One of the major welfare issues facing the egg industry is the high incidence of keel bone fractures or deformities in cage-free and cage housing systems. Bone fractures are not only welfare concerns, but also can negatively affect egg production. In particular, keel fractures account for 90 percent of bone breaks in alternative housing systems at end of lay.
Past studies to improve skeletal integrity have focused on manipulation of environment and nutrition during the layer phase; however, by this stage it may be too late to improve bone quality and reverse the onset of osteoporosis. Pullets reach their mature frame size by 12 weeks of age, with subsequent formation of medullary bone that eventually constitutes up to 19 percent of total body ash. The modern pullet experiences low feed intake at the onset of lay and has the genetic potential to come quickly into peak production; substantial body reserves at the onset of production are indispensable to achieve satisfactory hen performance.
1. Feed large particle limestone to pullets
In trials at the University of Nebraska, Lohmann Brown and Bovan White chicks were started on the floor or in battery brooders and were fed diets that contained either fine or coarse particle limestone, less than 0.431 and 0.879 millimeters, respectively. From 18 to 54 weeks of age, all hens were fed the same diet.
The coarse particle limestone diet increased bone mineral density at 18 weeks of age. Cage-reared pullets also had greater bone mineral density than the aviary birds at 18 weeks of age. White strain hens had more bone mineral density than brown strain hens. During the pullet phase, the odds of pullets fed fine particle limestone displaying keel curvatures were 2.8 times the odds of those fed coarse.
During the layer phase, hens fed the coarse blend as pullets laid eggs with heavier shells. At 54 weeks of age, hens fed coarse blend as pullets had lower odds of keel indentations. Taken together, feeding the coarse limestone blend to pullets improved bone mineralization at the onset of sexual maturity and reduced keel damage during the pullet and layer phases, regardless of strain.
2. Moderating the calcium to phosphorous ratio of pullet rations
Lowering the phosphorous concentration in the pullet grower and developer diets from 0.35 to 0.25 and from 0.30 to 0.20 percent, respectively, was tested in pullets fed either fine or coarse blended limestone particles, less than 0.431 and 0.878 millimeters, respectively. All birds were housed in floor pens and fed the same diets from zero to five weeks of age, the grower diet was fed from five to 14 weeks, and the developed fed from 14 to 18 weeks.
Feeding the coarse blended limestone to pullets increased body weight during the pullet and layer phase only when low phosphorous levels were fed to pullets. The use of low levels of phosphorous during the pullet phase improved late eggshell percentage. The inclusion of different levels of phosphorous and coarse blended limestone did not affect keel bone deformities incidence in the one-tier cage-free housing system. When pullets were fed moderate phosphorus, the pullets fed coarse blended limestone had higher bone area than those fed fine limestone particles at 14 weeks of ages. There were no significant effects on keel bone problems.
Cage-free housing systems offer opportunities for providing hens coarse forms of calcium like oyster shell outside of their regular ration.
3. Increasing level of calcium fed in pullet and layer rations
Pullets and hens were given isocaloric and isoprotein diets containing either standard or increased dietary calcium and phosphorous from seven to 52 weeks of age. The strain of hen and level of dietary calcium and phosphorous affected egg production regardless of housing type. White hens consistently produced more eggs than the Browns, and hens fed diets with supplemental calcium and phosphorus produced more eggs and were more persistent in lay after peak production. Egg weights were positively increased during early lay due to increased levels of calcium and phosphorous.
There was a significant interaction effect of housing system and strain of hen on the incidence of keel bone deformities. Brown hens housed in the aviary systems had the highest rate of keel bone deformities averaging more than 10 percent, followed by white hens in either cages or aviaries averaging more than 4 percent incidence of keel bone indentations. Brown caged hens had very little keel bone deformities. The effects of calcium and phosphorus supplementation were more marked early on in hens housed in cages. Floor pen housed hens did not show much benefit to supplemented calcium and phosphorus on eggshell strength.
4. Supplemental free choice calcium in floor pen systems
A study was started in the summer 2015 looking at the impact of offering free choice oyster shell to Hyline Brown hens housed in aviaries. The oyster shell is offered free choice in small feed pans to the hens and replenished biweekly. The hens love it and are eager to eat fresh shell; some dust bathe in it as well. Measurements of keel bone deformities, eggshell strength and bone mineral density are being made in the hens during this trial.
Research is demonstrating some benefits that can be obtained in skeletal integrity if more attention is paid to the mineral nutrition program of young developing pullets as they go through their developer and early lay stages. Providing large particle limestone during the pullet growth stages improves long-term bone health and possible eggshell quality. Cage-free housing systems offer new options for supplementation of calcium in non-traditional formats that may also improve shell quality and bone health, as well as being a housing enrichment.