In laying hens, animal welfare is particularly focused on feather pecking behaviour. In this respect nutrition plays an important role. Feed form, feeding strategy and nutritional factors all seem to have their influence on the birds satiety and pecking behaviour.
By Dr Marinus van Krimpen, Wageningen UR Livestock Research, Lelystad, the Netherlands
From 2012 onwards, a ban has been introduced on cage housing systems for laying hens in the European Union with some countries planning a ban on beak trimming as well. These changes could induce problems with feather pecking (FP) and cannibalism. FP is a multifactorial problem, influenced by genetics, environment and nutrition. Some theories support a nutritional approach of reducing FP. More specifically, we expect that imprinting of pullets on feed in early life might explain a decrease in feather damage at adult stage.
Effect of early life experiences Early life experiences seem to play an important role in the development of FP behaviour. Early life is a critical and sensitive period, in which imprinting takes place. In this period, social binding and environmental influences are important for the entire life period. In a study, pullets were raised on sand, straw, or wire between 0-4 weeks of age. Thereafter all groups were kept on sand and straw. The hens raised on wire had the lowest plumage condition, showed more FP, had lower dust bathing activity and had higher mortality rates due to cannibalism, compared to the other groups. This indicated that the first four weeks of life have a large influence on the development in FP behaviour.
In another study, the effect of early substrate exposure was investigated. Birds were kept on wire floors, and at different ages wire was replaced by solid floors with wood shavings. Adult hens kept on wire floors during their entire life, showed more FP compared to hens kept on floors with wood shavings, despite the time of exposure to wood shavings. Hens kept on wood shavings showed more ground pecking. Time of exposure seemed to influence FP rates. Pullets that had access to sand at the age of 10 days showed more FP, compared to pullets that had access to sand at one day after hatching. Pullets kept on wire floors without possibilities to explore, seemed to develop more gentle FP, which finally might lead to severe FP.
Feed form and feeding strategy In laying hens, feed is mostly given in mash form. In literature, it was found that supplementing pelleted diets resulted in more feather pecking. A significant interaction was shown between the presence/absence of foraging material (with or without long straw) and food form (mash or pellet).
High rates of feather pecking and pronounced feather damage were only found in laying hens housed without straw and fed on pellets, indicating that laying hens (especially when fed pellets) should be provided with an adequate amount of foraging material. Chickens engage in more feeding related behaviour when fed finely ground mash than when fed coarsely ground mash, crumbles or pellets, as shown by an increased eating time and a higher frequency of feed pecking. Increasing feeding related behaviour will fulfil the need of the foraging behaviour of the laying hens, which may lead to a decrease in feather pecking (Figure 1).
Diet composition influential The contents of protein, minerals, energy and fibre can affect FP behaviour. Reduced energy levels can improve plumage condition. In a study, an undiluted control diet and a diet diluted with 40% cellulose powder were compared in Japanese quail. Feed intake increased in the birds that received the diluted diet, indicating that they were able to compensate for the lower dietary energy content. Meal length was more prolonged, inter-meal interval length reduced, and a higher number of meals were consumed per day. The diluted diet left the crop faster, and showed a higher total tract transit time indicating that passage rate was also affected by diluting the diet and reducing the dietary energy content.
Especially insoluble fibres will increase eating time in laying hens. The passage rate of digesta through the gizzard was found to be reduced due to increased levels of coarse fibres in the diet. Pullets that were fed low energy diets increased their eating rate, without increasing eating time. During the rearing period, reduced energy levels had more effect on FP behaviour than increased Non-Starch Polysaccharides (NSP) levels. Providing high insoluble NSP diets during the laying period, however, resulted in less feather damage compared to the hens that were given standard diets. The positive effects of feeding NSP diluted diets on feather damage during the laying period were more expressed if these diets were provided during both the rearing and laying period, compared to hens that were fed these diets only during the rearing or the laying period (Figure 2).
Satiety in laying hens The mechanisms of regulation of satiety and related sensation of hunger in poultry and the associated effects on FP behaviour are not yet fully understood. The gizzard is a gastro intestinal tract (GIT) part that seems to play an important role in regulation of nutrient passage. Insoluble fibres play an important role in gizzard activity. They accumulate in the gizzard and are retained longer than other nutrients, probably because digesta has to be ground to a critical particle size before entering the small intestine.
It is expected that an increased mean retention time of digesta in the gizzard might increase satiety levels of the birds. The retention time of feed in the foregut and the development of the gizzard are increased in hens that were fed a coarsely ground NSP diluted diet compared to a finely ground NSP diluted diet. Moreover, gut viscosity and gut fill would be increased by insoluble dietary fibre, probably due to their water holding capacity. In the absence of dietary fibre, feather eating can occur. Until now, no causal factors for feather eating are known. These observations indicate that feather eating and pecking behaviour may be partly related to feed structure, which may affect the quantity of digesta in the gizzard.
Provide low energy diet Nutritional factors that increase feeding related behaviour and induce satiety are expected to reduce FP behaviour in rearing and laying hens. It is advised to provide rearing and laying hens a low energy diet (2,450 and 2,600 kcal, respectively) with a high insoluble NSP content (150 and 125 g/kg, respectively). NSP source should be provided in a course form during the second half of the rearing period and during the laying period.