Multi-suckling and sow-piglet separation: effects on lactation oestrus

Piglet sucking is the primary cause of lactation anoestrus in sows. It has been proven, separately, that enforced, protracted periods (12 h) of sow-piglet separation and daily boar contact can reliably stimulate a high incidence of lactation oestrus (Kemp and Soede 2012). Within multi-suckling systems, the frequency of suckling reduces as lactation progresses and has been associated with low, but unpredictable, incidences of lactation oestrus (Lindgren et al. 2013). The objective of the current study was to determine whether 6 h of sow-piglet separation of sows housed individually or in groups, increases the incidence of lactation oestrus in response to supervised, daily, boar contact.

Large White × Landrace sows (parity 1.2 ± 0.09; mean ± SEM) suckling 10.3 ± 0.22 piglets were used in a 2 × 2 factorial arrangement of treatments to compare the effect of two housing systems [farrowing crates (n = 23) vs multi suckling (n = 24)] and two periods of sow and piglet separation [zero (n = 23) versus 8 (n = 23) h]. Treatments commenced on d 18.4 ± 0.15 of lactation and ended at weaning on d 27.0 ± 0.15 post-partum. The multi-suckling treatment consisted of three sows and their litters housed together with 4.86 m² of space per sow and litter. The sow-piglet separation involved removing sows from their litters for 6 hours (0800 to 1400 h). From day 18.4 ± 0.15 to weaning or the end of lactation oestrus, whichever came first, sows received 20 min of full, boar contact in a detection mating area. Sow and piglet liveweight (LW) were measured at the start of treatment and at weaning. The timing and incidence of lactation oestrus and piglet mortalities were recorded. Data were analysed using a general ANOVA model, with litter size at the start of treatment included as a covariate (GenStat, 15th Edition; UK). Differences between proportions were analysed by Chi-square. There were no interactions between treatments, so main effects only are presented.

There was no difference in the expression of oestrus in lactation when sows and piglets were housed together as opposed to individually in farrowing crates (70.8% vs 52.2%, P < 0.2). Sows housed in groups took longer (P < 0.05) to express oestrus in lactation (Table 1). The weight and number of piglets at weaning was unaffected by treatment (Table 1). However, more piglets died in group housing compared to farrowing crates between d 18 and weaning (3.9% versus 0.4%, P < 0.05). Piglet mortality rate during late lactation was similar (P > 0.05) in the zero (2%) and 6-h (2%) separation groups.

Table 1.  Effect of two lactation housing systems and two periods of sow-piglet separation from day 18 to 27 of lactation on the expression of oestrus in lactation, piglet weaning weight and sow weight change. Values are means ± SEM

Group housing of sows and litters reduces suckling intensity and increases lactation oestrus in the absence of any additional stimuli (Lindgren et al. 2013), which may explain why lactation oestrus expression appeared to be higher in group housed sows in our study. It is plausible that less fertile sows may ovulate when housed in groups as opposed to individually, as they experience more positive inputs into the hypothalamic-pituitary-ovarian axis, thus explaining the increase in the mean interval to lactation oestrus. Strategies to prevent increased piglet mortalities are required before group lactation housing is a viable option. The apparent increase in lactation oestrus in groups housed sows requires validation using more replicates.