The Impact of Body Condition and Range Use on Free-Range Laying Hens - Identifying and Managing Performance Strategies

Abstract

<p>Cage free housing systems are continuously increasing in numbers, both within Australia and worldwide. Despite the fact that free-range flocks often perform poorly compared to hens housed in barns or cages, free-range egg production system is largely considered superior by consumers, as hens are permitted to express a variety of natural behaviours. Hens in free-range systems are futher permitted to express individual preferences for specific resources provided to them (e.g. outdoor range and litter areas and perches). These preferences may be related to individual differences in hen temperament. As such, in a free-range production system, some hens will always go outside on the range if given the opportunity (referred to hereafter as ‘rangers’), whilst others prefer to stay inside the sheds (referred to hereafter as ‘stayers’).</p> <p>Previous research has identified that these two subpopulations (rangers and stayers) differ in production parameters such as body weight and egg production; rangers were heavier and came into lay earlier than stayers; rangers had higher laying rate (88%) at 22 weeks of age compared to stayers (78.2%). Moreover, stayers were found to be lighter compared to rangers at the point of lay. Howerver, this changed at the age of 72 weeks where stayers had higher laying rate (95.5%) compared to rangers (85.1%). The reason for the differences in body weight and egg production between the subgroups was unknown. Previous studies have shown that bone quality forms a major role in layer production. Physical movement and body weight can have a significant impact on bone health. Moreover, studies have shown that free-range egg production is lower than caged production system which may be associated with greater stress in free-range housing systems specifically related to the outdoor range. If a hen is stressed, she will allocate energy towards a physiological stress response away from biological fitness traits such as growth and reproduction.</p> <p>Therefore, a chronic state of stress will have a long term impact on welfare and productivity. As such, we hypothesized that</p> <p>a. more time spent on the range might have increased activity and therefore, better bone quality in rangers compared to stayers. </p> <p>b. we further hypothesized that the differences in performance and body weight of the two subpopulations of rangers and stayers were reflective of limitations related to feed utilization and/or increased fearfulness and chronic stress between these subpopulations.</p> <p>c. rangers would utilise feed more efficiently, have greater bone strength and would be less fearful than stayer hens.</p> <p>Therefore, the objectives of this thesis were to identify the potential mechanisms that are responsible for the differences in egg production, and body weight between rangers and stayers subpopulations in commercial free-range flocks. </p> <p>There was no difference in any of the bone quality parameters measured between the rangers and stayers. This suggests that bone parameters are likely to be influenced by the opportunity to exercise rather than range as such. Perches and aviary system available in this study might have provided equal opportunity to exercise to the stayers as on the range. However, body weight was found to be related to bone health where heavier hens had stronger bones highlighting the importance of management to meet the targeted body weight. Additionally, we observed that rangers and stayers with light body weights differed in their ability to utilize dietary energy; light rangers utilize feed more efficiently compared to light stayers, meaning that the lighter rangers were able to produce more eggs with the same amount of feed consumed. Interestingly, intestinal organ weights, such as liver, gizzard and pancreas, which are important for nutrient utilization in hens, did not differ significantly between these light stayers and rangers. These results suggest that there were differences in how energy was diverted to either production, growth, maintenance or physiological stress between these two subpopulations. We found no evidence that rangers are less fearful than hens that did not use the range area as frequently. Rather range use was found to be related to curiosity. As this relationship was not reflective in the first few weeks of range access, our results suggest that novelty from the range environment may impact hen temperament and curiosity.</p> <p> This thesis highlighted the importance of body weight in relation to bone health, location use and energy utilisation in a free-range egg production system. Body weight seems to be the major driver of production and perhaps range use, however, causation remains unknown. This research contributes to the limited knowledge on the reasons behind the difference in energy utilisation between hens that access the range frequently and hens that prefer to stay indoor. The findings might suggest the ability of individual choice of use of various spaces in the shed by the stayers and rangers and may be important for hens to manage their own welfare. It is well established that the gut-brain axis induces a direct relationship between physical and psychological stress, behaviour and gut microbiota, dictating physiology, health and disease status of the host. Further study on causal relationships between the body weight and range use as well as microbiota profiling is needed.</p>