ABSTRACT Intact (85) and castrated (86) male pigs were slaughtered at 96.3 kg and at an average slaughter age of 150.1 days producing 79.1 kg carcasses. Either a corn or wheat‐based, nutritionally equivalent ration was fed ad libitum. Nine percent less feed was required to market entire (intact) males when compared with castrates. Entire males had at least 1.9% more lean content and perhaps as much as 10% more carcass value. Little evidence was found to suggest that entire males had reduced meat quality. Preslaughter handling was an important aspect, since detrimental effects from inadequate preslaughter handling techniques appeared to be greater than those associated with gender. Therefore, considering production aspects only, entire male pigs should be able to be successfully marketed in Canada. However, detection and control of “sex‐taint” and consumer acceptance of fresh pork from entire male pigs must be addressed.

ABSTRACT Ninety intact male, 89 castrated male, and 60 female pigs were slaughtered at a mean market weight of 95.7 kg and a mean age of 151.5 days. Skatole and steroid levels in 20 and 24% of the intact males respectively, exceeded acceptable levels. (i.e. 0.25 μg/g and 50 μg/g, respectively). In contrast 2.5 and 3.4% of the castrated male and 1.8 and 0.0% of the female pigs exceeded these skatole and steroid levels, respectively. To successfully predict the potential presence of sex taint, both 16‐androstnone steroid and skatole levels must be known. However, factors other than skatole and 16‐androstene steroid levels appear to be involved in sex taint development.

ABSTRACT Ninety intact male, 89 castrated male, and 60 female pigs were slaughtered at a mean market weight of 95.7 kg and a mean age of 151.5 days. All pigs were housed in groups of four and were fed ad libitum either a corn or wheat based ration, until 24 h preslaughter, at which time feed, but not water was withheld. Six percent of the samples from castrated and 30% of the samples from intact male pigs were perceived to have an inappropriate barnyard aromatic at a relatively high intensity. Only 2% of the samples from castrates, as opposed to 27% of the samples from intact males were perceived to have an inappropriate sex taint aromatic at a relatively high intensity. Although samples from females were perceived to have an inappropriate barnyard aromatic at a relatively high intensity, no sex taint aromatic was detected from these samples. There was no effect of diet on either palatability or consumer acceptance traits.

Three QM Hamline™ (HL; National Pig Development, Canada), four pure-bred Landrace (LR) and Large White (LW) sires were bred to 12, 18 and 8 Manor Hybrid™ (National Pig Development, Canada) sows, respectively, which provided 37 NN-, and 37 Nn- HL, 39 NN- and 37 Nn- LR and 34 NN- LW commercial pigs for a study on the effect of breed of sire and genotype at the halothane locus on pig performance, carcass yield and meat quality. Four pigs per pen, within breed of sire and genotype, were placed on performance test at 56 d of age until total pen weight was 440 kg. Large White, LR and HL NN-pigs were slaughtered at 178, 172 and 177 d of age, adjusted to 110 kg, while LR and HL Nn-pigs were slaughtered at 177 and 178 d of age. HL pigs had 12.7 mm backfat and 44.5 mm of muscle depth at the grade site, while LW and LR had greater backfat thickness (15.1 and 15.7 mm), and less muscle depth (41.1 and 38.7 mm). The halothane genotype did not affect live animal measurements. Feed utilisation was similar in all five groups of pigs. Lean yield of the HL NN-pigs (58.8%) was greater than that found in the NN-LW (56.6%) and NN-LR (56.8%) while the halothane gene made only modest improvement in lean yield in the leaner HL (P = 0.0789) and a more substantial improvement was observed in the fatter LR (P = 0.0161). Total dissected lean was 613, 596, and 639 g kg−1 in LW, LR and HL NN-pigs, respectively, while this increased to 611 and 649 g kg−1 in LR and HL Nn-pigs. QM Hamline™ NN-pigs had larger commercial hams (9878 g) compared with NN-LW and NN-LR sired pigs. Furthermore, they also had greater lean yield in all four lean cuts. The halothane gene had no consistent effect on carcass merit. While initial pH was similar (6.03–6.04) in the three NN-groups of pigs, it dropped to 5.73 and 5.84, among the Nn-LR and HL pigs. Luminosity (59.2%, 58.7%) and hue angle (31.1°, 30.5°) of Nn-LR and HL were higher, with greater drip (5.8%, 5.3%) losses and lower soluble protein (130, 148 g kg−1), compared with NN-LR (54.8%, 24.4°, 3.0%, 185 g kg−1) and HL (55.3%, 26.1°, 3.4%, 182 g kg−1) pigs, respectively. This study indicates carcass merit can be substantially improved without use of the halothane gene and without serious effects to meat quality. However, introduction of the halothane gene can seriously compromise meat quality. Key words: Large White, Landrace, Hamline, halothane gene

An image segmentation system was developed for detecting the muscle longissimus thoraces (LT) in ultrasonic images of live pigs. The images have a low contrast, a high level of noise, and a high degree of variance in terms of texture and shape. The segmentation algorithm starts with a region growing process, which provides a rough approximation of the LT. Morphological operations and curve fitting eliminate unwanted noise. Finally, an active contour process refines the shape of the resulting region. This system takes several segmentation techniques and builds a flow of information between them but does not rely on specific a priori information of the texture or the contrast. This is a first step towards automating the loin detection in ultrasonic images oflive pigs. Initial experiments provided encouraging results. It is a modular system so that different region growing and refinement algorithms can be easily substituted into the current design. This makes for a general system that can be adapted to other segmentation tasks involving low contrast images. A series ofthree ultrasound images was made along the dorsal surface of 30 live pigs. Using the images to estimate loin volume, 64 and 70% of the variation in commercial loin weight and lean yield ofloin were predicted. Augmenting the model with backfat measurements, the R2 increased to 79 and 89%, respectively. These values compare to 76 and 79%, respectively, from measurements made on the carcass with the Hennessey Grading Probe. Keywords: low contract images, segmentation, region growing, morphology, curve fitting, snake.

Lacombe breed pigs (72 gilts, 72 barrows) of three genotypes with respect to the porcine stress syndrome (normal, heterozygous, or homozygous for the halothane gene), were treated from 57 to 106 kg body weight with daily injections of 0.9% saline containing 0 or 3 mg of recombinant porcine somatotropin (pST) in a randomized block design. Pigs receiving pST had lower average daily feed intakes (ADF), greater average daily gains (ADG) and lower feed conversion efficiencies (FCE). Gilts relative to barrows had lower ADG, ADF and higher FCE. Gilts versus barrows and pigs treated with pST had reduced fat depths and greater loin depths at the 10th rib. Pigs homozygous for the halothane gene had reduced loin lean structure and color scores, greater light reflectance (L*), and lower soluble protein contents as expected, and these genotypic effects did not interact with pST treatment. Sex by pST treatment interactions (P < 0.05) were found for loin depth, moisture content, color score and L* values indicating barrows respond more favorably to pST treatment than gilts. Generally, pST treatment, gilts relative to barrows, and possession of the halothane gene increased carcass lean and reduced subcutaneous fat levels. Sex by pST treatment interactions were found for picnic lean (lower shoulder; P < 0.05), ham lean (P < 0.05), and total carcass lean (P = 0.09) further supporting the theory that barrows benefit more than gilts to pST treatment. No significant interactions were found between genotype and pST treatment for any qualitative muscle traits. Thus, pST treatment had no direct effect on meat quality and was not found to interact with the halothane gene. However, pST interactions with sex indicated barrows respond quantitatively and qualitatively more favorably than gilts to pST treatment. Key words: Somatotropin, porcine somatotropin, pork, porcine stress syndrome, stress, pigs, growth

The effects of the housing system (confinement versus free-range) and season (summer versus winter) on growth performance, carcass composition and meat quality were determined from commercial pigs with known NN genotype at the halothane locus. Free-range-housed pigs reared from 25 to 105 kg required 16 ± 1.2 (SEM) more days to reach market weight compared with confinement-housed pigs. Housing did not affect feed requirements during the summer, but food consumption increased by 13.7% for free-range pigs during the winter. Confinement-reared pigs had a 0.75 ± 0.28 kg heavier commercial carcass weight than free-range-reared pigs. While there was no difference in carcass fat thickness, muscle depth was 2.4 ± 1.02 mm greater in free-range-reared pigs with increased predicted lean yield from 59.1 ± 0.24% to 59.8 ± 24%. Free-range-reared pigs had heavier butts, loins and hams, and lighter bellies, which increased their wholesale carcass value by 2.9%. Furthermore, they had greater dissected lean in the picnic (2.0%) butt (4.0%), loin (4.5%) and ham (2.0%) with no compromise to pork quality. If the wholesale price is adjusted for the increased lean content of each cut by an additive or multiplicative model, apparent value was further increased to 5.7 or 8.1%. While these results suggest a beneficial effect on carcass merit when rearing hogs in outdoor facilities, they further suggest potential benefits to carcass grading using developing technologies that recognize differences in carcass conformation. Key words: Animal ethics, Landrace, carcass value, housing systems

A total of 60 female and 54 castrated male progeny of commercial Landrace × Large White F1 sows, backcrossed to Landrace or Large White boars, were slaughtered at an average liveweight of 102 kg. Four same-sex pigs were penned together. Large White sires were homozygous normal (NN) but Landrace sires were heterozygous carriers (Nn), at the halothane locus. Progeny genotypes at the halothane locus were determined by a DNA probe. Barrows grew 136 g d−1 faster (P < 0.0001), reaching market weight 13 d sooner (P < 0.0001) but with 3.2 mm more average back-fat (P < 0.0001) than gilts. Both sexes had similar feed requirements (P = 0.1221). Landrace and Large White-sired pigs had similar growth rate (P = 0.6458) and feed requirements (P = 0.9354), but Large White-sired pigs had 1.33 mm less grade fat thickness (P = 0.0131) and 1.72 more muscle depth (P = 0.0218) than Landrace-sired pigs. Nn pigs required 7 d longer (P < 0.0001) and 22 kg (P = 0.0393) more total feed to reach market weight than NN pigs, but they had 2.6 mm greater muscle depth (P = 0.0008) and had 1% greater commercial lean yield (P = 0.0291). However, meat quality of Nn pigs was reduced when compared with NN pigs. For example, colour reflectance and drip loss were higher (P < 0.0001) and soluble protein was lower (P < 0.0001) among the Nn pigs which also had less intrasmuscular fat (P = 0.0184). The results emphasize that the increased value of the carcass from Nn pigs may be offset by reduced feedlot performance and reduced meat quality, and questions the merit of the use of halothane gene to improve production efficiency in the commercial market. Key words: Swine production, halothane gene, breed effect, Landrace, Large White

Average backfat thickness measurements (liveweight of 92.5 kg) were made on 276 pigs using the Krautkramer USK7 ultrasonic machine. Immediately preceding and 1 h after slaughter real-time ultrasonic images were made between the 3rd and 4th last ribs with the Tokyo Keiki LS-1000 (n = 149) and/or CS-3000 (n = 240) machines. Image analysis software was used to measure fat thickness (FT), muscle depth (MD) and area (MA) as well as scoring the number of objects, object area and percentage object area of the loin to be used for predicting meat quality. Carcasses were also graded by the Hennessy Grading Probe (HGP). Prediction equations for lean in the primal cuts based on USK7 and LS-1000 animal fat measurements had R2-values (residual standard deviations, RSD) of 0.62 (27.0) and 0.66 (25.7). Adding MD or MA to LS-1000 FT measurements increased the R2-values to 0.68 and 0.66. Prediction equations using animal fat measurements made by the USK7 and CS-3000 had R2-values (RSD) of 0.66 (26.5) and 0.76 (22.4). Adding MD or MA to CS-3000 FT measurements made no further improvement in the R2-values. Estimation of commercial lean yield from carcass FT and MD measurements made by the HGP and LS-1000 had R2-values (RSD) of 0.58 (1.72) and 0.65 (1.56). Adding MA to LS-1000 measurements made no further improvement in the R2-values. Prediction equations based on carcass FT and MD measurements made by the HGPandCS-3000 had R2-values (RSD) of 0.68 (1.65) and 0.72 (1.54). Adding MA to CS-3000 measurements made no further improvement in the prediction equation. It was concluded that RTU has most value for predicting carcass lean content and further improvements in precision will come from more accurate FT measurements from RTU images made by image analysis software. Correlation of the number of objects, object area and of percent object area of image from RTU images with intramuscular fat or marbling score made on the live pig or carcass were low, and presently do not appear suitable for predicting intramuscular fat. Key words: Carcass composition, meat quality, marbling, intramuscular fat, sex, pigs

This paper reports on an image segmentation system primarily developed for detecting loins in ultrasonic images of live pigs. The images have a low contrast, high level of noise, and a high degree of variance in terms of texture and shape. Our segmentation algorithm starts with a region growing process, which provides a rough approximation of the loin region. Morphological operations and curve fitting eliminate unwanted noise. Finally, an active contour process refines the shape of the resulting region. This method does not rely on specific a priori information of the texture or the contrast. The system is based on the principle of modular design, so that different region growing and refinement algorithms can be easily substituted into the current design as modules. Therefore, the system is general enough to be adapted to other segmentation tasks involving low contrast images

A portable fat hardness meter (FHM) was used to measure the firmness of the inner fat layer on a cross sectional surface over the second thoracic vertebra of pork carcasses. This was a 4-yr study with data collected on 141 barrows, 214 gilts and 270 boars. A statistical model, after adjusting for year and breed of sire (i.e., Lacombe, Landrace, Yorkshire), included sex, linear and quadratic covariates for carcass growth rate (i.e., carcass weight per day of age), a linear covariate for leanness (i.e., carcass fat thickness or dissectible lean) within sex, and a linear by linear covariate of growth rate by leanness, and was used to describe a response surface with fat hardness. No pigs in this study had extremely soft fat (i.e., FHM < 420). However, 4, 2 and 0% of the boars, gilts and barrows had very soft fat (i.e., FHM 420–619). While 10% of the barrows had extremely hard (i.e., FHM > 970) or very hard fat (i.e., FHM 930–970), only 1% of the gilts had very hard fat, and no boars were included in these classes. Relative to the FHM readings of gilts (i.e., 805 ± 6.2), boars (i.e., 780 ± 5.6) had softer fat (P = 0.0002) while barrows (i.e., 835 ± 7.4) had harder fat (P = 0.0001). The majority of boars had slightly soft fat (i.e., FHM 750–829) while gilts and barrows had slightly hard (i.e., FHM 830–889) fat. Regression coefficients for growth rate on fat hardness were homogeneous among the sexes. As growth rate increased fat hardness increased, but was attenuated by a negative quadratic term. Increased leanness was linearly antagonistically related with fat hardness. There were differential effects across sexes (P = 0.0261). As leanness increased, fat became softer among boars and gilts compared with barrows. A linear by linear interaction of growth rate with leanness attenuated this effect. Holding growth rate constant, a 25% reduction of carcass fatness would be expected to reduce fat hardness by 40, 35 and 20 points in boars, gilts, and barrows, respectively. While selection for increased lean growth may result in some degradation in fat quality, the trend towards marketing heavy pigs as they become leaner should be sufficient to offset this effect. Key words: Swine, carcass, grading, growth rate, fat, lean

The effect of antemortem handling on behaviour, carcass yield and lean meat quality was determined on Lacombe and Yorkshire entire male pigs mixed within breed 24 h prior to slaughter and on entire males and gilts that were not mixed. In the period immediately after repenning (mixing), 40% of all recorded pen activity was observed, while 17% and 10% of the pen activities were recorded at 6 and 12 h after repenning. During the period immediately after transport to the abattoir, 33% of all pen activities were observed. Mixed pigs accounted for 78% of all activity. Yorkshire male pigs were three times as active as Lacombe male pigs during shipping. Thirty-six percent and 14% of the mixed Yorkshire and Lacombe male pigs had moderate skin blemishes, compared with 12% for unmixed Yorkshire male pigs. Moderate skin blemishes were absent in the unmixed Lacombe male and all female pigs. Dressing percentage and carcass shrinkage were unaffected by mixing during shipping. Dressing percentage was 23 g kg−1 higher in female than in male pigs, while male pigs had 20 g kg−1 greater lean than female pigs. Ultimate pH (48 h) was similar among unmixed pigs (5.53), but higher in mixed Lacombe (5.61) and Yorkshire (5.74) entire male pigs. Based on subjective meat quality evaluation, firm and dry pork was observed in 11% and 43% of the mixed Lacombe and Yorkshire male pigs, but was absent in unmixed male pigs. However, no consistent objective meat quality differences between unmixed male and female pigs were observed. Unmixed entire male pigs had superior carcass composition characteristics, with lean meat quality attributes at least equivalent to those of female pigs (e. g. pH, drip loss, CIE L*, hue angle). Mixing entire male pigs prior to slaughter had marginal but significant effects on carcass blemish scores and meat quality, particularly among Yorkshire pigs. This study suggests entire males, with appropriate antemortem handling, can produce superior carcasses, more efficiently and with pork quality at least equivalent to that of female pigs. Key words: Swine, behaviour, mixing, entire males, carcass yield, meat quality

The present study was initiated to investigate the effect of oral potassium (600 mg, slow release, 24 h preslaughter), intramuscular (IM) magnesium (500 mg MgSO4, 2 h preslaughter) or slow release magnesium (Magnesium-aspartate-hydrochloride (Mg Asp) 20 or 40 (g d−1 for 5 d) on animal physiology and pork quality. Experiments were undertaken on 318 barrows and gilts (100 kg ± 5 kg) represented by three genotypes segregating at the halothane locus (nn, Nn and NN genotypes). Experiment 1 indicated that the oral potassium effectively (P ≤ 0.05) reduced pCO2 values in the nn genotype. Intramuscular injectable magnesium treatments were also found to raise plasma magnesium (P < 0.05) but did not alter muscle, liver or heart tissue levels. Both oral potassium and i.m. magnesium exacerbated subjective pork structure and texture scores but were found to increase muscle brightness and hue (higher b* value). In exp. 2, oral magnesium-aspartate (Mg Asp) was found to raise plasma, but not tissue, levels of magnesium. When fed to a group of halothane carrier pigs (Nn genotype), Mg Asp reduced muscle temperature 45 min post-stunning, increased muscle redness (CIE a* value) and reduced muscle drip loss (P < 0.06). It was concluded that oral potassium and i.m. magnesium as administered in the present study had no beneficial effects on pork quality but that the beneficial effects of Mg Asp on meat colour and drip loss may warrant further investigation. Key words: Magnesium, potassium, preslaughter, pork quality, PSE pork

Fresh sperm motility declined from 79·2 (s.e. 0·9)% to 55·8 (s.e. 1·7)% while occurrence of normal acrosomes declined from 82·9 (s.e. 1·3)% to 71·3 (s.e. 1·2) % from the day of collection to 7 days after collection, and conception rate declined from 47·6% using 3-day-old semen to less than 30% from using 5· or 7-day-old semen. Neither the number of embryos nor embryo survival from pregnant sows were affected by the age of semen. Boar effects were evident but they did not interact with the effects of age of semen, indicating that semen quality after storage was proportional to initial semen quality.

ABSTRACTA total of 805 Lacombe pigs of different genotype with respect to halothane sensitivity (halothane positive, nn = 205; heterozygote, Nn = 214; halothane negative, NN = 386) were slaughtered over a range in live weight (70 to 120 kg) to assess tissue growth patterns using the allometric equation (y = aXh). The nn genotype was older at slaughter than the NN genotype, but pigs from each genotype were killed over a similar weight range. The relative growth of the primal cuts was influenced by genotype, with nn pigs having a lower coefficient for the bottom shoulder (picnic) and a higher coefficient for the belly. The relative growth of bone was similar for genotypes (P > 0·05) but the relative growth of lean was lower and the relative growth of total fat and depot fat (subcutaneous and intermuscular) was higher for the nn genotype compared with the Nn and NN genotypes. On a within-tissue basis, the relative growth of the tissues in each primal was similar, except for the ham, where the relative growth of lean was higher for nn pigs compared with the two other genotypes. Small differences in tissue distribution were evident, but seldom exceeded 30 g/kg. Although nn pigs had a higher lean content and higher lean: bone ratio than Nn or NN pigs at similar live weights, their relative advantage in composition decreased with increasing live weight.

The objective of the present study was to examine gestational diabetogenic effects in lean gilts and the influence that dietary protein may have on glucose tolerance, reproductive performance, maternal insulin and progesterone levels. Twenty-six Lacombe gilts (14 control, 12 treated) and 229 neonate offspring were examined. During gestation all gilts received a 13% crude protein balanced diet on the basis of body weight. The treated animals received the same diet plus an additional 1.3 g kg−1 body weight d−1 of casein starting on day 1 postcoitus. No differences in litter size or birth weight between treatments were observed. However, the proportion of mummified or still-birth fetuses, while within a normal range, tended to be higher (P < 0.10) in control (1.64 ± 0.43 per litter) than in treated pigs (0.58 ± 0.46). In addition, the muscle protein concentration in the neonatal offspring of treated gilts (91.3 ± 0.35 mg g−1) tended to be higher (P = 0.15) than that seen in the control animals (88.7 ± 0.34 mg g−1). All pregnant gilts, irrespective of treatment, displayed a degree of diabetogenesis two weeks prepartum (P ≤ 0.05). However, no differences in blood insulin or progesterone levels were observed between treatments. The data suggest that protein supplementation to the dam may slightly retard gestational onset diabetogenic effects but has only moderate effects on fetal outcome. Key words: Diabetogenesis, lean gilts, dietary protein

Carcasses, with an average weight of 80.8 kg, from 130 Lacombe and 96 Yorkshire pigs were probed for fat and muscle depth at the carcass grade site using the Hennessy Grading Probe (HGP). Similar data were collected by the Aloka SSD-210DXII Echo Camera (AEC) at the carcass grade site and at the Canadian Swine Improvement Program loin and mid-back sites. Muscle-width and muscle-area measurements were also made with the AEC. The R2 (residual standard deviation: RSD), using the HGP, for prediction of carcass lean yield at the grade site using fat and muscle depth was 0.58 (16.4). When fat and muscle depth were measured by the AEC, the R2 (RSD) at the mid-back, loin and grade sites to predict carcass lean yield was 0.41 (19.7), 0.47 (18.5), and 0.53 (17.5), respectively. When the AEC muscle-depth measurements were replaced with muscle-area measurements, the R2 increased (RSD decreased) at the mid-back, loin and grade sites to predict carcass lean yield (0.60 (16.0), 0.64 (15.2), and 0.59 (16.4), respectively). Real-time ultrasound (AEC) provides precision for the prediction of carcass lean content similar to that of the electronic grade probe (HGP). However, combining fat- and muscle-depth measurements made by the HGP with muscle-area measurements made by the AEC at the loin increased the R2 from 58 to 66% for the prediction of carcass lean yield. The suitability of the use of real-time ultrasound as an alternative to electronic grading probes, at this time, appears to be limited. Key words: Swine, real-time ultrasound, carcass grading

Production and meat quality traits were evaluated on 74 commercially raised heterozygous pigs (Nn) and 50 homozygous normal pigs (NN) at the halothane locus, with an average carcass weight of 79.7 kg. Eight-week weight, average daily gain and age to market, as well as measures of carcass quality (i.e., dressing percent, grade site fat and muscle depths and predicted lean yield) did not differ among pigs with Nn and NN genotypes. The longissimus dorsi muscle from Nn and NN pigs had similar subjective colour and structure scores. Reflectance meter readings (CIE L*-values) were significantly higher on chops from Nn than from NN pigs taken from the centre (57.4 vs. 55.6) and from the anterior portion (56.2 vs. 54.5) of the loin. Drip loss among Nn pigs was higher than among NN pigs for chops taken from the centre (4.8 vs. 3.8 g 100 g−1) and from the anterior portion (3.7 vs. 2.9 g 100 g−1) of the loin (P < 0.01). Soluble protein was 1.7% lower (P < 0.001) in Nn pigs compared with the NN pigs. Barrows attained market weight earlier (P < 0.05) than gilts, but they had a lower dressing percentage (P < 0.05) and greater grade fat depth (P < 0.001) and had 1.2% less predicted lean yield of carcass (P < 0.001) than gilts. Since meat quality declined without concomitant increases in growth rate or improvements in carcass quality, it was concluded that the intentional use of the halothane gene should be discouraged. Key words: Swine, production, carcass quality, meat quality, halothane gene

Data on 42 halothane-sensitive pigs (HSL, nn-genotype), 169 Lacombe pigs (LAC, NN-genotype), 41 crossbred pigs (XBD, Nn-genotype), and 72 Yorkshire pigs (YRK, NN-genotype) representing 145 gilts and 179 castrates, were obtained over the liveweight range from 74.0 to 134.5 kg (average 105 kg) to examine the effect of genotype, gender and slaughter weight on the composition of the four lean cuts (ham, loin, picnic and butt). Gilts had a greater proportion of dissectible lean from lean cuts than castrates (557 ± 2.8 vs. 525 ± 2.6 g kg−1). The HSL pigs had the highest and LAC pigs the lowest commercial dressing percentage, increasing respectively from 85.3 to 86.0% and 79.7 kg to 82.6% as slaughter weight increased from 80 to 130 kg. Corresponding figures for XBD and YRK pigs, were 82.5 to 85.4 and 80.6 to 84.6%, respectively. Dissectible lean from lean cuts from 65-kg carcasses was 606, 525, 536 and 575 g kg−1 for HSL, XBD, LAC and YRK pigs, respectively. Corresponding figures for 85-kg and 105-kg carcasses were 574, 525, 515, and 555 g kg−1 and 542, 525, 494, and 535 g kg−1, respectively from HSL, XBD, LAC and YRK pigs. LAC and YRK pigs, each with exclusively NN-genotypes but differing in composition of lean cuts, maintained their relative differences in composition over the weight range studied. Heterogeneity of slopes for changes in proportion of lean in the lean cuts with increasing weight among the HSL, XBD and LAC pigs implied a genotype × weight interaction that could best by explained by an apparent increase in the dominance of the halothane gene with increasing carcass weight. Key words: Swine, carcass composition, halothane gene, weight, Lacombe, Yorkshire

A total of 80 pigs, representing Large White and Landrace boars and gilts were slaughtered at an average live weight of 92.3 kg (80.5 – 102.5 kg). Boars were housed in groups of five pigs per pen, and were individually fed to appetite twice daily for a period of 45 min. Gilts were housed in groups of 12 pigs per pen. The diet consisted of 21% crude protein with 3300 kcal kg−1 digestible energy. Carcasses were weighed on the slaughter floor and cooled at 1 °C for 24 h prior to dissection of the left side into fat, bone and lean. There were no significant breed-by-gender interactions for growth, carcass and meat quality traits. These pigs had low average backfat, when measured ultrasonically according to Canadian Swine Improvement Program standards on the live pig (gilts 12.3 mm, boars 10.1 mm), high average daily gain (ADG: gilts 880, boars 940 g d−1) and low age adjusted to 90 kg (gilts 148, boars 145 d). Large White boars had a lower feed conversion ratio (2.18 vs. 2.32, P = 0.015) and less feed intake per day (2.05 vs. 2.14 kg d−1P = 0.020) than did Landrace boars. There were no significant differences in dissected lean yield between breeds (P = 0.389) or genders (P = 0.148). However, gilts had greater carcass grade fat and greater lean depth measurements than did boars, such that both genders had a predicted lean yield of 51.8%. Gilts (40.8 cm2) had a larger (P < 0.001) longissimus dorsi area than boars (38.0 cm2). There were no breed effects on the lean content of the four major cuts (P = 0.20), but boars had less fat (P = 0.01) and more bone than gilts (P < 0.01). There were few consistent differences in subjective or objective meat quality traits (i.e. color, drip loss) among breeds or genders. Boars had muscle with greater moisture than gilts (P < 0.001) as well as softer fat (P = 0.016). Thus, it appears possible to produce pork of high quality from lean animals and that lean boars efficiently produce carcasses of equivalent yield and quality to carcasses produced by lean gilts. Key words: Swine, boar, carcass composition, meat quality, Landrace, Large White