Comparing the intestinal transcriptome of Meishan and Large White piglets during late fetal development reveals genes involved in glucose and lipid metabolism and immunity as valuable clues of intestinal maturity

Background: Maturity of intestinal functions is critical for neonatal health and survival, but comprehensive description of mechanisms underlying intestinal maturation that occur during late gestation still remain poorly characterized. The aim of this study was to investigate biological processes specifically involved in intestinal maturation by comparing fetal jejunal transcriptomes of two representative porcine breeds (Large White, LW; Meishan, MS) with contrasting neonatal vitality and maturity, at two key time points during late gestation (gestational days 90 and 110). MS and LW sows inseminated with mixed semen (from breed LW and MS) gave birth to both purebred and crossbred fetuses. We hypothesized that part of the differences in neonatal maturity between the two breeds results from distinct developmental profiles of the fetal intestine during late gestation. Reciprocal crossed fetuses were used to analyze the effect of parental genome. Transcriptomic data and 23 phenotypic variables known to be associated with maturity trait were integrated using multivariate analysis with expectation of identifying relevant genes-phenotypic variable relationships involved in intestinal maturation. Results: A moderate maternal genotype effect, but no paternal genotype effect, was observed on offspring intestinal maturation. Four hundred and four differentially expressed probes, corresponding to 274 differentially expressed genes (DEGs), more specifically involved in the maturation process were further studied. In day 110-MS fetuses, Ingenuity® functional enrichment analysis revealed that 46% of DEGs were involved in glucose and lipid metabolism, cell proliferation, vasculogenesis and hormone synthesis compared to day 90-MS fetuses. Expression of genes involved in immune pathways including phagocytosis, inflammation and defense processes was changed in day 110-LW compared to day 90-LW fetuses (corresponding to 13% of DEGs). The transcriptional regulator PPARGC1A was predicted to be an important regulator of differentially expressed genes in MS. Fetal blood fructose level, intestinal lactase activity and villous height were the best predicted phenotypic variables with probes mostly involved in lipid metabolism, carbohydrate metabolism and cellular movement biological pathways. [b]Conclusions[/b]: Collectively, our findings indicate that the neonatal maturity of pig intestine may rely on functional development of glucose and lipid metabolisms, immune phagocyte differentiation and inflammatory pathways. This process may partially be governed by PPARGC1A

Genetic determinism of cortisol levels in pig

The plasma cortisol levels measured one hour after injection of ACTH reflects the hypothalamic-pituitary-adrenocortical (HPA) axis activity. The test was performed on piglets at 6 weeks of age. It was investigated as a potential selection criterion to improve pig robustness. From a base population of Large White pigs, two divergent lines were derived for 3 generations of selection, one selected for a high cortisol level (H line), one for a low cortisol level (L line). All breeders, as well as unselected animals, were also genotyped on a 70kSNP chip. At the 3rd generation of selection, the divergence between the two lines was about 5 genetic standard deviations. The high heritability of the trait was confirmed (h² = 0.64 ± 0.03). The genetic correlations with individual body weights and growth rates measured during lactation, post weaning and finishing periods were very low except for the genetic correlation between cortisol level and post-weaning growth rate (rg=-0.22 ± 0.10). The genome-wide association study revealed a quantitative trait locus influencing post-ACTH cortisol level, located on chromosome 2. It was suggested that divergent selection modified the frequency of NR3C1 alleles, favouring the hypersensitive glucocorticoid receptor in the low line

Analyse génétique de la réponse à l'ACTH chez le porc, relation avec des caractères de robustesse

L'axe corticotrope est une composante majeure des régulations métaboliques et des mécanismes biologiques de l'adaptation. L'activité de l'axe corticotrope et sa fonction sont fortement influencées par des facteurs génétiques. Les expériences présentes ont été conçues pour tester l'hypothèse que la sélection génétique pour un axe corticotrope plus actif peut améliorer la robustesse des porcs. Les expériences ont été faites avec des porcs Large White en race pure. Nous avons d'abord confirmé que la réponse du cortisol à l'ACTH est hautement héritable (h2 = 0,68 ± 0,12) dans cette population et peut donc être utilisée pour réaliser une expérience de sélection divergente. Dès la deuxième génération, de grandes différences dans le caractère de sélection ont été obtenues (concentration plasmatique de cortisol post-ACTH : 84,8 vs 127,5 ng/ml dans les lignées basse et haute, respectivement, P 0,10) et 1,5 porcelet vivant de plus par portée (P = 0,06) dans la lignée haute de reproducteurs G1). Les concentrations élevées de cortisol ont eu une influence négative sur la croissance en post-sevrage (418 vs 394 g/jour, P = 0,0013) et en engraissement (799 vs 754 g/jour, P 0.10), and 1.5 more piglets born alive per litter (P = 0.06) in the high line). Higher cortisol concentrations had a negative influence on growth rate during both post-weaning (418 vs 394 g/jour, P = 0.0013) and fattening (799 vs 754 g/jour, P < 0.0001) but improved carcass composition (lean%: 58.8 vs 60.4, low vs high line P < 0,001). These results confirm that the adrenocortical axis activity has a contrasted influence on functional and production traits. They have to be confirmed in the third generation for a comprehensive evaluation of the interest of selecting a more active adrenocortical axis to obtain animals that are more robust

Responses of pigs divergently selected for cortisol level or feed efficiency to a challenge diet during growth

Selection for feed efficiency is questioned as reducing the ability of farm animals to face stress and overcome challenges. The hypothalamic-pituitary-adrenocortical (HPA) axis activity, measured by the cortisol level in plasma after ACTH injection, has been proposed as an indicator of robustness. The objectives of this study were to evaluate 1. if a modified cortisol level in pigs alters their feed efficiency and their production performance, 2. if alternative dietary resources would affect these responses. Parallel trials including divergent lines for plasma cortisol 1 hour after ACTH injection and divergent lines for residual feed intake (RFI) were run during growth with a conventional diet and a diet with high fibres, low energy and low protein content. Selection for higher or lower plasma cortisol levels after stimulation of the adrenal gland did not impact growth and feed intake traits, but it had a significant impact on body composition and carcass yield, with improved composition in the high cortisol animals. The two lines had similar responses to an alternative diet, with decreased growth rate and feed intake, and increased feed conversion ratio. On the other hand, lines selected for divergent RFI had different responses to the alternative diet, the more efficient line having a more reduced growth rate with the diet with lower energy and AA contents. However, in terms of FCR it remained more efficient. The initial hypothesis of decreased efficiency associated to increased cortisol was not validated

Sélection divergente sur l’activité corticotrope chez le porc : étude des réponses aux stress d’élevage

Notice à Reprendre avec Recueil des ProceedingsThis experiment had the goal to analyze responses to various sources of stress (weaning, exposure to heat and pre-slaughter mixing) in the third generation of selection of two lines of pigs genetically selected on the basis of plasma cortisol levels (“high” or “low”) measured one hour after injection of adrenocorticotropin. This test assesses the activity of the adrenocortical axis, a major endocrine system of the stress response. Results show that the high line had a significantly lower post-weaning growth rate. However, its growth rate was higher in the late fattening period, so that the two lines had the same overall growth rate throughout their productive lives. Prolonged exposure to heat (29.9°C vs 26.1°C) during the late fattening period (D133-D158) reduced the growth rate of animals to the same extent in both lines. Group-mixing stress prior to slaughter increased cortisol levels measured in urine collected from the bladder as well as skin lesions on carcasses, and increased muscle pH measured 24h after slaughter. These consequences of pre-slaughter mixing, however, did not differ between lines. These results show that responses to different sources of stress are affected in different ways by the level of adrenocortical activity. Associated with production data, they will allow evaluation of the relevance of this selection criterion for increasing animal robustness

Thermorégulation des porcelets issus de deux lignées divergentes pour l’efficacité alimentaire

Hypothermia is a factor of piglet neonatal mortality. This study used Infra-Red Thermography (IRT) to assess thermoregulation abilities of piglets from two lines divergent for residual feed intake (RFI). Birth phenotypes (e.g. body weight, rectal temperature, physical measures, vitality test) were recorded from piglets selected for low RFI (more efficient; LRFI; n=34) or high RFI (less efficient; HRFI; n=28). The IRT images were taken at 8, 15, 30 and 60 min post-partum. Temperatures of the ear base and tip, and minimum, maximum and average temperatures of the back (i.e. shoulders to rumps) were extracted with Thermacam Researcher Pro 2.0 and analysed with linear mixed models. No difference in phenotypic data was detected between the two lines. All temperatures increased over time. Rectal temperature of piglets at birth was correlated with the initial temperature of the ear base and the maximum back temperature (0.36 and 0.35, respectively, P < 0.05). Overall, LRFI piglets, compared to HRFI piglets, had higher minimum (28.0 ± 0.2 °C vs 26.8 ± 0.2 °C, respectively, P < 0.001) and average (35.5 ± 0.2 °C vs 34.5 ± 0.1 °C, respectively, P < 0.001) back temperatures. Ear tip temperature decreased in HRFI piglets from 8 to 15 min post-partum, while it increased in LRFI piglets (-1.1 ± 0.4 °C vs 0.5 ± 0.5 °C, respectively, P < 0.05). In conclusion, IRT allowed non-invasive assessment of piglets’ thermoregulation abilities. Piglets selected for low RFI seemed to have better thermoregulation abilities at birth

Responses of pigs divergently selected for cortisol level or feed efficiency to a challenge diet during growth

Selection for feed efficiency is questioned as reducing the ability of farm animals to face stress and overcome challenges. The hypothalamic-pituitary-adrenocortical (HPA) axis activity, measured by the cortisol level in plasma after ACTH injection, has been proposed as an indicator of robustness. The objectives of this study were to evaluate 1. if a modified cortisol level in pigs alters their feed efficiency and their production performance, 2. if alternative dietary resources would affect these responses. Parallel trials including divergent lines for plasma cortisol 1 hour after ACTH injection and divergent lines for residual feed intake (RFI) were run during growth with a conventional diet and a diet with high fibres, low energy and low protein content. Selection for higher or lower plasma cortisol levels after stimulation of the adrenal gland did not impact growth and feed intake traits, but it had a significant impact on body composition and carcass yield, with improved composition in the high cortisol animals. The two lines had similar responses to an alternative diet, with decreased growth rate and feed intake, and increased feed conversion ratio. On the other hand, lines selected for divergent RFI had different responses to the alternative diet, the more efficient line having a more reduced growth rate with the diet with lower energy and AA contents. However, in terms of FCR it remained more efficient. The initial hypothesis of decreased efficiency associated to increased cortisol was not validated

Divergent selection on adrenocortical activity in Large White pigs: study of responses to breeding challenges

This experiment had the objective to analyze responses to various breeding challenges in the third generation of selection of two lines of pigs genetically selected on the basis of plasma cortisol levels measured one hour after injection of ACTH. This test allows to objectify the activity level of the hypothalamic-pituitary-adrenal (HPA) axis, a major neuroendocrine system of the stress response. The results presented here show that the post-weaning growth rate was significantly lower in the high line, although the two lines had the same overall growth rate throughout their productive lives. The effects of a prolonged exposure to high temperature (30°C) and of group mixing stress prior to slaughter did not differ between the lines. These results show that the responses to different challenges are not affected in the same way by the HPA axis activity. These results, together with production data, will allow to evaluate the relevance of this criterion of selection to increase the robustness of animals. With the financial support of the Agence Nationale de la Recherche, program ANR BIOADAPT, project SUSoSTRESS (ANR-12-ADAP-0008). Keywords: genetic selection, cortisol, stress, robustness, heat stress, weaning stress, mixing stress, pig

Responses of pigs divergently selected for cortisol response or feed efficiency to an ACTH challenge

Selection for feed efficiency can impair the animal’s ability to respond to stress. A key driver of this response is the hypothalamo-pituitary-adrenal (HPA) axis, which releases cortisol in response to stressors. Injection of a normalized dose of adrenocorticotropic hormone (ACTH) to stimulate cortisol release by the adrenal cortex is a standardized method to evaluate the activity of the HPA axis independently of the animal’s perception of stress. It has been used to select during three generations a highCortisol line and a lowCortisol line, that had divergent cortisol levels 1 h after ACTH injection (H1, peak of the response). A trial was set up to compare the responses to ACTH of these two lines and those of two other lines divergently selected for residual feed intake (RFI, measure of net feed efficiency) during nine generations. At 6 weeks of age, 48 pigs per line were tested. Blood samples were collected before and 1 (H1) and 4 h after injection (H4) when cortisol is expected to return to basal level. In the Cortisol lines, plasma cortisol was multiplied by 2 (P<0.0001) in highCortisol pigs compared to lowCortisol pigs at the 3 times. In both lines, cortisol was multiplied by 2.3 to 2.6 at H1 compared to H0. The highRFI (less efficient) line had a similar response to the ACTH injection as the Cortisol lines. The lowRFI line had higher cortisol levels at H0 (P=0.08) and H1 (P=0.0002) than the highRFI line. This difference was increased at H4 (P<0.0001), due to higher H4 than H0 cortisol levels in lowRFI pigs (P<0.0001). Blood counts, urea, glucose, IGF-I and free fatty acids (FFA) measurements were used to better understand the responses to ACTH, suggesting different underlying metabolisms. In contradiction with previous hypotheses, increased feed efficiency is not associated with a decreased HPA axis activity, but might be related to different dynamics of responses after stress. This study is part of the Feed-a-Gene Project, funded from the European Union’s H2020 programme under grant agreement no. 633531