Quantitative trait loci analysis of osteochondrosis traits in the elbow joint of pigs

Alleged predisposing dietary factors fail to increase the incidence of osteochondrosis-like lesions in growing pigs at 14 and 24 wk of age

Early lesions of osteochondrosis (OC) are exhibited by regions of cartilage retention along the growth plate and articular cartilage. Progression of OC lesions may impair locomotion and necessitate euthanasia in adherence to animal welfare guides. Little is known about the role of nutrition in the initiation and early stages of OC. However, dietary components are commonly implicated as predisposing factors. In this study, diets were altered as an attempt to induce early stage OC lesions under controlled conditions. At 8 wk of age, 96 crossbred gilts (body weight [BW] = 17.4 ± 0.18 kg) were randomly assigned to one of four corn-soybean meal-based diets (four pens per diet, six pigs per pen) to assess diet effects on the number and volume of OC lesions in the distal femur. Diets included a non-pelleted control diet (Ctl); Ctl plus 20% glucose (Glc); the Ctl with increased concentrations of lysine, Ca, and P (+CaP); and the +CaP diet in a pelleted form (PEL). Femurs were collected from pigs euthanized at either 14-wk (Wk 14) or 24-wk (Wk 14) of age for assessments of OC lesions. Based on a mixed model analysis with pen as the experimental unit, dietary treatments did not affect final BW (129.3 ± 3.8 kg) or average daily gain (ADG) (1.00 ± 0.03 kg/d) over the trial. As expected, pigs fed PEL and Glc diets were more efficient (P < 0.05) in feed conversion compared with Ctl and +CaP. Using femurs as the experimental unit at Wk 14 (collected from two of the six pigs per pen), bone mineral content, determined by dual-energy x-ray absorptiometry scans, was greater (P < 0.05) in pigs fed +CaP and PEL than Ctl or Glc diets; however, only +CaP group differed (P < 0.05) at Wk 24 (collected from four pigs per pen). Computed tomography (CT) scans of femurs were reconstructed as three-dimensional images to allow detection of the number, volume, and surface area of lesions in distal growth plates. At Wk 14, pigs fed Ctl had fewer number of lesions (P < 0.05); however, no differences were detected among dietary treatments in lesion volume or lesion surface area. Pigs had fewer lesions at Wk 24 than Wk 14; however, differences were not detected among dietary treatments. At Wk 24, pigs fed Ctl diets had the greatest lesion volume among dietary treatments (P < 0.05). In conclusion, none of the pigs exhibited symptoms of lameness regardless of dietary treatment or OC lesion traits. Diet modifications due to pelleting or inclusion of rapidly digestible ingredients, such as glucose, did not increase prevalence or size of OC lesions. Image analysis of CT scans was a reliable method to quantify the number, size, and location of OC lesions.

KRT8, FAF1 and PTH1R gene polymorphisms are associated with leg weakness traits in pigs

The liability to lesions of dysfunctions of bone and joints in pigs, summarized as leg weakness and mostly expressed as osteochondrosis, is an animal welfare and economic issue in pig production. The objective of this study was to identify polymorphisms in the functional and positional candidate genes keratin 8 (KRT8), Fas-associated factor 1 (FAF1) and parathyroid hormone type I receptor (PTH1R) and to evaluate their association with leg weakness traits. Therefore, osteochondrosis lesions were scored in animals of a Duroc × Pietrain F2 population (DuPi; n = 310) and commercial herds of the breed Large White (n = 298). In addition, bone mineralization traits were observed in DuPi population. SNPs were identified in genes KRT8 (g.8,039G > A), FAF1 (g.380,914T > C) and PTH1R (c.1,672C > T). KRT8 showed significant association with bone mineral density and content (P ≤ 0.05). FAF1 was association with OC lesions score of all joints inspected (P ≤ 0.05). PTH1R showed significant dominance effects on OC lesion scores of the distal femur articular cartilage (P = 0.01) and epiphysis of the distal ulna (P = 0.05) as well as sums of scores of all joints (OCsum, P = 0.04) and assignment to groups of either severely or gently affected animals (OCcat, P = 0.01). This study reveals clear genetic-statistical evidence for a link of KRT8, FAF1 and PTH1R with some of leg weakness related traits in pigs.

Association and expression study of MMP3, TGFβ1 and COL10A1 as candidate genes for leg weakness-related traits in pigs

The present study was aimed to determine the association between metalloproteinase 3 (MMP3), transforming growth factor beta 1 (TGFβ1) and collagen type X alpha I (COL10A1) gene polymorphisms with traits related to leg weakness in pigs. Three hundred Duroc × Pietrain cross breds (DuPi) and 299 pigs of a commercial population (CP) were used for the experiment. DuPi animals were examined for 10 different traits describing leg and feet structure, osteochondrosis (OC) scores and bone density status. Data of OC score at condylus medialis humeri, condylus medialis femoris and distal epiphysis ulna regions of CP were used for association analysis. Significant association (P < 0.05) was found for MMP3 SNP (g.158 C>T) with OC at head of femur and bone mineral density in the DuPi population. Association (P < 0.05) was found between SNP of TGFβ1 (g.180 G>A) with rear leg score and the principle component denoting both OC and feet and leg scores in the DuPi population. No association was found between COL10A1 (g.72 C>T) and leg weakness related traits. The associations of SNPs with OC traits could not be confirmed in the commercial population. Expression analysis of the three candidate genes was performed to compare between healthy and OC. TGFβ1 was found to be highly expressed (P < 0.05) in the OC compared to healthy cartilages, but no significant different expressions were observed for MMP3 and COL10A1 genes. The present finding suggested that TGFβ1 and MMP3 genes variants have an effect on some of the leg weakness related traits.

Genomic regions associated with ventro-cranial chronic pleuritis in pig

Ventro-cranial chronic pleuritis can be a result of pleuropneumonia and enzootic pneumonia. These diseases cause severe losses in intensive pig production worldwide, but host resistance is difficult to breed for. It could be beneficial to use marker-assisted selection, and a step towards this is to identify genomic regions associated with the trait. For this purpose, 7304 pigs from 11 boar families were analysed for associations between single nucleotide polymorphisms and ventro-cranial chronic pleuritis. The pigs were genotyped by the use of the iSelect Custom 7 K porcine SNP Chip. Quantitative trait loci (QTL), significant at the chromosome-wide level, were identified on Sus scrofa chromosomes (SSC) 2, 4, 11, 12 and 13 in four different boar families. The QTL on SSC 4 in family G was also significant at the genome-wide threshold according to Bonferroni correction. We have identified a number of candidate genes, but the causative mutations still need to be identified. Markers closely associated with the resistance traits have a strong potential for use in breeding towards animals with improved characteristics concerning ventro-cranial chronic pleuritis.

Quantitative trait loci analysis for leg weakness-related traits in a Duroc × Pietrain crossbred population

Background

Leg weakness issues are a great concern for the pig breeding industry, especially with regard to animal welfare. Traits associated with leg weakness are partly influenced by the genetic background of the animals but the genetic basis of these traits is not yet fully understood. The aim of this study was to identify quantitative trait loci (QTL) affecting leg weakness in pigs.

Methods

Three hundred and ten F₂ pigs from a Duroc × Pietrain resource population were genotyped using 82 genetic markers. Front and rear legs and feet scores were based on the standard scoring system. Osteochondrosis lesions were examined histologically at the head and the condylus medialis of the left femur and humerus. Bone mineral density, bone mineral content and bone mineral area were measured in the whole ulna and radius bones using dual energy X-ray absorptiometry. A line-cross model was applied to determine QTL regions associated with leg weakness using the QTL Express software.

Results

Eleven QTL affecting leg weakness were identified on eight autosomes. All QTL reached the 5% chromosome-wide significance level. Three QTL were associated with osteochondrosis on the humerus end, two with the fore feet score and two with the rear leg score. QTL on SSC2 and SSC3 influencing bone mineral content and bone mineral density, respectively, reached the 5% genome-wide significance level.

Conclusions

Our results confirm previous studies and provide information on new QTL associated with leg weakness in pigs. These results contribute towards a better understanding of the genetic background of leg weakness in pigs.

Quantitative trait loci analysis of swine meat quality traits

A QTL study was performed in large half-sib families to characterize the genetic background of variation in pork quality traits as well as to examine the possibilities of including QTL in a marker-assisted selection scheme. The quality traits included ultimate pH in LM and the semimembranosus, drip loss, and the Minolta color measurements L*, a*, and b* representing meat lightness, redness, and yellowness, respectively. The families consist of 3,883 progenies of 12 Duroc boars that were evaluated to identify the QTL. The linkage map consists of 462 SNP markers on 18 porcine autosomes. Quantitative trait loci were mapped using a linear mixed model with fixed factors (sire, sex, herd, month, sow age) and random factors (polygenic effect, QTL effects, and litter). Chromosome-wide and genome-wide significance thresholds were determined by Peipho's approach, and 95% Bayes credibility intervals were estimated from a posterior distribution of the QTL position. In total, 31 QTL for the 6 meat quality traits were found to be significant at the 5% chromosome-wide level, among which 11 QTL were significant at the 5% genome-wide level and 5 of these were significant at the 0.1% genome-wide level. Segregation of the identified QTL in different families was also investigated. Most of the identified QTL segregated in 1 or 2 families. For the QTL affecting ultimate pH in LM and semimembranosus and L* and b* value on SSC6, the positions of the QTL and the shapes of the likelihood curves were almost the same. In addition, a strong correlation of the estimated effects of these QTL was found between the 4 traits, indicating that the same genes control these traits. A similar pattern was seen on SSC15 for the QTL affecting ultimate pH in the 2 muscles and drip loss. The results from this study will be helpful for fine mapping and identifying genes affecting meat quality traits, and tightly linked markers may be incorporated into marker-assisted selection programs.

Osteochondrosis of the elbow joint in finishing pigs from three herds: associations among different types of joint changes and between osteochondrosis and growth rate

Osteochondrosis (OC) is a degenerative condition of the cartilage seen in growing animals. The objective of the study was to investigate (1) the prevalence of macroscopically visible OC in the elbow of finishing pigs, (2) the relationship between changes in the surface of the articular cartilage and changes in the underlying cartilage and bone and the synovial membrane, and (3) the association between growth rate and the occurrence of OC in the elbow. The study used 9696 finishing pigs from three herds. After slaughter, the left elbow joint of each pig was examined, and macroscopically visible lesions in the articular cartilage, subchondral bone and synovial membrane were recorded. The highest prevalences of OC lesions were found in the humeral condyle with thickening of the articular cartilage (53%), irregularity of the articular cartilage (32%), lesions in the subchondral bone (26%), fissures under the cartilage (21%) and osteochondrosis dissecans (OCD) (14%). Irregularity of the articular cartilage was strongly associated with fissures under the cartilage and lesions in the subchondral bone (OR 13.7 and 5.8, respectively). Irregularity of the articular cartilage and OCD were associated with villous proliferation of the synovial membrane. For each additional 100 g of average daily gain in the weaner period or in the finishing period, the risk of irregularity in the articular cartilage and OCD increased by approximately 20% (ORs ranging between 1.14 and 1.20 for both weaners and finishers).