A review of environmental enrichment for laying hens during rearing in relation to their behavioral and physiological development

Abstract

Globally, laying hen production systems are a focus of concern for animal welfare. Recently, the impacts of rearing environments have attracted attention, particularly with the trend toward more complex production systems including aviaries, furnished cages, barn, and free-range. Enriching the rearing environments with physical, sensory, and stimulatory additions can optimize the bird's development but commercial-scale research is limited. In this review, "enrichment" is defined as anything additional added to the bird's environment including structurally complex rearing systems. The impacts of enrichments on visual development, neurobehavioral development, auditory stimulation, skeletal development, immune function, behavioral development of fear and pecking, and specifically pullets destined for free-range systems are summarized and areas for future research identified. Visual enrichment and auditory stimulation may enhance neural development but specific mechanisms of impact and suitable commercial enrichments still need elucidating. Enrichments that target left/right brain hemispheres/behavioral traits may prepare birds for specific types of adult housing environments (caged, indoor, outdoor). Similarly, structural enrichments are needed to optimize skeletal development depending on the adult layer system, but specific physiological processes resulting from different types of exercise are poorly understood. Stimulating appropriate pecking behavior from hatch is critical but producers will need to adapt to different flock preferences to provide enrichments that are utilized by each rearing group. Enrichments have potential to enhance immune function through the application of mild stressors that promote adaptability, and this same principle applies to free-range pullets destined for variable outdoor environments. Complex rearing systems may have multiple benefits, including reducing fear, that improve the transition to the layer facility. Overall, there is a need to commercially validate positive impacts of cost-effective enrichments on bird behavior and physiology.

Effects of Lactobacillus plantarum on intestinal integrity and immune responses of egg-laying chickens infected with Clostridium perfringens under the free-range or the specific pathogen free environment

“…Probiotics are defined as a class of active microbial supplements that are beneficial to the host, improving host intestinal microbial balance and beneficially affecting the host [9]. A large number of studies have shown that probiotics have a variety of biological functions.…”

“…They can produce molecules with antimicrobial activity, target specific pathogens, and even inhibit the adhesion of pathogens. They can also improve intestinal morphology, maintain intestinal microbial balance, and interact with host to improve immunity [9,10,18]. Lactobacillus plantarum and Lactobacillus casei are the most commonly used probiotics.…”

Minimal Effects of Rearing Enrichments on Pullet Behaviour and Welfare

“…Rearing environments for laying hens are important for the physical and behavioural development of pullets [1]. Providing resources in the rearing environment such as litter substrate or perches can ensure appropriate behavioural patterns are formed [2], physical strength is enhanced [3], or immune function is strengthened [4,5], thereby optimising hen welfare as adults.…”

Effects of Lactobacillus plantarum on intestinal integrity and immune responses of egg-laying chickens infected with Clostridium perfringens under the free-range or the specific pathogen free environment

“…They can also improve intestinal morphology, maintain intestinal microbial balance, and interact with host to improve immunity [9,10,18]. Lactobacillus plantarum and Lactobacillus casei are the most commonly used probiotics.…”