Barriers and drivers of farmers to provide outdoor access in pig farming systems: a qualitative study

Part of the farmers have chosen to raise pigs with outdoor access. However, providing outdoor access to pigs is not a simple matter, and many farmers are hesitating or feel powerless to engage in this transition. A better understanding of their needs and challenges could facilitate the development of innovations that generate commitment. This survey aimed to identify the French pig farmers' barriers to and drivers for providing outdoor access to pigs. A total of 36 farmers, aged 25-60, who worked in all types of pig farming systems (from full indoor to free-range) participated in a semi-structured interview that lasted 1.25-2.25 h. The topics covered included a historical overview, a description of the farm and practices, as well as opinions about the impact of outdoor access on farmers, animals, production and economic performance, environment, and society. Qualitative data were analysed using thematic analysis. Most of the participants agreed that rearing pigs indoors is a different job from that of rearing pigs with outdoor access and that it is above all a matter of choice, farmer work conception, and work comfort. Farmers generally agreed that working outdoors is particularly arduous, but this could be compensated by the satisfaction of being in contact with nature and seeing animals in a more complex environment. A large majority of farmers managing a system with outdoor access raised the issue of lack of support, highlighting the need for refinement and diffusion of guides of practices as well as day-to-day support. The impact of outdoor access on the health and welfare of pigs was discussed, especially regarding climatic hazards and the risk of zoonoses, and several outdoor farmers explained how their relationship with the animals changes when pigs are raised outside. Given that zootechnical performance may significantly decrease in farms with outdoor access, various strategies can be employed to maintain profitability, such as feed production, circularity, direct sales, or work diversification. They could be either motivating or demotivating factors depending on the individuals. Concerns about social criticism were prominent among many indoor farmers while farmers providing outdoor access generally felt more serene and proud. Overall, this study can serve as a basis to identify levers that could remove barriers, foster the adherence of more farmers, and facilitate the transition towards more pig farming systems with outdoor access, provided that those systems are viable and beneficial for the welfare and health of the animals and farmers.

Physiological traits of newborn piglets associated with colostrum intake, neonatal survival and preweaning growth

Colostrum intake, which is critical for piglet survival after birth and growth up to weaning, greatly depends on piglet weight and vitality at birth. Our aim was to identify a set of biological variables explaining individual variations in colostrum intake, preweaning growth and risk of dying. Farrowing traits, morphological traits and colostrum intake were determined for 504 piglets born alive from 37 Landrace × Large White sows. A subset of 203 of these piglets was used to measure plasma neonatal concentrations of metabolites and hormones in blood collected from the umbilical cord at birth. From univariate analyses, we established that colostrum intake was positively associated with plasma neonatal concentrations of IGF-I, albumin, thyroid hormones (P < 0.001), and non-esterified fatty acids (P < 0.05), and was negatively associated with concentrations of lactate (P < 0.001). In a multivariable analysis, the variables explaining the variation in colostrum intake were piglet birth weight and rectal temperature 1 h after birth (positive effect, P < 0.001), time of birth after the onset of parturition, and fructose plasma concentrations at birth (negative effects, P < 0.001 and P < 0.05, respectively). Piglets that died within 3 days after birth had lower neonatal concentrations of albumin (P < 0.001), IGF-I and thyroxine (P < 0.01) than surviving piglets. Preweaning growth was positively associated with neonatal concentrations of IGF-I, thyroxine (P < 0.001), albumin and insulin (P < 0.05). Cortisol and glucose concentrations at birth were not related to colostrum intake, neonatal survival or preweaning growth. Multivariable analyses confirmed that colostrum intake was the predominant factor influencing piglet survival within 3 days after birth and preweaning growth. These results provide physiological indicators of piglet colostrum intake, besides birth weight. They also confirm the impact of time of birth during farrowing on colostrum intake and the crucial importance of physiological maturity at birth for postnatal adaptation.

Review: Implication of redox imbalance in animal health and performance at critical periods, insights from different farm species

The process of oxidative stress occurs all over the production chain of animals and food products. This review summarises insights obtained in different farm species (pigs, ruminants, poultry, and fishes) to underpin the most critical periods for the venue of oxidative stress, namely birth/hatching and weaning/start-feeding phase. Common responses between species are also unravelled in periods of high physiological demands when animals are facing dietary deficiencies in specific nutrients, suggesting that nutritional recommendations must consider the modulation of responses to oxidative stress for optimising production performance and quality of food products. These conditions concern challenges such as heat stress, social stress, and inflammation. The magnitude of the responses is partly dependent on the prior experience of the animals before the challenge, reinforcing the importance of nutrition and other management practices during early periods to promote the development of antioxidant reserves in the animal. When these practices also improved the performance and health of the animal, this further confirms the central role played by oxidative stress in physiologically and environmentally induced perturbations. Difficulties in interpreting responses to oxidative stress arise from the fact that the indicators are only partly shared between studies, and their modulations may also be challenge-specific. A consensus about the best indicators to assess pro-oxidative and antioxidant pathways is of huge demand to propose a synthetic index measurable in a non-invasive way and interpretable along the productive life of the animals.

Tissue-specific responses of antioxidant pathways to poor hygiene conditions in growing pigs divergently selected for feed efficiency

Background

Poor hygiene of housing induces a systemic inflammatory response. Because inflammation and oxidative stress are processes that can sustain each other, the ways pigs are able to activate their antioxidant defenses are critical for production performance and health during periods when the immune system is solicited. Selection for production performance can also influence reactive oxygen species (ROS) production and expression levels of genes involved in cellular response to oxidative stress in different tissues. To establish the extent by which poor hygiene and selection for feed efficiency affected redox status, pigs divergently selected for residual feed intake (RFI) were housed in poor or good hygiene during 6 weeks. At the end, blood was collected in all pigs, and half of them were killed for tissue sampling. The remaining pigs were reared in good hygiene conditions during a recovery period of 7–8 weeks.

Results

At week 6, poor hygiene was associated with a lower total antioxidant capacity assessed by plasma ferric reducing ability in all pigs, and with greater plasma levels of hydrogen peroxides in the high RFI pigs (less efficient). Adipose tissue of high RFI pigs exhibited higher activities of catalase and glutathione reductase, and greater thiobarbituric acid reactive substances (TBARS) concentrations when compared with the low RFI pigs (more efficient). Poor hygiene conditions activated the antioxidant enzymes activities (glutathione reductase, superoxide dismutase and catalase) in adipose tissue of both lines, but led to higher ROS production by mature adipocytes isolated from the high RFI pigs only. In liver and muscle, there were only minor changes in antioxidant molecules due to genetics and hygiene conditions. After the resilience period, adipose tissue of pigs previously challenged by poor hygiene maintained higher antioxidant enzyme activities, and for the high RFI line, displayed higher TBARS concentrations.

Conclusions

Pigs selected for improved feed efficiency showed a lower susceptibility to oxidative stress induced by poor hygiene conditions. This could led to a lower inflammatory response and less impaired growth when these pigs are facing sanitary challenges during the production period.

Review: divergent selection for residual feed intake in the growing pig

This review summarizes the results from the INRA (Institut National de la Recherche Agronomique) divergent selection experiment on residual feed intake (RFI) in growing Large White pigs during nine generations of selection. It discusses the remaining challenges and perspectives for the improvement of feed efficiency in growing pigs. The impacts on growing pigs raised under standard conditions and in alternative situations such as heat stress, inflammatory challenges or lactation have been studied. After nine generations of selection, the divergent selection for RFI led to highly significant (P<0.001) line differences for RFI (-165 g/day in the low RFI (LRFI) line compared with high RFI line) and daily feed intake (-270 g/day). Low responses were observed on growth rate (-12.8 g/day, P<0.05) and body composition (+0.9 mm backfat thickness, P=0.57; -2.64% lean meat content, P<0.001) with a marked response on feed conversion ratio (-0.32 kg feed/kg gain, P<0.001). Reduced ultimate pH and increased lightness of the meat (P<0.001) were observed in LRFI pigs with minor impact on the sensory quality of the meat. These changes in meat quality were associated with changes of the muscular energy metabolism. Reduced maintenance energy requirements (-10% after five generations of selection) and activity (-21% of time standing after six generations of selection) of LRFI pigs greatly contributed to the gain in energy efficiency. However, the impact of selection for RFI on the protein metabolism of the pig remains unclear. Digestibility of energy and nutrients was not affected by selection, neither for pigs fed conventional diets nor for pigs fed high-fibre diets. A significant improvement of digestive efficiency could likely be achieved by selecting pigs on fibre diets. No convincing genetic or blood biomarker has been identified for explaining the differences in RFI, suggesting that pigs have various ways to achieve an efficient use of feed. No deleterious impact of the selection on the sow reproduction performance was observed. The resource allocation theory states that low RFI may reduce the ability to cope with stressors, via the reduction of a buffer compartment dedicated to responses to stress. None of the experiments focussed on the response of pigs to stress or challenges could confirm this theory. Understanding the relationships between RFI and responses to stress and energy demanding processes, as such immunity and lactation, remains a major challenge for a better understanding of the underlying biological mechanisms of the trait and to reconcile the experimental results with the resource allocation theory.

Metabolic response to an inflammatory challenge in pigs divergently selected for residual feed intake

Selection for residual feed intake (RFI), which is used to select animals for feed efficiency, also influences nutrient partitioning between growth and maintenance functions. This study was designed to investigate if selection for reduced RFI can alter the trade-off between growth and immunity and contributes to differences in metabolic responses to an inflammatory challenge. Piglets from 2 lines divergently selected on RFI (low: RFI, = 10, and high: RFI, = 11) were challenged at 55 d of age (on d 0) with complete Freund's adjuvant (CFA) to induce a noninfectious pneumonia. Plasma haptoglobin and nutrient concentrations (in fasted state and 2 h after feeding) were determined from d -1 to d 7, and tissue protein metabolism was determined on d 8. Haptoglobin concentrations were greater from d 1 to d 7 relative to d -1 ( < 0.01). Feed intake was less on d 1 than on the other days ( < 0.001), as was total AA plasma concentrations at fasted state ( < 0.05). Fasted concentrations of His ( = 0.06) and Trp ( = 0.05) tended to be less, those of Val were less ( < 0.05), and fed concentrations of Lys were increased ( < 0.05) on d 7 compared to d -1. Uremia was less on d 7 than on d -1 at fasted state ( < 0.05), whereas it did not vary at fed state ( 0.1). Fasted glucose and insulin plasma concentrations were stable across days ( 0.1). In the fed state and in only RFI pigs, glucose concentration was greater on d 1 than on d 3, 5, and 7 ( < 0.05). Total AA, Gln, Ile, Leu, Pro ( < 0.05), and hydroxyproline ( = 0.07) were less in RFI than RFI pigs at fed state, whereas Ala and Gly were less in RFI pigs at fasted and fed states ( < 0.05). Citrulline ( < 0.05) and Met ( < 0.01) concentrations were greater in RFI than RFI pigs in the fasted state, whereas Asp was greater in RFI pigs in both fasted and fed states ( < 0.05). On d 8, liver and LM protein synthesis tended to be lower ( = 0.07 and 0.09, respectively) and liver calpain activity was greater ( = 0.07) in RFI than RFI pigs. Liver and LM proteasome did not differ between lines ( 0.1). The metabolic differences between lines were not associated with differences in feed intake, ADG between d -1 and d 8, and haptoglobin concentration ( 0.1). Thus, it seems that that, using different metabolic strategies, both lines coped similarly with the CFA challenge. Contrary to our hypothesis, this experiment showed, in young pigs, no advantage of RFI animals in response to an inflammatory challenge.

Genetic relationships between measures of sexual development, boar taint, health, and aggressiveness in pigs

Breeding intact boars is a promising alternative to surgical castration of piglets. Genetic selection should enable farmers to solve problems due to boar taint and aggressiveness while taking into account potential consequences on other traits of interest. The aim of the study was to estimate genetic relations between sexual development, boar taint, health, and aggressiveness. About 1,600 Pietrain (purebred) or Pietrain × Large White (crossbred) boars were raised in a testing station. Blood samples were collected at about 105 kg BW for measuring sex hormones (testosterone and estradiol) and indicators of the inflammatory status (C-reactive protein [CRP], pig major acute-phase protein [pigMAP], and blood formula). Animals were slaughtered 9 d later and measured for boar taint compounds present in fat (androstenone and skatole) and skin lesions on carcass, an indicator of aggressiveness. For both genetic types, heritability was moderate for sex hormones (from 0.17 to 0.29) and skatole (0.24 for purebred and 0.37 for crossbred) and high for androstenone (0.63 and 0.70 for purebred and crossbred, respectively). Genetic correlations between sex hormones and boar taint compounds were moderate to high (from 0.31 to 0.95). Heritability was moderate for CRP (0.24 and 0.46 for purebred and crossbred, respectively) and very low for pigMAP (0.06 and 0.05 for purebred and crossbred, respectively. Numbers of leukocytes had moderate to high heritabilities according to the genetic type (from 0.21 to 0.52). Heritability of skin lesions was moderate for both genetic types (0.31). Genetic correlations were negative between sex hormones and inflammatory measures (from -0.46 to -0.05), positive between testosterone and number of lesions (0.43 and 0.53 for purebred and crossbred, respectively), and low between androstenone and lesions (-0.06 and -0.17 for purebred and crossbred, respectively). Overall, both breeds of pigs had very similar estimations of heritabilities, but estimates of genetic correlations were different for some pairs of traits. It would be possible to select boars based on their plasma concentration of sex hormones to decrease boar taint and aggressiveness without important consequences on the immune response. However, because of the strong links between boar taint and reproductive function, the possible consequences on the reproductive performance should be evaluated.

Neonatal surgical castration of male pigs reduces thymic growth but has moderate consequences on thymocytes

Thymus integrates numerous signals from the neuroendocrine-immune system, including sex steroids, glucocorticoids, and catecholamines. Neonatal surgical castration, commonly practiced in pig husbandry, modifies thymic hormonal environment, for example, sex steroids and probably glucocorticoids and catecholamines, which are important modulators of thymic function. This study aimed at investigating, in pubescent male pigs, the consequences of neonatal suppression of testicular hormones on thymic T cell differentiation and hormonal control of thymocyte proliferation. A total of 34 male pigs were allocated to 2 experimental groups: control (CT) intact males and males surgically castrated (SC) at 5 or 6 d of age. At slaughter, thymus was weighed and thymic samples were collected to determine fat content and distribution of thymocyte subsets by identification of CD1, CD4, CD8, and γδ T cell receptor (TCR) cell surface markers and to measure thymocyte proliferation in presence of cortisol, norepinephrine, and sex steroids. Results showed that absolute and relative thymus weights were greater (P < 0.01 and P < 0.01, respectively) whereas thymic fat content was less (P < 0.01) in CT than in SC pigs. Surgical castration did not change the frequency of CD1+ immature thymocytes. The proportion of γδ T cells tended to be greater in CT than in SC pigs (P < 0.1) but the proportions of CD4+, CD8+, and CD4+CD8+ thymocytes were similar in both groups (P > 0.1) indicating that the Tαβ lineage was not influenced by early castration. Proliferation of thymocytes in response to concanavalin A (ConA) was greater in SC than in CT pigs (P < 0.05). Cortisol and norepinephrine decreased the ConA-induced proliferation in CT and SC pigs (P < 0.05). In addition, proliferation of thymocytes was less inhibited by norepinephrine in SC than in CT males (P < 0.05). The greatest concentration of testosterone (25 ng/mL) increased (SC males, P < 0.05) or tended to increase (CT males, P < 0.1) the proliferative responsiveness to ConA but the lowest dose (2.5 ng/mL) and the greatest dose of testosterone combined with estradiol had no significant effect (P > 0.1). Overall, our data show little effect of neonatal castration on thymocyte differentiation as well as of sex hormones on thymocyte proliferation. However, thymic cells seem to be more sensitive to the inhibitory influence of norepinephrine in CT than in CS pigs. The significance of such difference for animal health remains to be explored.

Comparison of immune and health markers in intact and neonatally castrated male pigs

Stress and sex hormones are known to regulate immune function. Castration of male piglets is used to avoid boar taint in the meat, but its consequences on immunity and health of male pigs are poorly known. In this study, intact and neonatally surgically castrated male pigs (n=20 per group) were compared along puberty for some immune parameters and hormone receptor expression in lymphoid organs. Pigs were immunised with keyhole limpet haemocyanin (KLH) at 113 and 133 days of age. Blood lymphocyte numbers and proliferation, immunoglobulin titres, haptoglobin and hormone levels at 89, 119 and 152 days and the mRNA expression of androgen, α-oestrogen, glucocorticoid and β2-adrenergic receptors in liver, spleen and thymus at 160 days were assessed. Blood lymphocyte numbers were lower (at 119 and 152 days) and total IgG and haptoglobin concentrations were higher (at 152 days) in castrated than intact males. The concanavalin A and KLH proliferation responses and anti-KLH IgG titres were not altered. At slaughter, intact pigs presented a heavier thymus and a lower hepatic expression of β2-adrenergic receptor. In conclusion, the effects of neonatal castration were moderate. Other studies are needed to clarify the possible detrimental outcomes of castration on lymphocyte numbers and thymic growth.

Feed restriction applied after weaning has different effects on pig performance and health depending on the sanitary conditions

Feed restriction may be a strategy used by farmers to limit digestive disorders after weaning. The objective of this study was to evaluate the effect of feed restriction applied 1 wk after weaning on growth performance and health of pigs reared in 2 different sanitary conditions (Good vs. Poor; managed in opposite ways with respect to cleaning, animal density, and preventive antibiotic use) and confronted with stressful common farming practices (i.e., diet transition and building transfer). At weaning at 4 wk of age, 48 pigs were assigned to 1 of the 4 experimental treatments consisting of 2 sanitary conditions and 2 feeding levels (ad libitum vs. restricted). At 2 d after weaning, restricted pigs received 20% of the feed quantity consumed by ad libitum pigs. The feeding level of the restricted pigs was gradually increased to attain ad libitum feeding on d 8. Imposed stressful conditions occurred at d 12 (the weaner diet replaced the starter diet), d 33 (transfer of pigs from the weaner unit to the grower unit), and d 47 (the grower diet replaced the weaner diet). This allowed 4 distinguishing phases: I, from 0 to 11 d; II, from 12 to 32 d; III, from 33 to 46 d; and IV, from 47 to 60 d after weaning. Poor sanitary conditions resulted in decreased growth performance during phase I (P < 0.001) and III (P < 0.01), and the final BW of pigs kept in Poor sanitary conditions was 4 kg less (P = 0.02) than those kept in Good sanitary conditions. Plasma haptoglobin concentration was increased on d 12 after weaning (P = 0.001) as was the occurrence of soft feces during phases II and III (P ≤ 0.05) in Poor sanitary conditions. In both sanitary conditions, the restricted feeding level resulted in decreased ADG (P < 0.001), increased plasma haptoglobin and salivary cortisol concentrations, and feeding-associated behaviors (P < 0.05) during phase I. In Poor sanitary conditions, feed restriction was very detrimental and differences in ADFI and ADG between restricted and ad libitum pigs increased with time (P = 0.05). Conversely, in Good sanitary conditions, restricted pigs attained the BW of ad libitum pigs before the end of the experiment. In conclusion, imposing feed restriction on pigs during the first days after weaning does not seem to be an effective strategy to decrease the negative effects of Poor sanitary conditions; rather, it reinforces these effects.

Maternal social stress during late pregnancy affects hypothalamic-pituitary-adrenal function and brain neurotransmitter systems in pig offspring

Maternal stress in pregnant sows may induce long-lasting alterations in the behavior, physiology, and immunity of their offspring. The aim of the present study was to investigate the consequences of repeated social stress during late gestation on determinants of the hypothalamic-pituitary-adrenal axis and on hippocampal neurotransmitter profiles in pig offspring. All pregnant gilts were housed in pairs. Each Stress gilt was mixed with an unfamiliar gilt twice a week between days 77 and 105 of gestation (n=18). Control gilts were housed in stable pairs over the same period (n=18). Plasma cortisol and corticosteroid binding globulin (CBG) were measured in 1 male and 1 female per litter in a basal situation on postnatal days (PND) 4, 26, and 60 and in a stressful situation at PND 28 (2 d after weaning) and 62 (2 d after relocation to a new building). Prenatal stress had no effect on plasma cortisol, but it decreased CBG at PND 26. Brain and adrenals were collected from 1 female per litter after weaning or relocation at PND 28 and PND 62. Adrenals were additionally collected at PND 4. Glucocorticoid receptor binding in the hippocampus and hypothalamus was not affected by prenatal treatment. However, prenatal stress increased the expression of 11beta-hydroxysteroid dehydrogenase type 1 mRNA in the hippocampus after weaning (P<0.05) and after relocation (P=0.08). In addition, prenatally stressed piglets showed an increased 5-hydroxyindole-3-acetic acid to 5-hydroxytryptamine ratio in the hippocampus after weaning and increased hippocampal c-fos mRNA expression and noradrenaline concentration after relocation (P<0.05). Prenatal stress also increased the relative adrenal weight at PND 4 and the cell density in the cortex and the medulla at PND 28, whereas no difference was found for activities of catecholamine-synthesising enzymes in the medulla. Overall, our data indicate that repeated social stress during pregnancy has long-lasting consequences on hypothalamic-pituitary-adrenal axis and hippocampal neurotransmitter activity in the offspring of pigs.

Prenatal stress, fetal imprinting and immunity

A comprehensive number of epidemiological and animal studies suggests that prenatal and early life events are important determinants for disorders later in life. Among them, prenatal stress (i.e. stress experienced by the pregnant mother with impact on the fetal ontogeny) has programming effects on the hypothalamic-pituitary-adrenocortical axis, brain neurotransmitter systems and cognitive abilities of the offspring. This review focuses on the impact of maternal stress during gestation on the immune function in the offspring. It compares results from different animal species and highlights potential mechanisms for the immune effects of prenatal stress, including maternal glucocorticoids and placental functions. The existence of possible windows of increased vulnerability of the immune system to prenatal stress during gestation is discussed. Several gaps in the present knowledge are pointed out, especially concerning the time when prenatal stress effects are expressed during postnatal life, why this expression is delayed after birth and whether prenatal stress predisposes to immune-related pathologies later in life.

Suppression of restraint-induced plasma cytokines in mice pretreated with LPS

A previous exposure to an inflammatory reaction is known to increase or decrease the activation of the hypothalamic-pituitary-adrenal (HPA) axis induced by a psychological/physical stress. Beside HPA activation, the non- specific responses to these two kinds of stresses involve the immune system including the production of cytokines. Therefore, they could interfere in cytokine production. In order to test this hypothesis, female C3H mice were first injected i.p. with 5 microg of lipopolysaccharide (LPS) or not (C). Eight days later, half of them were submitted to a 4 h-restraint (R) applied during the nocturnal part of the dark-light cycle and sacrificed immediately after (groups LPS-R and C-R), while the non restrained mice stayed in their home cages (groups LPS-C and C-C). Restraint induced an increase in corticosterone production that was not altered by the previous administration of LPS. It had no effect on mitogen-induced lymphoproliferation. However, restraint induced an augmentation of plasma concentrations of interleukin (IL)-1 and IL-6 that was not observed in animals previously exposed to LPS. These results show that restraint, which represents a psychological stress is able to induce the production of plasma cytokines in mice. They also suggest that LPS may induce a long lasting suppression of plasma cytokines through mechanisms that remain to be elucidated.