Abstract
Farm animals routinely undergo painful husbandry procedures early in life, including disbudding and castration in calves and goat kids, tail docking and castration in piglets and lambs, and beak trimming in chicks. In rodents, inflammatory events soon after birth, when physiological systems are developing and sensitive to perturbation, can profoundly alter phenotypic outcomes later in life. This review summarizes the current state of research on long-term phenotypic consequences of neonatal painful procedures in rodents and farm animals, and discusses the implications for farm animal welfare. Rodents exposed to early life inflammation show a hypo-/hyper-responsive profile to pain-, fear-, and anxiety-inducing stimuli, manifesting as an initial attenuation in responses that transitions into hyperresponsivity with increasing age or cumulative stress. Neonatal inflammation also predisposes rodents to cognitive, social, and reproductive deficits, and there is some evidence that adverse effects may be passed to offspring. The outcomes of neonatal inflammation are modulated by injury etiology, age at the time of injury and time of testing, sex, pain management, and rearing environment. Equivalent research examining long-term phenotypic consequences of early life painful procedures in farm animals is greatly lacking, despite obvious implications for welfare and performance. Improved understanding of how these procedures shape phenotypes will inform efforts to mitigate negative outcomes through reduction, replacement, and refinement of current practices.
Highlights
Animals in intensive farming systems routinely undergo painful procedures in early life that involve some form of anatomical modification
This finding—an initial attenuation in fear behavior following neonatal inflammation that is reversed by age and/or cumulative stress—parallels the hypo-/hyper-responsive profile observed for pain sensitivity discussed above
Some exceptions have been reported, with adult rodents exposed to early life inflammation exhibiting no change (Comim et al, 2016; Bukhari et al, 2018; Ranger et al, 2019; Mooney-Leber and Brummelte, 2020) or a reduction in anxiety behavior (Victoria et al, 2013, 2015)
Summary
Animals in intensive farming systems routinely undergo painful procedures in early life that involve some form of anatomical modification. Painful procedures are among the most emotive of public concerns about animal welfare, and are subject to increasing voluntary standards or legislation depending on country (Phillips et al, 2009; Lundmark et al, 2013). Many of these regulations recommend or mandate that mutilations are performed at the youngest age possible, in many cases within the 1st week of life, to minimize tissue damage and improve handling ease (Table 1). Removing the horn buds on calves or goat kids when they are free-floating under the skin (disbudding) is less invasive than removing horns that have attached to the skull (dehorning; Stafford and Mellor, 2011)
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