Can the way pigs are handled alter behavioural and physiological measures of affective state?

Cognitive tasks as measures of pig welfare: a systematic review

Cognitive approaches are increasingly used to assess animal welfare, but no systematic review has been conducted on pigs despite their cognitive capacities. Our aims were two-fold: first, to assess the popularity and heterogeneity of this approach by quantifying the different cognitive tasks used and welfare interventions studied. The second was to assess how often results from cognitive tasks supported treatment effects. The search yielded 36 studies that met our criteria. Eleven different cognitive tasks were applied (three most common: judgment bias, learned approach/aversion, and holeboard). Welfare interventions investigated were also diverse: the impact of 19 other different events/conditions/states were reported (most common: housing enrichment). We defined "supportive" as the observation of a significant difference between treatment groups consistent with an author's expectation or hypothesis. Supportive findings were reported in 44% of papers. Interventions yielded no significant difference in 33% of studies. In another 21% of reports, outcomes were mixed and a single study refuted the author's predictions. When considering specific cognitive tasks, authors' predictions of welfare differences were supported most often when using learned approach/aversion (55% of these studies). Similar supportive results were observed less commonly (40% each) when using judgment bias and holeboard tests. Analysis of additional concomitant measures of welfare (health, physiology or behavior) revealed that behavioral measures were most frequently supportive of author's expectations (41%) as well as often matching the actual outcomes of these cognitive tasks (47%). This systematic review highlights the growing popularity of cognitive tasks as measures of pig welfare. However, overall rates of supportive results, i.e., changes in performance on cognitive tasks due to welfare interventions, have been limited so far, even for the most employed task, judgment bias. The numerous different combinations of experimental paradigms and welfare interventions reported in the literature creates challenges for a critical meta-analysis of the field especially in evaluating the efficiency of specific cognitive tasks in assessing animal welfare. This work also highlights important knowledge gaps in the use of cognitive tasks that will require both further validation as well as novel innovation to ensure that their potential is fully realized in the measurement of pig welfare.

Like Mother Like Child: Do Fearful Sows Have Fearful Piglets?

Gestational and early life experiences affect subsequent behavioural and physical development. The objective of the current study was to investigate associations between gilts' fear of humans, gestational stress level, and feeding and maternal behaviour, as well as how these related to aspects of the personality and growth of their offspring. A total of 37 gilts were used. Four human approach tests were performed between d 104 and d 111 of gestation to classify gilts as fearful or friendly. Gilt feeding behaviour and salivary cortisol concentration was measured between d 90 and d 108 of gestation, and gilt nursing behaviour assessed at d 13 of lactation. Piglets were subject to a back test at d 13 of age, to an open field test and a human approach test at d 20 of age, and growth was monitored to weaning (d 26 of age). Gilts classified as having a fearful behavioural profile had higher cortisol levels than friendly gilts (p < 0.05). Human fear level did not affect reproductive performance or the growth of offspring (p > 0.05). The offspring of friendly gilts tended to have a more active response to the back test (p = 0.09), less freezing response in the open field test (p < 0.05), and received human contact more than piglets from fearful gilts (p < 0.05). The present study shows that gilt human fear level is linked to their stress levels, which can affect the personality of their piglets.

Identification of trailer heat zones and associated heat stress in weaner pigs transported by road in tropical climates

Heat stress is major welfare concern during transport of pigs in tropical climates, which can also lead to direct production costs. This study evaluated the dynamics of heat zones through the load and their relationship with heat stress of weaner pigs during road transport in a tropical climate. Both environmental (e.g. temperature and relative humidity) and physiological (e.g. respiratory frequency and lactate) measures were recorded from four vehicle journeys (70 km distance, 216 weaner pigs within each trailer load) within Ceará, northeastern Brazil. Geostatistics and fluid dynamics simulation techniques were applied to understand the dynamics of heat zones and ventilation patterns the truckload. Statistics based on canonical discriminant analysis and ANOVA were performed to verify the relationship between heat zones and heat stress in pigs. The results showed that, during transport, the generation of heat zones occurred with different magnitudes along the load (P < 0.05), which was harmonized by the ventilation dynamics. There was a heat core with high energy content, in the front region of the lower deck (LD) of the trailer. In this zone, weaners pigs had higher rectal temperature (+1.8 °C temperature difference), respiratory frequency (LD = 94 ± 1.3 breaths/min; UD = 86 ± 1.3 breaths/min), and blood cortisol concentration (LD = 32.9 ± 0.8 ng/mL; UD = 30.18 ± 0.6 ng/mL) (all P < 0.05). Weaners pigs transported in the upper deck (UD) compartments had the highest skin temperature (LD = 38.13 ± 0.3 °C; UD = 38.9 ± 0.22 °C) and the highest mean values of blood lactate (LD = 65.5 ± 1.11 m/M; UD = 71.60 ± 1.19 m/M) and Creatine kinase (LD = 3891.23 ± 69U/L; UD = 4107.43 ± 62U/L) (P < 0.05). Weaners transported in compartments of the LD of trailer were more susceptible to heat stress, while weaners in the UD compartments were more susceptible to physical stress and muscle exhaustion. These results provide additional evidence of heat zones within trailer compartments and highlight the requirement for the planning of pig transport operations in tropical climates to mitigate risks of heat stress.

Temperament, Plasticity, and Emotions in Defensive Behaviour of Paca (Mammalia, Hystricognatha)

Simple Summary

The paca (Cuniculus paca), a Neotropical caviomorph rodent, provides the most sought-after game meat in all its range, and it therefore faces high hunting pressure and consequent poor welfare. The species is categorised as having a conservation status of “least concern” and appears resilient to over-hunting by humans, which may be related to individuals’ behavioural characteristics. To investigate this, we submitted captive pacas to temperament (personality) tests designed to assess individual responses to short challenges and to evaluate individuals’ emotional states. Our results showed that paca with a “restless” temperament performed more abnormal behaviour and less exploratory behaviour in a test of defensive behaviour, which elevations in faecal glucocorticoid metabolites indicated to be stressful. Plasticity in defensive behaviour was inferred from changes in behavioural responses and apparently rapid adaptation to different levels of risk. Our results suggest that individual differences and consistency of behavioural responses displayed by paca toward challenges may reflect a generally flexible and successful defensive behavioural response that underpins the paca’s survival, despite the threat of overhunting throughout its range.

Abstract

Within a species, some individuals are better able to cope with threatening environments than others. Paca (Cuniculus paca) appear resilient to over-hunting by humans, which may be related to the behavioural plasticity shown by this species. To investigate this, we submitted captive pacas to temperament tests designed to assess individual responses to short challenges and judgement bias tests (JBT) to evaluate individuals’ affective states. Results indicated across-time and context stability in closely correlated “agitated”, “fearful” and “tense” responses; this temperament dimension was labelled “restless”. Individual “restless” scores predicted responses to novelty, although not to simulated chasing and capture by humans in a separate modified defence test battery (MDTB). Restless animals were more likely to show a greater proportion of positive responses to an ambiguous cue during JBT after the MDTB. Plasticity in defensive behaviour was inferred from changes in behavioural responses and apparently rapid adaptation to challenge in the different phases of the MDTB. The results indicate that both temperament and behavioural plasticity may play a role in influencing paca responses to risky situations. Therefore, our study highlights the importance of understanding the role of individual temperament traits and behavioural plasticity in order to better interpret the animals’ conservation status and vulnerabilities.

Quantifying defence cascade responses as indicators of pig affect and welfare using computer vision methods

Affective states are key determinants of animal welfare. Assessing such states under field conditions is thus an important goal in animal welfare science. The rapid Defence Cascade (DC) response (startle, freeze) to sudden unexpected stimuli is a potential indicator of animal affect; humans and rodents in negative affective states often show potentiated startle magnitude and freeze duration. To be a practical field welfare indicator, quick and easy measurement is necessary. Here we evaluate whether DC responses can be quantified in pigs using computer vision. 280 video clips of induced DC responses made by 12 pigs were analysed by eye to provide 'ground truth' measures of startle magnitude and freeze duration which were also estimated by (i) sparse feature tracking computer vision image analysis of 200 Hz video, (ii) load platform, (iii) Kinect depth camera, and (iv) Kinematic data. Image analysis data strongly predicted ground truth measures and were strongly positively correlated with these and all other estimates of DC responses. Characteristics of the DC-inducing stimulus, pig orientation relative to it, and 'relaxed-tense' pig behaviour prior to it moderated DC responses. Computer vision image analysis thus offers a practical approach to measuring pig DC responses, and potentially pig affect and welfare, under field conditions.

Investigation of influence of growing pigs' positive affective state on behavioral and physiological parameters using structural equation modeling

The aim of the present study was to investigate whether the primarily positive affective state of fattening pigs influences various behavioral and physiological parameters such as the pigs' playing behavior, way of behaving in behavioral tests, body language signals, or diameter, and astroglia cell numbers of hippocampi, salivary immunoglobulin A (IgA) content, or salivary protein composition. Additionally, the suitability of the variables mentioned was examined to assess the pigs' positive affective state in practice, which still constitutes a latent variable not itself measurable. For this, a dataset including behavioral and physiological data of 60 fattening pigs from 3 different farms with different housing systems was analyzed by the partial least squares structural equation modeling (PLS-SEM) method. A hierarchical component model (HCM) was used including the pigs' positive affective state as a higher-order component (HOC) and the behavioral and physiological parameters as lower-order components (LOC). Playing behavior, body language signals, and behavioral tests were revealed, in this order, to be most influenced by the pigs' positive affective state since these resulted in the corresponding path coefficients (PC) of PC = 0.83, PC = 0.79, and PC = 0.62, respectively. Additionally moderate and weak R2-values occurred for the endogenous latent variables playing behavior (R2 = 69.8%), body language signals (R2 = 62.7%), and behavioral tests (R2 = 39.5%). Furthermore, the indicator of the "locomotor play" showed the highest indicator reliability (IR) (IR = 0.85) to estimate the latent variable of pigs' positive affective state. The results of the present study supplement the comprehension and assessment of the pigs' positive affective state in general.

Agricultural Animals as Biomedical Models: Occupational Health and Safety Considerations

The use of agricultural animals in biomedical research is increasing. Their overall size and metabolic rate, organ size, longer gestation period, and other physiological similarities make them good candidates for animal models of human disease. There are a number of special considerations for use of traditional farm animals for biomedical research. Differences in physical plant infrastructure, handling equipment, training of personnel, and potential zoonoses are some of the important considerations when traditional farm animals are used in biomedical research. This article provides an overview of some of the special considerations for using traditional agricultural animals in biomedical research. With the growing need for improved translational research, it is reasonable to predict significant growth in these animal models.

Are Behavioral Tests Capable of Measuring Positive Affective States in Growing Pigs?

Simple Summary

This study aimed at deriving potential indicators to assess fattening pigs’ positive affective state in order to be able to assess animal welfare more objectively. For this purpose, 297 fattening pigs from two different housing systems (a barren and an enriched environment) were subjected three times to the human approach test and novel object test (at the start, middle and end of fattening). The barren-housed pigs showed quicker approach latencies to come into contact with the unknown human and the novel object compared to the enriched-housed pigs (e.g., latency time in the human approach test at the end of fattening: barren housing system: 7.4 ± 1.1 s vs. enriched housing system: 57.1 ± 1.1 s, respectively 58.3 ± 1.3 s). They also indicated longer durations of contact in the human approach test but not in the novel object test (e.g., duration of contact in the human approach test at the end of fattening: barren housing system: 83.8 ± 1.1 s vs. enriched housing system: 6.3 ± 1.1 s respectively, 7.6 ± 1.3 s). However, taking the literature into account, interpretation of these results is not straightforward as the reasoning for these findings could be boredom, and thus a higher motivation to explore, or less fear. Hence, behavioral tests as solitary indicators are probably less useful in the assessment of an affective state.

Abstract

This study examined whether the human approach test (HAT) or novel object test (NOT), which are considered as suitable tests for assessing the level of fear or anxiety in animals, are suitable to detect a positive affective state in 297 fattening pigs from three different farms. The investigated farms consisted of a barren (farm 1, n = 160) and an enriched (farm 2, n = 106; farm 3, n = 31) husbandry. Each pig was subjected three times to the HAT and NOT during fattening (at the start, middle, and end of fattening). The pigs housed in the barren environment showed quicker approach latencies than the enriched-housed pigs (HAT: farm 1: 7.4 ± 1.1 s vs. farm 2: 57.1 ± 1.1 s, respectively, farm 3: 58.3 ± 1.3 s (end of fattening); NOT: farm 1: 4.5 ± 1.1 s vs. farm 2: 23.0 ± 1.1 s, respectively, farm 3: 9.0 ± 1.2 s (end of fattening)). The same pattern of behavior was observed for the duration of contacts in the HAT but not in the NOT (HAT: farm 1: 83.8 ± 1.1 s vs. farm 2: 6.3 ± 1.1 s, respectively, farm 3: 7.6 ± 1.3 s (end of fattening)). However, due to controversially discussed literature, it is difficult to conclude whether the described differences in the pigs’ behavior between the two housing systems might indicate useful indicators to detect their affective state.