Effects of weaning age on the behavioural and neuroendocrine development of piglets

The effect of different weaning strategies on piglet growth, feed intake and gut health

The present study evaluated the effects of weaning strategy on piglet growth performance, onset of feed intake, and intestinal health. A total of 254 crossbred piglets were used and the experimental period lasted 45 days. The piglets were assigned to the fallowing treatments: early strategic weaning (ESW, n = 85), piglets weaned at 16 days of age and transferred to the pre-nursery unit; strategic segregated weaning (SSW, n = 85), piglets weaned at 21 days of age and kept in the farrowing crate until 24 days of age; and conventional weaning (CW, n = 84), piglet weaned at 24 days of age and transferred directly to the nursery unity; this experimental group was used as a control. Piglets from all treatments were transferred to the nursery unit at 24 days of age. For the nursery phase three periods of evaluation was considered: nursery phase I (0-7 d), nursery phase II (7-14 d), and nursery phase III (14-21 days). Piglets from the ESW and CW had greater (P < 0.001) ADG in the lactation period 16-21 days. The BW at 24 day of age was higher (P < 0.001) for piglets in the ESW and CW groups. In the nursery phase I, the ESW group had higher (P = 0.003) daily feed intake. Piglets from the ESW group had higher (P = 0.004) BW at the end of the experimental period. The ESW and SSW groups had a higher percentage of piglets (88% and 92%, respectively; P < 0,001) consuming feed in the first 24 h after transference to the nursery facility. When the total experimental period is considered, a reduction (P < 0.001) in the incidence of diarrhea was observed for ESW piglets. Overall, there was no effect of weaning strategy on intestinal permeability. In conclusion, the results of our study showed that the Segregated Strategic Weaning management can be used to mitigate the deleterious effects of early weaning.

Crude Blueberry Phenolic Extracts Improve Gut Barrier Integrity and Exert Anti-Inflammatory and Antimicrobial Activity in an In Vitro Weaning Stress Model

Piglet weaning is accompanied by gastrointestinal tract (GIT) dysfunction, resulting in post-weaning diarrhea (PWD). The treatment involves antibiotics due to the susceptibility of the weaned GIT to pathogens. However, antibiotic resistance has shifted attitudes toward a nutraceutical approach by enriching feed with functional compounds. Polyphenols are touted for their antimicrobial activity and ability to improve GIT function. Thus, we investigated the protective effects of crude blueberry phenolic extracts (BPE) in vitro using porcine cells challenged with lipopolysaccharide (LPS) as a weaning model. Cells were pretreated with 1 µg/mL and 2.5 µg/mL BPE for 24 h, followed by 10 µg/mL LPS stimulation for 6 h. Antioxidant status, paracellular permeability, the gene expression of proinflammatory cytokines, and tight junction proteins were measured. The antimicrobial activity of the extract was evaluated against porcine pathogens. The pretreatment of cells with 1 µg/mL BPE preserved catalase (CAT) activity. Reduced paracellular permeability was observed in a dose-dependent manner. The BPE preserved the relative mRNA abundance of tight junctions and reduced inflammatory cytokine expression. Pretreatment with the BPE was able to preserve occludin (OCLN) protein levels. The minimum inhibitory concentration of the BPE against Enterotoxigenic E. coli (ETEC) and Salmonella typhimurium (ST) was 62.50 µg/mL. These findings indicate that blueberry polyphenols hold potential as feed additives in swine weaning.

Welfare of pigs on farm

This scientific opinion focuses on the welfare of pigs on farm, and is based on literature and expert opinion. All pig categories were assessed: gilts and dry sows, farrowing and lactating sows, suckling piglets, weaners, rearing pigs and boars. The most relevant husbandry systems used in Europe are described. For each system, highly relevant welfare consequences were identified, as well as related animal-based measures (ABMs), and hazards leading to the welfare consequences. Moreover, measures to prevent or correct the hazards and/or mitigate the welfare consequences are recommended. Recommendations are also provided on quantitative or qualitative criteria to answer specific questions on the welfare of pigs related to tail biting and related to the European Citizen's Initiative 'End the Cage Age'. For example, the AHAW Panel recommends how to mitigate group stress when dry sows and gilts are grouped immediately after weaning or in early pregnancy. Results of a comparative qualitative assessment suggested that long-stemmed or long-cut straw, hay or haylage is the most suitable material for nest-building. A period of time will be needed for staff and animals to adapt to housing lactating sows and their piglets in farrowing pens (as opposed to crates) before achieving stable welfare outcomes. The panel recommends a minimum available space to the lactating sow to ensure piglet welfare (measured by live-born piglet mortality). Among the main risk factors for tail biting are space allowance, types of flooring, air quality, health status and diet composition, while weaning age was not associated directly with tail biting in later life. The relationship between the availability of space and growth rate, lying behaviour and tail biting in rearing pigs is quantified and presented. Finally, the panel suggests a set of ABMs to use at slaughter for monitoring on-farm welfare of cull sows and rearing pigs.

The Evidence for a Causal Link Between Disease and Damaging Behavior in Pigs

Damaging behaviors (DB) such as tail and ear biting are prevalent in pig production and reduce welfare and performance. Anecdotal reports suggest that health challenges increase the risk of tail-biting. The prevalence of tail damage and health problems show high correlations across batches within and between farms. There are many common risk factors for tail-biting and health problems, notably respiratory, enteric and locomotory diseases. These include suboptimal thermal climate, hygiene, stocking density and feed quality. The prevalence of tail damage and health problems also show high correlations across batches within and between farms. However, limited evidence supports two likely causal mechanisms for a direct link between DB and health problems. The first is that generalized poor health (e.g., enzootic pneumonia) on farm poses an increased risk of pigs performing DB. Recent studies indicate a possible causal link between an experimental inflammation and an increase in DB, and suggest a link between cytokines and tail-biting. The negative effects of poor health on the ingestion and processing of nutrients means that immune-stimulated pigs may develop specific nutrient deficiencies, increasing DB. The second causal mechanism involves tail-biting causing poor health. Indirectly, pathogens enter the body via the tail lesion and once infected, systemic spread of infection may occur. This occurs mainly via the venous route targeting the lungs, and to a lesser extent via cerebrospinal fluid and the lymphatic system. In carcasses with tail lesions, there is an increase in lung lesions, abscessation, arthritis and osteomyelitis. There is also evidence for the direct spread of pathogens between biters and victims. In summary, the literature supports the association between poor health and DB, particularly tail-biting. However, there is insufficient evidence to confirm causality in either direction. Nevertheless, the limited evidence is compelling enough to suggest that improvements to management and housing to enhance pig health will reduce DB. In the same way, improvements to housing and management designed to address DB, are likely to result in benefits to pig health. While most of the available literature relates to tail-biting, we suggest that similar mechanisms are responsible for links between health and other DB.

Tranquillizing Effect of Passiflora incarnata Extract: Outcome on Behavioral and Physiological Indicators in Weaning Pigs with Intact Tails

Simple Summary

Post-weaning is the most critical phase in pig farming, characterized by efforts to ensure health, performance and welfare of animals. Despite that EU Directive 2008/120/EC prohibits the practice of tail docking, it is still commonly applied in intensive farming to avoid tail biting. From a nutritional perspective, the dietary supplementation with natural extracts with calming properties could represent a promising approach to overcome common production stressors, reducing abnormal behaviors such as tail biting. This study intended to determine the effects of the dietary inclusion of Passiflora incarnata, known for its tranquillizing activity, on skin lesions, thermal imaging, behavior, salivary cortisol and IgA levels on post-weaning piglets reared with intact tails. Growth performances were also monitored. No differences were recorded between diets regarding growth performance, whereas findings concerning aggressive and abnormal behaviors, such as tail and ear biting, and lower levels of cortisol confirmed the hypothesis of the calming effect of P. incarnata on post-weaning piglets.

Abstract

Tail docking has been used in the pig industry to decrease the occurrence of tail biting behavior. This abnormal behavior has a multifactorial origin since it is a response to simultaneous environmental, nutritional and management changes. Given the calming properties of Passiflora incarnata, we hypothesized that dietary supplementation with the extract in weaned pigs could result in a modification of behavior and physiologic indicators linked to stress. Weaned piglets (n = 120, mean body weight 9.07 ± 2.30 kg) were randomly allocated to one of two dietary treatments: control diet (CON) and CON supplemented with 1 kg/t of P. incarnata (PAS). The trial was 28 days long. The presence of skin lesions was assessed at d-1, d-10, d-19, and d-28, and saliva samples were collected for IgA and cortisol determinations at the same sampling times. Results showed the PAS group was characterized by equal growth performance as the CON group, fewer ear lesions (p < 0.05), less aggressive behavior (p < 0.001), higher enrichment exploration (p < 0.001) and lower cortisol levels (p < 0.01). Time effect was observed for tail lesions (p < 0.001) and behavioral observations (p < 0.001). Additional research is required to determine the effect of P. incarnata extract using a larger number of animals and longer period of supplementation when risks associated with tail biting are uncontrolled.

Effects of Weaning Age at 21 and 28 Days on Growth Performance, Intestinal Morphology and Redox Status in Piglets

The study objective was to assess effects of different weaning ages on growth performance, intestinal morphology and redox status in Duroc × Landrace × Large White piglets (n = 96) fed diets without antibiotic growth promoters. Piglets were selected from 24 litters based on similar body weight at 14 d of age. All piglets were allocated to two groups in a completely random design with six replicates and eight pigs per replicate (four barrows and four gilts), which were weaned at 21 (n = 48; BW = 6.87 ± 0.33 kg) and 28 (n = 48; BW = 8.49 ± 0.41 kg) days of age. After weaning, pigs were fed a corn-soybean meal-based diet. Average daily gain (ADG), average daily feed intake (ADFI), feed conversion (F:G), diarrhea incidence, gastrointestinal pH, intestinal morphology and redox status were determined. Pigs weaned at 28 d displayed increased ADG from d 8 to 14 (p < 0.01) compared with pigs weaned at 21 d. Pigs weaned at 28 d had a higher ADFI from d 0 to 7 (p < 0.01), d 8 to 14 (p < 0.01), d 15 to 28 (p < 0.05) and during the entire experimental period (p < 0.01) compared with pigs weaned at 21 d. Pigs weaned at 21 d had an improved F:G from d 15 to 28 (p < 0.05) compared with pigs weaned at 28 d. Pigs weaned at 28 d had decreased diarrhea incidence from d 8 to 14 (p < 0.01) and the entire experimental period (p < 0.01) compared with pigs weaned at 21 d. On d 28, the pH of the stomach contents in pigs weaned at 21 d was significantly higher compared with pigs weaned at 28 d (p < 0.01). On d 14, the morphology of the duodenum, jejunum and ileum in pigs weaned at 28 d was improved compared with pigs weaned at 21 d. During the experiment period, the antioxidant abilities of pigs weaned at 28 d of the heart, liver, kidney, intestinal and serum were better than pigs weaned at 21 d. In conclusion, intestinal morphology, pH of the stomach and antioxidant status of pigs weaned at 28 d were better than pigs weaned at 21 d. These factors supported better growth performance and decreased diarrhea incidence.

Playful pigs: Evidence of consistency and change in play depending on litter and developmental stage

Play behaviour in pre-weaned piglets has previously been shown to vary consistently between litters. This study aimed to determine if these pre-weaning litter differences in play behaviour were also consistent in the post-weaning period. Seven litters of commercially bred piglets were raised in a free farrowing system (PigSAFE) and weaned at 28 days post-farrowing (+/-2 days). Post-weaning piglets were maintained in litter groups in the PigSAFE pen. Analyses have been adjusted for sex both within and between litter as the only statistically significant covariate to play behaviour. Litter differences were observed in locomotor play in both the pre- and post-weaning stage (Pre: F_(6,76) = 5.51 P < 0.001; Post: F_(6,69) = 4.71, P < 0.001) and run (Pre: F_(6,76) = 4.96, P < 0.001; Post: F_(6,69) = 4.58, P < 0.001; the major element of locomotor play). Twenty eight% of the variance for a single observed animal in pre-weaning locomotor play and 26% of variance post-weaning could be attributed to the litter. There was no statistical evidence of differences in social play between litters at either stage with only 8% of pre-weaning variance, and 1% of post-weaning variance being attributable to the litter level. However non-harmful fighting (the major element of social play), showed strong evidence of litter differences in both periods (Pre: F_(6,76) = 2.38, P = 0.037; Post: F_(6,69) = 2.60, P = 0.025), and was the only aspect of the play behaviour to correlate between the pre- and post-weaning periods (r = 0.765, df = 5, P = 0.045). On average play increased post-weaning. Litters showed a 'litter weaning effect' by differing in their locomotor play behavioural response to weaning, measured as the change in locomotor play behaviour from pre- to post-weaning (F_(6,70) = 5.95, P < 0.001). These results generally confirm previous work showing litter differences in aspects of play behaviour in both the pre and post-weaning period. However, there was no consistency in litter differences between pre- and post-weaning periods in the categories of play behaviour with the exception of non-harmful fighting. We demonstrated a 'litter weaning effect' where litters respond as a 'unit' to weaning in terms of their locomotory play behaviour. In general these results add further support to the use of play as a sensitive welfare indicator in neonatal pigs.

Early weaning increases aggression and stereotypic behaviour in cats

Behaviour problems are common in companion felines, and problematic behaviour may be a sign of chronic stress. In laboratory animals, early weaning increases the risk for aggression, anxiety, and stereotypic behaviour. However, very few studies have focused on early weaning in one of the world’s most popular pets, the domestic cat, although weaning soon after the critical period of socialisation is common practice. To study the effects of early weaning (<12 weeks) on behaviour, a large data set (N = 5726, 40 breeds) was collected from home-living domestic cats through a questionnaire survey. The results show that weaning before 8 weeks of age increases the risk for aggression, but not fearful behaviour. Moreover, cats weaned after 14 weeks of age have a lower probability for aggression towards strangers than early weaned cats and a lower probability for stereotypic behaviour (excessive grooming) than cats weaned at 12 weeks. The effect of weaning age on stereotypic behaviour is partially explained by the effects on aggression. These findings indicate that early weaning has a detrimental effect on behaviour, and suggest delayed weaning as a simple and inexpensive approach to significantly improve the welfare of millions of domestic cats.

PID temperature controller in pig nursery: improvements in performance, thermal comfort, and electricity use

The use of smarter temperature control technologies in heating systems can optimize the use of electric power and performance of piglets. Two control technologies of a resistive heating system were assessed in a pig nursery: a PID (proportional, integral, and derivative) controller and a thermostat. The systems were evaluated regarding thermal environment, piglet performance, and use of electric power for 99 days. The heating system with PID controller improved the thermal environment conditions and was significantly (P < 0.001) more efficient in terms of electricity use to produce 1 kg of body weight (2.88 kWh kg(-1)), specific cost (0.75 R$ kg(-1)), weight gain (7.3 kg), daily weight gain (0.21 kg day(-1)), and feed conversion (1.71) than the system with thermostat (3.98 kWh kg(-1); 1.03 R$ kg(-1); 5.2 kg; 0.15 kg day(-1), and 2.62, respectively). The results indicate that the PID-controlled heating system is more efficient in electricity use and provides better conditions for thermal comfort and animal performance than heating with thermostat.

The influences of weaning age and weight on carcass traits and meat quality of pigs

The purpose of this study was to establish the effects of weaning age and weight on pigs, and their interaction with carcass traits and meat quality. A total of 468 piglets were obtained from 57 sows and four boars and grouped by age at weaning (D21, 18-24 days; D28, 25-32 days). Each weaning group was subdivided into three weight groups (L, M and H) according to weaning weight. The D28 group had heavier carcass weight, redness and yellowness, but had lower marbling scores and less drip loss than the D21 group (P < 0.05). The pigs with a light weight at weaning had higher carcass weights and lower yellowness than did pigs with a medium or heavy weight at weaning (P < 0.05). Weaning age was found to have a negative correlation with drip loss, while weaning weight was negatively correlated with carcass weight and drip loss (P < 0.05). We concluded that carcass and meat quality traits in pigs were significantly related to their age and weight at weaning. Therefore, we find that piglet weaning age and weight are no less important than post-weaning growth performance and behavior, with regard to carcass traits and meat quality.

Physiological and behavioural responses to weaning conflict in free-ranging primate infants

Weaning, characterized by maternal reduction of resources, is both psychologically and energetically stressful to mammalian offspring. Despite the importance of physiology in this process, previous studies have reported only indirect measures of weaning stress from infants, because of the difficulties of collecting physiological measures from free-ranging mammalian infants. Here we present some of the first data on the relationship between weaning and energetic and psychological stress in infant mammals. We collected data on 47 free-ranging rhesus macaque infants on Cayo Santiago, Puerto Rico, showing that faecal glucocorticoid metabolite (fGCM) concentrations were directly related to the frequency of maternal rejection, with fGCM concentrations increasing as rates of rejection increased. Infants with higher fGCM concentrations also engaged in higher rates of mother following, and mother following was associated with increased time on the nipple, suggesting that infants that experienced greater weaning-related stress increased their efforts to maintain proximity and contact with their mothers. Infants experiencing more frequent rejection uttered more distress vocalizations when being rejected; however, there was no relationship between rates of distress vocalizations and fGCM concentrations, suggesting a disassociation between behavioural and physiological stress responses to weaning. Elevated glucocorticoid concentrations during weaning may function to mobilize energy reserves and prepare the infant for continued maternal rejection and shortage of energetic resources.

Effects of Transport at Weaning on the Behavior, Physiology and Performance of Pigs

Simple Summary

Pigs are commonly transported to separate production facilities at weaning to reduce disease transfer, enhance productivity and to improve overall operational efficiency. A review of the scientific literature suggests that these animals experience stress due to concurrent weaning and transport; however, gaps in the knowledge include the short and long term health and welfare implications of transporting pigs at weaning. Pig welfare and the efficiency of the swine industry may improve if science-based recommendations were in place.

Abstract

Transport of pigs to separate production facilities at the time of weaning is a common practice, primarily performed to reduce vertical transfer of disease and enhance production and overall farm efficiency. During transport, pigs are exposed to numerous stressors in conjunction with the stress experienced as a result of weaning. In this review, the behavioral and physiological response of pigs experiencing weaning and transport simultaneously will be described, including the effects of space allowance, season and transport duration. Based on the scientific literature, the gaps in the knowledge regarding potential welfare issues are discussed. Changes in behavior and physiology suggest that weaned pigs may experience stress due to transport. Space allowance, season and duration are aspects of transport that can have a marked impact on these responses. To date, the literature regarding the effects of transport on weaned pigs has primarily focused on the short term stress response and little is known about the effects of concurrent weaning and transport on other aspects of pig welfare including morbidity and mortality rates. Greater understanding of the short and long term consequences of transport on weaned pig welfare particularly in relation to factors such as trip duration, provision of feed and water, and best handling practices would benefit the swine industry. Furthermore, the development of guidelines and recommendations to enhance the short and long term welfare of weaned pigs in relation to transport are needed.

Piglets' weaning behavioural response is influenced by quality of human-animal interactions during suckling

The aim of this study was to compare the short-term post-weaning behaviour of piglets treated either neutrally or aversively during the suckling period. A total of 24 lactating sows and their litters were housed in different rooms according to treatment. A female experimenter (P1) was in charge of feeding and cleaning from days 10 to 27 after birth. For the aversive treatment (Aver), P1 was noisy, moved harshly and unpredictably and shouted frequently during routine cleaning of facilities and animal handling. For the neutral treatment (Neut), P1 used a soft tone of voice and was careful during the same routine. At weaning, the avoidance response of piglets to an approaching experimenter in a novel place was assessed in four piglets from each litter. Scores ranged from 1 (experimenter could touch piglet) to 4 (piglet escaped as soon as person moved). The test was repeated twice, with a 1-h interval, with P1, who wore blue trousers and white T-shirt, and a second handler unfamiliar to the piglets (P2, who wore blue coveralls). Thereafter, litters from the same treatment were mixed and housed in separate rooms, balanced for gender and live weight (n = 12 groups of 4 piglets/treatment). Behaviour time budgets were registered by scan sampling every 2-min, for 4 h per day, for 4 days. Piglets were weighed at birth, at weaning and on day 5. Effects of treatment and handler on responses to the avoidance test were analysed with non-parametric tests and effects of treatment with a mixed model for repeated measures. Avoidance score was higher for Aver than Neut piglets when tested with P1 (P = 0.04) but not with P2 (P = 0.8). When piglets' responses to the different handlers were compared within each treatment, no significant differences were found. Frequencies of resting were lower (P < 0.001), whereas escape attempts (P < 0.03), agonistic interactions (P < 0.02) and frequency of presence at feeder (P < 0.001) were higher in the Aver than in the Neut groups. Feed and water intake and weight gain did not differ between treatments. We conclude that 4-week-old piglets can discriminate a handler according to the nature of treatment received during suckling. In addition, piglets treated aversively seem to have more difficulty adapting to weaning than those treated neutrally during the suckling period.

High physiological demands in intensively raised pigs: impact on health and welfare

Genetic selection and better control of the environment of the pigs have resulted in increased production levels concerning both reproduction and growth. Such high performances imply high physiological demands that may deteriorate health and welfare. The aims of this paper are to review the physiological challenges that pigs are facing, to identify possible consequences on health and welfare, to propose ways of detecting and correcting problems whenever possible. At weaning, piglets are submitted to abrupt changes in food supply, housing and social environment. Behavioural changes and efficient adaptations of the digestive tract are critical for their health and welfare. Physiological demands to support these adaptations and risks of failure are inversely related to the age of the pigs. During fattening, modern pigs have high daily weight gain especially of lean tissue as well as elevated feed conversion rate. These high growth performances are suspected to favour stress and disease susceptibility, undesirable behaviours as well as leg weakness, but further experimental data are necessary to validate these effects and find their origin. In reproductive females, high prolificacy generates elevated foetal demands for nutrients and space that are not fully met as shown by an increased number of light piglets having difficulties to adapt successfully to the neonatal life. During lactation, sows with high milk production have high nutrient requirements leading to intense catabolism that may affect their health, welfare and future reproductive abilities.

Influence of housing and social changes on growth, behaviour and cortisol in piglets at weaning

The present experiment aimed at evaluating the relative effects of environmental and social changes on behaviour, growth and salivary cortisol of piglets at weaning. On Day 0, 26-day old piglets were weaned and allocated to one of four treatments: neither environmental nor social change (C), environmental change (E), social change (S), and both changes (SE). Overall, 6 replicates of 10-12 animals/pen/treatment were analysed. Piglets were video recorded during the first three days after weaning to observe social behaviour and general activity. Saliva was collected between 07:00 and 09:00 on Day 0 just before weaning (D0H7), on Day 1 (D1H7) and Day 2 (D2H7 and D2H16) to measure cortisol. Saliva cortisol did not change after weaning in C piglets but increased significantly at D1H7 in S and SE piglets, at D2H7 and D2H16 in E and SE piglets. Compared to C piglets, numerous behaviours were altered in SE piglets: more total lying (P<0.08), less lying on the belly, less environmental exploration, less playing, more fighting regardless the day, more lying awake inactive on Day 0 (P<0.05). Compared to C piglets, E piglets displayed more total lying but less environmental exploration whereas S piglets showed less lying on the belly but more fighting (P<0.05). Present results show that moving piglets to a new environment as well as mixing them with unfamiliar conspecifics at weaning have stressful effects which are additive.

Behavioral indexes of piglet welfare: comparison of indoor and outdoor housing systems

The purpose of this experiment was to establish behavioral indexes of piglet welfare. Forty-eight piglets were allocated to either four indoor pens or four outdoor pens (six piglets per pen). The indoor system was a commercial pen that consisted of a concrete floor and a slat floor. The outdoor system had a dirt paddock with a wooden hutch. Growth performance, salivary cortisol levels, skin lesions and behaviors of the piglets were monitored for 4 weeks. Sixteen types of behaviors were recorded by using 2-min instantaneous scan sampling for 8 h/day. Growth performance and salivary cortisol levels did not significantly differ between the two housing systems. On the other hand, skin lesions and behaviors were significantly affected by the housing system. The number of skin lesions was higher in the indoor system. In addition, piglets in the outdoor system showed more investigative and social-play behaviors than those in the indoor system. Piglets in the indoor system showed more resting, drinking, moving, fighting, and conflict behaviors than those in the outdoor system. We conclude that investigative, social-play and conflict behaviors may be effective indexes of the welfare level of piglets, especially investigative and conflict behaviors.

Behavioral assessment of cognitive function using a translational neonatal piglet model

Pigs are used in myriad research disciplines related to human health, but no studies have employed the piglet to directly assess cognitive function during the neonatal period. Our objective was to develop a behavioral assay for neonatal piglets to assess learning and memory. At 2-wk of age, piglets were trained to locate a milk reward in an 8-arm radial maze using colored intra-maze cues (acquisition phase, 60-s trials with 8 trials per d for 4d). Cue colors were then reversed and pigs re-tested to assess learning and working memory (reversal phase). Piglets quickly learned the simple associative acquisition task, and proficiency greatly improved throughout reversal testing. To further assess the behavioral assay, piglets received an i.p. injection of saline or polyinosinic:polycytidylic acid (poly I:C; 5mg/kg body weight) immediately preceding reversal testing. Poly I:C-treated piglets exhibited acute sickness behaviors, but observationally, were asymptomatic 12-h post-injection. Pro-inflammatory cytokine mRNA expression was elevated 4-h post-injection in both peripheral and central compartments, and plasma cytokine protein levels were concurrently elevated. Specifically, poly I:C elicited the largest increases in interleukin (IL)-1β mRNA in the liver, spleen, and hippocampus. At 24-, 48-, and 72-h post-injection (i.e., after acute sickness), poly I:C-treated piglets committed more incorrect arm entries, required more time to complete the reversal task, and moved a greater distance in the maze compared with control piglets. Collectively, these data demonstrate that neonatal piglets are capable of being trained in traditional learning and memory tests, and peripheral immune activation elicits alterations in cognitive processing in the neonate.

Metabolic indicators of nutritional stress are not predictive of abnormal oral behavior in piglets

Belly nosing is an abnormal oral-nasal behavior that can develop to high levels in newly weaned piglets and may signal nutritional need. The effects of feed restriction on both behavior and metabolic serum parameters were examined in 128 weaned piglets. All pigs were fed ad libitum during week 1, and during week 2, half of all pens (N=8) were restricted to 65% of ad libitum intake. Blood samples were collected on days 3 and 10 after weaning and behavior was observed from video recordings on days 5 and 12. Piglets were classified as early 'nosers' or early 'non-nosers' based on their behavior on day 5. Feed restriction resulted in elevated non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB) and both lower glucose and a NEFA/glucose ratio, but belly nosing was not affected. Piglets classified as 'nosers' did not have blood profiles indicating they were in greater nutritional need compared to 'non-nosers' in the first week of weaning, nor did they increase belly nosing or other piglet directed behaviors when restricted in week 2. Overall, no associations were found between blood parameters indicative of nutritional stress and belly nosing. This study identifies serum glucose, BHB and NEFA as well as the glucose/NEFA ratio as useful indicators of nutritional stress in newly weaned piglets.

Prenatal flavor exposure affects flavor recognition and stress-related behavior of piglets

Exposure to flavors in the amniotic fluid and mother's milk derived from the maternal diet has been shown to modulate food preferences and neophobia of young animals of several species. Aim of the experiment was to study the effects of pre- and postnatal flavor exposure on behavior of piglets during (re)exposure to this flavor. Furthermore, we investigated whether varying stress levels, caused by different test settings, affected behavior of animals during (re)exposure. Piglets were exposed to anisic flavor through the maternal diet during late gestation and/or during lactation or never. Piglets that were prenatally exposed to the flavor through the maternal diet behaved differently compared with unexposed pigs during reexposure to the flavor in several tests, suggesting recognition of the flavor. The differences between groups were more pronounced in tests with relatively high stress levels. This suggests that stress levels, caused by the design of the test, can affect the behavior shown in the presence of the flavor. We conclude that prenatal flavor exposure affects behaviors of piglets that are indicative of recognition and that these behaviors are influenced by stress levels during (re)exposure.

Early weaning results in less active behaviour, accompanied by lower 5-HT1A and higher 5-HT2A receptor mRNA expression in specific brain regions of female pigs

In rodents and humans stressful events in early life e.g. maternal deprivation, can increase sensitivity to stress in later life. Humans may become more susceptible to mood disorders, e.g. depression. In livestock species, such as pigs, early weaning is a form of maternal deprivation. We investigated behavioural consequences in 99 female pigs weaned at three different ages (12, 21 and 42 days; d12, d21, d42). Pigs were habituated to an open field arena over 6 days before being given 5-min open-field tests over three subsequent days (days 77-79). Early-weaned pigs (d12) showed behavioural inhibition (reduced vocalisations and lower activity) compared with later-weaned pigs, although in all groups these measures declined over the three tests, so this treatment difference might reflect more rapid habituation to the test in d12 pigs. Long-term effects on mood-related 5-HT receptor subtypes were measured in the brain at 90 days in a random sample of the d12 (n=8) and d42 pigs (n=8), using (3)H-ligand-binding and autoradiography and in situ hybridisation histochemistry. There were no differences between weaning ages in binding of (3)H-8-OH-DPAT (5-HT(1A) receptor agonist) or of (3)H-ketanserin (5-HT(2A) receptor antagonist) to any brain region studied. In d12 pigs, 5-HT(1A) receptor mRNA expression per unit area was 29%, 63%, 52% and 64% lower than in d42 pigs in the parvocellular PVN, amygdala and hippocampal dentate gyrus and pyramidal cell layer, respectively. The ratio of expression per cell to expressing cells per unit area was also lower, by 31%, in the pars horizontalis of the PVN in d12 pigs. Conversely, 5-HT(2A) receptor mRNA was expressed at a 25% and 28% higher density per unit area in the amygdala and pyramidal cell layer of the hippocampus, respectively, in these d12 pigs. In individual pigs, across brain regions, 5-HT(1A) receptor mRNA data were 70-79% correlated with binding data but no correlation was found for 5-HT(2A) data, suggesting different regulatory mechanisms. The behavioural and neurobiological responses to early weaning might represent either dysfunction or adaptation. Further investigation is required.