Egg Industry Center

Research Library

Research files are added periodically on a range of topics found in this library. Library resources consist of old and new research related to the egg production and processing industry.

Animal Welfare


Highlighting the economic differences of beak trimming through the study of sixteen replicates of laying hens housed in a commercial caged facility, this proceeding measured numerous egg production parameters. Findings show hens not beak trimmed had almost a 40% higher mortality rate and consumed 5.5% more feed over their production cycle. This translated into a cost advantage of $0.24 for a beak trimmed flock over 78 weeks of production.

Alternative housing styles may affect stress levels of hens. In the Coalition for Sustainable Egg Supply (CSES) study researchers reviewed the impact of housing systems on bird stress through assessment of laying hen blood chemistry.

The wing vein blood of two flocks at weeks 18 and 77 was used to determine the heterophil-lymphocyte ratios (H/L) and total white blood cell counts (TWBC). H/L values from aviary housed and conventional caged birds were not statistically significant, while the H/L ratio of enriched colony birds was two times higher. However, the high variability among cages suggests the H/L ratio is not an effective indicator of stress when applied alone.

The TWBC analysis indicated an increase in the number of white blood cells, and a high frequency of irregularly structured cells, which signify a higher stress response. However, it was noted that the presence of bacteria, fungi and yeasts in the blood could have accounted for these elevated levels as well.

Housing systems are found to affect the bone quality of pullets. The Coalition for Sustainable Egg Supply (CSES) study randomly selected and euthanized 120 pullets at 16 weeks of age from both conventional cage (CC) and aviary (AV) housing systems. Their tibia and humerus bones were collected and analyzed by computed tomography. Brachial vein blood samples were also taken from random birds at weeks 4, 8, 12 and 16 to analyze serum relevant in quantifying systemic bone markers. Overall, CC pullets were found to have longer bones while AV birds had stronger bones relative to bone width and cortical thickness. The improved load-bearing capabilities and stiffness in the AV pullet tibia and humerus bones were likely due to the number of activities available to birds in that housing style.

The Welfare Quality Assessment (WQA) was used in part of the Coalition for Sustainable Egg Supply (CSES) project to compare hens in three housing systems: aviary (AV), conventional cage (CC) and enriched colonies (EC). Lohmann LSL Classic White laying hens were placed in all three housing systems at 19 weeks of age and assessed at 52 and 72 weeks for the duration of two flocks. Evaluators used both the WQA and necropsies to assess welfare and found the WQA tool to be an acceptable method regarding hen welfare, as the results from both methods yielded similar results. AV and EC systems had more keel abnormalities and fewer foot abnormalities than CC houses. The overall feather cover was found to be the best in AV hens, although their feathers were the dirtiest.

The impact of open access to litter on hen behavior and welfare was studied to better understand its influence on overall bird wellbeing when in a commercial aviary housing system. This study observed two flocks of Lohmann White laying hens specifically regarding dust bathing and piling behaviors in an aviary system that had the ability to confine birds for part of the day. Hens were observed from weeks 19 and 17 to weeks 77 and 78 respectively. Hens did not appear to have a preference of location within the open litter area, as the entire area was used. Peak dust bathing was found to occur in the afternoon and late morning. 174 incidents of piling were recorded with variations in size, duration and time of occurrence. While dust bathing is a natural behavior important to hen welfare, further research is needed to investigate the implications of piling as it could lead to welfare concerns.

A study was conducted to analyze how space affects feeding behavior. Lohmann Selected Leghorn Lite hens were housed in both small furnished cages and large furnished cages at two different stocking densities for each type of cage: 748 cm 2/hen (116 in 2/hen) and 520 cm 2/hen (81 in 2/hen). Feeders were ran five times a day at 0500, 0800, 1100, 1400 and 1700 hours. Lights came on at 0500 and turned off at 1900. A digital recording was scanned at the chain feeder every 15 minutes after feeding for an hour to count the number of birds presently feeding. Aggressive pecks and displacements were recorded as well. Results concluded there was little evidence that space allowance and cage size influenced feeder competition or aggressive pecks and displacement behaviors, as the percentage of birds feeding was similar regardless. The frequency of aggressive pecking was low as well as the feeder competition; however, researchers did note that the greatest number of hens fed at 1700 hours.

A two-part study measured hen performance in relation to space allowance. At 18 weeks old, four groups of Lohmann Selected Leghorn Lite hens were housed in either smaller furnished cages (SFC) or larger furnished cages (LFC) with access to nesting areas, perches and scratch mats. Two stocking densities for each type of cage were used: 748 cm 2/hen (116 in 2/hen) and 520 cm 2/hen (81 in 2/hen). Feed was given five times a day. At weeks 30, 50, 60 and 70; 20% of the hens were randomly selected to evaluate production parameters such as hen day egg production, egg weight, egg shell deformation, breaking strength of femur, tibia or humerus, birds suffering from keel bone deformations or foot health scores. While performance and mortality were not significantly affected by cage size or space allowance, hens with less space had higher feed disappearance and poorer feather cleanliness and condition; hence, the animal welfare was found to decrease with lower space allowance. There was no difference in bone strength or foot health scores between the two treatments.

Can enrichment increase health?

Researchers aimed to investigate the relationship between commercially applied environmental enrichment (EE), plumage condition, and fearfulness. Forty-five indoor multi-tiered aviary system flocks of laying hens from across Norway were visited at end of lay (70-76 wk of age). Data was collected on five types of enrichment: pecking stones, gravel, oyster shells, scattered grains, and “toys”. Feather loss was assessed individually in 50 hens per flock using the NorWel method. Assessment was done visually, to avoid disturbing the flock, and scores were awarded using a 3-point scale. Fearfulness was measured using a novel object (NO) test which measured the number of hens that approach the NO in a set period of time. The NO test was performed in four different locations in each hen house.

The results of the study showed that there was no correlation found between the number of hens approaching the NO and the age at which each type of EE was provided. Providing toys at an early age was correlated with a reduction in the amount of tail damage at the end of the production period. Increasing the amount of gravel stones also showed a positive effect on the condition of the tail feathers.

While it could not be proven that gravel stones directly affected feather peaking incidence, results suggest that the grit provision most likely functions as a diversion for hens to focus foraging and pecking activity. Therefore, it seems that enrichment objects that increase the quality and complexity of litter can help minimize peaking behavior.

Producer Takeaway: In aviary systems, the impact of enrichment objects increases if provided early in life and in larger quantities. 

The combination of high temperatures and relative humidity can induce heat stress in birds.

Limited studies have been performed on the impact of humidity on laying hens because most studies have focused on thermal environments and adjustments.

Researchers investigated the role of relative humidity on production by using 180 Hy-Line brown laying hens (68-wk-old) and dividing them into three treatment groups; Low (25%), Moderate (50%), and High (75%) Relative Humidity (RH). Hens in treatment chambers were kept at 86 degrees F and exposed to the different levels of RH. Parameters were measured in birds and eggs at days 3, 7, 14, 21 and 28 days of trial. Plasma, yolk, and albumen corticosterone (CORT) concentrations were measured. CORT is a key stress hormone in laying hens and measuring CORT in egg yolks is a non-invasive method for assessing a hen’s stress response.

The RH treatments did not affect hen-day egg production, egg weight, feed conversion ratio, or egg mass. Feed intake was lower in the high RH group. The blood H/L ratio (stress indicator) was not affected by RH treatments throughout the experiment, but plasma, egg yolk and albumen CORT concentration was elevated in the High RH group. Relative humidity also changed lipid metabolism and further work is needed to understand if it affects mineral metabolism.

Producer Take Away: Relative humidity at or above 75% in environments at or above 86 degrees F may be an important environmental factor in triggering stress response in laying hens. Birds in these conditions exhibited significantly reduced feed intake, increased stress responses and decreased laying performance and egg quality. 

X-rays may help genetics companies.

The development of alternative housing systems has increased the opportunity for falls and collisions, which are associated with kneel injuries and bone damage. It has been suspected that genetic factors underlie susceptibility of hen’s bone quality issues; however, assessment of bone quality parameters is made post-mortem which makes it hard to implement genetic selection to improve bone quality. Previous technologies for live bird evaluation are too time consuming to be practical. Researchers used 50 end of lay (~65 wks) Lohmann brown hens to optimize the assessment of images obtained through X-ray exposure of the dead hens. Hen bones were then measured through the traditional post-modem bone quality measuring system. Next, diet manipulation of Hy-line Brown Layers was used to produce a large range of bone breaking strength and density values. Live radiographs were taken three times throughout the various feeding trials and the hens were culled for post-mortem assessment. The methodology developed for measuring bone qualities with x-ray imagery correlated strongly with accepted post-mortem bone quality measurements for bone density. Reproducibility and repeatability of this technology; in addition to its portability, rapid image-taking ability (45 sec), and lack of need for sedation makes this a practical method to measure laying hen leg bones for reduced damage and fracture. In addition, human radiation exposure allowed for over 60,000 radiographs to be taken per year before reaching regulated maximum annual dosage limits.

Producer Takeaway: New technology makes it possible for genetics companies to evaluate bone quality measurements in live birds. This may speed up the genetic selection process for laying hen leg bone strength traits. 

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