The U.S. egg industry is at a crossroads; the conventional cage, which has been the standard means of housing hens in this country for decades, has been challenged on animal welfare grounds. At this time, the two primary alternatives to conventional cage housing are enriched colony cages and cage-free aviaries. The Coalition for a Sustainable Egg Supply (see sidebar) is sponsoring commercial-scale research looking at the sustainability of these three hen housing systems in five key areas.
Dr. Darrin M. Karcher, poultry extension specialist, Michigan State University, speaking at the Midwest Poultry Federation Convention, presented some data on bird health and performance for the first flock of birds in the Sustainable Egg Project. This research project is being conducted on a scale that has not been attempted before, with each housing alternative having at least 50,000 birds per flock in the test. The first flock was housed in April of 2011 and has completed its laying cycle. Approximately 200,000 study hens were housed in conventional cages, and 50,000 each were housed in aviaries and enriched cages.
When comparing the attributes and shortcomings of the three housing systems, Karcher said that it is important to remember that it is likely that no housing system will yield the best or optimum result for each measurement taken. He said, “One of the challenges that you are presented with is that you have to decide what is most important? What is the thing you are willing to sacrifice to get another measure of performance? Which of these measures is most important to you or to the hen?”
This project attempts to provide information on a diverse group of measurements for birds in three housing alternatives all collected at the same time. Then it will be a matter of evaluating the pros and cons of each system to determine which holds the most promise for the future.
Birds housed in both the aviaries and the enriched cages used more feed per 100 birds than did the hens in conventional cages, which Karcher said came in very close to the expected results based on the genetic guide. He said that the increased room to move around was a primary reason for the increased feed consumption per 100 layers in the alternative housing systems. Feed conversion, measured as pounds of feed consumed per pound of egg produced, was best for the enriched colony hens and was worst for the aviary housed hens, with conventional cage hens in between the other two.
The highest water consumption was in the conventional cages. Karcher explained that the conventional cages were in operation prior to the beginning of this study, but the aviary and enriched colonies were new construction. He speculated that some of the increased water usage in the conventional cage houses was due to the age and condition of the equipment.
Hens housed in the enriched colonies utilized the nest area for laying eggs. Karcher said that 93-96 percent of eggs are laid in the nest area in the enriched colonies. In the aviary, 89 percent of the eggs were laid in the nest boxes. Conventional cages do not have nest areas.
Nest pads stay clean in both the enriched colonies and the aviaries, according to Karcher. Using a standard scoring system developed in Europe where zero is the cleanest and eight is the dirtiest, the median score for the nest pads in both systems was one. Scratch pads located in the scratch and foraging area of the enriched colony didn’t stay clean. The median score for scratch pads was seven.
A computer system was used for analyzing pictures of the litter area in the aviary system. The computer could distinguish between birds and litter. Heaviest use of the litter area is during the afternoon, and the litter area is used more the longer the flock is in the aviary system. Most dust bathing in the aviaries occurred in the afternoon, and approximately 22 percent of hens dust bathe in the litter area each day. In the enriched colony cages, approximately 30 percent of the hens exhibit dust bathing behavior each day with about half of these performing the behavior on the scratch pad.
Most of the foraging on the scratch pad occurs in the afternoon, but only 2-3 percent of birds in the enriched colony actually get to forage for food in the scratch pad area before the food is gone. Karcher said that the birds that are closest to the scratch pad when the auger turns on get the feed. Other hens will “race across the cage” to the scratch pad area when the auger runs, but most will be too late. He said the amount of soiling on the scratch pad raises questions as to whether the potential food safety and bird health issues that might arise from the exposure to manure on the scratch pad are worth the “benefit” derived from allowing the hens to forage and dust bathe here.
At the end of lay, at 72 weeks of age, the aviary birds have longer nails than did hens in conventional or enriched cages. Karcher said that they think the litter might have been too deep in the aviary; if the litter wasn’t as deep, the hens might have worn their nails down more on the concrete under the litter.
Conventional cages had the worst foot pad scores. Aviary birds tended to have slightly better foot pads than the enriched cages did.
At the end of the study, conventional cage hens had less feather coverage on the neck and breast due to abrasion of rubbing on the cages at the feeder. Aviary hens had less feather coverage on the top of the head, which researchers attribute to aggressive pecking. Karcher said that overall the aviary hens had the best feather coverage, yet they had the dirtiest feathers.
Enriched colony housed hens had feather loss on the neck and breast, presumably for the same reason as the caged hens, and they have some feather loss on the head probably coming from somewhat increased pecking that takes place in the enriched cage when compared to conventional cages.
Mortality necropsy results
Necropsies were performed on mortalities daily for the first 15 days, then every other day for a period, and finally, twice per week. In total, necropsies were performed on 252 conventional, 335 aviary and 244 enriched colony housed hens. Karcher said that the mortality rate was highest in the aviary system and that there were more “missed” mortalities in the two alternative systems.
Aviary housed hens had more “peck outs,” fractures and keel issues. The fewest keel issues were found in the conventional cages.
Hens in the enriched colonies had the most damage at placement. Karcher said that in the aviary system, most mortalities were due to bird behavior issues, from equipment and from worker issues. Conventional cage-housed hens had the least behavioral mortalities and the highest rate of egg yolk peritonitis mortality.
Dr. Hongwei Xin, professor, agricultural and biosystems engineering, Iowa State University, said that the aviary and enriched colony system utilized roughly three and two times, respectively, as much space per hen as the conventional cage system. All three housing systems utilized manure belts, but hens in the aviary system could defecate in portions of the enclosure without a manure belt. Manure is removed on belts every three to four days. The manure in the litter area of the aviary is left in for the entire flock, but they can cake out if necessary when the birds are in the system.
Air quality measurements were taken inside the layer house, of the layer house exhaust and from the exhaust from the manure storage areas. Houses were tunnel ventilated and supplemental heaters were provided for the aviary only.
Xin said that temperature and relative humidity were generally maintained in the thermo-comfort range for the birds in all houses, but the aviaries got a little warmer in the summer. Daily mean ammonia levels were below 15 parts per million in the conventional and enriched cages throughout the monitoring period. However, the aviary house, even with supplemental heat added, had days where medium ammonia levels went over 25 parts per million.
There was less ammonia produced per bird in the enriched house than in either of the other housing types. Ammonia production was 36, 33 and 16 grams per day per bird in the conventional cages, aviary and enriched colony houses, respectively. It would be interesting to know what impact the increased water use in the conventional house mentioned by Karcher had on ammonia production. Xin said that the manure was drier on the belts in the enriched colony house. He said that for all three housing systems, the majority of ammonia emissions come from the manure storage area, with between two thirds to three quarters of the ammonia emissions coming from there.
Dust levels were eight to 10 times greater in the aviary houses because of the litter and dust bathing. Dust levels are higher in afternoons for aviaries because birds do most dust bathing in the afternoon. The lowest particulate matter emissions were from the enriched colonies, and the highest were from the aviaries.
The winter of 2011-2012 was a relatively mild one in Iowa where the study took place. At $1.50 per gallon for propane, the cost of heating the aviaries added 0.2 cents per dozen eggs. If the aviary house had been maintained at the same temperature and air quality levels as those attained in the other two housing systems, then the heating cost would have been greater.