Open Access

A cross sectional study of prevalence, risk factors, population attributable fractions and pathology for foot and limb lesions in preweaning piglets on commercial farms in England

  • Amy L KilBride1,
  • Claire E Gillman1,
  • Pete Ossent2 and
  • Laura E Green1Email author
BMC Veterinary Research20095:31

DOI: 10.1186/1746-6148-5-31

Received: 16 September 2008

Accepted: 24 August 2009

Published: 24 August 2009

Abstract

Background

In a cross sectional study of 88 indoor and outdoor English pig farms, the prevalence of foot and limb lesions in 2843 preweaning piglets aged 1–4 weeks from 304 litters was recorded. The environmental risks for the prevalence of lesions and population attributable fractions were calculated. The risks for lesions in piglets were compared with those for limb and body lesions in their mothers. A small number of piglets with each type of lesion were examined post mortem to elucidate the pathology of the clinical lesions observed.

Results

The prevalence of sole bruising, sole erosion, skin abrasion and swollen joints or claws in 2843 piglets was 49.4% (1404), 15.5% (441), 43.6% (1240) and 4.7% (143) respectively. The prevalence of all foot and limb lesions was higher in indoor housed piglets than in outdoor housed piglets. The prevalence of sole bruising (OR 0.3) and skin abrasion (OR 0.6) decreased with each week of age from 1–4 weeks, but there was no significant association between piglet age and the prevalence of sole erosion or swollen joints and claws. There was an increased prevalence of sole bruising (OR 3.0) and swollen joints or claws (OR 3.0) and a decreased prevalence of skin abrasion (OR 0.3, piglets ≤ 1-week old), in piglets housed on slatted floors, compared with those on solid concrete floors with bedding. There was an increased risk of sole erosion associated with piglets housed on partly slatted floors with no bedding (OR 2.4) and partly slatted floors with small amounts of bedding (OR 2.9) compared with piglets housed on solid concrete floors with bedding in all areas of the pen. Post mortem examination of feet with lesions indicated that internal pathological changes were frequently more severe than the degree of external damage suggested.

Conclusion

Piglets housed outdoors had a very low prevalence of foot and limb injuries. Indoors, no one floor type was ideal to minimise all piglet foot and limb injuries and the flooring requirements of sows differed from those of piglets.

Background

Farrowing pen floors made from solid concrete or metal or plastic slats are much harder than the soil surface for which piglets' feet and limbs have evolved. Piglets housed on such floors often develop hairless patches or abrasions on the skin of their limbs [15] and bruising or erosion on the soles of their feet [2, 3, 6, 7]. These injuries may become infected if invaded by pathogens, resulting in swollen joints or claws [4, 7, 8].

The prevalence of skin abrasion, sole bruising, sole erosion and swollen joints or claws on single farms have been estimated to be 80–89% [4, 7], 87–100% [6, 7], 28% [6] and 6–8% [6, 9] respectively. In the only cross sectional study to date, the prevalence of skin abrasion was 36% and the prevalence of sole bruising was 50% in 264 piglets from 13 convenience selected farms in England, the prevalence of other lesions was not recorded [3].

Research to date indicates that skin abrasions are caused by kneeling on rough concrete surfaces [1, 3, 5]. A small quantity of bedding on the concrete offers little protection because it is easily pushed aside, and may even exacerbate abrasions because shards of sawdust or straw can be pushed into the skin [1, 3, 5, 6]. In contrast, sole bruising is less prevalent on solid concrete floors compared with slatted floors, and the risk of sole bruising decreases as the quantity of bedding on solid floors increases [3].

Bruising and abrasion on piglets' feet and limbs have mechanical causes, however the risks for foot and limb infections are multifactorial and determined by contact with infectious pathogens, a damaged epidermis, the piglet's immune response and treatments administered by the farmer [9]. The pathology associated with infection may be severe. Necrotic pododermatitis, osteomyelitis, arthritis and tenosynovitis were reported in the infected claws of seven lame piglets examined post mortem [8]. It is possible that the type of floor and the use of bedding could influence contact between piglets and pathogens [10]. However, on an experimental unit in Canada there was no difference in the prevalence of joint infections in piglets reared on different floor types [11].

Consideration of the environmental needs of piglets cannot be separated from the requirements of the lactating sow. The sow's needs include a comfortable surface for lying, sufficient space and a non slip surface for rising and standing, separation from excreta and a pen that is robust to her size and weight.

In this paper, the prevalence, risks and population attributable fractions for foot and limb lesions in preweaning piglets are presented. The risks are compared with those associated with limb and body lesions in the mothers of these piglets [12]. In addition, the pathology associated with examples of foot and limb lesions in piglets is reported.

Methods

Sample size

The data presented in this paper were collected as part of a larger study investigating the impact of commercial pig flooring on pigs of all ages, therefore selection criteria of breeder-to-finisher units with more than 100 breeding sows was applied. Assuming 95% of herds have piglets with foot and limb injuries [3], an approximate population of 1870 (number of herds fitting selection criteria in 2003 in Britain, DEFRA, personal communication), a 95% confidence interval and 5% precision; it was calculated that it would be necessary to sample piglets from 75 farms.

Assuming an approximate study population of 650 000 preweaning piglets on the target farms (DEFRA, 2003 data, personal communication), 50% lesion prevalence, a 95% confidence interval and 5% precision, with an intraclass coefficient of 0.1 at the level of farm and litter [13] it was calculated that a sample size of approximately 3000 preweaning piglets was required to estimate prevalence. To detect a two fold difference in risk between exposed and unexposed piglets with 95% confidence and 80% power, given a 10% prevalence of disease in the unexposed piglets, with an estimated farm and litter intracluster correlation coefficient of 0.1, a sample size of approximately 2700 piglets was required. Sample size calculations were carried out in Win Episcope 2.0.

Farm selection

A total of 549 breeder-finisher pig farms with more than 100 breeding sows in England and Wales were randomly selected from the Assured British Pig (ABP) database. A total of 101 farmers agreed to take part in the study (18% compliance); 7 of these farms were used to pilot test the recording systems and to train observers. Usable data on preweaning piglets were collected from 89 farms. There was only one farm in the study located in Wales so this farm was excluded from calculations of prevalence and population attributable fractions (n = 88). The Welsh farm, and a further 9 farms that were non-randomly selected for participation (5 from Scotland, recruited by Quality Meat Scotland and 4 from England recruited via their veterinarian), were included in the risk factor analysis giving a total of 98 farms. Because the quantity of missing data varied by outcome and predictor, the number of piglets or litters used in each analysis is reported on each table of results.

Piglet observations

A comprehensive protocol was written detailing every lesion and score definition. Scoring systems were tested and compared on seven on-farm training days before data collection. On each farm four litters, one each aged 3–7, 8–14, 15–21 and 22–28 days of age were randomly selected using random number tables (counting from the first pen/hut on the left of the entrance). All piglets in the selected litters were examined. All four limbs and feet were examined for foot and limb injuries (Table 1) whist the piglet was restrained by the observer. Eight researchers (all with science or agricultural degrees, experience with pigs and trained for this project) recorded data on the piglets.
Table 1

Definitions of foot and limb lesions

Lesion classification

Description

Limb lesion1

 

Hairless patch

Hair is missing but the epidermis is unbroken and no scab is present.

Skin abrasion

Loss of the outer epidermis resulting in an open wound or a healing wound with a scab

Foot lesion 1,2

 

Sole bruising

Congestion and bruising of the solar corium presenting as red or brown pigmentation

Sole erosion

Loss of horny tissue

Infection

 

Swollen joint or claw

Swelling of the tarsal, carpal, carpophalangeal, digital joint or the claws of the foot

1[3]

2 [2]

The size of the hairless patch, skin abrasion, sole bruising or sole erosion was scored on a 0–3 scale with 0 = no visible damage, 1 = damage on <25%, 2 = damage 25–50% and 3 = damage >50% of the surface area of the joint of the limb or the volar surface of the foot. The size of a swollen joint or claw was scored on a 0–3 scale by comparison with the size of the matching unaffected joint or claw with 0 = no visible swelling, 1 = swollen to <25%, 2 = swollen to 25–50%, 3 = swollen to >50% larger than the size of the normal joint/claw.

Farrowing pen observations

Observers recorded data on the pen or hut environment (Table 2). Indoor farrowing pen floors were divided into three areas to assess their condition; the pen outside the crate, the anterior part of the floor inside the crate, here after referred to as the sow lying area, and the sow dunging area.
Table 2

Definitions of variables observed in pens and paddocks

Variable

Definition

Pen construction

 

Floor type

Solid, partly slatted or fully slatted

Floor material

Soil, concrete, metal or plastic

Bedding

 

Bedding location

Outside the crate, sow lying area inside the crate, or sow dunging area inside the crate

Bedding type

Straw, wood shavings or paper

Floor condition

 

Cleanliness

Wet

- presence or absence

Dry slurry

 

Wet slurry

 

Spilled food

 

Fresh dung

Damage

Sharp edges

- presence or absence

Broken/cracked

 

Worn rough surface

Pathology

Two farms were selected; one with farrowing houses with partly solid concrete/partly slatted cast iron floors and one with farrowing houses with fully slatted plastic floors. Two samples of sole bruising, sole erosion, skin abrasion and swollen joints of each score 0–3 were selected from each farm. Pigs were euthanased and examined post mortem by a pathologist (PO). The claws and samples from the limb lesions were preserved in formalin. Relevant tissues were then routinely embedded in paraffin and H and E stained sections were examined histologically. Each lesion was described by the pathologist using gross and histological examination and the severity of the internal lesion was compared with the clinical presentation. The depth of the horn layer on the heel of the feet was measured.

Data checking and data analysis

Research assistants entered data into Microsoft Access 2003 databases. The databases were checked for errors and outliers and obviously incorrect codes were re-checked against the raw data and impossible values were coded as missing.

Lesion prevalence was calculated separately for each type of lesion. A piglet was defined as affected with a particular lesion if one or more lesions greater than score zero were present on any foot or limb. When piglets had multiple lesions of the same type, the score of the largest lesion was used in analysis. The crude prevalence for each different type of lesion was calculated in the pigs from the ABP farms as follows;
The outcome variable used in the risk factor analysis was the proportion of piglets affected within the litter. The outcome was;

The data had a multilevel structure. That is, litters within the same farm were more likely to be similar (correlated) to each other than litters from different farms. To account for this clustering of litters within farms a 2-level binomial logistic regression model was used with litters (level 1) nested within farms (level 2). MLwiN version 2.01 [14] was used for all multilevel analysis. Models were built to compare indoor and outdoor housed piglets. Separate models were built for the indoor pens to investigate floor construction, bedding use and floor condition controlling for age. The risks associated with skin abrasion in piglets 1 week old or less were investigated separately. Finally partly slatted floors with varying amounts of bedding were compared to investigate the effect of slat material and type of bedding on piglet injury.

Age was included in the models throughout the initial screening of variables for all outcomes and forced into the final models. To check for a linear association with the outcome, continuous variables were tested in the model as a categorical variable and examined for a pattern of increasing or decreasing coefficients. Non linear associations were left as categorical variables. Variables were taken forward for multivariable analysis when significant at p < 0.2 [13]. Where variables were highly correlated the most biologically plausible variable, based on biological knowledge and previous research, was selected for inclusion in the model. Both forward addition and backward elimination were used to identify the variables that had a significant association (p < 0.05) with the outcome [13]. Finally, all variables rejected at the screening stage were retested in the final model to check for residual confounding [15].

The model took the form;

Where pij = is the proportion of the litter affected with a particular lesion, investigated with a logit link function, β0 = constant, βx is a vector of fixed effects varying at level 1 (ij) or level 2 (j), i is litters, j is farms and vj and uij are the level two and level one residual variance respectively.

Observer identity was forced into each final model to investigate whether it altered the interpretation of the fixed effects. The Hosmer-Lemeshow goodness of fit test [13] was used to investigate the difference between observed values and values predicted by the model. Pearson correlation coefficients were calculated to investigate the association between the ordinal score of lesions within piglets. The population attributable fractions for each lesion were calculated for all floor types that were significantly different from soil from the ABP farms in England using;

Where AFp is the population attributable fraction, RD is the risk of a lesion in the exposed group minus the risk in the reference category group, p(E+) is the proportion of piglets on each floor type and p(D+) is the proportion of piglets with the lesion on each floor type [13]. Fractions are converted to percentages for presentation of the results

Results

Farm and pen characteristics

A total of 3206 piglets from 338 litters were examined; 288 litters were housed indoors and 50 outdoors. The litter size at the time of examination ranged from 3–16 with a mean of 9.7 (SD 1.9). All piglets kept outdoors were housed in huts set on soil with deep straw bedding on the floor. In the 288 litters housed indoors, 11.9% were kept on solid concrete floors with bedding, 19.9% on part slatted floors with bedding, 17.8% on partly slatted floors with some bedding, 35.0% on partly slatted floors without bedding and 15.0% on fully slatted floors. In the 251 pens with slatted floors, 41.4% had metal slats, 43.4% plastic, 14.3% both metal and plastic and 0.8% had concrete slats. Pens with concrete slats were excluded from further analysis because there were only two such pens. Bedding was present in 50.0% of the 288 indoor pens at the time of observation. This was straw in 58.3% and wood shavings in 35.4% of the pens; the remaining 6.3% of pens were bedded with paper or a combination of beddings.

Prevalence of foot and limb lesions in 2843 preweaning piglets

The prevalence of sole bruising and sole erosion on the piglets' feet was 48.8% and 15.3% respectively. The prevalence of skin abrasions and hairless patches on the limbs was 43.0% and 61.3% respectively. There were 4.7% of piglets with swollen joints or claws. The prevalence and severity of all lesions was lower in piglets housed outdoors compared with piglets housed indoors (Table 3). None of the outdoor housed piglets had swollen joints or claws and the modal maximum lesion severity for all other lesions was one. In indoor housed piglets the modal maximum lesion severity for sole bruising and erosion was one and for hairless patches, skin abrasions and swellings it was two (Table 3).
Table 3

Number and percent of 2843 indoor and outdoor housed piglets from 88 English farms with foot and limb lesions score 0 – 3

 

Score1

Score 0

Score 1

Score 2

Score 3

Lesion

 

n

%

n

%

n

%

n

%

Sole bruising

Indoor

1042

43.0

807

33.3

452

18.6

123

5.1

 

Outdoor

415

99.0

3

0.7

1

0.2

0

0.0

Sole erosion

Indoor

2010

82.9

281

11.6

104

4.3

29

1.2

 

Outdoor

398

95.0

14

3.3

6

1.4

1

0.2

Skin abrasion

Indoor

1218

50.2

424

17.5

523

21.6

259

10.7

 

Outdoor

400

95.5

19

4.5

0

0.0

0

0.0

Hairless patch

Indoor

769

31.7

502

20.7

707

29.2

446

15.7

 

Outdoor

330

78.8

53

12.6

33

7.9

3

0.1

Swollen joint/claw

Indoor

2291

94.5

43

1.8

56

2.3

34

1.4

1 0 = no visible damage, 1 = damage on <25%, 2 = damage 25–50% and 3 = damage >50% of the surface area of the joint of the limb, the volar surface of the foot or for swollen joints and claws, swollen by this proportion compared to the size of a normal joint or claw.

The prevalence of lesions varied by limb and foot (Table 4), skin abrasions and hairless patches occurred at the highest prevalence on the fore limb carpal joints and at a lower prevalence on the carpophalangeal joints and on the hind limb tarsal joints. There was a slightly higher prevalence of sole bruising on the fore feet compared with the hind and conversely a higher prevalence of sole erosion on the hind feet compared with the fore. Lesions were equally prevalent on the right and left sides (Table 4).
Table 4

Number and percent of 2843 piglets from 88 English farms with foot and limb lesions by location

  

Sole bruising

Sole erosion

Skin abrasion

Hairless patch

Swollen joint/claw

Limb

Location

n

%

n

%

n

%

n

%

n

%

Fore right

Carpal1

    

1032

36.3

1308

46.0

14

0.5

 

Carpoph.2

    

532

18.7

1077

37.9

17

0.6

 

Foot

1146

40.3

489

17.2

    

11

0.4

Fore left

Carpal

    

873

30.7

1305

45.9

26

0.9

 

Carpoph.

    

517

18.2

1109

39.0

26

0.9

 

Foot

1140

40.1

478

16.8

    

14

0.5

Hind right

Tarsal3

    

287

10.1

574

20.2

28

1.0

 

Carpoph.

        

11

0.4

 

Foot

1060

37.3

589

20.7

    

6

0.2

Hind left

Tarsal

    

279

9.8

583

20.5

9

0.3

 

Carpoph.

        

14

0.5

 

Foot

1035

36.4

577

20.3

    

14

0.5

1carpal joint

2carpophalangeal joint

3 tarsal joint

The prevalence of foot and limb lesions in preweaning piglets varied by age, floor type and floor condition (Table 5). The farm level prevalence of skin abrasions, sole bruising, sole erosion and swollen joints or claws was 87.6%, 83.1.5, 68.5% and 56.2% respectively.
Table 5

Number and percent of preweaning piglets from 88 English farms with foot and limb lesions by age, floor type and floor condition

 

Sole bruising

Sole Erosion

Skin abrasion

Swollen joint/claw

 
 

n

%

n

%

n

%

n

%

Total

n

Age

         

   1-week

551

75.8

97

13.3

415

57.1

28

3.9

727

   2-week

465

55.4

130

15.5

431

51.4

41

4.9

839

   3-week

240

36.9

117

18.0

212

32.6

32

4.9

651

   4-week

130

20.8

91

14.5

167

26.7

32

5.1

626

Floor/bedding

         

   Solid with bedding

124

37.6

41

12.4

167

50.6

13

3.9

330

   Partly slatted with bedding

320

58.3

72

13.1

250

45.5

24

4.4

549

   Partly slatted with bedding in some areas

351

72.1

146

30.0

293

60.2

40

8.2

487

   Part slatted no bedding

546

56.4

215

22.2

432

44.6

53

5.5

969

   Fully slatted

253

61.6

49

11.9

209

50.9

34

8.3

411

   Outdoor

4

1.0

21

5.0

19

4.5

0

0.0

419

Worn rough sow lying area

         

   No

1084

56.3

320

16.6

918

47.7

109

5.7

1925

   Yes

270

65.5

86

20.9

257

62.4

27

6.6

412

Worn rough sow dunging area

         

   No

1278

56.5

381

16.8

1117

49.4

120

5.3

2262

   Yes

79

63.7

32

25.8

71

57.3

17

13.7

124

Wet floor in the lying area

         

   No

1273

58.3

430

19.7

1068

48.9

130

6.0

2184

   Yes

303

62.5

84

17.3

261

53.8

32

6.6

485

Bedding type

         

   Straw

327

33.1

98

9.9

335

33.9

25

2.5

989

   Wood shavings

270

63.2

96

22.5

232

54.3

29

6.8

427

   Paper

49

89.1

8

14.5

39

70.9

1

1.8

55

Slat material

         

   Metal

424

53.5

179

22.6

356

44.9

41

5.2

792

   Plastic

595

63.3

147

15.6

509

54.1

57

6.1

940

   Metal and plastic

209

65.3

42

13.1

162

50.6

19

5.9

320

Risk factors associated with foot and limb lesions in preweaning piglets

Sole erosion

There was a reduced risk of sole erosion associated with piglets housed outdoors compared with piglets housed indoors (OR 0.1, CI 0.1, 0.5). Indoors, there was an increased risk of sole erosion in piglets kept on partly slatted floors with bedding in some areas or no bedding compared with those housed on solid concrete floors with bedding throughout the pen. There was no significant difference in the prevalence of sole erosion in piglets housed on partly slatted floors with bedding or fully slatted floors, compared with those on solid concrete floors with bedding. A wet floor in the sow lying area was associated with a reduced risk of sole erosion compared with a dry floor. There was no significant association between the prevalence of sole erosion and the age of the piglet (Table 6).
Table 6

Two level logistic binomial models of the risks associated with foot lesions and swollen joints and claws in preweaning piglets from 98 British farms

All pens

Sole bruise

286 litters

Sole erosion

278 litters

Swollen joint/claw

284 litters

Intercept coefficient

2.2

-2.0

-3.8

 

OR

CI

OR

CI

OR

CI

Age

0.3

0.3, 0.4

1.0

0.9, 1.2

1.1

0.9, 1.3

Floor/bedding

      

   Solid with bedding

      

   Partly slatted with bedding

2.2

1.1, 4.6

1.3

0.5, 3.0

1.4

0.6, 3.5

   Partly slatted with bedding in some areas

4.2

2.0, 9.0

2.9

1.2, 7.1

2.5

1.1, 6.1

   Partly slatted no bedding

2.6

1.3, 5.0

2.4

1.1, 5.5

1.7

0.7, 3.9

   Fully slatted

3.0

1.4, 6.5

1.3

0.5, 3.3

3.0

1.2, 7.4

Wet sow lying area

      

   No

      

   Yes

  

0.5

0.3, 0.9

  

Worn sow dunging area

      

   No

      

   Yes

    

2.8

1.3, 6.0

Random effects

Var.

SE

Var.

SE

Var.

SE

   Farms

0.5

0.2

1.1

0.3

0.3

0.2

   Pens

1.0

0.2

0.8

0.2

0.6

0.3

Hosmer-Lemeshow goodness-of-fit

χ 2

P value

χ 2

P value

χ 2

P value

 

0.5

0.78

6.2

0.10

3.8

0.20

Sole bruising

There was a reduced risk of sole bruising associated with outdoor housed piglets compared with indoor housed piglets (OR 0.005, CI 0.002, 0.01). In indoor housed piglets, the risk of sole bruising decreased with each increasing week of age. There was an increased risk of sole bruising associated with being housed on partly slatted floors with and without bedding and fully slatted floors, compared with solid concrete floors with bedding (Table 6).

Swollen joints or claws

There was increased risk of swollen joints or claws in pigs housed on partly slatted floors with some bedding and fully slatted floors, compared with those housed on solid concrete floors with bedding. There was an increased risk of swollen joints and claws when the sow dunging area was rough and worn compared with a smooth floor in the sow dunging area (Table 6). On partly slatted floors with bedding, there was a trend for a reduced risk of joint swelling associated with plastic slats compared with metal (OR 0.4, CI 0.2, 1.1).

Skin abrasion

There was a reduced risk of skin abrasion in piglets housed outdoors compared with piglets housed indoors (OR 0.04, CI 0.02, 0.07). In indoor housed piglets the risk of skin abrasion decreased with each week of age from 1–4 weeks. There was no significant difference in the prevalence of skin abrasions in piglets aged 1–4 weeks housed indoors on different floor types (Table 7).
Table 7

Two level logistic binomial models of the risks associated skin abrasions in preweaning piglets from 98 British farms

All pens

Skin abrasion

278 litters

Skin abrasion <1-wk

71 litters

Intercept coefficient

1.5

1.2

 

OR

CI

OR

CI

Age

0.6

0.5, 0.7

  

Floor/bedding

    

   Solid with bedding

    

   Partly slatted with bedding

0.6

0.3, 1.1

0.6

0.2, 2.0

   Partly slatted with bedding in some areas

1.0

0.6, 1.8

0.8

0.2, 2.8

   Partly slatted no bedding

0.7

0.4, 1.1

0.4

0.1, 1.2

   Fully slatted

0.9

0.5, 1.7

0.3

0.0, 0.9

Worn sow lying area

    

   No

    

   Yes

1.6

1.1, 2.4

3.0

1.5, 6.0

Random effects

Var.

SE

Var.

SE

   Farms

0.2

0.1

0.7

0.2

   Pens

0.8

0.1

  

Hosmer-Lemeshow goodness-of-fit

χ 2

P value

χ 2

P value

 

3.2

0.52

0.4

0.98

There was a trend for a reduced risk of skin abrasion associated with piglets 1-week of age or less housed on partly slatted floors with no bedding and a significantly reduced risk on fully slatted floors, compared with piglets housed on solid concrete floors with bedding. There was an increased risk of skin abrasion in piglets 1-week old or less in pens with a worn rough floor surface in the sow lying area compared with a even floor surface (Table 7).

Model fit and observer differences

For all models the Hosmer-Lemeshow goodness-of-fit statistic and the graphs indicated that the difference between the observed and predicted values was small (Tables 6 and 7 and Figure 1). Controlling for observer did not alter the interpretation of the fixed effects in any of the models.
Figure 1

Graphs a – e observed verses predicted values for foot and limb lesion in preweaning piglets.

Associations between limb and foot lesions and slat materials and bedding type

Having accounted for floor type there were no significant associations between slat material (metal or plastic) or bedding type (wood shavings or straw) and the prevalence of any foot and limb lesions in indoor housed piglets (data not shown).

Associations between foot and limb lesions

Correlated variables were statistically significant at low values because of the large sample size (Table 8). The strongest statistical correlations were sole bruising positively correlated with skin abrasion and sole erosion, and hairless patches negatively correlated with sole bruising and skin abrasion.
Table 8

Pearson correlation coefficients between limb and foot lesions in 3206 indoor and outdoor housed piglets from 98 British farms

 

Sole bruising

Sole erosion

Skin abrasion

Hairless patch

Swollen joint/claw

Sole bruising

1.00

    

Sole erosion

0.16*

1.00

   

Skin abrasion

0.30*

0.12*

1.00

  

Hairless patch

-0.17*

0.13*

-0.20*

1.00

 

Swollen joint/claw

0.05*

0.06*

0.12*

0.07*

1.00

* correlated at p < 0.01

Pathology

A total of 24 samples of foot and limb lesions were taken for pathological examination from 17 piglets. The median age of the piglets was 7 days (IQR 6, 9). The thickness of the volar heel horn was 1–2 mm.

Skin abrasions were mainly without secondary infection (Figure 2). However, the pathology associated with the foot lesions was more severe. Pathological alterations included necrosis in the horn layers with inflammation of the heel and formation of a flap of horn (B) (Figure 3). Ulceration of the heel horn with focal pododermatitis also occurred (Figure 4). In the most severe examples large abscesses were present, between the coronary band and the wall horn (Figure 5D). In this case inflammatory infiltrates extended all the way down the wall to the tip of the toe (Figure 5E) and there was osteomyelitis of the third phalanx with purulent inflammation and extensive necrosis and dissolution of the bone (Figure 5F).
Figure 2

Histological section of a skin abrasion on the fore limb of a preweaning piglet with inflamation and ulceration of the skin (A).

Figure 3

Histological section of a piglet's heel (toe to the left) with inflammation of the heel and a flap of loose horn tissue (B).

Figure 4

Histological section of a piglet's claw (toe to the left) with focal pododermatitis (C) of the heel.

Figure 5

Histological section of a piglet's claw (toe to the left) with an abscess (D) inflammatory infiltrates (E) and osteomyelitis (F).

There was poor correlation between the external appearance of lesions on feet and the extent of inflammation and infection evident at pathological examination. Not all claws that were infected were visibly swollen. The samples selected clinically as examples of unaffected feet and limbs were normal post-mortem.

Population attributable fractions

Based on the association between floor type and foot and limb lesions reported in the current study, the prevalence of lesions in the affected population would be reduced by between 68% and 100%, if piglets currently housed indoors were housed outdoors. For all types of foot and limb injury the largest proportion of lesions was attributable to partly slatted pens without bedding because this was the most common floor type (Table 9).
Table 9

Population attributable fractions for foot and limb lesions in 2878 preweaning piglets from 88 English farms

 

Sole bruising

Sole erosion

Skin abrasion

Swollen joint/claw

Outdoors

    

Solid with bedding

8.7

5.5

12.3

9.4

Part slatted with bedding

19.5

8.5

15.9

9.2

Part slatted some bedding

19.6

19.1

18.0

23.6

Part slatted no bedding

35.2

33.8

29.9

35.4

Fully slatted

14.3

1.4

13.0

21.4

Total reduction

97.3

68.3

89.1

100

Discussion

The current study is, to the authors' knowledge, the largest cross sectional study of the prevalence of foot and limb lesions in preweaning piglets to date. The study farms were approximately 5% of the target population and were a good representation of the English pig farm population in herd size, geographical location and ratio of indoor to outdoor farms from DEFRA 2003 statistics [12]. There may have been a bias towards herds with higher health and welfare standards because the sampling frame was membership of an assurance scheme and compliance in this study was voluntary. As such, prevalence of lesions may be underestimated, which only highlights further the high prevalence of injury in piglets on commercial farms in England. Associations between exposures and disease are unlikely to be affected by self-selection bias.

This study is the first to examine piglets housed outdoors. Soil, with a deep covering of straw, provides a soft, non abrasive surface that was associated with a very low prevalence of foot and limb lesions in piglets. None of the indoor floor types currently used in commercial pig farms in Britain were similar to the outdoor environment and the prevalence of foot and limb lesions was very much higher on all these floors, consequently none can be considered ideal for piglets. Current research of pain in non human animals indicates that injures to the epidermis and deeper tissues and associated inflammation and infection, such as those observed in indoor housed piglets, are likely to be painful [16] and therefore associated with a welfare cost. While it is not possible to measure the pain an animal might be experiencing, the welfare cost associated with foot and limb lesions has been illustrated by reduced activity and play in affected piglets [2]. This is not to say that the welfare of piglets overall can be considered to be better outdoors, such an assessment is beyond the scope of this article and housing pigs outdoors is not a viable option in all localities.

The type of injury that occurred indoors was associated with the floor construction and condition. Slatted floors were associated with an increased risk of sole bruising, perhaps because of the lack of bedding and the increased pressure on the weight bearing areas of the foot resulting from the voids in the floor. The voids might also cause a particular problem when the piglets' claws were small enough to enter the void and pressure from the edge of the slat might bruise the sole.

Areas of solid concrete without bedding (occurring in partly slatted pens) were probably associated with sole erosion because concrete was abrasive. However, even a sparse covering of bedding over concrete floors gave piglets some protection against this lesion. The reduced risk of sole erosion associated with a wet floor in the sow lying area might have occurred because this deterred piglets from this area and they spent more time in dry, possibly bedded creep areas [3]. Alternatively, a wet floor might be a proxy for a floor construction variable that was not measured. There was a trend for a higher prevalence and larger size of sole erosion on the hind feet. This might occur because the piglets push forward with their hind limbs when suckling from the sow [6].

The risk of skin abrasion also increased when the floor was worn and rough and, in contrast to sole erosion, with small amounts of bedding, as reported in previous studies [1, 3, 5]. It is possible that bedding does not protect against skin abrasions, as it does sole erosions, because skin abrasions occur predominantly while the piglets are scrabbling on their knees to feed, therefore small amounts of bedding quickly get pushed aside, and may even get forced into the skin. Fully slatted floors were associated with a reduced risk of skin abrasion in piglets aged 1-week old or less compared with solid concrete floors. It is likely this occurred because metal or plastic slats are less abrasive than solid concrete. It is possibly that there were also less skin abrasions on partly slatted floors without bedding because these floors had a greater proportion slatted than pens in which bedding was provided. The effect of floor type might only have been significant in young piglets because older piglets, where the abrasions had healed, were misclassified as unaffected.

The results from this study do not support the hypothesis that slatted floors reduce contact between piglets and pathogens and therefore reduce the risk of infections in the feet and limbs. In contrast, slatted floors were associated with an increased risk of swollen joints and claws. Further research is required to understand whether floor type is causal or whether a correlated herd or management factor explains the association. The increased risk of swollen joints and claws associated with a worn floor surface, and a trend for an increased risk with metal slats compared with plastic, might have occurred because these floors are harder to keep clean, or because these features occurred in older pens which may be associated with generally lower standards of housing and management. It is unclear whether the zero prevalence of foot and limb infections in piglets housed outdoors occurred because there were fewer entry sites for infection e.g. tail and tooth clipping and fewer foot and limb injuries, or because the piglets had less contact with pathogens, it is likely to be a combination of both effects.

Overall the association between injuries that might act as entry sites for infection (skin abrasions or sole erosions) and swollen joints or claws was weak, although statistically significant due to the large sample size. A cross sectional design is not ideal to identify such associations because external lesions might have resolved by the time swollen joints or claws developed. The results from the pathology study indicated that the internal pathological changes were commonly more severe than the degree of external damage suggested and infection could be present without visible swelling. Therefore, the reported prevalence of infection might be an underestimation of the true prevalence. It is also possible that not all entry sites for infection were recorded in the cross sectional dataset. Infection in some feet examined post-mortem appeared to derive from damage (necrosis) to the coronary band, possibly caused by pressure on the coronary band from the edge of a slat when the claw is small enough to go into the void. This lesion was not recorded in the cross sectional study therefore the prevalence is unknown. This should be addressed in future studies of foot lesions in piglets.

As previously reported [1, 4, 5], hairless patches and skin abrasions were more prevalent and larger on the fore limbs. The highest prevalence occurred on the carpal joint, which takes the majority of the weight of the piglet when it kneels to suckle. The high prevalence of sole bruising and skin abrasion in the first week of life which then decreased with age has been reported in several previous studies [2, 3, 5, 7, 17]. It is likely that the feet and limbs of newborn piglets are particularly soft and vulnerable and then harden with age. But it is unknown whether piglets protected against injury at this stage would simply develop this damage at a later age.

One of the strengths of the current study is that the impact of the floor on the sow [12] and piglets can be compared (Table 10). Lactating sows housed outdoors also had a significantly lower prevalence of limb lesions compared with sows housed indoors. Although the prevalence of limb lesions in outdoor housed lactating sows was considerably higher than in outdoor housed piglets. This might indicate that these lesions develop over time even in the softer outdoor environment, or that these sows have been housed indoors previously. One of the advantages of sampling piglets, compared with older pigs, is that they do not usually move housing during the preweaning period and so it is easier to be sure that the injuries are associated with the environment in which they were observed.
Table 10

Summary of associations between limb, body and foot lesions and farrowing pen floor type in lactating sows and piglets

 

Lactating sows

Piglets

Floor type

Callus

Wound on limb

Bursitis

Capped hock

Body lesion

Skin abrasion

Sole bruise

Sole erosion

Solid with bedding

        

Partly slatted with bedding

 

-

 

-

-

-

-

Partly slatted with bedding in some areas*

NA

NA

NA

NA

NA

-

Partly slatted with no bedding

-

-

-

Fully slatted

-

-

-

Outdoor housing

▲ = an increase in risk compared with solid concrete floors with bedding

= a decrease in risk compared with solid concrete floors with bedding

- = no significant difference compared with solid concrete floors with bedding

*this category was not applicable to sows restrained within farrowing crates

The potential conflict between the optimal flooring for sows and piglets reported by previous researchers [1] was evident in the current study. Slatted floors increased the prevalence of wounds on the limbs, and possibly bodies, of lactating sows; perhaps because they increase the pressure on weight bearing areas whilst sows are lying and because these floors were not bedded. Conversely, these same slatted floors were associated with a lower prevalence of skin abrasions on the piglets' limbs in their first week of life. However, it is worth noting that if it were practical to provide sows and piglets housed indoors with solid floors with sufficiently deep bedding to protect the pig from the surface of the concrete, then there might be a lower prevalence of lesions in both sows and piglets, as observed in outdoor housed pigs.

Conclusion

Piglets housed outdoors in huts with deep straw bedding had a very low prevalence of foot and limb lesions. In piglets housed indoors, no one floor type was ideal; slatted floors were associated with an increased risk of sole bruising and swollen joints or claws but were associated with a reduced risk of skin abrasions in young piglets. Partly slatted floors without bedding were associated with an increased risk of sole erosion. When compared with the risks for limb and body lesions in the piglets' mothers, the lactating sows, outdoor housing was again associated with the lowest prevalence of injury, indicating a good physical environment for both sows and litters. However, indoors no floor type was associated with the lowest prevalence of all types in lesions in sows and piglets. It is likely that the optimal indoor floor type for sows and piglets foot and limb injuries would be a solid floor with deep bedding.

Abbreviations

The following abbreviations were used in this paper

(OR): 

Odds ratio

(CI): 

Confidence interval

(IQR): 

Interquartile range

(SE): 

Standard error

(Var.): 

Variance

(ABP): 

Assured British Pigs

(DEFRA): 

Department for Environment, Food and Rural Affairs.

Declarations

Acknowledgements

DEFRA funded this project (AW0135). We thank Assured British Pigs and Quality Meat Scotland for assistance recruiting farmers and the farmers who kindly participate in the project. We thank the field technicians and research staff who helped collecting the data; Jane Slevin, Kerry Woodbine, Megan Turner, Emma Novell, Fiona Boyd, Charlotte Boss, Maureen Horne, Martin Crockett, Lucy Reilly and Bart van den Borne.

Authors’ Affiliations

(1)
Department of Biological Sciences, University of Warwick
(2)
Institute for Veterinary Pathology, University of Zürich

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Copyright

© KilBride et al; licensee BioMed Central Ltd. 2009

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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