Sow performance in multi-suckling pens with different management routines
© The Author(s) 2018
Received: 2 October 2017
Accepted: 5 February 2018
Published: 8 February 2018
Production systems with group housing of sows during a part of the lactation are used in certified organic production and can increase the occurrence of lactational estrus thus making batch-wise breeding difficult. The aim of this study was to investigate the occurrence of lactational estrus and time at return to estrus after weaning by following the performance of the sow (change in body weight, back fat and litter size) in three different management routines. The sows and their litters were moved from individual to multi-suckling pen at one (W1; n = 14), two (W2; n = 13), or 3 weeks (W3; n = 16) post farrowing. All sows had a total lactation of 6 weeks. Ovulation was monitored by analysis of fecal progesterone metabolites. Only one sow (W3) ovulated during lactation. Sows in the W2 and W3 groups had a shorter weaning-to-standing estrus interval than W1-sows (2.6 ± 0.3; 2.7 ± 0.2 and 4.0 ± 0.3 days respectively, P < 0.001). The W1-sows and piglets might have kept their nursing bond more intact all through the group housing since the piglets were completely dependent on the nursing at the time of their move to the group pen, thereby staying in lactational anestrus and retaining standard weaning-estrous interval. There was no difference in litter size at grouping or at weaning between management routines and parities. Third and later parity sows had significantly thicker back fat at farrowing and at weaning than 1st and 2nd parity sows (P < 0.05). In conclusion, the occurrence of lactational estrus can be low in a multi-suckling pen and the interval between farrowing and move to a multi-suckling pen can affect the weaning to estrus interval. The short weaning-to-standing estrus interval seen in W2 and W3 suggests that estrus detection should start immediately post weaning for sows kept in multi-suckling pens.
Production systems with group housing of sows during a part of the lactation are used in some niche production systems such as certified organic production . Keeping lactating sows in multi-suckling pens rather than individual farrowing pens can impair production through increased occurrence of lactational estrus [2, 3]. The return to estrus usually occurs in late lactation, particularly among older sows and sows in good body condition, and this late occurrence results in a prolonged weaning-to-service interval, making batch-wise breeding difficult [2, 4, 5].
The aims of this study were to investigate (1) occurrence of estrus during lactation and weaning-to-estrus interval in three management routines and (2) differences in other aspects of sow performance, i.e. weight, back fat, weight loss, and back fat loss during lactation, and litter size at onset of group housing and at weaning.
Differences between management routines (W1–W3) with regard to litter size, lactation length, weight, and back fat at farrowing and weaning (Lsmeans ± S.E), and parity (number of sows)
12.5 ± 0.7
13.3 ± 0.8
11.8 ± 0.7
10.4 ± 0.6
10.4 ± 0.7
9.8 ± 0.6
9.0 ± 0.6
9.6 ± 0.6
9.6 ± 0.5
Lactation period (days)
44.2 ± 0.6
43.6 ± 0.6
43.7 ± 0.6
Sow weight (kg)
257.7 ± 7.8
266.7 ± 8.2
256.1 ± 7.6
246.8 ± 7.3ab
263.6 ± 7.6a
233.5 ± 7.1b
− 11.2 ± 5.7ab
− 1.0 ± 6.1a
− 22.4 ± 5.5b
Back fat (mm)
17.5 ± 1.2
17.4 ± 1.3
19.0 ± 1.2
14.0 ± 1.0
16.8 ± 1.1
15.2 ± 1.0
− 3.6 ± 0.8a
− 0.5 ± 0.9b
− 3.8 ± 0.8a
> 2nd parity
Differences between parities with regard to litter size, lactation length, weight, and back fat at farrowing and weaning (Lsmeans ± S.E)
1st party sows
2nd parity sows
> 2nd parity sows
12.4 ± 0.9
12.6 ± 0.7
12.6 ± 0.7
10.5 ± 0.7
10.1 ± 0.6
10.0 ± 0.6
9.3 ± 0.7
10.0 ± 0.6
9.0 ± 0.5
Lactation period (days)
43.5 ± 0.4
43.9 ± 0.4
44.1 ± 0.4
Sow weight (kg)
213.3 ± 7.2a
264.4 ± 6.1b
302.9 ± 6.3c
210.9 ± 8.1a
244.3 ± 6.5b
288.7 ± 6.5c
− 0.2 ± 6.3a
− 20.1 ± 5.0b
− 14.4 ± 5.1ab
Back fat (mm)
16.1 ± 1.1a
18.0 ± 1.0a
20.3 ± 1.0b
12.6 ± 1.3a
14.8 ± 1.0a
18.5 ± 1.0b
− 3.0 ± 1.0
− 3.0 ± 0.8
− 1.8 ± 0.8
During the group housing period daily manual estrus detection tests were performed by inspection vulva swelling and reddening and by applying back pressure. Post weaning, manual estrus detection was performed twice a day with a boar present until estrus was detected.
Fecal samples were collected from the rectum every third day from day 21 post farrowing until the day of weaning and stored at − 20 °C until analysis.
Sows were slaughtered after the first reported standing estrus post weaning and the reproductive tract was retrieved and examined macroscopically.
At farrowing and weaning, each sow’s back fat thickness was measured ultrasonically by experienced staff using a Krautkramer USM22 device (GE Inspection Technology GmBH, Hürth, Germany) at the last rib, between 7 and 8 cm from the middle of the back .
Most of the progesterone in feces is present in a metabolized form  and progesterone and its metabolites are referred to hereafter as progestin. The method used for extracting progestin from feces was modified from Palme et al.  and Wasser et al. . One gram feces was mixed with 10 mL methanol (≥ 99.9%) and the slurry obtained was shaken for 1 h, followed by 15 min of centrifugation at 3000×g at room temperature. Three milliliters of the supernatant was then stored at − 20 °C until analysis. The analysis was conducted using a solid-phase 125I-radioimmunassay (Coat-a-count Progesterone, Siemens Healthcare Diagnostic Inc, Los Angeles, CA, USA) previously validated for pig feces . The analysis was performed according to the manufacturer’s instructions. The inter-assay coefficient of variation for high, medium, and low concentrations was 12, 12 and 14%, respectively. The intra-assay coefficient of variation was below 10%, within the working range of 0.3–127 nmol/L.
All statistical analyses were performed using SAS software ver. 9.3 (SAS Inst., Cary, NC, USA). To analyze differences between management routines regarding days from weaning to standing estrus, the procedure Mixed was used. Fixed effects included were management routine, repeat, parity, and subset. Litter size at group housing was added as covariate. Random effect was repeat nested within management routine and subset. Subset did not influence the outcomes. To analyze progestin profiles, the 99th and 97.5th ‰ were calculated from the progestin concentration in every fecal sample  collected at day 21 post farrowing. The progestin concentration in the fecal samples collected at day 21 post farrowing was considered to represent anestral levels of progesterone. The 99th ‰ was 67 nmol/L and the 97.5th ‰ was 48 nmol/L. Ovulation was considered to be possible if one fecal sample had a concentration above 67 nmol/L or if two consecutive fecal samples had a concentration above 48 nmol/L. P < 0.05 were considered significant.
There were no differences between management routines or between parities in the number of live born piglets and litter size at grouping and at weaning (Tables 1 and 2). Body condition loss during lactation also seemed influenced by timing of grouping (with the W2-sows having less body weight and back fat loss) but could be due to individual variation and that the W2 group had numerically less first parity sows than the W1 and W3 group (Table 1). The > 2nd parity sows were heavier and had more back fat than 1st and 2nd parity sows at farrowing and weaning (Table 2). This difference is not surprising, as young sows are still growing and have not accumulated as much back fat as older sows [19, 20]. There was no apparent connection between back fat loss or body weight loss and weaning-to-standing estrus interval. Previous studies have also reported a lack of significant correlation between back fat loss and weaning-to-standing estrus interval [19, 21].
In conclusion, sows group housed at 2 or 3 weeks post farrowing in multi-suckling pens had a shorter interval from weaning to standing estrus than sows group housed at 1 week post farrowing, which had a normal interval. This could be due to differences in nursing–suckling establishment and interaction in the group housing pen. These results suggest that estrus detection should start immediately post weaning for sows kept in multi-suckling pens, in order to avoid missing the onset of estrus. The occurrence of lactational estrus was found to be low in these multi-suckling pens.
OT, ASB, YCBS, UM and LES participated in the planning of the project. OT, ASB and YCBS performed the collection of feces and reproductive tract examination. OT and YCBS were responsible for drafting the manuscript. ASB, UM and LES revised the manuscript. All authors read and approved the final manuscript.
We want to thank the staff at Lövsta Research Station, Swedish University of Agricultural Sciences. Figure no. 1 was first published in “Aggression and cortisol levels in three different group housing routines for lactating sows” .
The authors declare that they have no competing interests.
Availability of data and materials
The datasets created during and/or analysed during the current study are available from the corresponding author on reasonable request.
Consent for publication
Ethics approval and consent to participate
The study was approved by the Uppsala Animal Ethics Committee (C154/11). No human data or tissue were used in this study and consent to participate is therefore not applicable.
This study was financially supported by the Swedish Research Council Formas. The funding body had no role in the design of the study, collection, analysis, or interpretation of data or in writing of the manuscript.
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