R. Preisinger and M. Schmutz
Lohmann Tierzucht GmbH,
Cuxhaven
Germany
From a breeder's perspective, biological constraints and changes in consumer preference and regulatory requirements are key factors determining specific breeding goals. The controlled housing in single bird and group cages has been considered as the most favourable environment for testing birds and lines which are dedicated for cage production units.
Cage testing can result in birds that are specifically adapted to cages and less capable of adapting to far more stressful alternative systems. Feather pecking and cannibalism, along with increased infection pressure through bacteria, are the main reasons for reduced performance and higher mortality rate in these systems. The higher energy requirement of hens in alternative management systems can lead to weight loss at an age when the hens should still be gaining weight. This is associated with physiological stresses, which impose a heavy challenge to the metabolism and may increase susceptibility to disease.
Differences in ranking for income over feed cost between testing stations indicate that there is a variable degree of adaptability of strains to various environments. Field and test station results indicate, that data recording and selection has to be done in an environment that resembles the production environment as closely as possible to minimise the risk of selection errors due to genotype x environment interactions. Metabolic stability, plumage condition and docility continue to be valid selection priorities, especially for alternative housing systems. Scores of plumage quality in full and half sib hens caged together are used as input for breeding value estimation and selection but a disadvantage of this approach is that feather pecking, aggressive pecking and cloacal cannibalism can not be recorded as single traits. Exposure to a challenge test increases the variation between families. With increasing heritability the genetic merit of each bird can be estimated more accurately, resulting in increased genetic progress.
Introduction
The breeding of agricultural livestock in general is geared towards producing animal protein in an efficient and environmentally sensitive manner. Changing consumer preferences and regulatory requirements, along with biological constraints, are among the key factors that determine specific breeding goals.
Egg production from conventional cages will be further scaled down in the EU over the next few years. Modified enriched cages can be a compromise between conventional cages and floor or aviary systems that will be used to different extent in EU states.
Current situation
The controlled housing in single bird and group cages has been considered as the most favourable environment for testing birds and lines which are dedicated for cage production units. It has been suggested from time to time that cage testing of pure line and cross line stock results in birds that are specifically adapted to cages and less capable of adapting to alternative systems. This view is reinforced by the fact that alternative systems are far more stressful to laying hens than cages. Feather pecking and cannibalism, along with increased infection pressure through bacteria, are the main reasons for reduced performance and higher mortality rate in these systems. As shown in Table 1 field studies confirm this tendency.
Breeders have to be aware of differences in housing system to avoid genotype x environment interaction in their breeding programme if testing and production environment are significant different. Strains found to be superior in the cage environment may not be able to maintain their superiority in the floor management environment. Therefore the magnitude of genotype by environment interactions has to be estimated to optimise testing systems for within line selection and to select the most suitable line combination for cross line breeding. For example in organic farming, which is strongly supported and nominated as the most favourable production system by the German Ministry of Agriculture, some protein sources are banned. Feed formulation according to the nutrient demand of efficient and very productive layers is more complicated in comparison to regular farming.
The challenge for birds is much higher in comparison with housing in cages and feeding with well balanced diets based on the latest scientific knowledge. It is well known that light intensity, feed quality, feed structure, floor quality, group size, stocking density and air quality may influence the redirection of pecking towards other birds. However, no single causal factor has so far been identified and it is widely accepted that the development of feather pecking reflects multifactorial processes.
Differences in performance between cage and floor housing
Similar to field experiences, in random sample tests with floor management a major increase of mortality and a reduced efficiency of production in comparison to cage testing can be observed (Table 2 and Table 3). Differences in ranking for income over feed cost between testing stations indicate that there is a variable degree of adaptability of strains to various environments. For both stations egg weight profile and feed efficiency are very similar on strain level. Rate of lay and mortality are showing the biggest changes from one environment to another. On the other hand number of tested birds per strain is very limited and general liveability in the cage environment was very good.
Field and test station results indicate, that data recording and selection has to be done in an environment that resembles the production environment as closely as possible to minimise the risk of selection errors due to genotype x environment interactions.
Energy requirements of laying hens
The higher energy requirement of hens in alternative management systems leads to a reduction in egg weight unless the shortfall is made up by increased feed consumption or by raising the energy density of the diet. In the past bodyweight and feed intake capacity of brown laying hens were continuously reduced in an effort to improve feed conversion efficacy and hence reduce production costs per egg.
Attempts to increase feed consumption in the short term to cover supply deficits, especially at the onset of production, often fail on commercial farms. The consequence may be weight loss at an age when the hens should still be gaining weight. This is associated with physiological stresses, which impose a heavy strain on the metabolism and may increase susceptibility to disease. Until these stress factors can be identified and alleviated by changes in management and feeding practices, the birds are at high risk of sustaining permanent damage. Poor egg weight is the least of the problems encountered. Far more serious consequences are feather loss and coli infections because these may also be associated with increasing losses due to cannibalism.
In order to ensure metabolic stability of laying hens and reduce their general susceptibility to stress, producers are increasingly looking for hens with a higher bodyweight. But heavier hens must eat more every day to maintain their bodyweight. The energy requirement of a laying hen is determined by the maintenance requirement, which is linked to liveweight, the requirement for egg production and the requirement for liveweight gain. Maintenance requirement of laying hens in cage systems differs from that of free-range hens, not only because of the far greater freedom of movement of free-range hens, but also because the latter expend more energy on heat formation and conduction. In addition, the energy required for maintaining body temperature is greatly influenced by the condition of the plumage.
In order to allow for the greater energy needs under alternative management systems, the energy requirement should be increased by 10% for floor-housed hens and by 15% for free-range hens. These figures are recommendations only and are not backed up by accurate measurements.
As ambient temperatures in floor and free-range systems can fall considerably below the optimum range during the winter months, feeding capacity and feed supply have to be flexible to maintain a constant level of production. For example, if the ambient temperature falls by 10°C, the maintenance requirement rises by 15%. This implies that for the same level of production the feed intake needs to be raised by about 10 g to maintain body temperature.
Breeding target
To generate a genetic stock, which is most suitable for this management and environment, specific breeding goals and tailor made selection strategies have to be defined.The improvement of layer hybrids for cage production through breeding work has essentially the following objectives:
- Maximum number of 'saleable' eggs per hen housed;
- Minimum feed costs per egg or per kg egg mass;
- Optimum egg quality;
- Low losses, resistance to stress, high adaptability;
- Good parent stock performance.
Selection priorities for alternative housing:
- Strong plumage;
- Docile behaviour;
- Metabolic stability;
- Performance related feed intake opposed to indirect selection for a higher bodyweight.
Performance testing
If selection against feather pecking is part of a breeding programme, data recording and selection have to be done in an environment that resembles the production environment as closely as possible to minimise the risk of selection errors due to genotype x environment interaction. Group size has a significant effect on the social structure within an environment. If the group is small the hierarchy among its members will be very stable. With increasing group size the frequency of changes in ranking will be much greater, including the risk of fighting. Both feather pecking and cannibalism will become much more prevalent.
Scoring the plumage quality on different parts of the body is a common tool for studying the genetics of feather pecking behaviour in laying hens. Individual scores of full and half sib daughters caged together are used as input for breeding value estimation and selection. With increasing age a higher frequency of damage can be observed. Higher heritability estimates indicating that genetic variability is more visibly expressed in older birds. A disadvantage of this testing system is that feather pecking, aggressive pecking and cloacal cannibalism cannot be recorded as single traits.
Exposure to a challenge test (high light intensity and stocking density, no beak trimming, large group size up to 28 birds/cage) increases the variation between families. With increasing heritability the genetic merit for each bird can be estimated more accurately, resulting in a wider genetic selection differential and increased genetic progress. This enables us to select for lower frequency of feather pecking and lower prevalence of cannibalism. Special attention is paid to docile behaviour. Group cage tests have shown marked differences in behaviour and losses due to cannibalism not only between lines but also between families.
Figures 1 and 2 compare losses due to cannibalism per family among non-beaktrimmed hens at high light intensity.
Whereas in line 1 (Figure 1) 12% of the hens on average had to be prematurely removed from the groups as a result of cannibalism, only 6% of the hens in line 2 were affected (Figure 2).
It became apparent that within the lines few families exhibit extreme values in excess of 10%.
In Figure 1 the extremes range from over 50% to 70%.
This illustrates that it is not only line selection but also strict selection within lines which can contribute to a reduction in the incidence of cannibalism and feather pecking. Preference is given to direct selection with testing of individual families rather than indirect selection for a higher bodyweight.
There is no firm correlation within the lines between bodyweight and the cull rate as a result of cannibalism. This eliminates indirect selection for higher bodyweights as a long-term strategy for reducing cannibalism. The more docile behaviour and, consequently, the lower risk of cannibalism and feather pecking can reduce the loss rate in alternative systems.
Conclusion
The energy requirement of hens reared in floor and free-range systems is considerably higher than in cage systems. The actual requirement for the same level of production is determined by the ambient temperature and the condition of the hens' plumage. With increasing age feather cover will be damaged and energy requirement to keep body temperature will increase. In order to achieve rapidly rising egg weights at the start of production, the hens' feed intake must be maximised. Direct selection for a performance related feed intake at the onset of production reduces the risk of metabolic strain as a result of an energy deficit. From a management point of view every effort should be made to ensure that the feed intake rises as fast as possible at the start of production to reduce any risk of nutrient imbalance.
Recording of mortality and the reason of death in wing-banded pedigree stock is a major part of the selection procedure. But separation between aggressors and victims is more important when losses due to cannibalism have to be reduced. In breeding programmes preference is given to sire ranking for rate of mortality in different housing systems to optimise within line selection and to avoid the risk genotype x environment interaction. New line combinations are tested in different environments including cages with different stocking density and group size varying from 4 bird cages up to 28 hens and floor housing. Scoring individual birds for plumage quality and estimation of breeding values for liveability are the most effective tools to adapt the breeding stocks to customer demands for alternative housing.
Preference in breeding programmes for birds dedicated to alternative farming systems is given to direct selection against premature losses and for a stronger plumage of the hens as opposed to indirect selection for a higher bodyweight. In order to improve egg number, shell colour and strength, the proven testing procedures established for all commercial lines are used throughout and implemented in the selection process. Optimising feed intake increase and egg mass output increase in the first third of the production cycle are the most critical trait combination in selecting birds for alternative housing systems.
From Proceedings of 11th European Poultry Conference, Bremen, Germany.
