Sorting by parity to reduce aggression toward first-parity sows in group-gestation housing systems1

Abstract

Young sows are subordinate and vulnerable in group-housing systems because they usually lose most fights and suffer more injuries than mature sows at mixing. This study was conducted to evaluate effects of sorting by parity on reducing aggression and associated stress with the aim to improve welfare and performance of first-parity sows in a group-housed system. Sows and gilts (n = 180) from 6 breeding groups were used. Within each group, 2 groups of 15 females were mixed in each of 2 treatment pens after weaning and remained there throughout the entire gestation period. The control pen consisted of 11 multiparous and 4 first-parity sows, and the treatment pen consisted of 11 gilts and 4 first-parity sows. Before mixing and at the end of the gestation period, sows and gilts were weighed individually, assessed for BCS, and measured for backfat thickness. Injury scores were assessed before and 48 h after mixing and wean-to-mating intervals, farrowing rate, and litter performance at the subsequent farrowing were recorded for all females. Aggressive interactions involving first-parity sows were video recorded for 72 h immediately after mixing in each pen. Data were analyzed using the Glimmix procedure of SAS with a Poisson regression model for count data and a Gaussian model for continuous data. All females in treatment pens sustained fewer scratches (P = 0.01) after mixing than females in control pens. First-parity sows in treatment pens fought more frequently (P = 0.01), tended to fight for longer periods (P = 0.08), and won more fights (P = 0.04) of parallel pressing but had fewer injures (P = 0.03) after mixing, gained more BW (P = 0.01) during gestation, and had greater farrowing rates (P = 0.03) compared with first-parity sows in control pens. The results suggest that sorting by parity shielded first-parity sows from severe injuries caused by mixing-induced aggression so that their welfare and performance can be improved in group housing systems.

Hierarchy formation in newly mixed, group housed sows and management strategies aimed at reducing its impact

“…The authors suggest that primiparous sows should not be grouped with older and bigger animals, as increased attacks and increased injury scores in the younger animals were identified ). Others agree with this and state young sows are more likely to be classified as subordinate, thus making them vulnerable in group housing systems (Bench et al, 2012;Li et al, 2012). The weight difference between parity one sows and multiparous sows is on average 25% (Li et al, 2012) equating to around 200 kg versus 250 kg (Li et al, 2010).…”

“…Others agree with this and state young sows are more likely to be classified as subordinate, thus making them vulnerable in group housing systems (Bench et al, 2012;Li et al, 2012). The weight difference between parity one sows and multiparous sows is on average 25% (Li et al, 2012) equating to around 200 kg versus 250 kg (Li et al, 2010). This weight disparity may help to explain the vulnerability of younger animals in mixed-parity groups.…”

“…When attempting to study the vulnerability of lower parity sows, Li et al (2012) mixed four parity one sows with either 11 gilts or 11 multiparous sows and found that the parity one sows mixed with gilts had fewer scratches and fought and won fights more frequently in the first 72 h following mixing. The authors concluded that housing parity one sows with gilts shielded the young sows from the social and physical stressors that they meet when housed with older parity sows.…”

Validation of an enzyme-linked immunosorbent assay developed for measuring cortisol concentration in human saliva and serum for its applicability to analyze cortisol in pig saliva

“…It has also been reported that mixing of pigs has an effect on cortisol levels as it is considered a result of social stress [9–11]. Further young sows experience more social stress when housed together with older sows and young sows have a higher cortisol level compared to the older sows [12]. An increase in cortisol levels could also be linked to a reduced on-farm animal welfare [13].…”

Behavior, Displacement and Pregnancy Loss in Pigs under an Electronic Sow Feeder

“…Gilts are generally subordinate to sows, and would be likely to receive more aggression and injuries compared with sows (Levis, 2013). Therefore, gilts under ESF systems would have more adaptation failure than sows, and it has been recommended that gilts are housed separately from sows (Levis, 2013;Li, Wang, & Johnston, 2012). Also, difficulties in adapting to ESF systems could be eased by training the pigs before they are introduced into such a system (Chapinal et al, 2010b).…”