Hepatic Ethoxy‐, Methoxy‐ and Pentoxyresorufin O‐Dealkylase Activities in Landrace and Duroc Pigs Stimulated with hCG

The effect of human chorionic gonadotropin (hCG) stimulation on the activities of ethoxyresorufin O‐deethylase (EROD), methoxyresorufin O‐demethylase (MROD) and pentoxyresorufin O‐depentylase (PROD) was studied in intact male pigs of purebred Landrace and Duroc breeds. Pigs were divided into four groups: two control groups of each breed, without hCG stimulation (n = 20 for each breed), and two experimental groups (n = 18 for each breed), with hCG stimulation (Pregnyl^®; N.V. Organon, Oss, The Netherlands, 30 IU/kg live weight). Pigs were slaughtered 3 days after hCG stimulation and enzyme activities were measured in hepatic microsomes using two approaches. First, only one substrate concentration was used for the analysis of each enzyme activity. We found that EROD activity was suppressed by hCG‐stimulation in Landrace (p = 0.004), but not Duroc pigs (p > 0.05). Generally, EROD activity was higher in Duroc pigs compared with Landrace (p = 0.017). Methoxyresorufin O‐demethylase and PROD activities did not differ between groups (p > 0.05). To further characterize EROD, MROD and PROD, enzyme kinetic studies were performed. V_max values for EROD and MROD in both breeds were lower after hCG stimuation (p < 0.001 for Landrace and p < 0.05 for Duroc). Additionally, V_max values for EROD significantly differed between Landrace and Duroc pigs being higher in Duroc pigs (p < 0.05). We concluded that both hCG stimulation and breed differences may be important in the regulation of EROD and MROD activities. This study provides the first data on the effect of hCG stimulation and thus high testicular steroids, on EROD, MROD and PROD activities. Further studies are needed to investigate individual CYP450 enzymes and their regulation in porcine tissues.     

PRKAG3基因在不同品种猪不同生长阶段骨骼肌中的表达差异及其表达量与肉质的关系

本试验中旨在比较PRKAG3基因在不同品种猪不同生长阶段骨骼肌中的表达差异,并探讨PRKAG3基因与肉质的关系。挑选15 kg左右的汉普夏阉公猪17头和长撒阉公猪16头,饲喂相同饲粮,当体重分别达到20和50 kg时,2个品种的猪分别屠宰5头,体重达到100 kg时分别屠宰7和6头。各生长阶段屠宰后均测定骨骼肌pH、肌糖原含量以及PRKAG3基因表达量,且在100 kg阶段屠宰后同时测定肉质性状。结果表明:1)在不同生长阶段长撒猪骨骼肌中PRKAG3基因的表达量均高于汉普夏猪,特别是在100 kg阶段,长撒猪骨骼肌中PRKAG3基因的表达量是汉普夏猪的6.81倍(P0.05)。长撒猪与汉普夏猪骨骼肌中PRKAG3基因的表达量均随体重的增加而增加,但汉普夏猪不同生长阶段PRKAG3基因的表达量差异不显著(P0.05),而长撒猪PRKAG3基因的表达量在100 kg阶段时显著高于20和50 kg阶段时(P0.05)。2)汉普夏猪和长撒猪的肉质存在差异。汉普夏猪的滴水损失和失水率显著高于长撒猪(P0.05),而熟肉率、黄度(b)值极显著低于长撒猪(P0.01),剪切力和pH2(屠宰后24 h的pH)显著低于长撒猪(P0.05)。与长撒猪相比,汉普夏猪具有较高的肌糖原含量(P0.05)。3)猪骨骼肌中PRKAG3基因的表达量与肉质的相关性存在品种效应。汉普夏猪骨骼肌中PRKAG3基因表达量与滴水损失呈正相关,与熟肉率呈负相关,与pH2呈显著负相关(P0.05)。长撒猪骨骼肌中PRKAG3基因表达量与滴水损失和失水率呈正相关,与pH2呈负相关。上述结果表明,猪骨骼肌中PRKAG3基因具有品种和生长阶段表达差异;猪骨骼肌中PRKAG3基因的表达量与肉质性状相关,特别是与pH2,二者呈显著负相关。     

Correlated responses in reproductive and carcass traits to selection for 70-day weight in Landrace swine.

Correlated responses in reproductive and carcass traits were studied in 181 litters and 218 pigs from a line of Landrace pigs selected six generations for increased weight at 70 d of age and a contemporaneous, randomly selected control line. The reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th-rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle, and lean gain per day. Total weighted cumulative selection differential for 70-d weight was 30.2 kg. The realized heritability for 70-d weight was .13 +/- .06, and the change in 70-d weight was .65 +/- .29 kg per generation. The regression coefficient of litter size at 21 d on generation was .24 +/- .10 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Carcass length, specific gravity, and ham weight decreased (P less than .10) -.075 +/- .036 cm, -.00054 +/- .00027, and -.102 +/- .048 kg, respectively, per generation. Color score and lean gain per day increased .046 +/- .021 points and .0032 +/- .0013 kg/d, respectively, each generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of growth performances,carcass characteristics,and meat qualities of Okinawan indigenous Agu pigs and crossbred pigs sired by Agu or Duroc boar

Indigenous Okinawa Agu pigs are crossed with Large White × Landrace (WL) pigs to improve their meat production, but there is little information regarding the crossbreeding effects. The study aims to compare growth, carcass characteristics, and meat qualities of Agu pigs with those of WL crossbreeds with Agu sires (WLA) or Duroc sires (WLD). WLA pigs showed better growth performance and carcass characteristics and less intramuscular fat (IMF) contents than Agu ones, but they had higher fat deposition, smaller longissimus dorsi muscle area, and higher IMF contents than WLD pigs. Agu pigs showed higher water holding capacity than the other two breeds. The inner layer of Agu backfat contains higher and lower proportions of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acid (PUFA), respectively, than that in WLD animals. WLA animals had intermediate values for the fatty acid content in the inner backfat, although MUFA contents were equal to those of Agu pigs. Fatty acid profiles in IMF were similar to those in the backfat. These results indicate that crossbreeding of Agu with WL pigs improves growth performance and carcass quality. Particularly, WLA pigs have higher IMF contents and MUFA concentrations and lower PUFA concentrations than WLD pigs.     

Osteochondrosis in six breeds of slaughter pigs

Summary

The severity and extent of osteochondral lesions have been examined, macroscopically, radiographically as well as histopathologically, in six different breeds of pigs (Belgian Landrace (B), Duroc (D), Dutch Landrace (N), Dutch Yorkshire (G), Hampshire (H) and Piétrain (P)). In these pigs three different levels of feeding were used.

Duroc pigs had significantly more severe lesions in the fore limbs than Dutch Landrace (N), Dutch Yorkshire (G), Hampshire (H) and Piétrain (P) pigs, while Belgian Landrace pigs (B) had significant more severe lesions than Dutch Yorkshire (G) pigs. The differences between breeds related more to the degree of severity of the lesions in the articular surfaces of the distal humerus and proximal radius‐ulna and in the distal ulnar growth plate than to the presence of the lesions per se. In the hind limbs Belgian Landrace pigs (B) had significantly more severe osteochondral lesions than all other breeds, while Dutch Landrace pigs (N) had significantly more severe lesions than Duroc (D), Dutch Yorkshire (G), Hampshire (H) and Piétran (P) pigs.

Pigs with the highest growth rate showed sginificantly more severe osteochondral lesions in the distal ulnar growth plate and in the medial fe,moral condyle than pigs with a more restricted growth rate.     

Impact of MYOD family genes on pork traits in Large White and Landrace pigs

Summary Porcine myogenic differentiation genes ( MYOD ) family play a key role in growth and muscle development and are therefore considered as candidate genes for meat production traits. The objective of the study was to investigate the polymorphisms at four loci belonging to the MYOD genes family and analyse their associations with variation in meat production traits in Czech pig breeds. To verify the associations between the polymorphisms and the selected meat traits, altogether 254 pigs, including full- and half-sibs, of Large White and Landrace breeds were tested. The studied meat characteristics were weight of neck, loin, shoulder and ham, lean meat content (LMC), backfat thickness, intramuscular fat (IMF), remission, dry matter content and test daily gain. Statistically significant associations were observed between MYOG gene and fat and neck weight, and between MYF5 gene and IMF and LMC. High significant differences were observed between genotypes AA and AB of MYOD1 in IMF and between genotypes AB and BB of MYF5 in loin weight.     

Identification of single-nucleotide polymorphisms in 5' end and exons of the PRKAG3 gene in Hubbard White broiler, Leghorn layer, and three Chinese indigenous chicken breeds

5′‐AMP‐activated protein kinase plays an important role in regulating the level of ATP in the presence of metabolic stress. Previous studies revealed that polymorphisms in 5′‐AMP‐activated protein kinase gamma 3 subunit (PRKAG3) gene are associated with meat quality in pigs. In the present study, single‐nucleotide polymorphisms (SNPs) in the 5′‐end and exons of chicken PRKAG3 gene were identified with the method of single‐strand conformation polymorphism in Hubbard ISA White broiler, Leghorn layer, and three Chinese indigenous chicken breeds, Tibet Chicken, Shouguang Chicken and Beijing Yellow Chicken. Two SNPs in the 5′‐end of the gene and 10 SNPs in exons 3, 4, 9 and 11, of which three caused amino acid substitutions, were identified in the PRKAG3 gene of the five chicken breeds. The results will facilitate further study on the association between the mutations of PRKAG3 and chicken meat quality.     

Genotype × Environment interactions in pig breeding programmes. II. Environmental effects and genetic parameters in central test

Environmental effects were investigated and genetic parameters estimated in central test results from Dutch Landrance and Dutch Yorkshire pigs, tested on two stations under a restricted feeding regime.To investigate the environmental effects within test stations, different definitions of environmental effects were included separately in models for analysis of variance. Batch effects were significant (P < 0.001) for daily gain and feed conversion ratio, and explained 7–12% of the variance. Backfat measurements and ham + loin percentage were significantly (P < 0.05) influenced by month effects. Indications for an optimal environmental classification were shown only for daily gain and feed conversion ratio. For the carcass characteristics no balance could be found between chance and environmental fluctuations.The estimated heritabilities for daily gain, feed conversion ratio and ultrasonic backfatàt thickness were 0.18, 0.21 and 0.28, respectively, if averaged over the two breeds, and were lower than those reported in the literature for pigs on restricted feeding. A different genetic structure (only A.I. data were used) and the chosen definition of environmental effects may have contributed to these differences. The differences between the two breeds in heritability, especially for ham + loin percentage (h² = 0.34 for Dutch Landrace and h² = 0.75 for Dutch Yorkshire), may be the result of the selection against halothane-positive animals in the first breed.     

A genome‐wide SNP scan in a porcine Large White × Minzhu intercross population reveals a locus influencing muscle mass on chromosome 2

A high‐density single nucleotide polymorphism (SNP) array containing 62 163 markers was employed for a genome‐wide association study (GWAS) to identify variants associated with lean meat in ham (LMH, %) and lean meat percentage (LMP, %) within a porcine Large White × Minzhu intercross population. For each individual, LMH and LMP were measured after slaughter at the age of 240 ± 7 days. A total of 557 F2 animals were genotyped. The GWAS revealed that 21 SNPs showed significant genome‐wide or chromosome‐wide associations with LMH and LMP by the Genome‐wide Rapid Association using Mixed Model and Regression‐Genomic Control approach. Nineteen significant genome‐wide SNPs were mapped to the distal end of Sus Scrofa Chromosome (SSC) 2, where a major known gene responsible for muscle mass, IGF2 is located. A conditioned analysis, in which the genotype of the strongest associated SNP is included as a fixed effect in the model, showed that those significant SNPs on SSC2 were derived from a single quantitative trait locus. The two chromosome‐wide association SNPs on SSC1 disappeared after conditioned analysis suggested the association signal is a false association derived from using a F2 population. The present result is expected to lead to novel insights into muscle mass in different pig breeds and lays a preliminary foundation for follow‐up studies for identification of causal mutations for subsequent application in marker‐assisted selection programs for improving muscle mass in pigs.     

Effects of an immune stimulant,inactivated Mycobacterium phlei,on the growth performance as well as meat quality of fattening pigs

Inactivated mycobacterium phlei (M. phlei) is well known for its immune‐stimulatory functions in humans and livestock, but less information is available about the influence on meat quality of pigs when used as a feed additive. This study was designed to evaluate the effects of inactivated M. phlei on growth performance as well as meat quality of fattening pigs. A total of 240 cross‐bred pigs ([Landrace × Yorkshire] × Duroc) with initial body weight of 80.14 ± 0.29 kg were randomly allocated to five treatments, each of which consisted of eight replicates with 6six pigs per replicate. The basal diet supplemented with five levels of inactivated M. phlei preparations (0, 3.5 × 10⁹ [0.1% w/w], 7 × 10⁹ [0.2%], 1.4 × 10¹⁰ [0.4%] or 2.1 × 10¹⁰ [0.6%] colony‐forming units/kg) was respectively fed to the control group and four treatment groups for 30 days. Adding 0.4% of inactivated M. phlei to diet increased the average daily feed intake and average daily gain of pigs. Importantly, intramuscular fat percentage in the Longissimus dorsi (LD) was increased by feeding diet containing 0.2%, 0.4% and 0.6% of inactivated M. phlei, despite the pH value, drip loss, cooking loss and filter paper fluid uptake not being influenced. Analysis of the fatty acid components showed that some saturated fatty acids were decreased in LD after feeding inactivated M. phlei, but some monounsaturated fat acids (MUFAs) and polyunsaturated fatty acids were increased (PUFAs), which induced the total contents of MUFAs and PUFAs were improved. RT‐PCR assay revealed that feeding inactivated M. phlei up‐regulated genes implicated in fat metabolism in muscle, including ELOVL6, FASN, SCD1 and H‐FABP. This study revealed that feeding inactivated M. phlei not only increased growth performance of fattening pigs, but also improved the meat quality by increasing intramuscular fat content, thus inactivated M. phlei probably has high utilization value in modern pig production.     

Genetic parameter estimation and gene association analyses for meat quality traits in open-air free-range Iberian pigs

Meat quality of Iberian pigs is defined by the combination of their genetic characteristics and the particular production system. To carry out a genetic analysis of the main meat quality traits, we estimated their heritabilities, genetic correlations and the association effects of 32 selected SNPs of 12 candidate genes. A total of ten traits were measured in longissimus dorsi samples from 1,199 Iberian pigs fattened in the traditional free-range system: water holding capacity (thawing, cooking and centrifuge force water losses), instrumental colour (lightness L*, redness a* and yellowness b*), myoglobin content, shear force on cooked meat, and shear force and maximum compression force on dry-cured loin. Estimated heritability values were low to moderate (0.01 to 0.43) being the lowest for L* and the highest for cooking loss. Strong genetic correlations between water holding capacity traits (0.93 to 0.96) and between myoglobin content and a* (0.94) were observed. The association analyses revealed 19 SNPs significantly associated with different traits. Consistent and strong effects were observed between PRKAG3 SNPs (rs319678464G > C and rs330427832C > T), MYH3_rs81437544T > C, CASP3_rs319658214G > T and CTSL_rs332171512A > G and water losses. Also for CAPN1_rs81358667G > A and CASP3_rs319658214G > T and shear force. The SNPs mapping on PRKAG3 showed the highest effects on Minolta colour traits. Genotyping of these SNPs could be useful for the selection of Iberian young boars with similar estimated breeding values for productive traits.     

Correlated responses in reproductive and carcass traits to selection for 200-day weight in Duroc swine.

Correlated responses in reproductive and carcass traits from a line of Duroc pigs selected for increased 200-d weight along with a randomly selected control line were studied in 189 litters (116 select, 73 control) and 191 pigs (106 select, 85 control), respectively. Reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle and lean gain per day. Total weighted cumulative selection differential for 200-d weight was 81.7 kg. The realized heritability for 200-d weight was .18 +/- .08, and the change in 200-d weight was 2.5 +/- 1.2 kg per generation. The regression coefficient of litter size born on generation was -.29 +/- .12 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Average backfat thickness, 10th rib backfat thickness, and belly weight increased by .093 +/- .016 cm, .122 +/- .029 cm, and .089 +/- .040 kg, respectively, per generation. Specific gravity, ham weight, shoulder weight, color score, and percentage of muscle decreased -.00086 +/- .00024, -.165 +/- .013 kg, -.104 +/- .011 kg, -.035 +/- .015 points, and -.47 +/- .12%, respectively, per generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Polymorphisms in the promoter region of myostatin gene are associated with carcass traits in pigs

Higher average daily gain, more lean meat yield and less fat yield of porcine carcass increase selling profits for animal producers. Myostatin (MSTN), previously called GDF8, is a member of transforming growth factor‐β (TGF‐β) superfamily. It is a negative regulator for both embryonic development and adult homeostasis of skeletal muscle. In this study, the genotypes of the previously described SNPs MSTN g.435G>A and g.447A>G SNPs in 66 Duroc pigs, 33 Landrace pigs, 180 Duroc × Landrace (DL) pigs and 155 Duroc × Yorkshire × Landrace (DYL) pigs were determined by Taqman SNP Genotyping Assays. For Duroc and Landrace pigs, MSTN g.435GG/g.447AA individual had greater backfat thickness (p < 0.05) than g.435AA/g.447GG individual, whereas MSTN g.435AA/g.447GG had greater meat (p < 0.05) and meat percentage (p < 0.05) than g.435GA/g.447AG individual. For DL and DYL pigs, the MSTN g.435GG/g.447AA animals were greater in backfat at ultrasound 10th rib (p < 0.05) and carcass 10th rib (p < 0.01) than g.435AA/g.447GG individual. The MSTN g.435AA/g.447GG individual also had higher values than g.435GG/g.447AA for anterior‐end meat (p < 0.05), posterior‐end meat (p < 0.01), total meat weight (p < 0.01) and meat percentage (p < 0.01). This study confirmed evidence that MSTN g.435G>A and g.447A>G affected carcass traits in pigs. The effects of the mutated alleles were additive with the maximal effects resulting from two copies of the mutated allele. Selection for MSTN g.435A/g.447G allele is expected to increase muscle of limb and total meat production and decrease backfat thickness.     

Screening 52 single nucleotide polymorphisms for extreme value of glycolytic potential and drip loss in pigs

Low heritability of meat quality traits and the lack of their systematic registration in breeding programs have encouraged the search for single nucleotide polymorphisms (SNPs) located within genes coding the proteins involved in muscle and fat metabolism. In this report, a panel of 52 SNPs was used to find which alleles and genotypes are more/less frequent in groups of pigs differentiated by extreme value of glycolytic potential (GP) and drip loss (DL). The analysis was carried out in 52 fatteners (chosen from 246 pigs), of which 28 were Landrace and 27 Landrace × Yorkshire. Two designs were performed: I, fatteners were divided into two groups showing extreme value of GP (<125 versus >145), II, fatteners were divided into two groups showing extreme value of DL (<6.0 versus >6.0). Allele frequency differences between the phenotypic groups of extreme GL or DL were not influenced by the breed. The frequency of 52 SNPs alleles for each of group was calculated and a chi‐squared test was used to estimate the significance of differences in allele frequencies between alternative groups in each experimental design. Three SNPs (DECR1, PPARGC1, MC4R) and another two (CYP21, SFRS1) showed significant differences between groups of extreme GP and DL, respectively. To exemplify and validate potential associations of candidate SNPs for GP and DL, 293 fatteners representing three commercial breeds/crosses (95 Landrace, 66 Landrace × Yorkshire and 132 Landrace × Yorkshire × Duroc were genotyped for DECR1 and CYP21 by PCR‐RFLP assays. DECR1 showed significant associations with GP in Landrace and Landrace × Yorkshire × Duroc fatteners. CYP21 showed significant associations with DL in all breeds/crosses. Interestingly, the CYP21 polymorphism revealed adverse associations trend in Landrace × Yorkshire × Duroc pigs in comparison to Landrace and Landrace × Yorkshire fatteners.     

A retrospective analysis of allele frequency changes of major genes during 20 years of selection in the Italian Large White pig breed

In this study, we investigated whether a selection programme based on boar genetic evaluation obtained with a classical BLUP animal model can change allele frequencies in a pig population. All Italian Large White boars born from 1992 to 2012 with estimated breeding value reliability >0.85 (n = 200) were selected among all boars of this breed. Boars were genotyped with markers in major genes (IGF2 intron3‐g.3072G>A, MC4R p.D298N, VRTN PRE1 insertion, PRKAG3 p.I199V and FTO g.276T>G). Genotyping data were analysed grouping boars in eight classes according to their year of birth. To evaluate the influence of time on allele frequencies of the genotyped markers, multinomial logistic regression models were computed. Four of five polymorphic sites (IGF2, MC4R, VRTN and FTO) showed significant (p < 0.01) changes in allele frequencies over time due to a progressive and continuous increase of one allele (associated with higher lean meat content, higher average daily gain and favourable feed: gain ratio) and, consequently, decrease of the other one, following the directional selection of the selection programme of this pig breed. The retrospective analysis that was carried out in Italian Large White boars suggests that selection based on methodologies assuming the infinitesimal model is able to modify in a quite short period of time allele frequencies in major genes, increasing the frequency of alleles explaining a relevant (non‐infinitesimal) fraction of the overall genetic variability for production traits.     

The effects of sex and slaughter weight on growth performance and carcass traits of pigs intended for dry-cured ham from Teruel (Spain)

Crossbred pigs (n = 200) from Duroc sires mated to Landrace x Large White dams, with a mean BW of 107.0 +/- 2.4 kg and intended for highquality dry-cured hams (Teruel ham) from Spain, were used to investigate the effects of sex (barrows and gilts) and slaughter weight (SW; 120, 125, 130, 135, and 140 kg of BW) on growth performance and carcass characteristics. For productive performance, there were 5 treatments based on 5 SW; each treatment was replicated 4 times and the replicate was a pen made up of 5 barrows and 5 gilts allotted together. For carcass traits, there were 10 treatments based on 2 sexes and 5 SW; each treatment was replicated 20 times and the replicate was a carcass. Barrows had fatter carcasses (P < 0.001) and wider hams (P < 0.01) but a lower yield of trimmed shoulder (P < 0.05), loin (P < 0.001), and ham (P < 0.001) than gilts. Also, castrates tended to show a greater proportion of final suitable carcasses for Teruel ham (P < 0.10) than females because more barrows than gilts fulfilled the minimum requirement of carcass weight and fat thickness in the gluteus medius (GM) muscle (P < 0.01). An increase in SW tended to decrease ADG and G:F (P < 0.10). In addition, dressing percentage, fat, and dimensions of carcass and ham increased as SW increased (P < 0.001). Although the weight of trimmed primal cuts (shoulder, loin, and ham) increased with SW, the yield of trimmed loin or ham decreased (P < 0.01). The proportion of final suitable carcasses for Teruel ham improved as SW increased up to 130 kg of BW but not thereafter (P < 0.001) because of an increase in percentage carcasses that fulfilled the minimum carcass and ham weight (P < 0.001) and fat in GM (P < 0.05). We can conclude that barrows were better than gilts when intended for Teruel ham. Furthermore, an increase in SW up to 130 kg in pigs impaired growth performance but improved some aspects of carcass quality that are required by the Teruel ham industry.     

In vitro and In vivo Association of Porcine Hepatic Cytochrome P450 3A and 2C Activities with Testicular Steroids

The aim of this study was to screen the inhibitory potential of several testicular steroids on cytochrome P450 3A (CYP3A) and 2C (CYP2C) activities in porcine liver microsomes. The microsomes used in this study were obtained from pubertal male pigs of two breeds, Landrace and Duroc. For the in vitro inhibition study, porcine microsomes were incubated in the presence of 17β‐estradiol, 17α‐estradiol, androstenone, dehydroepiandrosterone and dihydrotestosterone. Both reversible and mechanism‐based inhibitions were examined. 7‐benzyloxyresorufin (BR) and 7‐benzyloxy‐4‐trifluoromethylcoumarin (BFC) were used as substrates for CYP3A, and diclofenac and tolbutamide (TB) as substrates for CYP2C. 7‐benzyloxyresorufin O‐dealkylase (BROD) activity was inhibited by all tested steroids in the microsomes from Landrace pigs via mechanism‐based mode, but in the microsomes from Duroc pigs, BROD activities were inhibited only in the presence of 17β‐oestradiol. Mechanism‐based inhibition of BFC metabolism by the tested steroids was observed in the microsomes from both breeds, but this inhibition was weak and did not exceed 20%. TB hydroxylase (TBOH) activity in the microsomes from Duroc pigs was inhibited by 17α‐oestradiol through the mechanism‐based mode of inhibition. None of the investigated steroids inhibited TBOH activity in Landrace pigs. For the in vivo study, male pigs were injected with a single dose of human chorionic gonadotropin (hCG) to stimulate testicular steroid production by the Leydig cells. In vivo stimulation with hGC did not alter BROD activity either in Landrace or in Duroc pigs. BFC metabolism was significantly induced by hCG stimulation in both breeds and TBOH activity only in Duroc pigs. Activity of diclofenac hydroxylase was not detected in either Landrace or Duroc pigs. Breed significantly affected BROD and TBOH activity with BROD being higher in Landrace and TBOH in Duroc pigs. This study improved our understanding of the role of testicular steroids in the regulation of porcine CYP450 activity.     

不同猪种5-羟色胺受体基因的表达及其与肉质的相关性分析

为研究5-羟色胺（5-HT）受体基因在不同猪种的表达及其与肉质的关系,试验选取淳安花猪与杜长大三元猪各12头,同时饲喂,达上市体重时分别屠宰,测定胴体、肉质性状及肌肉、脂肪中的5-HT受体基因表达量。结果表明：淳安花猪、杜长大三元猪的平均屠宰体重分别为88.1、102.4kg;淳安花猪的板油率、背膘厚、肌内脂肪等指标均显著高于杜长大三元猪（P〈0.05）;屠宰率、眼肌面积杜长大三元猪显著高于淳安花猪（P〈0.05）。5-HT2A、5-HT7受体基因在2个猪种脂肪组织中的表达量均显著高于肌肉组织（P〈0.05）,杜长大三元猪的肌肉中5-HT2A、5-HT7表达量显著低于淳安花猪（P〈0.05）,而脂肪中表达量两猪种间差异不显著。5-HT2A、5-HT7受体基因表达量与屠宰肉质指标之间基本呈负相关,尤其是肌肉中的5-HT2A表达量,呈较强负相关（杜长大三元猪）或显著负相关（淳安花猪）。研究初步认为,5-HT受体基因在中外猪种之间存在表达差异,并与屠宰肉质性状具有相关性。     

不同品种猪肌肉组织miR-1和miR-133基因的表达分析

本研究旨在探讨猪miR-1和miR-133基因在不同品种猪肌肉组织中的表达情况。试验以180日龄的蓝塘猪、长白猪以及大花白猪的背最长肌为材料,采用Stem-loop实时定量RT-PCR法检测miR-1和miR-133在长白猪、大花白猪及蓝塘猪背最长肌组织中的表达情况。结果表明,在蓝塘猪中,miR-1的表达量分别为长白猪和大花白猪的4.7和6.4倍,前者与后两者之间表达水平有显著的差异(P<0.05),而后两者之间表达量差异不显著(P>0.05);同样,miR-133在蓝塘猪中的表达量最高,其次为长白猪,两者分别是大花白猪的7.2和5.7倍,且差异显著(P<0.05),但蓝塘猪与长白猪之间差异不显著(P>0.05)。miR-1和miR-133在不同品种猪中存在特异性表达,提示可能与肌肉发育性状相关。