Increased foraging in organic layers

Ph.D. thesis of Klaus Horsted

Department of Large Animal Sciences
The Royal Veterinary and Agricultural University and Department of Agroecology
Danish Institute of Agricultural Sciences

Summary
In this thesis, it was hypothesised that hens are capable of finding and utilizing a considerable amount of feed items from a forage area, dependent on the type of supplementary feed and forage vegetation offered.

Thus, increased foraging in organic laying hens may be a way to increase the utilisation of local resources in organic egg production systems. This could increase the cycling of nutrients within the system, ease the transition to 100% organic feed supply, and benefit the economy of the egg production.

Further, this may lead to a greater dispersion of the poultry in the open-air run that in turn may benefit the welfare of the hens and reduce the risk of nutrient leaching in the area closest to the henhouse. On this background, the main objective of this study was to provide better knowledge on the potential of utilizing the foraging of laying hens in a forage-based system.

More specific the aims were: to estimate the intake of herbage from the open-air run, to determine selectivity of forage material in relation to restriction of nutrients in the supplementary feed, to estimate the possible contribution of foraging in meeting nutritional requirements of the poultry, and to suggest forage-based systems.

In this study, experimental work has been done concerning productivity and welfare in a foragebased system, egg quality, estimating feed intake from forage and estimating selectivity of feed from forage. These subjects were investigated in relation to different forage crops and two types of supplementary feed (a complete layer ration versus whole wheat and oyster shells).

Three experimental setups were carried out in this study. In 2004, two short-term experiments (23 days each), each with 12 flocks with 20 hens and one cock in each flock, were carried out. The forage crops consisted of grass/clover versus a mixture of forbs in Experiment 1, and grass/clover versus chicory in Experiment 2. In 2005, a third experiment (130 days), with six flocks with 26 hens and one cock, were conducted. The flocks were moved regularly between grass/clover, pea/vetch/oats, lupin and quinoa.

A discussion on herbage intake from forage is made, using the results from a swardbased method and using the amount of herbage in the crops from hens slaughtered in the evening. The results indicate that hens consume a considerable amount of herbage irrespectively of type of forage and type of supplementary feed, even though nutrient-restricted hens were found to have approximately 50% higher intake.

Thus, intake of grass/clover may be 10-30g per hen per day for non-restricted hens and 20-40g per hen per day for nutrient-restricted hens. However, hens foraging the chicory plots particularly seemed to benefit from forage with approximately twice as high intake of this forage crop as of grass/clover.

Discussion on feed selection using the crop content and microhistological analyses of faeces is made. Analyses of crop content indicate that selectivity among feed items was found to differ in relation to type of supplementary feed. Thus, it was found that wheat-fed hens had more plant material, grit stone, soil, and oyster shells in the crops and less seeds than concentrate-fed hens.

Moreover, wheat-fed hens gave priority to earthworms and larvae even though the amount of this feed item seemed to decrease after a few days in a given forage vegetation. Only to a minor degree did type of forage influence the amount of different feed items in the crops, though the crop rotation experiment indicated a higher intake of quinoa seeds compared with seed of lupin and pea/vetch/oats.

In Experiment 1 microhistological analyses of faeces indicated that nutrient-restricted hens had significantly more of the species of grass Elytriga repens in the faeces, whereas non-restricted hens had more white clover (Trifolium repens).

Further, in the plots with the mixture of forbs, selectivity indices suggested that hens gave priority to plant species nearer the ground, since positive selectivity indices were found for the grasses, Elytriga repens and Lolium perenne as well as for the clover Trifolium repens.

Negative selectivity indices were found for the much taller species of plants, Fagopyrum esculentum and Phacelia tanacetifolia. The possible contribution of metabolizable energy, lysine, methionine and calcium from forage is estimated using the requirements for laying hens and the results on productivity.

After a period of adaptation it was estimated that hens, irrespectively of type of supplementary feed, may consume up to 0.25 MJ ME of their requirements of ME from forage; presumably a little higher for nutrient-restricted hens due to a higher foraging activity. Moreover, it was estimated that the forage area on average had supplied the nutrient-restricted hens with approximately 70% of their requirements according to the feeding standards for lysine and methionine, and approximately 25% of their requirements according to the feeding standards for calcium. Concentrate-fed hens were fully covered through the supplementary feed.

The production in forage-based systems is discussed. On a short-term basis nutrientrestricted hens had a decline in egg production, except for hens foraging the chicory. Further, a tendency to a darker and redder yolk colour was found when hens were foraging the chicory plots. Also albumen DM was higher in eggs from hens foraging chicory. Eggshell parameters were not affected by forage crops or by type of supplementary feed, suggesting that nutrient-restricted hens were provided with the required amount of calcium through oyster shells and foraging material.

After a period of adaptation nutrient-restricted hens were found to produce well in a crop rotation system, since laying rate was comparable to non-restricted hens. Egg weight and body weight was lower in nutrient-restricted hens, though increasing at the end of the experiment. In general, hens fed whole wheat had a lower intake of supplementary feed, even though a distinct increase in this feed was seen after a few weeks.

At the end of the experiment, gizzards were found to be significantly larger for the wheat-fed hens than for the concentrate-fed hens. The effects of productivity and intake of supplementary feed were reflected in the nitrogen and phosphorus balances in the way that N and P surpluses were considerably lower for nutrient-restricted hens. The welfare of hens in forage-based systems was found to be excellent irrespectively of type of supplementary feed.

It was concluded that high-producing layer strains are able to consume considerable amounts of herbage and that forage can provide laying hens with important nutrients. Chicory and quinoa seem promising, just as focus on earthworms has potential. Moreover, it seems possible to lower the standards of important nutrients in the supplementary feed, provided that good forage is available and that the production system supports good welfare of the poultry. A crop rotation system was suggested.

 

Complete Ph.D. Thesis (PDF, 593 kb)

Français

Posted November 2007