10.
Robinson, D., Trappett, P.C., Barram, K.M. and Davis,
B.A. (1996). Management of imported laying strains. Queensland Poultry
Science Symposium 5, pp 8-1 – 8-8.
Robinson, D. and Davis, B.A. (1997). Feeding hens to limit
disease. Queensland Poultry Science Symposium 6, pp 21-1
– 21-8.
Robinson, D., Davis, B.A., Trappett, P.C. and Barram,
K.M. (1997). Effect of manipulation of age at maturity on performance of
slow and fast maturing strains of layer. Australian Poultry Science
Symposium 9: 236.
Robinson, D. (1998). Resting and diet in the recovery
of laying hens from an egg production drop associated with avian encephalomyelitis.
Australian
Poultry Science Symposium 10: 212.
Robinson, D. (1998). Is resting or diet the answer to
severe production drops? In an Eggshell, No. 5: 6.
Robinson, D. and Datugan, M.J. (1998). Effects of pre-rest
and post-rest diets on second cycle performance of local and imported layer
strains. Queensland Poultry Science Symposium 7, pp 7-1 –
7-6.
Robinson, D. and Datugan, M.J. (1998). Effect of protein
and linoleic acid on egg weight of three layer strains. Australian Poultry
Science Symposium 10: 197. |
