Social Status Differentially Affects Behavioral and Immunological Outcomes of Group-Kept Sows Fed Different Dietary Fiber Using Different Length Feeding Barriers

Eridia Pacheco,Mayra Lopez,Janeen L Salak-Johnson

doi:10.3389/fanim.2021.719136

Abstract

Social conflict is inevitable among group-housed sows and may contribute to poorer welfare among those sows experiencing more social stress. The degree of individual welfare is associated with social position within the group. Therefore, this study examined the effects of social status on behavior, immune, endocrine, and productivity of group-housed pregnant sows fed a diet supplemented with 30% wheat middlings and 15% soybean hulls (MID-SH) or 30% distillers dried grains with solubles and 30% corn germ meal (DDGS-GM) and in pens with individual feeding places made from short (58.4 cm) or long (203.2 cm) barriers. A 2 × 2 factorial design resulted in 4 experimental treatment groups (n= 9 sows/diet-length-block combination): (1) MID-SHshort; (2) MID-SHlong; (3) DDGS-GMshort; (4) DDGS-GMlong. Groups of sows equally representing all diet-length combinations across 4 blocks (n= 36 sows/block) were subjected to a feeding competition test to identify highest (dominant) and lowest (subordinate) ranked sows within each group resulting in 64 sows (n= 16 sows/treatment;n= 32 sows/social status). Data revealed 2- and 3-way interactive effects on aggressive behavior (P&lt; 0.005), postural (P&lt; 0.01), oral (P&lt; 0.0001), and eating (P&lt; 0.005) behaviors, sow mean body weights and gains (P&lt; 0.05) and litter weaning weights (P&lt; 0.05), especially among subordinates in pens with long barriers. Subordinates in pens with long barriers received 21% less aggression and were 73% less likely to be displaced than subordinates in pens with short ones (P&lt; 0.0001). Dietary treatment also influenced some of these measures among the subordinates in pens with long barriers. For example, subordinates in DDGS-GMlongreceived 64 and 67% less aggression than subordinates in DDGS-GMshortand MID-SHshort(P&lt; 0.005). Eat bouts were greatest among subordinates in MID-SHlong, and sitting and sham-chewing were less. However, those in DDGS-GMlongspent less time standing and laying, and their litters were 15.28 kg heavier (P= 0.01), but overall subordinates fed DDGS-GM diet were lightest and gained less total body weight than those fed MID-SH (P&lt; 0.05). Other measures such as neutrophil-to-lymphocyte ratio were elevated among dominants in MID-SHlong(P&lt; 0.05); whereas, cortisol (P= 0.06) was lowest and glucose (P= 0.09) highest for subordinates in DDGS-GMlong.These data imply that subordinates benefited from being housed in pens with long barriers, but the type of dietary fiber consumed differentially influenced behavioral budget and several sow- or litter-related traits among subordinates in pens with long barriers. In contrast, the subordinates in pens with short barriers had poorer welfare regardless of diet. Collectively, these data imply that social status is a crucial factor contributing to variation in individual well-being among group-housed sows and that sows of different social positions within a group may evoke different biological responses in an attempt to cope.

Highlights

Group housing of gestating sows provides the opportunity for sows to exercise, express normal behaviors, and socially interact with conspecifics
Sow social status may be one of the most critical and overlooked factors influencing welfare variation among grouphoused gestating sows. These results revealed that the biological consequences of adapting to social conflict and the degree of individual welfare among loose-housed pregnant sows are partly influenced by social status
Social status may explain the differential behavioral and immunological responses and productivity outcomes between sows in the same pen environments. These data imply that dominant and subordinate sows use different coping mechanisms to adapt to their pen environment constraints, indicating that the stress they experienced was different due to their social position within the group or individual perception. These results validate that the interactive role of social status, the housing infrastructure, and fiber diets can differentially affect the individual welfare of gestating sows, but reducing competition around feeding, especially for the subordinate sows, may be beneficial

Summary

Introduction

Group housing of gestating sows provides the opportunity for sows to exercise, express normal behaviors, and socially interact with conspecifics. The social interactions are not always positive, and for some sows in the group, it may result in chronic stress. Sows kept in group pens experience acute stress due to inevitable social conflicts. Others experience chronic stress often associated with prolonged social stress or aggression, resulting in compromised well-being. Social relationships affect individuals’ ability to access resources, which, in turn, affects the level of aggression and, individual welfare, especially lower-ranked sows (Verdon et al, 2015). Previous research implies that subordinate sows are more likely to receive more aggression and be displaced more often from resources; they are most vulnerable and more likely to experience poorer welfare than higher-rank sows (Hoy et al, 2009; Zhao et al, 2013)

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