Intermittent suckling causes a stress response in piglets that is attenuated over time

Intermittent suckling (IS), where a sow and her piglets are separated for a period of time each day before weaning, can induce oestrus in lactation (Downing et al. 2007). However, the effects of repeated maternal separation on aspects of the piglets’ stress response and the welfare implications of this require examination. This study tested the hypothesis that piglets subjected to IS in the week before weaning would show changes in cortisol, neutrophil : lymphocyte ratios (N : L) and injury scores indicative of a stress response in the peri-weaning period.

Gilt litters (n = 21) were allocated to one of two weaning regimes: conventional weaning (CW), where piglets had continuous access to the sow until weaning at d 29 ± 2.3 (mean ± SD), and IS, where piglets were separated from the sow for 8 h per day (0700 to 1500 h) starting at d 22 ± 1.3 for a week before weaning (d 29 ± 1.3). Creep feed was provided ad libitum from d 14 of lactation. At weaning, litters were mixed within treatment and housed in pens according to sex and size (24–25 pigs per pen, approximately 0.23 m² per piglet). Blood samples were taken from two randomly selected piglets per litter at 1 and 7 days before weaning and six randomly selected pigs per pen at 1 and 7 days after weaning. Blood sampling started at noon and each sample took approximately 90 sec to collect. Samples were not collected from the same piglets at each time point due to ethics requirements. Injury scores adapted from Widowski et al. (2003) were also recorded the day after weaning. Plasma cortisol, N : L ratios and injury scores were compared between treatments using GLM procedures (IBM SPSS, Version 21.0; USA).

Cortisol levels were higher (P = 0.01) in IS piglets 7 days before weaning (i.e. the day after IS began) (Table 1). However the N : L ratio, another measure of the stress response (Davis et al. 2008), tended to be higher (P = 0.07) in CW piglets 7 days before weaning. There was no treatment effect for cortisol or N : L at the other time points. This lack of treatment effect was also reflected in post-weaning injury scores (P = 0.26 for redness and P = 0.32 for scratches). Apart from a peak in cortisol at the start of IS, piglets subjected to IS did not display physiological or behavioural indicators indicative of a stress response the day before weaning and 1 and 7 d after weaning, suggesting that short periods of maternal separation (such as, 8 h/day) do not appear to compromise piglet welfare over the peri-weaning period.

Table 1.  Mean total plasma cortisol and neutrophil : lymphocyte (N : L) ratios before and after weaning for conventionally weaned (CW) and intermittently suckled (IS) piglets