ANALISIS DE SEGURIDAD DEL MODELO

Laying performance has grown continuously in recent decades. At the same time, animal losses could be reduced drastically (see Tab. 3-5). The increase in performance is based partly on breeding progress and partly on the fact that the genetic performance capacity can be better exploited as a result of optimisation in feeding, husbandry and animal hygiene.

Tab. 3-5: Average performance in laying hens per animal and year

1950 1960 1970 1980 1990 Laying performance (eggs) 170 210 240 280 300

Egg weight (g) 53 56 60 63 -

Feed conversion

(g feed/100 g egg weight) 350 340 320 260 -

Mortality (%) 25 18 12 6 -

Source SCHOLTYSSEK, 1987 PINGEL &

JEROCH, 1995

With the laying hens used today there is no clear distinction between breeds and strains. One of the most important breeds is the white leghorn (single comb), within which the various strains make up the modern hybrid lines. They are distinguished by a low live weight, which results in a low requirement for maintenance. The laying performance of pure leghorns is between 220 and 240 white-shelled eggs per year, the leghorn crosses about 300 a year (PINGEL & JEROCH, 1995). Another important breed is the dark-red brown Rhode Island Red, which produces medium-heavy brown-shelled eggs. Besides these two main breeds there are others, such as New Hampshire, Plymouth Rock and Sussex that are important for the development of breeding strains.

The laying performance, which is usually between the 141st and 504th day (a period of 364 days), shows clear differences between the strains. With the increase of laying performance the requirements of energy and essential amino acids also increases.

LANGE (2002) reports on a laying performance test with four different brown- feathered strains and a white-feathered strain (LsL). On average the brown hens laid fewer eggs (306) than the LsL white ones (324). The same tendency could be observed in the egg weight, although all animals received the same feed. The amino acid pattern of the egg protein is genetically programmed and is not affected by the feed (JEROCH et al., 1993).

3.3.1.2 Age and live weight

The laying hens reach laying maturity aged about 20 to 24 weeks. The laying period is generally divided into three phases (see fig. 4-6). Phase 1 is from week 22 to week 34, phase 2 to the 53rd week and phase 3 to the end of the laying period, which normally lasts until the 65th week. After about 40 weeks the animals are fully grown and achieve the highest laying

performance. This then decreases continuously, while the egg weight still increases slightly.

Fig. 3-5: Development of egg production, live weight a Egg production in the laying period is shown in fig. 3-5.

nd feed intake of laying hens (Light

the first laying month the laying performance is about 10 % of the maximum, becaus

egg weight multiplied by egg number) achieve

.3.1.3 Environmental factors

hens in that it affects the hormonal

periods of light, which results in high egg production in the succeeding laying phase. Laying Hybrids) during the laying period (KIRCHGESSNER, 1997)

In

e the hens are still growing in this period. Then the laying performance increases in about 8 weeks to approx. 80% to 85 % and then continually decreases. The growth changes in this phase only slightly (JEROCH & DÄNICKE, 2002).

Hybrids with up to 20 kg egg weight a year (

an enormous protein synthesis, more than 1 kg egg protein per kilogram of live weight (VOGT, 1987). KIRCHGESSNER (1997) has calculated that for an egg of 61 g weight approx. 157 g crude protein per kg DM in the feed are required. According to GFE (1999) an evaluation of the literature shows a great range with respect to crude protein need values from 15g to 21 g per hen per day. This range depends on the variation in the live weight and performance.

3

Light has a strong effect on the performance of the laying

control of the laying performance and regulates the feed intake. During the breeding the lighting is normally reduced up to the 20th week gradually to ten hours a day. From the 20th week and during the laying period the light is slowly increased to 17 hours a day and interrupted by periods of darkness. The light regime at the end of the laying phase is particularly effective in terms of the egg size and shell stability (SCHOLTYSSEK, 1987). In the breeding phase the light favours early maturity in that the feed intake is higher during long

3.3.1.4 Amino acid supply

There are numerous studies on the amino acid requirement of laying hens at various ages and JEROCH & DÄNICKE, 2002). With laying hens the

ino acid requirement. The starting

uirement in laying hens, depending on body weight

laying periods (NRC, 1994; GFE, 1999;

criteria of laying performance and duration, egg weight, shell stability and live weight are significant. A chicken egg has an average weight of about 60 g. The largest proportion (58%) consists of egg white, the yolk amounting to approx. 32 % and the shell stability approx. 10 %. A medium egg of 60 g thus contains approx. 7.3 g protein. According to variety this content fluctuates and can be affected only to a limited extent by feed. The protein of chicken eggs has a high proportion of methionine and cystine. These amino acids are also required to a large extent in building feather protein (KIRCHGESSNER, 1997).

The data on the total requirement of amino acids are formulated as gross amino acids or digestible amino acids. NRC (1994) specifies the gross am

point of data presented in Tab. 3-6 is a 90 % laying performance. The requirement values for brown-shell eggs are approx. 10 % higher than for white-shell eggs. The principal reason for this is the higher live weight of the hens.

Tab. 3-6: Recommendations for the amino acid req

Body weight

medium light medium medium heavy light

Lys. 670 680 690 760 - -

Met. + Cys. 580 595 580 645 595 615

Met. 330 335 300 330 3 35 350

Source GFE, 1999 NRC, 1994 JEROCH, 2002

he protein r of laying h , among others, on laying perform nce, live weight, variety, age, feed components, the digestibility of the feed and environ

he data vary to a high degree. While JENSEN

ning 15% crude protein and sh

T equirements ens depend

a

mental factors. Protein requirements of laying hens are higher for the best possible feed conversion than for maximum egg weight, and this in turn is higher than for maximum laying performance (JENSEN et al., 1974; SCHUTTE & VAN WEERDEN, 1978; SCHOLTYSSEK, 1987; CALDERON & JENSEN, 1990; HARMS et al., 1998).

The methionine and SAA requirement of laying hens has been investigated in many studies on the basis of varying performance potential. T

et al. (1974) report on values between 290g to 300 mg methionine per hen per day for optimal egg production, SCHUTTE et al. (1994) recommend provision of 440 mg methionine per hen per day to achieve high performances.

CHERRY & SIEGEL (1981) have studied the compensatory effect in feed consumption as a reaction to low contents of SAA. Three iso-caloric rations contai

owing differences in methionine content were fed to young hens from two different genetic strains with different live weight. The effects on live weight, sexual maturity, egg

production, egg size and egg quality were not significant. The conclusion was that young hens are able to compensate for a limited deficiency of SAA by increased feed intake.