Relationships between individual behavioural traits and post-weaning growth in segregated early-weaned piglets

Interacting impact of maternal inflammatory response and stress on the amygdala transcriptome of pigs

Changes at the molecular level capacitate the plasticity displayed by the brain in response to stress stimuli. Weaning stress can trigger molecular changes that influence the physiology of the offspring. Likewise, maternal immune activation (MIA) during gestation has been associated with behavior disorders and molecular changes in the amygdala of the offspring. This study advances the understanding of the effects of pre- and postnatal stressors in amygdala gene networks. The amygdala transcriptome was profiled on female and male pigs that were either exposed to viral-elicited MIA or not and were weaned or nursed. Overall, 111 genes presented interacting or independent effects of weaning, MIA, or sex (FDR-adjusted P-value <0.05). PIGY upstream reading frame and orthodenticle homeobox 2 are genes associated with MIA-related neurological disorders, and presented significant under-expression in weaned relative to nursed pigs exposed to MIA, with a moderate pattern observed in non-MIA pigs. Enriched among the genes presenting highly over- or under-expression profiles were 24 Kyoto Encyclopedia of Genes and Genomes pathways including inflammation, and neurological disorders. Our results indicate that MIA and sex can modulate the effect of weaning stress on the molecular mechanisms in the developing brain. Our findings can help identify molecular targets to ameliorate the effects of pre- and postnatal stressors on behaviors regulated by the amygdala such as aggression and feeding.

Effect of omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation to lactating sows on growth and indicators of stress in the postweaned pig1,2

Dietary omega-3 polyunsaturated fatty acids (n-3 PUFA) are precursors for lipid metabolites that reduce inflammation. Two experiments were conducted to test the hypothesis that enriching the sow diet in n-3 PUFA during late gestation and throughout lactation reduces stress and inflammation and promotes growth in weaned pigs. A protected fish oil product (PFO; Gromega) was used to enrich the diet in n-3 PUFA. In the initial experiment, time-bred gilts were fed a gestation and lactation diet supplemented with 0% (control; n = 5), 0.25% (n = 4), 0.5% (n = 4), or 1% (n = 5) PFO from 101 ± 2 d of gestation to day 16 of lactation. Adding 1% PFO to the diet increased the n-3:n-6 PUFA ratio in colostrum and milk compared with controls (P = 0.05). A subsequent experiment was performed to determine whether supplementing the sow diet with 1% PFO improved growth and reduced circulating markers of acute inflammation and stress in the offspring. Plasma was harvested from piglets (16 per treatment group) on day 0 (d of weaning) and days 1 and 3 postweaning. Pigs from the 1% PFO treatment group weighed more (P = 0.03) on day 3 postweaning and had a greater (P ˂ 0.05) n-3:n-6 PUFA ratio in plasma on each day sampled compared with 0% PFO controls. There was an overall treatment effect on plasma total cortisol (P = 0.03) and haptoglobin (P = 0.04), with lesser concentrations in pigs on the 1% PFO diet. Plasma corticosteroid-binding globulin (CBG) concentrations were not different between treatment groups but were less (P ˂ 0.001) on days 1 and 3 when compared with day 0. The resultant free cortisol index [FCI (cortisol/CBG)] was less (P = 0.02) on days 1 and 3 for pigs from the 1% treatment group compared with the controls. An ex vivo lipopolysaccharide (LPS) challenge of whole blood collected on days 0 and 1 was used to determine whether 1% PFO attenuated release of inflammatory cytokines (IL-1β, IL-6, and TNF-α). Blood from pigs within the 1% PFO treatment group tended (P = 0.098) to have a lesser mean concentration of TNF-α in response to LPS compared with blood from controls. These results suggest that providing a PFO supplement as 1% of the diet to sows beginning in late gestation and during lactation can increase the n-3:n-6 PUFA ratio in their offspring, which may improve growth and reduce the acute physiological stress response in the pigs postweaning.

Predicting in vivo starch digestibility coefficients in newly weaned piglets from in vitro assessment of diets using multivariate analysis

The study was based on correlating a dataset of in vivo mean starch digestibility coefficients obtained in the immediate post-weaning phase of piglets with a range of dietary in vitro variables. The paper presents a model that predicts (R2 0·71) in vivo average starch digestibility coefficients in the 0·5 small-intestinal region of newly weaned piglets fed cereal-based diets using seven in vitro variables describing starch properties that are fundamentally associated with the quality of feed materials, i.e. hydration, structure and amylolytic digestion. The variables were: Rapid Visco Analyser (RVA; measures the viscosity of materials when sheared under defined hydration and temperature regimens); RVA end viscosity; RVA (gelatinisation) peak viscosity; ΔH (gelatinisation enthalpy that provides an estimate of helical order or degree of crystallinity in starch); water solubility index (WSI; that denotes the amount of soluble polysaccharides released from starch granules to the aqueous phase); grain endogenous amylase (concentration of endogenous α-amylase in cereals, assessed by pasting cereal flours in 25 g of AgNO3, an amylase inhibitor v. water using RVA).

A critical review of fear tests used on cattle, pigs, sheep, poultry and horses

Fear is arguably the most commonly investigated emotion in domestic animals. In the current review we attempt to establish the level of repeatability and validity found for fear tests used on cattle, pigs, sheep and goats, poultry and horses. We focus the review on the three most common types of fear tests: the arena test (open field), the novel object test, and the restraint test. For some tests, e.g. tonic immobility in poultry, there is a good and broad literature on factors that affect the outcome of the test, the validity of the test and its age dependency. However, there are comparatively few of these well defined and validated tests and what is especially missing for most tests is information on the robustness, i.e., what aspects can be changed without affecting the validity of the tests. The relative absence of standardized tests hampers the development of applied ethology as a science.

Evidence of phenotypic relationships among behavioral characteristics of individual pigs and performance

The objective of this research was to estimate phenotypic relationships among backtest scores (BTS), resident-intruder test scores (RIS), growth rate, LM area, and backfat in pigs. Little is known about the relationships among measures of behavioral characteristics of individual pigs and economically important traits. However, it may be expected that a pig's behavior affects its performance and that of its pen mates. The backtest was used in this experiment because it was previously shown to be a measure of individual stress-coping behavior and was related to lean gain. The resident-intruder test was used because it is a measure of a pig's tendency for aggressive behavior toward an unfamiliar pig. Each test was performed twice on pigs (n = 150) from 20 litters, and complete performance data was available on 140 pigs. Between 7 and 14 d of age, the backtest was performed by placing each pig in a supine position and gently restraining it for 60 s. The number of escape attempts (bouts of struggling) and total time spent struggling were recorded. The BTS was the summation of escape attempts during both tests. Resident intruder tests were assessed when pigs were between 30 and 50 d of age. A solid divider was placed in the resident pig's pen. The resident was placed alone on 1 side of the divider, away from its penmates. An intruder pig of the same sex and smaller size was then placed into the pen. When an attack was initiated by the resident, the pigs were immediately separated, the test was terminated, and a score of 1 was recorded. If no attack occurred by 5 min, the test was terminated and was given a score of zero. The cumulative score from both tests was the RIS. Dam effects influenced BTS (P < 0.01) and RIS (P < 0.03). Preweaning ADG of pigs with a BTS of 8 was 120 g greater than that of pigs with a BTS of 2. However, ADG from 20 to 76 d of age was 131 g greater in pigs with BTS = 2 than in pigs with BTS = 8. Lean gain of pigs with RIS = 2 was 25 g/d greater than in those with RIS = 0 or 1. This resulted in pigs with RIS = 2 having 1.6 kg more acceptable, standardized, fat-free lean. Conflicting results were found when relating the BTS to performance. However, with the RIS, greater aggression toward other pigs was associated with better performance. It was concluded that an unfavorable phenotypic relationship existed between RIS and lean growth.

Cortisol administration to pregnant sows affects novelty-induced locomotion, aggressive behaviour, and blunts gender differences in their offspring

Several behavioural effects of prenatal stress are reported in literature, and these seem to depend, among other factors, on the gender studied and the period of gestation in which prenatal stress is applied. In the present study, oral administration of hydrocortisone-acetate (HCA) to 41 pregnant sows was used as a model for prenatal stress, since corticosteroids are considered a key mediator in the effects of prenatal stress. HCA was orally administered to pregnant sows during three periods of gestation: 21-50 (period 1, P1, n = 10), 51-80 (period 2, P2, n = 10) and 81-110 (period 3, P3, n = 10) days after insemination (term 115 days). Control sows (n = 11) received vehicle from 21 to 110 days after insemination. Between days 9 and 48 after birth, treatment effects on male and female piglet behaviour were determined in the home pen and in four different behavioural tests. During the backtest, no gender differences were observed in vocalisations in HCA-piglets, while control males vocalised more than control females. In the home pen at 14 days of age, HCA-piglets spent less time in social interactions than control piglets. During the novel environment test, P1- and P3-piglets walked more than control piglets, but this was not observed during the novel object test, four days later. At weaning, P2- and P3-piglets performed less individual play. Prior to mixing with an unfamiliar piglet (male piglets only), HCA-piglets had lower salivary cortisol concentrations than control piglets, but no difference was observed after mixing. P1-, P2-, and P3- piglets had fewer non-aggressive encounters, and P2-piglets continued fighting longer than control piglets. The present study demonstrates that elevated maternal cortisol concentrations during gestation affect piglet behaviour, and effects do differ between male and female piglets. In addition, effects depend on the period of cortisol administration.

Modeling the effects of stressors on the performance of populations of pigs

A simulation model that predicts the effect of the social, physical, and nutritional environments on pig food intake and performance was extended to deal with individual variation. The aim was to investigate the effect of between-animal variation on the performance of a population of growing pigs. Variation was generated in initial state, growth potential, and ability to cope when exposed to social "stressors" (EX). Variation in initial state is described by initial body weight (BW0), from which the chemical composition of the pig is calculated. Variation in growth potential is described by creating variation in the genetic growth descriptors. Variation in EX exists between genotypes, where it has been suggested that leaner, more modern genotype pigs tend to be less able to cope. It is expected that within a population or group that the social environment (i.e., position within the social hierarchy) also affects an individual's ability to cope. In the model, it is assumed that the larger, more dominant individuals are better able to cope when exposed to social stressors. Consequently, within a population, EX is correlated with body weight around the genotype mean. Model predictions showed that increasing the variation in BW0 and EX increased the variation in pig performance. This is an important practical consideration in commercial pig production, where the heterogeneity of the population at slaughter may affect the profitability of an enterprise. The way a stressor constrains performance determines whether the mean population response to a given stressor is the same as the average individual response. If all pigs in a group are affected at the same stressor intensity (e.g., all are either mixed or not), then the predicted average individual and mean population responses will be the same. If, however, the intensity of stressor at which performance becomes limiting differs between individuals (such as space allowance or temperature), differences between the individual and mean population responses will be predicted. Variation in the growth response of a population was determined to a greater extent by variation in EX and BW0 than by variation in growth potential, when pigs were housed in simulated conditions likely to be encountered in commercial environments. Consequently, decreasing the variation in initial body weight and improving ability of pigs to cope may be a better way of improving pig performance than selecting only for increased growth potential.

Gastrointestinal transit time of nondisintegrating radio-opaque pellets in suckling and recently weaned piglets

The objective was to determine the gastrointestinal (GI) transit times of pellets in piglets at different time points around weaning, as transit times are essential criteria to develop oral drug delivery systems. Nondisintegrating radio-opaque pellets were given orally in order to define the transit times by radiography. The radiographs were analysed with a software programme to calculate the number of pellets present in the different parts of the GI tract. In suckling piglets, the gastric emptying was faster (75% in 1.5 to 3.5 h), and the colonic accumulation (to 73%) was greater than in weaned piglets (3 days, 2 and 3 weeks postweaning, 65% gastric emptying in 18 h, 75% in 17 h, and 75% in 7 h, respectively; maximal colonic accumulations of 48%). Immediately after weaning, the transit was markedly prolonged but shortened with increased postweaning time (3 days, 2 and 3 weeks postweaning, 85% excretion in 175.5, 77, and 50.5 h, respectively). Three weeks postweaning, the transit was no longer affected by weaning as transit times were similar to values reported in growing and adult pigs, and retention appeared to be restricted to the stomach and the colon. These data are of crucial importance in the design of enteric-coated formulations for oral administration of vaccines and therapeutics to young piglets and for human research using the pig model.