Verlengde productiecyclus bij leghennen

Laying hens are kept in production until the age of 75-80 wk, but the actual egg production period is only 55-60 weeks long, as young pullets start producing eggs approximately at 20 wk of age. During a single laying cycle a hen can produce on average 360 eggs. Extending the egg production period and keeping hens longer, possibly until 100 wk of age would not only contribute to increased profitability but also to more sustainable food production. In a longer laying cycle, the costs of egg production (e.g.: pullet purchase price, feed) are balanced by the earnings of a longer productive period and replacement of hens, depopulation and cleaning of stables would be less often required. However, there are several bottlenecks in extending the production period of laying hens such as declining persistency and egg quality, decreased bone quality, health and welfare. To tackle these problems, a multifactorial approach is needed. Improved genetic selection has to be accompanied by optimal nutrition and management to be able to produce 500 eggs until 100 wk of age which should be feasible by 2020, as layer breeding companies predict. This PhD research focused on the role of nutrition and management in extended production cycles in laying hens. First, a field study was conducted to have a better understanding how eggshell quality changes in the last phase of the production cycle in layer flocks. Secondly, small-scale experiments were conducted where an alternative feeding concept, split feeding was tested to investigate its potential to improve shell quality in aged laying hens. Finally, it was investigated whether split feeding would also be applicable under field conditions in commercial egg production. Apart from nutritional factors, management techniques were also investigated under commercial conditions, such as the effect of an adjusted light stimulation program to achieve a more optimal development of the young pullet during rearing and pre-lay which can contribute to a longer productive laying period. Results of the field study showed that egg quality decreased in the last phase of the production cycle and shell quality became more heterogeneous. However, at end of lay, when flocks were depopulated, shell quality was still acceptable according to table egg standards, as flocks were replaced before decreasing shell quality could cause economic losses. In the concept of a split feeding system hens are fed two nutritionally contrasting diets during the day. In contrast, in conventional layer nutrition, hens are fed one single diet during the day. Offering different nutrients at the moment when these are required during the daily egg formation cycle in the split feeding system might improve feed efficiency, Ca utilization and possibly shell quality. In the small-scale experiments besides testing different nutrient levels in the first and second half of the day, the effect of the particle size of the Ca source (fine and coarse limestone, FL and CL, respectively) in the diet was also assessed. For brown aged laying hens (72-83 wk) significantly lower feed intake and a considerably lower cracked eggs percentage was found when hens were fed a morning diet without added Ca source (0FL:0CL) combined with an afternoon diet with reduced levels of energy, protein and P but increased Ca level with 30FL:70CL compared to a conventional diet offering the same nutrients. Despite the reduced % of cracked eggs with the split feeding system, shell thickness could not be improved. For white aged laying hens (75-92 wk) the same approach in split feeding resulted in increased egg weight but no improvement in shell quality. For white hens providing the same amount of Ca, but only as fine limestone (50FL) in the first half and as coarse limestone (50CL) in the second half of the day, proved to be the most beneficial diet in the split feeding system. Following the small-scale trials, it was investigated whether split feeding would also be applicable under field conditions in commercial egg production. For this, white laying hens were placed in enriched cages and brown laying hens were placed both in enriched cages and aviaries. The results of the large scale experiments in enriched cages suggest that for optimal performance and egg quality white and brown hybrids might require a different nutritional strategy with regard to the amount of Ca source and its particle size in the diet fed in the first and second half of the day. For brown hens varying Ca levels throughout the day in the split feeding system proved to be beneficial in reducing the percentage of cracked eggs, whereas for white hens the best strategy to maintain egg production and quality was the supply of constant Ca levels throughout the day, but in the form of 50FL in the first half and as 50CL in the second half of the day. However, differences between the effects of split vs conventional dietary treatments on eggshell quality were limited. The results of the large scale experiments in enriched cages highlighted that split feeding could improve feed efficiency in aged flocks. In the aviary system however, the practical application of split feeding was more challenging and neither performance nor egg quality could be improved. The benefits of a delayed onset of lay could not be proven with the adjusted lighting program during rearing and the onset of lay compared to a standard program. However, the applied programs were very similar and therefore the intended delay in sexual maturation could not be achieved. Therefore, this study could not confirm that hens raised on a delayed lighting program are more suitable for an extended production cycle. Based on the observations during the field study and the results of the experimental work conducted during this PhD, it can be concluded that there is a potential in commercial layer hybrids for extended production cycles until 100 wk of age and the goal of producing 500 eggs appears to be feasible in 2017. However, results also showed that there are considerable differences between layer hybrids: white hens are more suitable for longer production cycles compared to brown hybrids (in enriched cages as well as in aviary systems). The split feeding concept proved to have potential for aged laying hens, but its successful application requires thorough knowledge of the feeding equipment installed on the farm. Although Ca supplementation is the most important nutritional factor influencing eggshell quality, additional factors related to intestinal health also need to be considered. Maintaining gut health and the integrity of the intestinal segments, with special attention to the duodenum – the main site of Ca and P absorption – is a pre-requisite for good shell quality during a productive extended laying cycle. To successfully extend the laying cycle an overall strategy is needed including optimized nutrition with the focus on improving shell quality, and various management practices with the focus on tackling specific health and welfare problems (such as bone integrity, gut health, feather pecking) arising in different hybrids kept in different housing systems.status: publishe