Sow mortality: why, who, where, when, what?

Ciarán Carroll addresses the increasing sow mortality rates in Ireland, highlighting factors contributing to these rates, and outlines strategies for reducing mortality, emphasizing the importance of accurate records.

By international levels, the Irish figure is not high. Data from InterPig 2022 shows sow mortality levels at 14.5% in the US, 14.3% in Spain, 12.6% in Denmark and 11.3% in Sweden. That said, the increase in Ireland in recent years (2.7% since 2015) merits attention. Economically, it has resulted in losses of over €1.6 million to the National herd. Why are mortality levels increasing, who (what sows) are we losing, when are we losing them and what can we do about it?

Sow Mortality on Irish farms (2015-2022 – Teagasc Profit Monitor)

Why?

Sow mortality can be categorised by type, i.e. sows intentionally euthanized on-farm or sows that died naturally (unassisted). With increased focus on sow welfare, the pig sector has responded and farmers are now more likely to euthanize sows on- farm rather than send them to the slaughter house. This improved attention to welfare accounts for some of the increase in sow mortality that we’ve seen. A Danish study (Pedersen and Brendstrup, 1998) investigating the causes of sow mortality reported that 42 % were euthanized and 58 % died unassisted. The same study showed that the most likely cause of death for sows being euthanized was leg problems, and for sows dying unassisted most died of stomach or intestine problems, categorized after necropsy, but often referred to as “other causes”. Similar results have been reported in other studies.

Of sows euthanized, information from farmers indicated that over 76% of them were for locomotor (leg) problems. This has been further supported by necropsy studies of sows euthanized, showing 70% for leg problems (Vestergaard et al, 2004). In the same study, information from farmers indicated that for sows dying unassisted, the majority of the problems can be summarized as 52.1% “other causes”, 21.6% disease and 13% farrowing complications while the necropsies reported 24% torsion of organs, 23% farrowing complications, 18% stomach & intestine, and 24% other/no specific cause. This shows the disparity between what the farmer can think caused the problem and what the necropsy actually shows. Thus, it’s important that you get your vet to regularly carry out a necropsy on a proportion of your sow deaths.

Who, Where & When?

Teagasc research showed that 30% of sows were culled before their third parity, with up to 15% of gilts selected not even having one litter. Another study (Kirk et al. 2005) found that almost 40 % of the sows in their study were dead before the second parity. Engblom et al. (2007) found that it was among young sows (parity 1-3) that the highest proportion died unassisted (naturally). The percentage of euthanized sows increased with parity, i.e. older sows were more often euthanized than found unassisted dead.

A pilot study of a sample of Danish pig farms in 2015 showed that for sows that died unassisted, most occurred in the farrowing and service area, whereas for sows that were euthanized, more were in the sick pens. In the dry sow section, there was an equal distribution between euthanasia and unassisted deaths.

The same study showed that leg problems were the most frequent cause of death in the sick pens housing animals from the dry sow and service area. Stomach ulcers and rectal prolapse were most frequent in sick pens where the animals came from the farrowing unit.

Many studies (Vestergaard et al. 2004; Thorup et al. 2010 and Kirk et al. 2005) have shown that the time around farrowing was associated with a higher risk of death. Work presented by Dr. Mark Knauer, NCSU on the SowBridge programme (January 2024) detailed how sows with recorded abnormalities (perineal swelling, leg problems, or “looked bad”) in late gestation were three times more likely to die than sows that were normal. While this helped somewhat regarding the focus on abnormalities and treating or removing such sows, there were still 85% of sows that showed no abnormalities (that had died).

What?

So, having identified the why, who, where, and when of sow mortality, what can be done to reduce it? It has to begin with accurate records. If we don’t measure, we can’t control! We need records of culling and mortality reasons (both euthanized and unassisted).

A detailed report by Sorensen & Thomsen, Aarhus University (2017) titled ‘Identification of Risk Factors and Strategies for Reducing Sow Mortality’ listed some strategies and recommendations to reduce sow mortality from a Danish project ‘Soliv’, involving vets and advisor consultants, where over a three-year period (2007-2010) herds reduced their sow mortality by 5 percentage points.

The recommendations included: optimizing housing and feeding systems; improved feed hygiene; strategies for introducing sows and gilts into loose housing reducing the numbers of movement and mixing; better body condition control by feeding; 3-5 daily feeds in the farrowing room; systematic planning of daily observation of sows; systematic use of sick pens with daily recording; quarterly stomach examinations of culled sows by vets.

Regarding the daily surveillance suggestion, work in the US presented by Chris Rademacher (DVM at Iowa SU) in the SowBridge programme (October 2023) detailed an approach to identify and treat “at-risk sows” in stalls and group housing on a 4,000 sow farm. The farm vet trained farm staff to identify the disadvantaged or “at-risk” sows and advised as to how they should be treated. The process involved staff observing sows at feeding time and flagging those sows by hanging a card at the stall/pen. The sows were either treated on identification or later in the day, as per the farm SOP. The main issues identified were “off-feed”, lame, fever, respiratory, discharge, open wound. Sows “off-feed” was the primary sign, while 30% had two symptoms (mostly off-feed + lame). Gilts were the primary parity identified as at-risk (35%). In stalled sows this strategy took almost two hours per day and resulted in a 4.25% reduction in annualised sow mortality (from 16.75% to 12.5%) and was worth $50 (€46) per sow. In group-housed pregnant sows the process takes a little longer (more difficult to identify at-risk sows in groups) but has similar benefits for the herd.

In the Sorensen & Thomsen 2017 report, they further listed some recommendations to reduce sow mortality for both euthanized and unassisted deaths separately.

Euthanized sows

• A major reason for euthanized sows is lameness, therefore systematic observation, including seeing all sows walk every day, using an easy recording of lame sows and using observation lists is recommended.
• Teagasc research (Lagoda et 2021) on a commercial farm and presented at the Annual Pig Farmers’ Conference 2023 highlighted the importance of locomotion scoring for the early detection and treatment of lameness. Detecting subtle changes in a gilts walking ability requires a sensitive method and Teagasc developed a ‘visual analogue scale’ scoring system.
• Systematic action for lame sows : use of sick pens and planned use of antibiotics/analgesics (under veterinary approval).
• Hospital pens: quality and capacity are important.
• Improved self-inspection procedures made by the farmer and followed up by PVP welfare visits should include sow mortality as a key focus area.
• Systematic strategies and clear criteria for euthanasia should be implemented, check out the infographic.
• There is a need for more research in the prevention of lameness in sow herds.

Unassisted death of sows

• Information on time of death and the body condition of a dead sow should be gathered.
• Systematic strategies for using necropsies should be an integral part of the herd health plan (agreed with your PVP).
• Information on stomach ulcers and organ torsions from culled sows should be provided systematically by the slaughter house (there may be a future role for this via the DAFM AM/PM Data reporting system).
• Systematic plans for diagnoses leading to action on all main diseases should be available in all sow herds.
• More research into the causes and methods for preventing unassisted death focusing on farrowing and lactation is needed.

References available from the author.