Effects of early life and current housing on sensitivity to reward loss in a successive negative contrast test in pigs.

Animals in a negative affective state seem to be more sensitive to reward loss, i.e. an unexpected decrease in reward size. The aim of this study was to investigate whether early-life and current enriched vs. barren housing conditions affect the sensitivity to reward loss in pigs using a successive negative contrast test. Pigs (n = 64 from 32 pens) were housed in barren or enriched conditions from birth onwards, and at 7 weeks of age experienced either a switch in housing conditions (from barren to enriched or vice versa) or not. Allotting pigs to the different treatments was balanced for coping style (proactive vs. reactive). One pig per pen was trained to run for a large reward and one for a small reward. Reward loss was introduced for pigs receiving the large reward after 11 days (reward downshift), i.e. from then onwards, they received the small reward. Pigs housed in barren conditions throughout life generally had a lower probability and higher latency to get the reward than other pigs. Proactive pigs ran overall slower than reactive pigs. After the reward downshift, all pigs ran slower. Nevertheless, reward downshift increased the latency and reduced the probability to get to the reward, but only in pigs exposed to barren conditions in early life, which thus were more sensitive to reward loss than pigs from enriched early life housing. In conclusion, barren housed pigs seemed overall less motivated for the reward, and early life housing conditions had long-term effects on the sensitivity to reward loss.

Review: Towards an integrated concept of animal welfare.

Animal welfare is an important field of study due to animal sentience, yet there is to date no consensus on the definition of animal welfare. There have been four key developments in the field of animal welfare science since its birth: the theoretical and empirical study of affective states, and hence our understanding thereof, has increased; there has been a shift from a primary focus on unpleasant experiences towards an inclusion of pleasant experiences; there has been an increasing mention and investigation of the notion of cumulation of experiences in time, and with this, the importance of the time component of both affective states and animal welfare has come forward. Following others, we define welfare as a balance or cumulation of pleasant and unpleasant experiences over time. The time period of welfare depends on when welfare considerations are necessary, and may range from the duration of single and relatively short-term experiences to the entire life of an animal. We further propose that animal welfare conceptualised in this way can be assessed at three levels: level 1 represents the assessment of the environment and 'internal factors' such as health and personality, which interact in their impact on the affective experiences of animals; level 2 represents the assessment of affective states; and level 3 represents the assessment of the balance or cumulation of these affective states in time. The advancement of research necessitates studies to be more or less comparable, and this would be facilitated by researchers mentioning which concept of animal welfare they are basing their work on, at which level of assessment they are working, which assumptions they might be drawing from to infer welfare and which time period of interest they are focusing on, even if this is not mirrored by the timing of the assessment in practice. Assessment at levels 2 and 3 still needs much study, at both the theoretical and empirical levels, including agreements on validation tools.

Variation in piglet body weight gain and feed intake during a 9-week lactation in a multi-suckling system.

A multi-suckling (MS) system for sows and piglets has been developed aiming to improve animal welfare. In this system, large variation in BW gain exists between piglets up to weaning at 9 weeks of age. We aimed to study the causes of variation in BW gain and DM intake of solid feed (DFI) (piglet + sow feed) of piglets during lactation in the MS system. A total of 15 sows and 60 focal piglets across three batches were studied. Individual intake of piglet and sow feed was measured by the dual marker method, and multiple variables were recorded. Multiple linear regression analysis with forward selection was conducted on BW gain and DFI after correcting for piglet sex and batch, using multiple explanatory variables including genetic background, birthweight (BiW), DM feed intake, behaviours and number of skin lesions. These factors jointly explained less than 45 % and 21 % of the variation in BW gain and DFI, respectively. In weeks 2-4, variation in BW gain was mainly explained by BiW (12.0 %) and play and nosing behaviours (7.6 %). In weeks 4-6 and 6-8, it was largely explained by DM intake of piglet feed with 15.1 % and 25.9 %, respectively. Individual variation in DFI in weeks 2-4 was explained by the presence at front and middle teats during suckling bouts (2.9 %), in weeks 4-6 by BiW (9.6 %), and in weeks 6-8 by the number of skin lesions (5.1 %). The unexplained variation in BW gain and DFI warrants further investigation.

The nuts and bolts of animal emotion.

The study of animal emotion, as with its human equivalent, can be confusing due to the complicated and inconsistent use of terminology, and the number of interlinked fields and topics it encompasses. With this review, we aim to provide an up-to-date and, to the best of our knowledge, complete overview of the field of animal emotion, especially intended for new-comers to the field who wish to get a grasp of this field. We start by tackling the terminology and proposing definitions of commonly used terms, and present the different frameworks used for the study of animal emotion. Here, we heavily draw from human literature, as the definitions of animal emotion are derived originally from human research. We follow-up with an overview of current methodologies for the study of animal emotion, in particular the valence dimension of emotion, and include some of the associated limitations linked to these methodologies. We end by pointing out key areas for future research.

Heritability of the backtest response in piglets and its genetic correlations with production traits.

The backtest response of a pig gives an indication of its coping style, that is, its preferred strategy to cope with stressful situations, which may in turn be related to production traits. The objective of this study was therefore to estimate the heritability of the backtest response and estimate genetic correlations with production traits (birth weight, growth, fat depth and loin depth). The backtest was performed by placing the piglet on its back for 60 s and the number of struggles (NrS) and vocalizations (NrV), and the latency to struggle and vocalize (LV) was recorded. In total, 992 piglets were subjected to the backtest. Heritability estimates for backtest traits were statistically moderate (although high for behavioral traits), with LV having the highest heritability estimate (0.56±0.10, P<0.001) and NrS having the lowest estimate (0.37±0.09, P<0.001). Backtest traits also had high genetic correlations with each other, with vocalization traits (NrV and LV) having the highest (-0.94±0.03, P<0.001), and NrS with NrV the lowest correlation (0.70±0.09, P<0.001). No significant correlations were found between backtest traits and production traits, but correlations between NrS and birth weight (-0.38±0.25), and NrV and loin depth (-0.28±0.19) approached significance (P=0.07). More research into genotype-by-environment interactions may be needed to assess possible connections between backtest traits and production traits, as this may depend on the circumstances (environment, experiences, etc.). In conclusion, heritability estimates of backtest traits are high and it would therefore be possible to select for them. The high genetic correlations between backtest traits indicate that it may be possible to only consider one or two traits for characterization and selection purposes. There were no significant genetic correlations found between backtest traits and production traits, although some of the correlations approached significance and hence warrant further research.

Effects of environmental enrichment and regrouping on natural autoantibodies-binding danger and neural antigens in healthy pigs with different individual characteristics.

Pigs living in commercial husbandry systems may experience both acute stress due to standard management procedures and chronic stress through limitations in their barren housing environment. This might influence their immune status, including antibody responses to neural and danger autoantigens. Levels of natural autoantibody (NAAb)-binding phosphorylcholine-conjugated bovine serum albumin (PC-BSA) and myelin basic protein (MBP) were measured over time in pigs that were kept in environmental enriched v. barren housing, and that underwent a regrouping test. In total, 480 pigs were housed in 80 pens in either barren or straw-enriched pens from 4 through 23 weeks of age. Blood samples were taken from pigs before (week 8), and 3 days after a 24 h regrouping test (week 9), and at 22 weeks of age. Phosphorylcholine-conjugated bovine serum albumin (PC-BSA) and MBP antibody titres in serum were measured using ELISA. Enriched-housed pigs had higher levels of IgM-binding MBP, and tended to have higher levels of IgG-binding MBP and IgA-binding PC-BSA than barren-housed pigs. Each NAAb measured in this study was affected by gender and litter. These results suggest that enriched housing conditions, as well as acute regrouping stress, have an influence on levels of serum NAAb-binding danger and neural antigens in pigs.

Backtest and novelty behavior of female and castrated male piglets, with diverging social breeding values for growth.

Pigs housed together in a group influence each other's growth. Part of this effect is genetic and can be represented in a social breeding value. It is unknown, however, which traits are associated with social breeding values. The aim of this study was, therefore, to investigate whether personality and response to novelty could be associated with social breeding values for growth in piglets. Female and castrated male piglets from 80 litters, with either an estimated relative positive or negative social breeding value (+SBV or -SBV) for growth, were individually tested in a backtest and novel environment test, and group-wise in a novel object (i.e., a feeder with feed) test and human approach test. All tests were performed during the suckling period. No differences between +SBV and -SBV piglets were found for the frequency and latency of struggling and vocalizing in the backtest (at least, P > 0.30). In the novel object test, piglets with a +SBV for growth touched the feeder faster than piglets with -SBV for growth (P = 0.01) and were more frequently present near the person in the human approach test (P < 0.01). No behavioral differences between +SBV and -SBV piglets were found in the novel environment test (at least, P > 0.40), but piglets that struggled more in the backtest walked more in this test (P = 0.02). Behavior was affected by gender in each test. Female piglets were faster than castrated male piglets to start struggling in the backtest (P = 0.047). In the novel object test, females were faster than males to touch the feeder and sample the feed. In the human approach test, they were also faster than male piglets to touch a person (all, P < 0.001). Females were also more frequently present near the feeder (P < 0.001) and person (P = 0.03). In the novel environment test, female piglets explored the floor more (P = 0.046), produced less low- (P = 0.04) and high-pitched vocalizations (P = 0.02), and defecated (P = 0.08) and urinated less than male piglets (P < 0.01). It was concluded that +SBV and -SBV piglets do not differ in their response to the backtest, and only subtle differences were found in their response to novelty. More research is warranted to identify the traits underlying SBV for growth in pigs. Moreover, castrated male piglets seemed to react more fearfully to each test than female piglets.