CASE NOTES

An investigation into pre-weaning mortality in piglets during Spring 2022 in the Murray LLS region

Katelyn Braine, District Veterinarian, Murray Local Land Services, Deniliquin NSW

Posted Flock and Herd August 2025

Prepared as part of the author's participation in the 2024 NSW Animal Health Frontline Field Epidemiology Training Program

Introduction

Pre-weaning mortality can be a major cause of production loss in piggeries.¹ There are several causes of pre-weaning mortality in pigs including starvation, overlay, savaging and disease.² Poor husbandry may also be a contributing factor to pre-weaning mortalities. This report describes an investigation into increased preweaning mortalities on a small piggery located in the Murray LLS region from October to December 2022.

Methods

The investigative period was identified from October to December 2022. Two farm visits were conducted during the investigative period on 22 November and 7 December 2022.

Data were collected through discussions with the producer regarding the history of the case, and observations of the piggery. Variables recorded included the number and age of pigs on farm, number of litters, litter mortalities, farrowing dates, farrowing pens, environmental conditions at the time of the event, and feed and water sources. Mud maps were drawn of the location of the piggery on the farm and the farrowing shed. A timeline was drawn to outline the disease event and investigative period.

Necropsies were performed on two piglets from a suspect case. Laboratory testing was carried out on samples collected from the necropsies. During the investigative period, a suspect case was defined as a litter born to any sow on the farm during October and November 2022 where the litter mortality rate exceeded the expected mortality rate of the producer on this farm.

Ethics approval was not required as the investigation was conducted under routine surveillance and response activities.

Data from the case were analysed and graphed using Microsoft Excel.

Description of the outbreak

The piggery was located on a mixed enterprise property that also produced fodder, crops and opportunistically ran sheep and cattle.

The piggery consisted of 15 second-parity sows and two boars that were paddock mated. Expected farrowing dates were unknown. The pigs on the property were run predominately free-range, apart from farrowing sows that were moved into an old, naturally ventilated, wooden and corrugated iron pig shed when they started 'bagging up' in the udder. The shed consisted of seven pens containing a wooden flooring covered in dirt. The producer would rotate between the pens being used for farrowing between sows. Lime was used as a disinfectant in each pen between sows.

The farrowing sows were fed a commercial pellet for dry sows in feeders or fed on ground and water through nipple drinkers. Weaner pigs were also being fed the same commercial pellet as the sows and had access to water in troughs. Free-range pigs grazed grass pastures and had access to water in dams.

Usual pre-weaning mortality rates on the farm were described by the producer as he would normally lose the odd piglet or a couple of piglets here and there.

During the investigative period it was reported that there were two litters, litter one and two, born on 18^th October in farrowing pens where all piglets died. Another litter, litter three, was born on 1^st November in a hay bale in the free-range area and did not experience mortalities. Mortalities occurred again in litters, litters four and five, born in farrowing pens on 18 November and 19 November, respectively (Figure 1 and Table 1).

Figure 1. Timeline of investigative period on farm, October to December 2022. Legend: L1 = litter one, L2 = litter two, L3 = litter three, L4 = litter four, L5 = litter five, P = piglets, DV = District Vet, N = necropsy.

Table 1. Demographic litter data collected on farm during investigative period in October to December 2022

Litter	Farrowing date	Sow parity	Farrowing pen	Dry sow pellet fed	# piglets born alive	# preweaning piglet deaths
1	18/10/2022	2	1	feeder	17	17
2	18/10/2022	2	2	feeder	15	15
3	1/11/2022	2	Unknown *running free range	on ground	9	0
4	18/11/2022	2	7	feeder	17	14
5	19/11/2022	2	6	feeder	19	7

The deaths occurred from two days post-farrowing, affecting both large and small piglets. No stillborn or mummified foetuses had been observed.

At the time of the event, the farm was affected by flood water (Figure 2). The water came up to the south side of the pig shed and seeped under the wooden flooring at the western end of the shed (Figure 3). There was a significant mosquito population on the farm.

Figure 2. Mud map of pig area on property (note: map not to scale)

Figure 3. Mud map of farrowing shed (note: map not to scale). Legend: F = farrowing, M = mortality, L1 = litter 1, L2 = litter 2, L3 = litter 3, L4 = litter 4, L5 = litter 5.

An on-farm visit was conducted by the District Veterinarian (DV) on 22 November, following a call from the producer for further investigation into the mortalities. At the time of the visit, litters three, four and five were examined.

Litter four, located in pen seven, contained six piglets. One piglet was observed to be small, lethargic, tremoring and dyspnoeic (Figure 4). This piglet was euthanised for necropsy. Necropsy findings showed mildly fibrinous lungs and a moderately thickened pericardium with fibrinous attachments. The remaining five piglets from litter four were of average size and not showing any clinical signs of disease.

Litter five, located in pen six, contained 12 piglets. There were no clinical signs of disease observed in these piglets.

It was observed that the piglets in litters four and five could fit through internal and external fencing in the farrowing shed and therefore the piglets were not restricted to a single pen.

Litter three was observed to be running free range and contained nine piglets. No clinical signs of disease were observed in these piglets.

Figure 4. Video. Four-day old piglet from litter four showing signs of tremors and dyspnoea

A follow-up farm visit was conducted on 7 December 2022 following the death of a second piglet from litter four. The piglet was 19 days old and had clinical signs of lethargy and weakness prior to death. The piglet had received three days of penicillin treatment. No signs of shaking were noted in this piglet.

Necropsy findings of this piglet included suppurative pleuritis, thickening of the pericardium, and suppurative peritonitis affecting the surface of the liver, kidneys and spleen (Figure 5).

Figure 5. Necropsy performed on 19-day-old piglet from litter four showing extensive suppurative pleuritis and peritonitis

Analysis of the data collected showed that there were five litters born during the investigative period with a total of 77 piglets born alive. Piglets born alive per litter ranged from nine to 19, with an average of 15.4.

Neonatal mortalities occurred in four of the five litters. Mortality rates in suspect cases ranged from 37-100%. As shown in Figure 6, mortalities were observed in litters one, two, four and five, but not in litter three. Litter three was noticeably the only sow with a litter size below the Australian average litter size of approximately 11 piglets born alive.³

Figure 6. Number of dead and alive piglets per litter on farm in October to December 2022

Figure 7 shows days post-farrowing when mortalities from suspect cases occurred. A total of 50 (94%) of the piglet mortalities occurred two days post-farrowing. The remaining three mortalities occurring after day two were from litter four.

Figure 7. Total piglet deaths from five litters on farm October to December 2022

Laboratory investigation

A range of fresh and fixed samples from the piglet necropsied from litter four on 22 November were sent to the NSW Animal and Plant Health Laboratories (APHL) for testing.

Laboratory results from this piglet returned a negative result for Japanese encephalitis (JE) on PCR, atypical porcine pestivirus (APPV) on PCR and porcine circovirus type 2 (PCV-2) on PCR.

Histology revealed evidence of a strong inflammatory response affecting most tissues, predominantly within the meninges and serosa of the thoracic and abdominal organs. A bacterial septicaemia was the most likely cause. Culture from heart tissue grew non-haemolytic Escherichia coli (E. coli).

A sample from this piglet was sent from APHL to the Australian Centre for Disease Preparedness (ACDP) for testing for Porcine respiratory and reproductive syndrome (PRRS), which returned negative results.

The clinical significance of the E. coli culture from initial laboratory testing was uncertain. Samples from the second piglet from litter four necropsied on 7 December 2022 were subsequently sent to APHL. Culture results from fresh heart and brain samples, as well as amies swab of the liver, were positive for E. coli.

Following the confirmed diagnosis of neonatal colibacillosis, a sample was sent from APHL to the Pig Services Centre Diagnostic Laboratory in Victoria for serotyping of the E.coli. The serotyping results were negative for K88, 987P & K99 fimbria, but positive for O:20.

Communication and response

Advice was provided to the producer regarding changes to management of the sows that would enhance piglet immunity and survival. This advice included:

Switching from a dry sow pellet to a lactating sow pellet to help promote initial colostrum production and milk supply.
Fostering piglets from large litters to ensure they can have access to colostrum/milk from the sow within the first 24 hours.
If fostering is not an option, the producer could administer a colostrum supplement to piglets which may not have received enough colostrum within the first 24 hours.
Vaccination of sows against E. coli prior to farrowing. Given the serotyping results of the E. coli from the lab, the commercial E. coli vaccination would not provide complete protection against the E. coli on farm. The possibility of having an autogenous vaccination made by a lab for the specific strain of E. coli on farm was discussed.
Providing good environmental conditions and hygiene for farrowing and piglet survival. Ideally sows should farrow in a clean, disinfected environment with optimal temperatures for piglet survival. It was recommended to provide an abundant amount of good quality straw for clean bedding and allowing the sow to build a nest to aid in temperature control for piglets. The possibility of moving the farrowing sows away from the flood water was also discussed.

Following provision of this advice, the producer contacted his nutritionist and changed to a lactating sow pellet that has promoted milk production. The producer also provided more adequate bedding in the farrowing shed to aid in hygiene and temperature control for piglets. As a result of these changes the preweaning mortality decreased to what was deemed acceptable by the producer.

Due to flood damage to the wooden floorboards, the producer was also considering conducting shed maintenance or building a new shed that would improve hygiene.

Discussion

Initial differential diagnoses for this case were JE, APPV causing congenital tremors, and a bacterial infection/meningitis. A JE incursion was detected in NSW in March 2022 and due to the nature of the surrounding flood water, the high mosquito population and the clinical signs of piglet deaths and tremors, it was important to rule out JE as a differential diagnosis. Although exotic to Australia, laboratory testing for PRRS was also conducted as a notifiable disease exclusion as it can present with clinical signs of increased pre-weaning mortality, respiratory distress, lethargy and weakness⁴, as was seen in this case.

A diagnosis of neonatal colibacillosis was made following the culture of E. coli from two piglets. Whilst laboratory investigation in this case was only conducted on piglets from the same litter, the investigator thought that the neonatal mortality in litters one, two and five was also likely due to a lack of colostrum and associated secondary neonatal colibacillosis.

The Australian Pork Limited (APL) guidelines for fostering (2018) report that around 80% of piglet losses occur in the first 72 hours after farrowing. These losses often occur due to a lack of colostrum and mortality rate also rise with increasing litter size.¹ A lack of colostrum intake was thought to be contributing to the piglet mortalities in this case as 94% of the mortalities occurred within two days of farrowing.

Pre-weaning mortality can also result from piglets being laid on by sows. Given the sows in this case were farrowed in a pen situation, rather than a farrowing crate, the risk of overlaid piglets is greater. However, it was thought unlikely that multiple sows would consistently lay on a high percentage of the litter on a single day.

It was observed that the smallest litter containing nine piglets born alive and had zero piglet mortalities compared to the larger litters on farm. This litter was free-range and not housed in the farrowing shed like the other affected litters. The sow had farrowed unexpectedly, nesting in a bale of hay without the producer realising she was due to farrow. Following farrowing, this litter was fed the same dry sow pellet as the sows in the farrowing shed, although on the ground instead of in a feeder. This litter may have experienced no mortalities compared to the other litters on farm due to multiple reasons. These include the colostrum and milk production by the sow was sufficient to meet the demands of the smaller litter size, the nesting and farrowing in a bale of hay provided increased warmth to the piglets and the outdoor environment may have been less contaminated with E. coli compared to the farrowing shed. As the dataset in this case was small, further analyses, including measures of association between litter size or farrowing location and mortality, could not be undertaken.

Given that mortalities were observed in multiple pens of the shed and piglets were observed to move through internal and external fencing, no relationship was observed between the mortality and a specific location. Litter three was not housed in the farrowing shed but was reported not to have any mortalities. However, as they were free range, they also had access to similar surrounding environmental conditions to the other litters. For this reason, there did not appear to be an association between litter mortalities and the surrounding flood water.

It was also noted that the largest litter containing 19 piglets born alive did not have the highest mortality rate. This finding may have been due to individual factors of the sow and/or piglets such as immunity, milk production and piglet birth weight.

E. coli is an important cause of diseases in pigs worldwide, including neonatal diarrhoea, post weaning diarrhoea, oedema disease, septicaemia, polyserositis, coliform mastitis and urinary tract infection.² In this case, two of the piglets were confirmed with septicaemia caused by E. coli serotype O:20.

Septicaemia due to E. coli can occur sporadically or as small outbreaks usually in piglets up to four days old but can also occur at any stage throughout the suckling period. Piglets lacking immunity due to a lack of colostrum intake or colostrum lacking specific antibodies are most at risk of developing septicaemia associated with E. coli. Poor environmental temperature control and sub-standard hygiene can increase the risk of systemic infection.²

Commercial vaccines for protection against E. coli in pigs are available in Australia, however they do not provide protection against all serotypes of E. coli. E. coli vaccination requirements of unvaccinated sows generally involve two doses administered four to eight weeks apart, with the second dose administered three weeks prior to farrowing. In previously vaccinated sows, one dose is administered three weeks prior to farrowing. Commercial E. coli vaccines available in Australia such as Neovac® (Zoetis)⁵ and ECOvac® (MSD Animal Health)⁶ provide protection against K88, K99 and 987P serotypes of E. coli. These serotypes found in the commercial vaccines cover the important serotypes involved in neonatal scours. Autogenous vaccines can also be developed by some laboratories to provide protection against types of E. coli that are not protected against by commercial vaccinations.

Serotyping of the E. coli cultured in this investigation was undertaken to confirm whether commercial E. coli vaccination for sows would provide protection against the type of E. coli on the farm. The negative K99, K88 and 987P serotyping results indicated that the commercial E. coli vaccines does not provide protection against this E. coli.

In this case, the producer opted not to pursue an autogenous vaccine for E. coli and instead chose to focus on promoting milk production in sows and providing environmental conditions that would promote piglet survival.

Essential requirements for piglet survival include warmth and an adequate supply of colostrum soon after birth. Newborn piglets have little stored energy reserves. If temperature requirements of piglets are not met, they will mobilise their energy reserves quickly. Once cold, a piglet cannot compete for teats, suckle properly, is more susceptible to infections and may not be quick to move around the pen increasing the risk of being overlaid. Warmth for piglets can be provided using heat lamps or through the provision of sufficient straw to provide warmth and protection to piglets.¹ In this case, the facilities did not allow for the use of heat lamps, so the producer opted to use straw as bedding to control temperature as much as possible and to improve hygiene.

Colostrum is a good source of energy, contains antibodies and has many nutritional factors that are required for piglet growth and development. As piglets begin to suckle and receive colostrum, both energy and warmth are provided that also increase body temperature and survival. The production of colostrum from the sow decreases rapidly during the first 14 hours post-farrowing and is completely replaced by fatty milk 34 hours post-farrowing. Antibodies from colostrum can only be absorbed effectively by the piglets in the first 24 hours after birth.¹ Very large litter sizes may also pose a problem with accessing enough colostrum due to increased competition for viable teats.³ Without access to adequate colostrum, piglets will not survive.

Other factors that promote piglet survival relate to the sow and ensuring that she is comfortable, is being fed adequately and has access to an adequate supply of clean water.¹

In this case, given the sows were being fed a dry sow diet, the investigator suspected that the sows were not producing enough colostrum and milk to meet the demand of the large litter sizes. It was noted by the producer that once they switched from feeding a dry sow ration to a lactating sow ration, sow milk production increased, which contributed to the decrease in mortalities in subsequent litters.

Acknowledgements:

This investigation was completed in collaboration with APHL, ACDP, and Pig Services Centre Diagnostic Laboratory VIC. I would like to thank Pedro Pinczowski and Anthony Chamings from APHL for their assistance with laboratory testing and discussing this case with me.

I would also like to thank the assistance of pig industry veterinarians Bernie Gleeson and Kat Linn for their advice in the management of this case.

This investigation report was completed as part of the NSW Animal Health Frontline Field Epidemiology Training Program. I would like to particularly thank Heidi Austin and Amanda Walker, for their mentorship during this training program.

References

Australian Pork Limited (2018) Guidelines for fostering: getting the 'one percenters' right australianpork.com.au Retrieved 13 November 2024
Zimmerman, JJ et al. (2019) Diseases of swine 11^th edn. Wiley Blackwell, Hoboken
RSPCA Australia (2018) RSPCA Approved Farming Scheme Information Notes: Pigs rspcaapproved.org.au Retrieved 13 November 2024
NSW Department of Primary Industries (2023) Recognising exotic diseases of pigs. www.dpi.nsw.gov.au Retrieved 13 November 2024
Zoetis. Neovac (2022) www.zoetis.com.au Retrieved 17 November 2024
MSD Animal Health. ECOvac www.msd-animal-health.com.au Retrieved 17 November 2024