The development of novel approaches to assess and improve skeletal integrity in laying hens

Kemp, A.D., 2021. The development of novel approaches to assess and improve skeletal integrity in laying hens. PhD, Nottingham Trent University.

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High demand for egg products over the last couple of decades has increased the need of supply in egg production. As a consequence, modern laying hens are being put under increased pressure from extended periods of egg production causing increased susceptibility to skeletal disorders such as osteoporosis and skeletal damage. Assessment of skeletal health through measuring bone parameters such as bone strength or bone mineral density is common practice, however, the methods used in previous research vary between research groups and studies. The overarching aim of this study was to assess the effect of different housing systems on skeletal health and egg qualities of laying hens over the period of lay, using new methodology and modelling parameters to help maintain hen welfare whilst possibly increasing the laying cycle of future flocks. A series of trials were carried out to achieve this aim.

Three pilot studies were carried out in the initial stages to determine the optimal bones to be measured in subsequent trials. These studies concluded that multiple bones showed differences due to differences in form and function, and that future studies would therefore need to measure several bones to get a true picture of the birds’ skeletal health. Using methodologies influenced by the pilot studies a longer study, split into two parts was carried out to assess the effect of housing system on skeletal integrity and egg quality over the laying period. After the larger trial, another trial was performed using the previously established methodologies to see if they could be used to assess the effectiveness of a novel supplement.

Part one focussed on the effects on bone parameters while part two focussed on the effects on egg quality. The longitudinal study showed that bone strength of the keel, tibiae and humeri were significantly affected by age (p < 0.001), housing system (p < 0.001), and the interaction effect between age and housing system (p < 0.001) with the caged system showing some of the poorest results ((18 weeks MT keel = 173.13N (13.542), 18 weeks C keel = 105.38N (13.542), 72 weeks MT keel = 130.80N (13.542), 72 weeks C keel = 81.74N (14.363)). Bone ash content of the keel, humerus and tibia was also significantly affected by age (p < 0.001), housing system (p < 0.001) and age*housing system (p < 0.001). Caged bone ash content showed some of the lowest values though organic some of the highest ((24 weeks O tibia = 44.36% (0.677), 24 weeks C tibia = 41.91% (0.677), 60 weeks O tibia = 44.28% (0.742), 60 weeks C tibia = 42.73% (0.697)). It was highlighted that bone strength may be more informative than bone ash content when assessing skeletal integrity, as bone ash content results are thought to be more influenced by the presence of medullary bone than bone strength. Furthermore, the modelling estimates of bone data in this chapter showed that bone weight was a significant predictor of bones strength (p < 0.001; estimate = 23.60), showing as bone weight increases, bone strength would increase at the estimated rate. Model parameters also showed free-range flat deck (p = 0.020; estimate 27.37), free-range multi-tier (p < 0.001; estimate = 38.30) and organic bone strength were significantly stronger than caged tibia strength (p < 0.001; estimate = 56.78). Barn (p = 0.024; estimate = -10.64) and free-range flat deck (p = 0.025; estimate = -10.92) bone strength declined significantly faster than caged bone strength between 18-72 weeks of age, with free range flat deck declining slightly faster than barn. Humerus bone strength declined significantly faster than tibia bone strength (p < 0.001). Keel bone strength also declined significantly faster than tibia bone strength (p < 0.001).

In part two of the longitudinal study - investigating the effect of housing system on egg quality traits over the laying period - results showed that all egg quality parameters were significantly affected by age, housing system and the interaction effect (p = 0.007 or less). Egg weight increased from mid lay onwards (36 weeks onwards) with organic showing the heaviest weights of all systems. Egg height showed an increase over age (p < 0.001) from 24 weeks of age to 36 weeks of age and then another increase from 48 weeks to 72 weeks of age. Organic egg height was the largest towards the end of lay with multi-tier and cage being some of the smallest. Eggshell strength of the multi-tier and flat deck systems were highest at the beginning of lay, though declined quicker than other systems between weeks 24 and 36. In barn systems, eggshell strength was some of the weakest results during mid to late lay, whilst organic showed some of the highest breaking strengths in the same period. Results for eggshell ash content were somewhat unclear as barn data was significantly higher at 72 weeks compared to all other systems, where in other measurements barn data showed some of the lowest results. It was shown that in late lay (between 60-72 weeks) eggshell thickness is greatly influenced by age (p < 0.001), however multi-tier eggshell thickness and caged eggshell thickness increased slightly while other systems declined sharply.

Regarding egg modelling data, ash weight was a significant predictor of eggshell strength (p < 0.001; estimate = 3.73), showing as ash weight increases eggshell strength would increase at the estimated rate. Furthermore, model parameters showed as age increased eggshell strength decreased when using caged eggshell strength as the baseline (p < 0.001; estimate = -0.16). Barn eggshell strength was also shown to decline significantly faster over the laying period than caged eggshell strength (p = 0.036; estimate = -0.29). When assessing if a relationship was present between egg and bone strength residual data, no relationship was found. It may be that the lack of interaction between data sets were caused by how broadly egg and bone strength data was collapsed at farm level to enable a comparison.

The last part of this project was to determine if these methodologies created from the pilot studies and longitudinal study could identify differences in the effects of a novel supplement. This was done by investigating the effects of a novel silicon supplement on skeletal health and egg quality traits post laying cycle. The study found little effect of the diet on any bone parameters of any bone throughout (diet effect - bone length; p = 0.099 or higher, bone width; p = 0.285 or higher, bone weight; p = 0.157 or higher, bone strength; p = 0.083 or higher), making it difficult to the determine the useful of the methods developed previously. It was suggested that the effect of changing housing system may have concealed the effect of silicon supplementation, due to the change in exercise which is known to improve skeletal health.

It was concluded from the project that when assessing skeletal health, multiple bones be used to ensure all areas of the skeletal system are assessed due to form and function varying between bone. For example, a wing bone performs a different locomotory movement compared to a leg bone. It would be recommended from work in this project that utilising the keel, humerus and tibia would be adequate to cover all aspects of skeletal form and function in the bird, in relation to assessing skeletal health. Measuring bone geometry along with strength was also considered important as these parameters were found to be sensitive to factor effects even after sexual maturity. It was unexpected that results for bone lengths and widths in pilot studies 1 and 2 were still affected by housing system, post maturity. Additionally, egg parameters were not considered meaningful data for skeletal assessment as it was somewhat evident egg production likely takes precedent over skeletal maintenance. Model parameters to assess skeletal health in laying hens would be beneficial in future work. Ultimately, the modelling of skeletal data could act as an early warning system to indicate any potential decline in skeletal parameters within the laying period and allow producers to be proactive in their response. An early response to a skeletal problem could help maintain or possibly improve productivity at a time when there is a drive to produce more eggs per bird, whilst simultaneously maintaining a high standard of hen welfare.

Item Type: Thesis
Description: Abridged version
Creators: Kemp, A.D.
Date: September 2021
Rights: This copyright in this work is held by the author, Alexander Kemp. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required should be directed to the author.
Divisions: Schools > School of Animal, Rural and Environmental Sciences
Record created by: Linda Sullivan
Date Added: 14 Feb 2023 12:14
Last Modified: 14 Feb 2023 12:14

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