Abstract

1. INTRODUCTION

This research was part of a broader study evaluating animal‐based welfare outcomes in slaughter pigs assessed on farm and at the abattoir to support the use of ante‐mortem and post‐mortem meat inspections as an animal health and welfare diagnostic tool. The study was focused on evaluating the prevalence of ear, tail, and skin lesions, hernias, bursitis, and rectal prolapses in pigs, as well as associated on‐farm risk factors, association with post‐mortem inspection outcomes and financial implications. These animal‐based welfare outcomes were chosen due to their relevance to the pig sector but also because they are visible animal‐based welfare outcomes easily detectable on farm and at ante‐mortem and post‐mortem inspections.

To discover the association between the presence of these animal‐based welfare outcomes at ante‐mortem inspection (both on farm and at the abattoir) and post‐mortem inspection outcomes is useful to address the organization of official controls in abattoirs (Ghidini et al., ²⁰²¹). Pigs affected by gross abnormalities have an increased probability of showing post‐mortem abnormalities (Harbers et al., ¹⁹⁹²) and have a higher probability of having meat rejected at post‐mortem inspection (Jackowiak et al., ²⁰⁰⁶). Therefore, on‐farm assessments can complement (Teixeira et al., ²⁰²⁰) or facilitate (rather than replace) abattoir‐based ante‐mortem inspection by segregating sick or injured animals and animals with impaired welfare prior to transport into groups with and without visible lesions (Harbers et al., ¹⁹⁹²). It can also prevent animals that are not “fit” from being sent to the abattoir for slaughter (EFSA, ²⁰¹¹) thereby protecting animal welfare.

Unhealthy pigs that have, or are suspected of having, injuries or illnesses on farm may be housed in “hospital,” “recovery,” or “isolation” pens to help improve their condition and/or to avoid infecting healthy animals, with on‐farm euthanasia as an alternative for sick/infected pigs in extreme situations. Knowing the likelihood that the carcass of these sick or injured animals might be condemned could also justify earlier euthanasia on farm, which would help avoid financial losses associated with treatment and reduced feed efficiency, misuse of antibiotics, and unnecessary animal suffering.

In the case of ante‐mortem inspection during unloading or in lairage at the abattoir, animals can be detained for closer examination if there are concerns regarding animal health and welfare. Usually, it must occur within 24h of animals arriving at the abattoir, and slaughter must occur within 24h of the ante‐mortem inspection. Ante‐mortem inspection is important to enable early detection of clinically observable zoonotic diseases and animal identification enabling traceability and evaluation of visual cleanliness of animals (EFSA, ²⁰¹¹). It is also essential for detecting conditions that cannot be detected at post‐mortem inspection and detection of animal welfare conditions (Stark, ¹⁹⁹⁶), such as lameness (EFSA, ²⁰¹¹). Therefore, the veterinary inspector (VI) in charge of ante‐mortem inspections at the abattoir can advise the VI on the slaughter line that some pigs or batches require more thorough inspection rather than just a visual inspection.

The ability of data obtained from the ante‐mortem inspection to predict post‐mortem outcomes was investigated by Ghidini et al. (²⁰²¹). However, Ghidini et al. (²⁰²¹) assessed conditions typically found during ante‐mortem and post‐mortem inspections in slaughter pigs at batch level, and unfortunately, their pigs were not followed individually during ante‐mortem and post‐mortem inspections. Research is lacking on the association between the animal‐based welfare outcomes that can be detected on farm, at ante‐mortem and post‐mortem inspections, and the associated post‐mortem outcome at individual level. Therefore, the aim of this study was to investigate associations between ear, tail, and skin lesions, hernias, bursitis, and rectal prolapses at the abattoir and meat inspection outcomes in slaughter pigs, including carcass condemnations and trimmings, carcass weight, and carcass quality.

2. MATERIALS AND METHODS

This study was part of a research project approved by the Scientific Ethics Committee for Animals and Environmental Care of the Pontificia Universidad Católica de Chile (protocol number 170529006) and by the Research Department Ethic Committee of the Universidad de O'Higgins (No. 002‐2020).

This was an observational study whereby pigs were managed according to routine practices in a pig abattoir located in Chile. Data were collected from November 2018 to April 2019. On each day, data were collected from 9:00h to approximately 15:00h. Two observers (a veterinarian and a veterinary technician) were trained before the beginning of the study to ensure interobserver reliability, and the study consisted in two phases described below.

2.1. Phase 1: Animal‐based welfare outcomes, viscera condemnations, and cold carcass weight

The first phase of the study was carried out during 24 slaughter days using a convenience sample of 1500 slaughter pigs. The methodology was based on Teixeira et al. (²⁰¹⁶), and data were collected at three points on the slaughter line: (I) before dehairing and evisceration; (II) at post‐mortem meat inspection; and (III) at the weighing scales. To avoiding biosecurity issues associated with moving between collection points on the slaughter line, cleaning and sanitation programs were in place to ensure all the hygiene standard required in a plant manufacturing meat products.

At the first data collection point, groups of carcasses (range 12–35) were randomly selected in rounds of approximately 30min, to ensure that the observer had enough time to move to the next point to continue with data collection. Each study carcass received an individual tattoo (slap number) on the shoulder for further carcass identification; the sex (female or castrated male) and the presence or absence of animal‐based welfare outcomes (ear, tail, and skin lesions, hernias, bursitis, and rectal prolapses) were recorded according to Teixeira et al. (²⁰²⁰) (Figure 1). Only severe cases of ear, tail, and skin lesions (i.e., evidence of puncture wound) were considered. It was not possible to record herd identification codes.

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FIGURE 1

Welfare outcomes recorded at post‐mortem evaluation

At the second data collection point, the reason and anatomical locations of carcass condemnations and carcass trimmings and associated disease lesions were recorded as present or absent on the basis of the decision of the VI on the slaughter line as per Teixeira et al. (²⁰¹⁶) (Table 1). As the VI changed according to shifts, their identity (later codified from 1 to 5) was also recorded. VI 1 inspected 169 carcasses, VI 2 inspected 234 carcasses, VI 3 inspected 297 carcasses, VI 4 inspected 401 carcasses, and VI 5 inspected 399 carcasses. At the third data collection point, one observer recorded the line “kill number” of the study carcass in order to retrieve cold carcass weights from abattoir records.

TABLE 1

Definition of carcass condemnations and disease lesions associated with viscera condemnations detected at meat inspection

	Appearance/definition
Carcass condemnation detected at meat inspection
Entire carcass	Removal of the entire carcass due to systemic disease
Partial carcass	Removal of part of the carcass due to disease or injury affecting hind limbs, forelimbs, or head
Trimmings	Removal of superficial or small part of the carcass (e.g., ear, tail, skin, hand, and feet) due to superficial disease/injury lesion/external abscess
Main disease lesions associated with carcass and viscera condemnations detected at meat inspection a
Abscess	Single or multiple focal, spherical, encapsulated purulent lesions
Viscera adherence	Adherence of the viscera to the abdominal or chest cavity
Tail lesion	Partial or full amputation of tail with wound or abscess evident
Fracture	Broken bone
Lesion	Wound or abscess evident
Nephritis	Inflamed nephrons (the functional units of the kidney)
Cysts	Presence of numerous, mostly small cysts located in the renal parenchyma

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^a Only those disease lesions with more than five cases were considered. Pericarditis (n=4), dermatitis (n=5), edema (n=4), bruise (n=5), nephrosis (n=1), pneumonia (n=1), septicemia (n=3), and tuberculosis (n=2) were group as “other reasons.”

Source: Adapted from Teixeira et al. (²⁰²⁰) and Teixeira et al. (²⁰¹⁶).

3. RESULTS

4. DISCUSSION

Data recording at abattoir ante‐mortem and post‐mortem meat inspections is a valuable way of assessing the health and welfare conditions that affect food‐producing animals. The present study found that, out of the animal‐based welfare outcomes evaluated in this study, tail lesions were a risk factor for entire carcass condemnations, reduced carcass weight, and pH of the carcass. The other welfare lesions evaluated were not associated with carcass condemnations, but the presence of a hernia affected carcass weight, and bursitis affected carcass pH and temperature. These results confirm previous findings that pigs affected by gross abnormalities have an increased risk of showing post‐mortem abnormalities (Harbers et al., ¹⁹⁹²) and of having meat rejected at post‐mortem inspection (Jackowiak et al., ²⁰⁰⁶). Also, they confirm the hypothesis that ante‐mortem inspection can be used to predict post‐mortem outcomes in the same pigs, especially in cases of tail lesions and hernia, which might trigger attention of the VI in charge of the post‐mortem inspection.

This study did not aim to evaluate the prevalence of the selected animal‐based welfare outcomes. However, previous research carried out at the same abattoir (see Teixeira et al., ²⁰²⁰, for details) also found that bursitis and tail lesions were the most common welfare outcomes. It is important to note that any comparison with the prevalence of welfare lesions from the present study is not pertinent as batches with animals from hospital pens were purposely evaluated and included in this study to increase the probability of collecting data from more animals with the selected welfare outcomes and its association with post‐mortem outcomes. However, the association between the prevalence reported by Teixeira et al. (²⁰²⁰) and the carcass condemnations in the current study shows the magnitude of the tail biting behavior problem on farm, corroborating findings from previous studies in Finland and Ireland (Harley et al., ²⁰¹⁴; Valros et al., ²⁰⁰⁴). However, similar to Harley et al. (²⁰¹⁴), our findings do not show an association between tail lesions and lung condemnations or carcass abscessation. This was unexpected as the majority of papers shows such an association between tail lesions and these post‐mortem outcomes (Heinonen et al., ²⁰¹⁰; Huey, ¹⁹⁹⁶; Teixeira et al., ²⁰¹⁶; Valros et al., ²⁰⁰⁴; van Staaveren et al., ²⁰¹⁶) a potential mechanism for which was outlined by Boyle et al. (²⁰²²).

Carcasses from pigs affected by tail lesions showed a reduction in weight of 3.6 kg, corroborating previous studies (Harley et al., ²⁰¹⁴; Valros et al., ²⁰¹³; Vom Brocke et al., ²⁰¹⁹). In fact, Harley et al. (²⁰¹⁴) reported a reduction in carcass weight of 1.2, 3.27, and 12kg in cases of mild, moderate, and severe tail lesions, respectively. Although we did not differentiate the severity of tail lesions, the finding associated with the reduction in carcass weight supports the association between tail lesion and the reduction in animal growth performance, which could be due to inflammatory processes (Boyle et al., ²⁰²²; Teixeira, Boyle, & Enríquez‐Hidalgo, ²⁰²⁰; Valros et al., ²⁰⁰⁴) or pain and stress in the victims of tail biting (Schrøder‐Petersen & Simonsen, ²⁰⁰¹).

Carcasses from pigs affected by tail lesions also showed a lower muscle pH than carcasses with no other welfare outcomes, contradicting Valros et al.'s (²⁰¹³) findings. The lower muscle pH of carcasses with tail lesions could be explained by the stress associated with tail biting (Taylor et al., ²⁰¹⁰). It is possible that tail‐bitten pigs are more prone to psychological and/or physical stress just before slaughter (Valros et al., ²⁰¹³) and, therefore, have higher blood lactate concentration at slaughter, which in the end is associated with lower initial muscle pH value (Dokmanovic et al., ²⁰¹⁵). This might also explain the lower muscle pH value in animals affected by bursitis. In these cases, bursitis also affected muscle temperature, which again might be related to stress in animals affected by this condition (Schäfer et al., ²⁰⁰²).

Our study corroborated findings of previous studies showing that male sex increases the risk of tail lesions (Kritas & Morrison, ²⁰⁰⁷; Sinisalo et al., ²⁰¹²; Valros et al., ²⁰⁰⁴), independent of whether they are entire (Harley et al., ^{2012, 2014}; van Staaveren et al., ²⁰¹⁶) or castrated (Hunter et al., ¹⁹⁹⁹; Valros et al., ²⁰⁰⁴). Mixed sex groups were implicated in the reasons why males are at greater risk of being bitten (Boyle et al., ²⁰²²). One reason for the postulated higher propensity of females to bite than to be bitten could be that males in the pen out compete them for access to food and that they then employ tail biting to displace the males from the feeder/trough. In fact, the heavier carcasses from male compared with female pigs supports this theory. This finding is in line with Gispert et al. (²⁰¹⁰) and is possibly explained by a greater average daily gain of castrated male pigs during the fattening period relative to female pigs (Fàbrega et al., ²⁰¹⁰). However, Teixeira and Boyle (²⁰¹⁴) found that entire males were heavier than female pigs prior to transport to the abattoir but there was no effect of sex on carcass weight, suggesting a higher weight of gut contents but similar kill out weight.

Carcasses from male pigs also presented higher carcass pH and temperature than carcasses from females which contrasts with Gispert et al. (²⁰¹⁰), at least in regard to pH of the Longissimus muscle. Even though there was no association between sex and carcass condemnations, it is probable that the increased carcass pH in males is linked to their higher likelihood to have tail lesions. However, further studies with larger numbers of animals are needed to confirm this.

The presence of a hernia was associated with kidney condemnations, which differs from Ghidini et al. (²⁰²¹) who found no association between kidney lesions and umbilical hernias. Also, carcasses from pigs affected by hernias were about 4.5 kg lighter relative to carcasses with no other welfare outcomes. Although growth weights from weaning to about 45kg did not differ, weight gain prior to weaning is lower in pigs that develop hernias (Searcy‐Bernal et al., ¹⁹⁹⁴), which could help to explain the lighter carcass weight relative to carcasses with no other welfare outcomes.

VI was also associated with heart and kidney condemnations. This finding confirms that the veterinary inspection can cause variation in the post‐mortem outcome. Such inconsistences have major implications for the use of post‐mortem inspection outcomes in disease surveillances. Common educational background, standardization of meat inspection criteria, and automated systems could help to mitigate these issues (Harley et al., ²⁰¹²; Heinonen et al., ²⁰²¹).

From the animal‐based welfare outcomes evaluated in this study, only tail lesions were associated with entire carcass condemnations and trimmings, a reduction in carcass weight, and a potential to impair carcass quality by reducing muscle pH, especially in carcasses from male pigs. Additionally, hernias were associated with viscera condemnation and a reduction in carcass weight. Therefore, our findings confirm that ante‐mortem inspection could be useful to predict post‐mortem outcomes in the same pigs, especially in cases of tail lesions and hernia, which might trigger attention of the VI in charge of the post‐mortem inspection.

These findings again illustrate the magnitude of the impact of tail biting on pig welfare and the health status of the herd on farm (Boyle et al., ²⁰²²). Raising animal health and welfare standards on farms, with concurrent improvements in animal performance (Nielsen, ²⁰¹¹), would promote a better image of the pig industry and inspire consumer confidence in the health and safety of pig meat.

CONFLICT OF INTEREST

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

ACKNOWLEDGMENTS

Notes

Teixeira, D. L. , Salazar, L. C. , Larraín, R. , & Boyle, L. A. (2023). The capacity of inspection on farm and at the abattoir to predict post‐mortem outcomes in slaughter pigs: A study at animal level. Animal Science Journal, 94(1), e13798. 10.1111/asj.13798 [Europe PMC free article] [Abstract] [CrossRef] [Google Scholar]

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