Behavioral and physiological responses of Meishan, Yorkshire and crossbred gilts to conventional and turn-around gestation stalls

Old breeds, new solutions? Effects of two different traditional sire breeds on skin lesions, tail lesions, tail losses, performance and behaviour of rearing pigs

Some studies indicated a relationship between modern, fast-growing, lean-meat-producing hybrid pigs and the occurrence of tail-biting, one of the major issues of conventional pig husbandry. Therefore, this study investigated the effects of different local, traditional sire breeds on the behaviour and performance of rearing pigs. Between December 2019 and November 2020, a total of 1 561 piglets were weaned from hybrid sows (Bundes Hybrid Zucht Programm (BHZP) Landrace × BHZP Large White) that were paired with either Swabian-Hall (SH), Bentheim Black Pied (BB) or BHZP-Piétrain (Pi) boars. Tails of the piglets were left intact (43.5%) or docked (56.5%), and male piglets were castrated. Piglets were conventionally reared on fully slatted plastic flooring in mixed-sex groups. Starting one day after weaning, skin lesions were scored once per pig, and tail lesions and losses were scored weekly until the end of rearing. The average daily gain was documented for the suckling and rearing period. The activity behaviour of eight focal pens was analysed using video recordings. Differences between modern and traditional breeds were found in this study for so-called aggressive and non-aggressive biting pronounced by skin and tail lesions and tail losses. Significantly fewer BB pigs had severe skin lesions on the front body than SH or Pi pigs (P < 0.05). Additionally, piglets that were classified as light (<5.6 kg) at weaning showed skin lesion scores of 0 more often than piglets that were classified with a medium (≥5.6-≤8.3 kg) or heavy (>8.3 kg) weaning weight (P < 0.05). In the first half of the rearing period, significantly more BB pigs were assessed as having no tail lesions and tail losses than SH and Pi pigs (P < 0.01). However, these differences disappeared in the second half of rearing. Either docked or undocked Pi pigs had significantly higher average daily gains than SH and BB pigs (P < 0.05). The activity of the focal pens was not influenced by the sire breed or tail lesion class, which might be due to the limited sample size of eight pens. To conclude, the use of the traditional sire breed BB has the potential to reduce injurious behaviour in the offspring. However, adjustments to the housing and feeding should be taken to further reduce the incidence of tail lesions and losses and to enhance performance.

Genetic diversity in the stress regulatory gene LUMAN/CREB3 of Yorkshire and Meishan pigs

A candidate-gene high-density single-nucleotide polymorphism (SNP) scanning approach was used to investigate the swine LUMAN/CREB3 locus for polymorphisms in 232 Ontario Yorkshire and 29 Chinese Meishan pigs. Inter- and intra-breed differences in genetic diversity were characterized. In the Yorkshire breed, eight variations (three coding and five non-coding) were identified. Two linkage disequilibrium (LD) blocks (550 bp and ∼4 kb in length) featuring two and three haplotypes, respectively, were reconstructed. In the Meishan breed, six variations (two coding and four non-coding) and one LD block (∼3 kb in length) with three haplotypes were detected. This investigation may provide insight into variable stress responsiveness among pigs.

Genetic variation in LUMAN/CREB3 and association with stress and meat quality traits in Yorkshire pigs

LUMAN/CREB3 is a stress regulatory gene that affects the activity of the hypothalamic–pituitary–adrenal axis in mice and presents a promising avenue for exploring variable stress-responsiveness in pigs. Pigs with similar characteristics to LUMAN-deficient mice, including greater resilience to stress and receptivity to human handling, would be valuable in the pork industry from animal welfare and production efficiency perspectives. We previously identified eight genetic variations and five haplotypes throughout the LUMAN locus in Yorkshire pigs. In this study, we analysed associations between LUMAN variations with behavioural stress response during three tests (open field test, novel object test, and human approach test), physiological stress responsiveness (cortisol), and carcass/meat quality measurements from purebred Yorkshire pigs. Haplotypes A1 and A2 were associated with decreased activity levels in novel environments and greater plasma cortisol concentrations at slaughter. Haplotype A1 was associated with lower carcass scratch scores and meat with lower cooking losses and greater tenderness. Haplotypes B1 and B2 were associated with the opposite traits including increased activity levels in novel environments and characteristics for lower meat quality including greater cooking losses, lower marbling, and paler coloured meat. We conclude that DNA variations in the LUMAN locus could potentially be used as genetic markers for stress resistance and meat quality in pig breeding.

Behavioural genetic differences between Chinese and European pigs

Aggression is a heritable trait and genetically related to neurotransmitter-related genes. Behavioural characteristics of some pig breeds are different. To compare the genetic differences between breeds, backtest and aggressive behaviour assessments, and genotyped using Sequenom iPLEX platform were performed in 50 Chinese indigenous Mi pigs and 100 landrace-large white (LLW) cross pigs with 32 SNPs localized in 11 neurotransmitter-related genes. The genetic polymorphisms of 26 SNPs had notable differences (P < 0.05) between Mi and LLW. The most frequent haplotypes were different in DBH, HTR2A, GAD1, HTR2B,MAOA and MAOB genes between Mi and LLW. The mean of backtest scores was significantly lower (P < 0.001) for Mi than LLW pigs. Skin lesion scores were greater (P < 0.01) in LLW pigs than Mi pigs. In this study, we have confirmed that Chinese Mi pigs are less active and less aggressive than European LLW pigs, and the genetic polymorphisms of neurotransmitter-related genes, which have been proved previously associated with aggressive behaviour, have considerable differences between Mi and LLW pigs.

Genetics of behavioural adaptation of livestock to farming conditions

Behavioural adaptation of farm animals to environmental changes contributes to high levels of production under a wide range of farming conditions, from highly controlled indoor systems to harsh outdoor systems. The genetic variation in livestock behaviour is considerable. Animals and genotypes with a larger behavioural capacity for adaptation may cope more readily with varying farming conditions than those with a lower capacity for adaptation. This capacity should be exploited when the aim is to use a limited number of species extensively across the world. The genetics of behavioural traits is understood to some extent, but it is seldom accounted for in breeding programmes. This review summarizes the estimates of genetic parameters for behavioural traits in cattle, pigs, poultry and fish. On the basis of the major studies performed in the last two decades, we focus the review on traits of common interest in the four species. These concern the behavioural responses to both acute and chronic stressors in the physical environment (feed, temperature, etc.) and those in the social environment (other group members, progeny, humans). The genetic strategies used to improve the behavioural capacity for adaptation of animals differ between species. There is a greater emphasis on responses to acute environmental stress in fish and birds, and on responses to chronic social stress in mammals.

Molecular genetics of the adrenocortical axis and breeding for robustness

The concept of robustness refers to the combination of a high production potential and a low sensitivity to environmental perturbations. The importance of robustness-related traits in breeding objectives is progressively increasing toward the production of animals with a high production level in a wide range of climatic conditions and production systems, together with a high level of animal welfare. Current strategies to increase robustness include selection for "functional traits," such as skeletal and cardiovascular integrity, disease resistance, and mortality at various stages. It is also possible to use global evaluation of sensitivity to the environment (eg reaction norm analysis or canalization), but these techniques are difficult to implement in practice. The glucocorticoid hormones released by the adrenal cortex exert a wide range of effects on metabolism, the cardiovascular system, inflammatory processes, and brain function, for example. Protein catabolism toward energy production and storage (lipids and glycogen) supports their pivotal role in stress responses aiming at the adaptation and survival of individuals under strong environmental pressure. Large individual variations have been described in adrenocortical axis activity, with important physiopathological consequences. In terms of animal production, higher cortisol levels have negative effects on growth rate and feed efficiency and increase the fat:lean ratio of carcasses. On the contrary, cortisol has positive effects on functional traits and adaptation. Intense selection for lean tissue growth and more generally high protein output during the past decades has concomitantly reduced cortisol production, which may be responsible for the negative effects of selection on functional traits. In this paper, we review experimental evidence suggesting that the balance between production and functional traits was modified in favor of improved robustness by selecting animals with higher adrenocortical axis activity, as well as the molecular genetic tools that can be used to fine-tune this objective.

Stress hormones, carcass composition and meat quality in Large White×Duroc pigs

The levels of stress hormones, cortisol and catecholamines (adrenaline and noradrenaline), were measured in urine collected after slaughter from the bladder, in 309 pigs (females and castrated males) from an F2 intercross between the Large White and Duroc breeds to analyze the relationships between stress-responsive neuroendocrine systems, carcass composition and meat quality. Intramuscular fat content was measured from a biopsy sample taken at a live weight of 70 kg from the longissimus lumborum muscle, and carcass and meat quality traits were also collected. Carcass fat content was higher and estimated carcass lean meat content was lower with increasing urinary levels of cortisol and adrenaline (that are highly correlated with each other), but was not related to the levels of noradrenaline, showing that adrenal hormones favor the accretion of fat at the expense of muscle proteins, a typical physiological effect of cortisol. On the contrary, intramuscular fat levels were unrelated to either hormone level. Finally, muscle pH measured 24 h after death was positively correlated with catecholamine levels, an effect related to the catabolism of muscle glycogen by catecholamines released by preslaughter stress, which impairs post-mortem acidification of meat. These results show the importance of a control over stress neuroendocrine systems to increase pork production and product quality, and the value of the genetic approach to reach this goal.

Effects of Breed, Parity, and Folic Acid Supplement on the Expression of Folate Metabolism Genes in Endometrial and Embryonic Tissues from Sows in Early Pregnancy1

Folic acid and glycine are factors of great importance in early gestation. In sows, folic acid supplement can increase litter size through a decrease in embryonic mortality, while glycine, the most abundant amino acid in the sow oviduct, uterine, and allantoic fluids, is reported to act as an organic osmoregulator. In this study, we report the characterization of cytoplasmic serine hydroxymethyltransferase (cSHMT), T-protein, and vT-protein (variant T-protein) mRNA expression levels in endometrial and embryonic tissues in gestating sows on Day 25 of gestation according to the breed, parity, and folic acid + glycine supplementation. Expression levels of cSHMT, T-protein, and vT-protein mRNA in endometrial and embryonic tissues were performed using semiquantitative reverse transcription-polymerase chain reaction. We also report, for the first time, an alternative splicing event in the porcine T-protein gene. Results showed that a T-protein splice variant, vT-protein, is present in all the tested sow populations. Further characterizations revealed that this T-protein splice variant contains a coding intron that can adopt a secondary structure. Results demonstrated that cSHMT mRNA expression levels were significantly higher in sows receiving the folic acid + glycine supplementation, independently of the breed or parity and in both endometrial and embryonic tissues. Upon receiving the same treatment, the vT-protein and T-protein mRNA expression levels were significantly reduced in the endometrial tissue of Yorkshire-Landrace sows only. These results indicate that modulation of specific gene expression levels in endometrial and embryonic tissues of sows in early gestation could be one of the mechanism involved with the role of folic acid on improving swine reproduction traits.

Molecular genetic approaches to investigate individual variations in behavioral and neuroendocrine stress responses

A large response range can be observed in both behavioral and neuroendocrine responses to environmental challenges. This variation can arise from central mechanisms such as those involved in the shaping of general response tendencies (temperaments) or involves only one or the other output system (behavioral vs. endocrine response). The participation of genetic factors in this variability is demonstrated by family and twin studies in humans, the comparison of inbred strains and selection experiments in animals. Those inbred strains diverging for specific traits of stress reactivity are invaluable tools for the study of the molecular bases of this genetic variability. Until recently, it was only possible to study biological differences between contrasting strains, such as neurotransmitter pathways in the brain or hormone receptor properties, in order to suggest structural differences in candidate genes. The increase of the power of molecular biology tools allows the systematic screening of significant genes for the search of molecular variants. More recently, it was possible to search for genes without any preliminary functional hypothesis (mRNA differential expression, nucleic acid arrays, QTL search). The approach known as quantitative trait loci (QTL) analysis is based on the association between polymorphic anonymous markers and the phenotypical value of the trait under study in a segregating population (such as F2 or backcross). It allows the location of chromosomal regions involved in trait variability and ultimately the identification of the mutated gene(s). Therefore, in a first step, those studies skip the 'black box' of intermediate mechanisms, but the knowledge of the gene(s) responsible for trait variability will point out to the pathway responsible for the phenotypical differences. Since variations in stress-related responses may be related to numerous pathological conditions such as behavioral and mood disorders, drug abuse, cardiovascular diseases or obesity, and production traits in farm animals, these studies can be expected to bring significant knowledge for new therapeutic approaches in humans and improved efficiency of selection in farm animals.

Mammary gland development and hormone levels in pregnant Upton-Meishan and large white gilts

Genetic differences between Upton-Meishan (UM, n = 13) and Large White (LW, n = 14) gilts were studied with regard to mammary gland development and concentrations of hormones. Gilts were weighed and their backfat measured at mating, and at d 70 and 109 of gestation. Jugular blood samples were also collected at these times and assayed for prolactin, cortisol, IGF-I, insulin, glucose, progesterone, and estradiol. Gilts were slaughtered on d 110 of gestation. One row of mammary glands was used for dissection and biochemical analyses. The other row was used for determination of prolactin receptor number and affinity. UM gilts weighed less (P<0.05) and had more backfat (P<0.01) than LW gilts at all times. Parenchymal tissue weight was less (P<0.05) in UM gilts. Percent fat (P<0.001) and dry matter (P<0.001) in parenchymal tissue were greater in UM gilts while that of protein (P<0.001) was lower. Total protein weight in parenchyma was also lower in parenchyma was also lower in UM gilts (P = 0.01). Both DNA (P<0.001) and RNA (P<0.001) contents were lower in UM gilts while RNA/DNA remained similar (P>0.1). Number of prolactin receptors were lower (P = 0.06) and affinity greater (P<0.05) in UM gilts. Cortisol levels were greater (P<0.01) in UM gilts while other hormones were not affected (P> 0.1). Results clearly demonstrate genetic differences with regard to mammogenesis in gilts and suggest that the less mammary gland development in Upton-Meishan compared with Large White breed of gilts may be related to lower number of prolactin receptors.

Behavior and pituitary-adrenal function in large white and Meishan pigs

Six-wk-old piglets of both sexes from European Large White (LW, n = 36) and Chinese Meishan (MS, n = 24) breeds were individually exposed to a novel environment, a stressful stimulation. Behavioral and pituitary-adrenal reactivity were investigated. When compared with LW, MS pigs displayed low locomotion (18.5 +/- 2.2 vs. 41.0 +/- 3.8 squares crossed/10 min; P < 0.0001), and defecation scores (0.58 +/- 0.15 vs. 4.86 +/- 0.37 fecal boli; P < 0.0001). Basal concentrations of cortisol were higher in MS (96.1 +/- 1.1 vs. 44.9 +/- 1.1 ng/ml; P < 0.0001), although no differences between breeds were found in basal concentrations of adrenocorticotropic hormone (ACTH). In response to novel environment exposure, the ACTH increase was greater in LW than in MS, but the cortisol response was not different on a log scale. To further investigate the pituitary-adrenal differences between the two breeds, the 24-hr profile of ACTH and cortisol plasma concentrations, a corticotropin-releasing factor (CRF) and a coupled dexamethasone-ACTH test were studied. Five castrated male 9-wk-old piglets from each breed were fitted surgically with a jugular vein catheter. A classic marked circadian rhythm of cortisol and a weak nycthemeral variation of ACTH were found. Cortisol concentrations were approximately twice higher in MS exclusively during the early light phase (from 0800-1200 hr) of the cycle, but no significant interbreed difference was found in the circadian rhythm of ACTH. Administration of CRF (1 microgram/kg iv) induced the same significant increase in plasma ACTH and cortisol concentrations in both breeds. Administration of ACTH (10 micrograms/kg i.v.) increased significantly cortisol concentrations and revealed no difference in plasma cortisol response to ACTH. These data suggest that the hypercortisolism of MS pigs is of adrenal origin, and related to extrapituitary factors that control the adrenal sensitivity during the light phase of the diurnal cycle.