Livestock Research for Rural Development 31 (5) 2019 Guide for preparation of papers LRRD Newsletter

Citation of this paper

Reasons for sow removal and its effect on stayability in a production unit in the Southeast of Mexico

J C Segura Correa, J R Aké-Villanueva, J G Magaña-Monforte, R H Santos-Ricalde and V M Segura-Correa1

Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán, Km 15.5 carretera Mérida-Xmatkuil, Mérida, Yucatán, México. C.P. 97315
1 Centro de Investigación Regional del Sureste, INIFAP km 25 carretera Mérida-Motul, C.P. 97454, Mocochá, Yucatán, México


Sow removal is a common practice in commercial pig production units to ensure acceptable production levels within the herd. The aims of this study were to estimate the reasons for sow removal, to determine the effect of parity number when removal occurred and its effect on stayability of the sow in the herd. A retrospective study was carried out using records of 302 sow removed from a production unit located in the Southeast of Mexico. Descriptive statistics were used for the reason of removing and analysis of variance for the stayability of sows in the herd.

Reproductive problems accounted for 40.7 % (n =123) of sow removed, old age (38.7 %, n = 117), disease (8.61 %, n = 26), miscellaneous (5.96 %, n = 18), low production (3.97 %, n = 12) and lameness (1.99 %, n = 6). Removal was highest in old (>5 parities) and primiparous sows. First parity sows and gilts had the highest frequencies of removal (24.4 and 13.8%, respectively) due to reproductive failure reasons. Within the reproductive failure category (n=123), abortion (10.3%) and repeated estrous (8.61%) were the most common reasons for removal. Sows removed for old age stayed longer in the herd (1076 days) and those removed for low production reason stayed the least time. There is a need to improve the selection criteria of gilts, reproductive efficiency and health to increase productivity in the farm.

Key words: culling, parity, reproduction, season, tropics


Sow removal is a common practice in commercial pig production units to ensure acceptable production levels within the sow herd. The reasons for removal in a commercial sow herd have been documented, and many studies mention that the major reasons are associated with reproductive problems, lameness and low production (Engblom et al 2007; Mote et al 2009; Segura-Correa et al 2011a). The contribution of each of these reasons varies depending on herd, region and management practices. Management decisions rule in great measure the implementation of removal policies, which give more control to pig farmers over which animals remain in the herd and which ones will be removed (Sasaki and Koketsu 2012). Lack of such guidelines will result in an increase in unplanned sow removal. In addition, the effect of removal reasons on stayability of sows in the herd was investigated. Sow stayability in the herd is a large component of profitability for commercial pigs operations taking into account that at least three litters per sow are neccesary to recover the investment costs (Mote et al 2009).

The aims of this study were to estimate the frequency of reasons for sow removal, to determine the effect of parity number when removal occurred and its effect on stayability of the sow in a commercial farm in the Southeast of Mexico.

Material and methods

Location and climate

The study was carried out at a commercial sow farm located in the east of Yucatán, Mexico. The climate of the region is sub-humid tropical, with a range in temperature from 18 to 36 °C, an average rainfall of 1,100 mm and relative humidity of 78% (INEGI 2004).

Data and variables

The study was undertaken using information of 302 removed females, recorded from 2010 to 2014, in a commercial farrow-to-finish farm. Data were collected from sow record books kept in the PigChamp software. The information collected corresponded to sow identification, date of entrance to breeding, date of removal, removal reason and number of parity at removal. Thirty-four specific reasons were identified, which were grouped into six general categories (Table 1). Reproductive failure included anestrous, repeated estrous, conception failure, prolapse, dystocia, abortion, and vaginal discharge. Locomotor problems included lameness, bad aplombs and downer sow syndrome. The downer sow syndrome consisted of any condition that impedes a sow to stand or walk. Low production comprises low litter size and disgalactea. Disease category was associated with ileitis, peritonitis, mastitis, digestive problems, pneumonia and ulcer. The miscellaneous category included sows removed because of poor body condition, injuries, trauma or unidentified causes. Parity was defined as the number of farrowings of a sow. Sows with nine farrowings were grouped into eight-parity group, due to a low number of observations.

Table 1. Categories of removal reasons
Removal reason Components
Reproduction Anoestrous, repeated estrous, vaginal discharge, empty, excess service, abortion, prolapse, dystocia
Locomotion problems Downer sow syndrome, lameness, bad aplomb
Low production Small litter size <6, disgalactea
Disease Ileitis, peritonitis, mastitis, digestive problems, pneumonia, ulcer
Old age Old age
Miscellaneous Poor body condition, nutritional causes, unidentified causes
Statistical analysis

Descriptive statistics to calculate frequencies of removal reasons across parities was used. The hypothesis of an equal proportion of sows removed across parities was tested, for the total number of sows removed and for reproductive reasons, using chi-square tests. Furthermore, the effect of reasons for removal on staying of sows was evaluated using analysis of variance. Statistical analyses were carried out with the SAS program (SAS 2010).


Removal reasons

Reproductive failure contributed to the largest proportion of sow removals, followed by old age (Table 2). Throughout all parities, reproduction failure was an important reason for removal. Old age was an important reason for sows with 5 or more parities. Locomotion problems started to be important after parity 2. Within the specific reasons for removal in the reproductive failure category, abortion, anestrous and repeated estrous were the most common reasons (Table 3). In the disease category, ulcers were the most common reason for removal. According to the Chi-square test, the proportions of sows removed considering all reasons and due to only reproductive failure reasons were significantly different among parities (p<0.01). In Table 2, it is appreciated that of the 302 females studied, more sows were removed when they had 7 or 8 parities, follow by primiparous sows. From all females removed due to reproductive failures, 38.2 % were gilts and primiparous sows.

Table 2. Frequency (%) of gilt/sow removed by removal reason
Reason Parity at removal No. %
0 1 2 3 4 5 6 7 8
Reproductive failure 13.8 24.4 14.6 12.2 12.2 10.6 8.94 2.44 0.81 123 40.7
Locomotion problems 0 0 0 33.3 33.3 16.7 0 16.67 0 6 1.99
Low production 0 16.7 25.0 33.3 0 16.7 0 8.33 0 12 3.97
Disease 19.2 23.1 3.85 11.5 15.4 15.4 3.85 7.69 0 26 8.61
Old Age 0 0 0 0 0 0.85 20.5 43.6 35.04 117 38.7
Miscellaneous 11.1 22.2 22.2 0 16.7 16.7 0 11.1 0 18 5.96
Total 8.61 13.3 8.61 7.95 7.95 7.95 11.9 19.9 13.91 302 100

Table 3. Removal reasons given as number of gilts/ sows within each specific reason, frequencies within each removal reason and as a percentage of the total gilts/sows culled
Specific reason Number (%) Specific reason Number (%)
Reproduction (n=123): Locomotion (n=6):
Abortion 31 (10.3) Downer sow syndrome 3 (0.99)
Repeated estrous 26 (8.61) Lameness 2 (0.66)
Anestrous 14(4.64) Bad aplombs 1 (0.33)
Dystocia 13 (4.30) Disease (n=26):
Vaginal discharge 11 (3.64) Ileitis 2 (0.66)
Prolapse 6 (1.99) Digestive problems 1 (0.33)
Empty 5 (1.65) Mastitis 1(0.33)
Cesarean 3 (0.99) Pneumonia 1(0.33)
Others 14 (4.64) Peritonitis 4(1.32)
Age (n=117): Ulcer 17(5.63)
Old age 117(38.7) Miscellaneous (n=18):
Production (n=12): Body condition 8 (2.65)
Disgalactea 9 (2.98) Injury 4 (1.32)
Low litter size 3 (0.99) Unknown 6 (1.98)

The mean estimated stayability of the sows in the herd was 712 days. The longest stayability of sows by removal reason corresponded to old age category (1076 days) and the lowest to low production (Table 4). Sows removed because of small litter size and disgalactea stayed the shortest time in the herd (444 days), followed by disease reason (449 days). As suspected, sows removed for old age, stayed the longest time in the herd (Table 4). Season of the year when gilts went into the breeding herd and season when sows were removed had no effect (p>0.05) on stayability in the herd.

Table 4. Least squares means and standard errors by sow removal reason for days from the entrance to the breeding herd until removal (stayability)
Reason n Stayability
Old age 117 1076+25.4a
Locomotion problems 6 685+107b
Reproduction failure 123 478+24.1bc
Disease 26 449+51.5c
Low production 12 434+75.3c
Miscellaneous 18 511+62.8bc


Removal reasons

From the young females, 8.61% failed to produce even a single litter, 13.3% were removed from the herd before they produced a second litter. Another 8.61% was removed after producing a second litter and 7.95% were removed after a third litter. Thus, 37.8% of the young females were withdrawn from the herd before they produced the fourth litter when sows start to payoff (Mote et al 2009). The most frequent removal reason was reproductive failure (40.7% of 302 sows) which agree with what was observed by Segura-Correa et al (2011a) in three farms located in the same region of study. However, they found that reproductive problems accounted for 26.9% of the total sows removed. In the United States, Mote et al (2009) found 35.2% of females were removed for that reason. Other authors have also reported reproductive problems of sows as the main reason for removal (Dhliwayo 2007; Engblom et al 2007; Engblom et al 2008b; Mote et al 2009).

Within the reproductive failure reasons, abortion (10.3%) was the major reason for sow removal. Anestrous was the second reason (4.64%), which had a lower value than the relative frequency (34.2%) reported by Segura-Correa et al (2011a) and 25.2% recorded in Japan by Koketsu et al (1997). Some authors have found returns to estrous as the most frequent reason for reproductive failure (Engblom et al 2007; Vargas et al 2009). Vargas et al (2009) mention that differences in the reasons behind reproductive failure (anestrous and repeated returns) in different units of production could be attributed to inaccurate heat detection and suboptimal feed intake during lactation in first and second parity sows. Tummaruk et al (2009) observed that out of the 200 genital tracts of a sample of gilts removed due to reproductive reasons, 50.5% had normal genital organs. This indicates that it was very probable that sows removed due to anestrous and repeated estrous could have been removed due to failure to detect estrous. Anestrous and returns to service seem to be more frequent in early parities (Koketsu et al 1997). This is consistent with the results of the current study that show that 63.5 % of sows removed due to anestrous were primiparous sows, while the same group accounted for 38.2 % of removals due to repeated returns to estrous.

The frequency of abortions, which constituted approximately 10.3% of the total culling, is quite high. Such a high level of abortion is indicative of underlying problems within the herd particularly since the frequency of abortion within each parity is >7 %. Fekete (1999), in a review, reported that environmental influences, immunological and nutritional causes could combine to increase the risk of abortion in a herd if management of those factors is not taken care of. Since data from this study show no evidence that suggests infectious causes of abortion, it is likely that high abortion risk was due to failure to identify and eliminate predisposing factors to sow removal.

 The second reason for removal was old age, which agrees with what was found by Segura-Correa et al (2011a) in three farms in the same region of study. Removal for old age started after parity 5. This agrees with other authors who reported an increase in removal frequency due to age as parity increased (D’Allaire et al 1991; Lucia Jr et al 2000). However, these authors also reported removal due to age in lower parities. The difference with this study is due to allocation of removal reasons, where removals due to age were probably influenced by other factors such as keeping younger sows that have failed to reproduce, and removal due to age and not to reproductive problems. The higher frequencies of removal due to age reported in the literature compared to the current study could be explained by the overlap between removal due to age and productivity (Dhliwayo, 2007; Segura-Correa et al 2011a) as well as inclusion of other factors within the age classification such as overweight sows in lower parities (D’Allaire et al 1991).

The frequency of sows removed because of locomotion problems (1.99%) was much lower than the value of 22.3% reported by Mote et al (2009) for the leg soundness/lameness category. Removal frequencies due to lameness, reported in the literature, exhibit a wide range from 8 to 27 % (D’Allaire et al 1991; Lucia Jr et al 2000; Dhliwayo, 2007; Engblom et al 2007; Segura-Correa et al 2011a). The reason for this wide range of frequencies could be that some authors exclude sows that were euthanized, due to locomotor problems, from the total removed due to this reason, while others opt to include sows euthanized under this group. Euthanasia due to lameness has been observed to be one of the top reasons for sow mortality in commercial herds (D’Allaire et al 1991; Engblom et al 2008a). This might explain why in the current study sow mortality is high while removal due to locomotion problems was low. Locomotion problems were observed in parities 3, 4, 5 and 7, which partially agrees with Lucia Jr et al (2000) and Segura-Correa et al (2011a), where it was observed that the risk of lameness decreases as parity increases. This is probably due to poor selection for structural soundness when sows are still in lower parities. Failure to select for structural soundness in early parities will increase the likelihood of sows suffering from locomotion problems, i.e. footrot, overgrown claws and torn dew-claws when they reach older parities (Dewey et al 1992; Dewey et al 1993).

Removal due to low production of sows had a lower frequency (3.97%) than that reported in the literature, which has a range of 7-37 % (D’Allaire et al 1991; Dhliwayo 2007; Mote et al 2009; Segura-Correa et al 2011a). Here, low production was defined as a sow having a small litter size. However, other authors had additional specific reasons under this category, including low birth and weaning weights of the litter, high preweaning mortality (D’Allaire et al 1991), old age (Dhliwayo 2007; Mote et al 2009), disgalactia (Segura-Correa et al 2011a) and poor body condition score (Soltesz and Balogh 2013). More factors included in this category will result in an increase in the frequency of removal due to low production as observed in the literature.


The average time spent until removal by sows (712 days) was longer than the average found in four farms located in the same region of study (496 days; Segura-Correa et al 2011b). It was also longer than the means estimated for Landrace (617 days), Landrace x Yorkshire (579 days), and Large White (602 days) sows in Switzerland (Yazdi et al 2000; Engblom et al 2008b; Tarrés et al 2006, respectively). Differences between farms could be due to policy decisions, disease presence and genetic lines used (Engblom et al 2007). Other studies (Babot et al 2003; Serenius and Stalder 2007) also noted differences between farms on stayability.



The authors thank the owner of the pig unit for providing the information for this study.

Conflict of interest

The authors declare that they have no conflict of interest.


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Received 17 January 2019; Accepted 4 March 2019; Published 1 May 2019

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