FACTORS THAT INFLUENCE EGG WEIGHT: HOW TO CHANGE IT

Transcription

FACTORS THAT INFLUENCE EGG WEIGHT:
HOW TO CHANGE IT TO MEET MARKET REQUIREMENTS
By Philippe Joly
Abstract: The ability to make significant changes to egg weight enables the egg producer to adapt to
market demands. By changing the age at sexual maturity, or the body weight at start of lay, it is possible
to change egg weight by 1 to 3 g. Incorporating oil in the diet raises feed intake and can cause an
increase of 2 g in mean egg weight. This effect only occurs, when non-saturated fats are used.
Reducing the level of one or several amino acids can lead to a decrease in egg weight, but always
results in a reduced rate of lay. Finally, the use of cyclical lighting patterns can increase mean egg
weight by 1 to 1.5 g, without affecting the total egg mass. The use of these patterns does, however,
require the use of buildings, which are almost light proof. These effects enable us to obtain worthwhile
changes in egg weight.
1. Introduction
The control of egg size is an extremely important facility to the egg producer. He should seek the best
compromise between market demand for size and the best shell quality possible. Too low an egg weight
often leads to a reduction in income and too heavy an egg weight tends to result in an increase in the
proportion of downgrades towards the end of lay. The breeder seeks the best compromise. In hot
countries, or in summer, heat has a marked limiting effect on feed intake and causes a reduction in
performance. Good management of the lighting program and good control of feeding timetable allows us
to reduce the harmful effects of high temperatures.
The producer can change average egg weight appreciably (say 2 to 3 g) by altering the age at sexual
maturity or by changing the body weight of the pullet at sexual maturity.
The use of unsaturated oils enables us to increase egg weight by 1 to 2 g. Reducing egg weight by
lowering the dietary amino acid content is hardly practicable because of the reduction in rate of lay,
which it induces. The use of cyclical lighting programmes in blacked out buildings enables us to increase
egg weight by 1.5 to 2 g. The scope for changing egg weight considerably by these techniques really
does exist.
In this article, we will only deal with those techniques, which can easily be put to use by the egg
producer or the nutritionist.
2. Genetic aspects
Management techniques and nutritional characteristics of the diet can both change egg weight. The
breeding company defines his objectives according to the position of his strain relative to the
requirements of his clients. Each strain has, therefore, a potential range of egg weights, which can vary
by about 3.5 g. For some strains a real effort has been made to reach marketable egg weights rapidly
from start of lay while avoiding an increase in egg weight at the end of lay.
To illustrate this, we have taken the results of the Leystad Random Sample Test (2000) for the main
brown egg strains. These tests have the merit of being able to compare the different strains in the same
environment.
Factors that influence egg weight
2009-12 Page | 1
TABLE 1. Mean egg weights during different periods for the main Brown egg strains recorded in
the Lelystad (RST 2000)
Mean
Period
Period
Difference
Strain
Weight
22 – 34 weeks
54 – 66 weeks
in g
A
60.94
57.83
63.37
+ 5.54
B
61.27
57.70
64.13
+ 6.43
C
62.05
58.93
64.58
+ 5.65
D
62.61
59.43
65.23
+ 5.80
E
62.64
58.57
65.93
+ 7.36
F
63.29
59.83
65.90
+ 6.17
G
64.31
60.50
67.50
+ 7.00
3. Sexual maturity and bodyweight of pullet
Variability in sexual maturity
Sexual maturity changes according to variations in day length during the rearing period. With increasing
day lengths, it is brought forward; with decreasing day lengths, it is retarded. Morris (1967) noticed that
the difference in sexual maturity between spring and autumn depends on the amplitude of the variation
in day length.
TABLE 2. Differences in sexual maturity observed between springs and autumn under different
latitudes
Latitude
Difference in sexual maturity
10 °
3 days
30 °
12 days
40 °
18 days
50 °
26 days
60 °
41 days
The purpose of lighting programmes is to control the age at start of lay and to avoid the influence of the
variation in sexual maturity on performance (number and average weight of eggs). Under latitudes close
to the equator, they are of less use.
Sexual maturity
The variation in sexual maturity is associated with considerable variations in the number of eggs
produced as well as their average weight. This was studied in detail during the nineteen seventies, when
lighting programmes were researched thoroughly. To illustrate these effects, we reproduce the results
of trials carried out by Morris (1980) and Koutoulis (1997), who stimulated ISABROWN pullets at 8
weeks of age by increasing day length by 0, 4 and 8 hours. They obtained a change in mean egg weight
of 3 g without changing the overall egg mass.
2009-12 Page | 2
TABLE 3. The influence of age at 50% lay on the performance of layers
Age at
Number
Egg Weight
Egg mass
50 % lay
of eggs
(g)
g/d or kg
148
153
155
156
160
162
167
173
107.6
109.9
136.6
1
20 to 74 weeks
Morris (1980)
272
264
268
269
266
264
263
260
1
59.2
60.4
60.1
60.4
60.8
61.4
61.9
62.5
Koutoulis (1997)2
61.73
61.42
64.82
342
340
318
2
to 72 weeks
42.6
42.2
42.6
43.1
42.7
42.9
43.1
43.0
Feed conversion
( Feed (g) / egg
(g) )
2.86
2.89
2.89
2.83
2.83
2.82
2.83
2.81
21.11
20.90
20.61
These investigations have shown that mean egg weight increases by 1 g, when sexual maturity is
retarded by one week. Compensating for this, the number of eggs was reduced or increased by about
4.5 eggs for each change of one week in age at start of lay. By using appropriate techniques, the age at
start of lay can be changed so as to produce eggs of a weight required by the market without affecting
the total egg mass-produced.
Instead of giving light stimulation as a function of age, we recommend that day length should only be
increased, when the birds have reached the body weight intended. We can thus prevent the birds
coming into lay at too low a body weight, which would be detrimental to egg weight and to overall
performance.
It is the variation in pullet body weight at sexual maturity, which fixes the average egg weight. The
variation in day length during the rearing period stimulates or retards the hormone production, which
brings about the onset of sexual maturity.
The relevance of pullet body weight at sexual maturity
The body weight of the pullet at sexual maturity is the principle cause of variation in average egg weight.
The 2 experiments using ISABROWN shown below in table 4 (Bougon, 1996) illustrate this
phenomenon.
TABLE 4. The influence of pullet body weight at sexual maturity on performance
Pullet body weight (g)
Trial 1 (18-71 s.)
Trial 2 (23-47 s.)
1
1
2
2
2
1343
1539
1535
1585
1620
Age at 50% lay (days)
141
142
141
141
143
Rate of lay (%)
82.8
83.8
91.3
92.1
91.0
a
b
x
x
y
Mean egg weight (g)
59.9
61.4
60.5
60.7
61.8
a
b
Egg mass (g/d)
49.6
51.4
55.3
55.8
56.2
a
b
Total egg mass (g)
17.830
18.520
a
b
Food conversion ratio (g. feed/g.
2.23
2.18
2.02
2.01
2.01
egg)
1
body weight at 119 days
1665
142
91.0
y
61.7
56.1
2
2.03
2
body weight at 123 days
2009-12 Page | 3
From these two pieces of work we can conclude that the age at start of lay is conditional on the age at
which light stimulation has been carried out and that it does not depend on pullet body weight. On the
other hand, average egg weight is dependent upon the pullet body weight at start of lay. Lewis (1992)
gives an example of the relationship pullet body weight egg weight throughout a production cycle. He
has also shown (Lewis et al, 1995) that sexual maturity has also an influence on pullet body weight. This
relationship is shown in Figure 1.
TABLE 5. The influence of ISA brown pullet body weight at first egg on egg weight (g) over
different periods
Period
Pullet body weight at first egg (g)
(weeks)
1300 à 1500 g
1500 à 1700 g
1700 à 1900 g
> à 1900 g
18 – 28
49.75
53.25
56.05
57.60
28 – 40
57.55
59.20
61.03
62.35
40 – 60
61.65
62.55
64.55
65.80
From all of the above we can conclude that the body weight of the pullet at sexual maturity is the main
factor determining average egg weight. Changing sexual maturity is one method, which we can use to
vary the body weight of the pullet at start of lay. For brown egg strains, and particularly the ISABROWN,
a strain on which very many experiments have been carried out, we think that a variation in pullet body
weight of 80 g at sexual maturity will lead to a change in mean egg weight of about 1 g.
FIGURE 1. GROWTH CURVES OF ISA BROWN PULLETS REACHING A 50% RATE OF LAY
AT 130, 140 AND 150 DAYS OF AGE
Sexual maturity in the absence of light stimulation
At latitudes close to the equator, and in the absence of light stimulation, we have noticed that the
principal factor triggering sexual maturity was body weight. For example, with the ISA brown, a rate of
lay of 10% is obtained when the body weight reaches 1600 g. Light stimulation is not needed to trigger
sexual maturity. In this case body weight plays the major role in the fixing of sexual maturity and the
duration of light plays a dominant role in the control of growth.
2009-12 Page | 4
Practical aspects
The management practices, which influence the growth of pullets and, therefore, their weight at sexual
maturity, are going to have a considerable effect on mean egg weight and productivity. Among these, we
will mention the role of the lighting programme used during rearing and especially during the first weeks
of life, the role of and importance of form of feed on it's consumption and, therefore, on growth and
finally on the amino acid concentration of the diet.
Any light stimulation tends to change body weight at sexual maturity and adult body weight.
Disappointment is experienced, when pullets are stimulated at too low a body weight. For that reason,
we recommend stimulating at a given body weight rather than at a given age.
4. Nutritional factors
Influence of oil
Egg weight is influenced by the level of oil in the diet. This effect used to be attributed to the level of
linoleic acid in the ration, but Whitehead (1981) has shown that the effect on egg weight can be
attributed to oil and not to the level of linoleic acid. In rations, where the cereals were either wheat or a
mixture of wheat and barley, he compared the addition of either corn oil, which is rich in linoleic acid, or
olive oil, which is poor in linoleic acid. From this it is preferable to speak in terms of the effects of oil,
rather than the effects of linoleic acid. If a requirement for linoleic acid exists, it should not be more than
1%.
TABLE 6. The effect of oil or linoleic acid level on the performance of layers over the period 2173 weeks
Oil, %
0%
0.4% maize
3% olive
3% maize
Linoleic acid %
0.65
0.88
0.87
2.28
Rate of lay
77.9
78.5
78.1
77.3
a
a
b
b
Egg weight, g
56.7
57.3
58.8
59.2
a
a
b
b
Egg mass, g/d
44.2
44.9
45.9
45.8
a
a
b
b
F.C.R
2.60
2.59
2.53
2.54
The effect of fatty ingredients on egg weight depends on their components. Halle (1996) compared
additions of maize oil, soya bean oil and coconut oil to wheat based diets at levels of 2.5 or 5%. The
results, which are shown below are the means of 2 experiments over the period 19-71 weeks.
TABLE 7. The influence of the type and quantity of fatty ingredients on the performance of
layers
Type of oil
Coconut
Maize
Soyabean
Level of
2.5
5
2.5
5
2.5
5
incorporation
Rate of lay, %
83.8
85.3
84.7
85.1
86.7
86.6
Egg weight, g.
64.6
64.8
65.2
65.8
65.9
66.5
Egg mass, g/d
54.3
55.3
55.2
55.7
57.2
57.4
The mean egg weight on the control diet was 63.5 g. The increase in egg weight varies according to the
type of fatty ingredient used, but also according to it's level of incorporation. The work of Meluzzi et al
(2001) demonstrates the role played by the level of saturated fatty acids in fatty ingredients on egg
weight. The diets were made up of maize (61%) and soya (24%) and were supplemented with 2% of
different oils over a period of 8 weeks.
2009-12 Page | 5
TABLE 8. The influence of different oils incorporated at the rate of 2% on egg weight
Oil
Palm
Seaweed
Lard
Grape
Linseed
Level of palmitic acid
in oil (%)
Level of linoleic acid
in diet (%)
Egg weight
(g)
28.4
18.0
17.8
11.2
10.5
1.52
1.37
1.64
2.67
1.65
63.0
63.1
64.3
65.5
65.3
Recent work by Grobas et al (1999) carried out with 720 ISABROWN enables us to differentiate
between the effects of the dietary energy level and the effect of oil. They compared 2 dietary energy
levels (2680 and 2810 kcal/kg) containing either 0% or 4% of added oil (a mixture of soya and olive oils)
or 4% animal fat.
The energy level of the diet modified neither the performance of the layers nor the dietary energy intake.
The addition of 4% of a fatty substance brought about an increase in dietary energy intake, body weight
gain and egg weight.
TABLE 9. The effect of dietery energy level on the performance of Hens
Performances
Dietary Energy
Added oil
2680 kcal
2810 kcal
0%
a
a
a
Rate of lay%
88.8
88.9
88.0
a
a
a
Egg weight, g.
64.9
64.5
64.1
a
a
a
Egg mass g/d
57.7
57.3
56.4
Energy intake, kcal/d
327
326
322
Weight gain, g
140
218
88
4%
b
89.8
b
65.3
b
58.6
331
270
The comparison between 2 types of fatty ingredients did not have any effect on performance despite a
linoleic acid level of 1.15% in the diet incorporating 4% fat and 1.65% for the diet containing 4% added
oil.
Practical factors.
The presentation of diets is improved, when one uses oils, which give an increase in feed consumption.
If the grinding is inadequate, the addition of oil may improve the texture. Egg weight varies as a function
of the type of oil used. The requirement of layers for linoleic acid is relatively low and not more than 1%.
The increase in egg weight does not seem to rely on the level of linoleic acid. The addition of
unsaturated fats leads to an increase in the energy intake, the body weight of the bird, the egg weight
and the egg mass-produced. The effect on egg weight will not be produced, when oils or fats, which are
rich in saturated fatty acids or in palmitic acid are used. Soya bean oil seems to be the oil which gives
the best increase in egg weight.
The influence of a deficiency of amino acids on egg weight.
For all the amino acids studied, without exception, a deficiency leads to a reduction in performance, of
which 60-65% is due to a lowering of rate of lay and 35-40% to a reduction in egg weight. Over recent
years we have studied the amino acid requirements of layers, identifying the most limiting and producing
a collected bibliography (Joly, 1995, 1997, 1999, 2001, 2003). We present below the results of this
series in terms of the effects obtained on egg weight.
2009-12 Page | 6
TABLE 10. The percentage reduction of egg mass due to reduction in egg weight following an
introduction of diets deficient in an amino acid.
Number of
Number of reviewed
Percent of egg
experiments
studies
mass loss
Amino Acids
studied
due to egg weight
loss
(%)
Meth + Cystine
16
44
39
Lysine
11
20
35
Isoleucine
11
24
27
Tryptophane
12
12
Valine
4
6
22
Threonine
3
8
8
In these studies, it stands out that a deficiency of amino acids leads to a more marked reduction in rate
of lay than in egg weight and that each amino acid tends to show a very similar pattern. Of the reduction
in egg mass consequent upon a deficiency of an amino acid, about 30-35% can be ascribed to a loss of
egg weight. The work of Jais (1995) has shown that, when one introduces a shortage of amino acids,
egg weight is affected more than rate of lay in the first 4-6 weeks following the introduction of the
deficiency. This is explained by the fact, that during this period of 4-6 weeks, catabolism allows the bird
to maintain a similar rate of lay. Stabilisation in performance is observed, when the bird reaches it's
minimal body weight.
Food consumption adjusts itself in line with productivity and the equilibrium obtained between protein
and energy intake ensures that fattening is to some extent limited. Methionine escapes this general rule.
In this case increased-consumption is always observed when the birds are on deficient diets. To
illustrate the influence of an amino acid deficiency, we reproduce the work of Huyghebaert (1991) on
Threonine.
TABLE 11. The influence of Threonine intake on the performance of ISA brown (34-38 weeks) and
on the amount of Threonine required to produce 1 of egg
mg
Dig threonine
Rate
Egg
Egg mass
Body weight threonine
Intake
F.C.R
of lay (%)
weigh (g)
(g/d )
change (g/d)
per g of
(mg/d)
egg
149
30.2
50.3
15.2
5.16
- 4.2
9.80
187
20.2
51.7
20.8
4.09
- 3.6
9.00
224
52.4
53.6
28.1
3.32
- 3.4
7.87
294
67.0
55.4
37.1
2.94
- 0.9
7.92
341
72.0
56.1
40.4
2.82
- 1.6
8.44
387
80.8
57.8
46.7
2.59
1.3
8.29
447
86.2
59.2
51.6
2.47
1.4
8.66
478
85.5
60.0
51.3
2.45
3.3
9.31
500
86.9
60.5
52.6
2.38
2.8
9.51
531
86.8
59.4
51.6
2.39
3.1
10.29
Below 447 mg intake the rate of lay falls markedly (6%), whereas egg weight only falls by 2.4%.
2009-12 Page | 7
Practical aspects
It is an illusion to want to reduce egg weight by reducing one or more amino acids without reducing rate
of lay. The reduction in the level of methionine or of other amino acids towards the end of lay is
prejudicial to performance, to rate of lay, to feed conversion ratio and to egg weight.
Influence of feed texture
Feed consumption is very dependent on its texture. The chicken has a definite preference for particles.
They are easier to gather and do not lead to pasting up of the beak. A chicken always has a tendency to
leave the fine particles.
We have carried out the following trial (ISA 1999): A commercial diet, with a good particle size was remilled through a finer screen. The two diets were then fed from 19 weeks of age. The results are shown
in Table 12.
TABLE 12. The influence of feed grist on the performance of layers between 23 and 51 weeks
Particle size
Correct diet
Fine diet
Difference %
< 0.5 mm
9%
31 %
> 3.2 mm
10 %
0%
0.5 a 3.2 mm
81 %
69 %
> 1.6 mm
65 %
21 %
Rate of lay %
Egg weight g.
Egg mass g/d
Feed consumption g/d
F.C.R.
Body weight @ 33 wks. g
93.9
63.3
59.41
118.1
1.989
1.930
90.7
62.7
56.85
114.2
2.008
1.883
- 3.4
- 0.9
- 4.3
- 3.4
+ 0.9
Food consumption is reduced by about 4 g/d when it is finely milled. As a result there is a reduction of
3.4% in rate of lay (6.3 eggs), a reduction of about 1% in egg weight and a reduction in egg mass of 2.6
g/day.
Using a finely ground feed is the equivalent of rationing the layers. Rate of lay will be found to be
affected more than egg weight. Nowadays any feed restriction always leads to a lowering of egg
production.
5. Influence of heat
Influence on performance
o
o
Rate of lay is generally only affected at temperatures above 30 C. Egg weight falls by about 0.4% per C
o
o
o
between 23 and 27 C; above 27 C the reduction is about 0.8% per C. Growth at start of lay is reduced
o
o
above 24 C and is extremely low above 28 C. The feed conversion ratio is minimum at a temperature
o
o
around 28 C, above 28 C it increases due to the lowering of production. These figures are only
indicative, because air movement speed and relative humidity affect thermoregulation. In the absence of
any specific methods of temperature control, the heat loss by convection is proportional to the difference
between environmental and bird body temperatures. The quantity of heat, which needs to be removed,
increases dramatically with increases in ambient temperature. If it is not possible to lose this, the
thermoregulatory mechanisms gradually come into play with the consequential lowering of feed
consumption.
The table below gives the results obtained with foods varying in energy level between 2645 and 2975
kcal/kg. The results shown are those obtained by Zollitsch (1996) under 3 temperature regimes over the
period 20-36 weeks.
2009-12 Page | 8
TABLE 13. The influence of dietary energy level on performance of layers at different
temperatures
Temperature
Dietary energy
kcal/kg
14 to 19 °C
2645 kcal
2755 kcal
2865 kcal
2975 kcal
297
308
310
315
2645 kcal
2755 kcal
2865 kcal
2975 kcal
52,73
52,82
53,43
53,29
2645 kcal
2755 kcal
2865 kcal
2975 kcal
44.4
45.2
45.5
45.3
21,9 to 27,7 °C
Energy intake (kcal/d)
273
281
288
289
Egg weight (g)
52,24
52,41
52,82
52,75
Egg mass (g/d)
43.5
44.3
44.7
44.8
30,5 to 35 °C
204
207
209
205
47,30
47,30
46,92
47,01
34.4
34.8
34.8
34.5
During the laying period energy intake is not modified by dietary energy level. Growth and production are
reduced more and more as the temperature is increased. In rearing, as in production, increasing the
level of energy in the feed does not avoid the loss of production due to heat.
In the following trial, Peguri (1993)studied the performance between 59 and 65 weeks as a function of
temperature in perfectly feathered pullets and others from which 50% or all of the feathers had been
removed.
TABLE 14. The influence of level of feathering and temperature on performance
Performances
Feed consumption (g/day)
Egg mass (g/day)
Rate of lay (%)
Egg weight (g)
Temperature
°C
23,9
33,9
23,9
33,9
23,9
33,9
23,9
33,9
100%
105
82
49,9
39,6
84,3
70
59,2
56,4
Degree of feathering
50%
112
91
49,0
47,3
84,3
81,4
58,1
58,0
0%
128
99
47,0
43,3
77,9
75,4
60,4
57,6
At high temperatures, the feed consumption and egg production of fully feathered hens are considerably
lower than for hens with 50% plumage. This shows that in a hot climate, the factor limiting production is
really the capacity to discard the heat produced. As the temperature rises more and more, the
thermoregulatory mechanisms gradually come into operation e.g. spreading wings wide open, increasing
respiratory and cardiac rates.
2009-12 Page | 9
Practical aspects
In hot climates or during hot periods, heat reduces the birds' feed consumption. That can be attributed to
2 phenomena; on the one hand the reduction in the capacity to eliminate heat and, on the other, a
reduction in the period of effective access to the feeder.
A lighting programme allowing the pullets and hens to eliminate the heat of digestion in the cooler parts
of the day has a beneficial impact on performance. For that we recommend using the following lighting
program :
"lights on"
=
3 h 30
"lights out" or night
=
19 h
"night lighting"
=
from 23 h 00 - 0 h 30
6. Lighting programmes during production
The programmes called "cyclical programmes" allow an increase in egg weight. An analysis has been
carried out by ISA (1988). They can only be used, when the buildings are completely light proof. The 24
hour day is broken down into cycles of 2, 4, or 6 hours. Each cycle is made up of a period of light and a
period of darkness. The length of lighting in each cycle can be varied throughout the laying period.
These fragmented programmes can be used:


either at any time in the laying cycle, including at the start of lay, if it is considered economically
worthwhile to increase egg weight.
or after 40 - 50 weeks, if one wants to improve the eggshell quality at the end of lay.
When operating these programmes we recommend keeping the same total lighting period for several
weeks. The physiological repercussions of these programmes are as follows;
oviposition is
desynchronised, with egg laying occurring throughout 24 hours and increasing the length of time taken
in egg formation, which allows an increase in egg weight of 2-3% but reduces the number of eggs by the
same proportion.
In association with the increase in the period of egg formation one observes an improvement in the shell
density and colour, from which there is a reduction in the quantity of downgrades.
Other lighting programmes called "ahemeral" have a large effect on egg weight.
A day length longer than 24 hours, for example 25 or 26 hours, leads to a reduction in rate of lay. Since
they do not have any use, we will not describe these programmes, which are the subject of an analysis
by Shamawany (1982). The effects of these programmes seem similar to those obtained with a cyclic
programme, a reduction rate of lay, an increase in egg weight and of shell quality. For cycle lengths of
23 - 26 hours, the egg mass-produced does not seem to be affected.
7. Conclusion
The egg producer and the nutritionist can bring about quite large variations in egg weight. An increase in
egg weight can be obtained immediately by using a cyclical lighting programme or by adding
unsaturated oils to the feed. A reduction in egg weight can be obtained by replacing unsaturated oils
with saturated fats. A change in egg weight can easily be obtained by modifying age at sexual maturity
or by changing body weight at sexual maturity. In hot periods, the best timetable permits the birds to eat
food during the cooler hours, with positive effects on performance.
2009-12 Page | 10
References
-Bougon, M., 1996. Influence du poids de la poulette à l’entrée en ponte sur les performances des
pondeuses. Journée Itavi. Décembre 1996.
-Halle, I., 1996. Untersuchungen zum Einfluss untershiedlicher Nahrungsfette auf leistungsparameter
und Dotterfettsäurespektrum bei Legehennen. Arch. Geflügelk 60:65-72.
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FACTORS THAT INFLUENCE EGG WEIGHT: HOW TO CHANGE IT

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