Exploring the Effects of Slaughter Weight Class on Belly Quality Attributes of Gilts and Barrows

Justice Bless Dorleku; Tawanda Tayengwa; Benjamin M. Bohrer; Marcio Duarte; Philip Soladoye; Manuel Juarez; Justice B. Dorleku; Tawanda Tayengwa; Benjamin M. Bohrer; Marcio S. Duarte; Philip O. Soladoye; Manuel Juárez

doi:10.22175/mmb.20126

Introduction

Slaughter weight (SW), a key economic factor in modern pig production, is significantly influenced by pig growth and feed efficiency. It determines both the quantity and quality of pork, thereby affecting overall profitability (Kim et al., 2005; Park and Lee, 2011; Wu et al., 2017). In recent decades, there has been a consistent increase in pig SW in North America, driven in part by genetic improvements, nutritional advancements, and enhanced management practices, but also by efficiency advantages associated with heavier SW observed by the packing industry. In North America, commercial pig SW has increased by 10% to 27% since 2000. Specifically, in the United States, the average SW rose from 119 to 131 kg (a 10% increase), while in Canada it increased from 109 to 138 kg (a 27% increase) (US Department of Agriculture, Economic Research Service, 2025; Agriculture and Agri-Food Canada, 2025).

This increase in SW has contributed not only to heavier carcasses but also to enhanced economic returns from high-value primal cuts, especially the pork belly. Furthermore, the increase also affects pork quality traits, partly due to changes in chilling rates, which differ between gilts and barrows. Currently, the pork belly ranks as the most valuable primal cut on the carcass (US Department of Agriculture, Agricultural Marketing Service, 2025). The rise in pork belly value is largely attributed to increased consumer demand for bacon (Soladoye et al., 2015). However, concerns have emerged regarding the potential impact of heavier carcasses on pork belly quality, including firmness, fat content, and processing suitability. For instance, heavier bellies typically have higher fat content, which can influence both quality and processing. Krause et al. (2018) and Hoa et al. (2021) indicate that higher fat and heavier pork bellies tend to exhibit improved technological and eating quality traits. Heavier carcasses generally enhance attributes such as belly thickness, firmness, and fat content, which are beneficial for processing. However, the associated increase in fat deposition may lead to greater trimmed losses and negatively impact consumer perception and acceptance of bacon appearance. A study found that there is an improvement in belly thickness and firmness as hot carcass weight (HCW) increases, enhancing their suitability for bacon production (Harsh et al., 2017a). Likewise, other studies have also shown that increasing SW can lead to higher curing yields for bellies, making them more economically favorable (Cisneros et al., 1996; Wu et al., 2017).

Several studies have identified factors that influence both fresh and processed pork belly quality. These include breed, sex, growth promoters, age, SW, and processing traits such as belly thickness, length, width, fat-to-lean ratio, and firmness (Soladoye et al., 2015). Harsh et al. (2017a) quantified that HCW explains a significant proportion of variation in belly thickness (37.81%), subjective flop score (20.35%), and iodine value (IV; 10.35%). In terms of belly composition, Albano-Gaglio et al. (2024) reported substantial variation in belly fat content within the Spanish market yet noted that the overall fatness remained proportionate despite anatomical differences. Nonetheless, findings from recent studies are inconsistent regarding the effects of SW and sex on belly composition. A large-scale Chinese study involving approximately 2000 pigs found that carcass weight, sex, and breed influence belly cut proportions (Xie et al., 2023). This finding contrasts with Bohrer et al. (2023), who observed no significant differences in belly weights or cut percentages between barrows and gilts from a sample of 343 pigs.

Due to these conflicting findings and the limited number of studies examining a comprehensive range of pork belly traits across a large population, further research is necessary. Thus, this study aimed to investigate how SW class (SWC) impacts various quality attributes of pork belly in both barrows and gilts, utilizing a large representative sample. To provide context for the biological and compositional shifts influencing belly quality, the effects of key carcass traits, such as lean meat yield, total lean, total fat, and intramuscular fat (IMF), were also examined.

Materials and Methods

All experimental procedures were approved by the Agriculture and Agri-Food Canada Lacombe Research and Development Centre’s (AAFC-LRDC; AB, Canada) Animal Care Committee (AUP#201807). Pigs were cared for following commercial practices, as outlined under the guidelines established by the Canadian Council on Animal Care (2009).

Animal background

A total of 2110 commercial pigs (n = 2110; 1055 barrows and 1055 gilts; large white × Landrace sows bred to Duroc boars; Genesus Genetic Technology, MB, Canada) were used in this study. All pigs were managed under the same commercial feeding program, receiving identical diet formulations adjusted according to standard phase feeding protocols. The pigs remained on feed for similar durations relative to their weight class and target SW to ensure consistency in growth and nutritional exposure across groups. All experimental procedures were conducted at the AAFC-LRDC swine unit (Lacombe, AB). Pigs were fed ad libitum and selected for slaughter weekly based on 2 preset SW (115 or 128 kg).

Slaughtering conditions

When the animals were due for slaughter, pigs were transported to the AAFC-LRDC federally inspected abattoir (1.6 km away from the swine unit). All pigs were slaughtered at 2 targeted different SW (weight 1: 114.7 kg; weight 2: 128.1 kg) on 75 different days over 4 y, covering all seasons (Spring, Summer, Fall, and Winter) under the supervision of the Canadian Food Inspection Agency. Prior to slaughter, pigs were fasted for 12 h with continuous access to water to reduce gut fill and ensure standard processing conditions. Pigs were weighed before being stunned using a head-to-heart electrical stunner (2.1 A for 5 s), followed immediately by exsanguination, scalding, singeing, and pasteurization under standard commercial conditions. Individual carcasses were numbered, sex (barrow or gilt) identified, eviscerated, and HCW was recorded before splitting. Afterward, the muscle and fat depths of the loin were measured between the 3rd and 4th last ribs, 7 cm off the midline, to obtain the predicted lean meat yield (PLMY), using a Viewtrak PG-309 (Viewtrak Technologies Inc., Markham, ON, Canada). The grading probe measures fat and muscle depths and then uses a prediction equation, as outlined below, to estimate lean meat yield:

PLMY (%) = 68.1863 − 0.7833 f + 0.0689 m + 0.0080 f 2 − 0.0002 m 2 + 0.0006 fm

After grading, carcasses were washed and kept in a conventional chiller for 22 to 24 h at 2°C ambient temperature with wind speeds of 0.5 m/s.

Carcass fabrication and carcass traits

After chilling, the left sides of the carcasses were fabricated into primal cuts: whole loin (Institutional Meat Purpose Specification [IMPS] #410; skin-on, untrimmed, bone-in), Boston butt (IMPS #406; skin-on, semiboneless), shoulder picnic (IMPS #405; skin-on, semiboneless), whole belly (IMPS #408B; skin-on, untrimmed, bone-in), and whole ham (IMPS #401A; untrimmed, bone-in) according to the IMPS (US Department of Agriculture, 2014) for pork. Pork bellies were prepared based on descriptions by Uttaro and Zawadski (2010) and Uttaro et al. (2024). The anterior portion of the bellies was separated from the shoulder between the 2nd and 3rd ribs with a fairly straight cut perpendicular to the longitudinal axis of the carcass side, and the posterior ends were separated from the leg with a cut placed about 5 cm cranially to the aitch bone with the ventral end of the cut angled cranially at approximately 65° to the longitudinal axis of the back (i.e., perpendicular to the longest axis of the back leg). The loin was removed along a line running from just ventral to the thoracic vertebra at the anterior end, to immediately ventral to the psoas major at the posterior end. All bones and cartilages remained at this point. Immediately following fabrication, each primal cut was weighed and analyzed using dual-energy X-ray absorptiometry (DEXA; encore 2011, version 13.60.033, GE Lunar, General Electric, Madison, WI, USA) to estimate lean and fat tissues (Soladoye et al., 2016). The total lean and fat content of the carcass was calculated as the sum of the lean and fat tissues from all the individual primal cuts. For IMF content, a 2.5-cm thick boneless pork chop taken from the center of the loin was finely comminuted and analyzed using the Smart Trac Fat Analyzer Model 907,955 (CEM Corporation, Matthews, NC, USA). A 5-g sample of backfat from the shoulder was sampled from each carcass and stored at −80°C until further fatty acid analyses following the protocol described previously (Turner et al., 2014), and the IV was then calculated through the equation described by the American Oil Chemists’ Society (American Oil Chemists’ Society, 1998):

IV = [16 : 1] × 0.95 + [18 : 1] × 0.86 + [18 : 2] × 1.732 + [18 : 3] × 2.616 + [20 : 1] × 0.785 + [22 : 1] × 0.723,

where square brackets indicate the proportion of a particular fatty acid (% of total fatty acid).

Belly quality traits

Following the completion of DEXA scans, bellies were handled carefully to avoid flexing them before their assessments in a cooler set at a temperature of 2 to 4°C. An experienced assessor used a ruler to record measurements at the specified sites on the belly (Figure 1), following the procedure outlined by Uttaro and Zawadski (2010). The side lean was measured by drawing a perpendicular line to the skin at the thickest point of the latissimus dorsi, which represents the leanest area of the belly. Belly side fat, including subcutaneous and intermuscular fat as well as cutaneous trunci (CuTr1) if present, was recorded at the anterior end where the side lean was measured. The thickness of the side subcutaneous fat was measured above the cutaneous trunci at the midpoint location (CuTr2) to the skin. For belly side thickness, a perpendicular axis was drawn to the skin through the 1st rib at or beyond the caudal end of the latissimus dorsi. Along this line, the side thickness was measured from below the rib to the skin, including the cutaneous trunci (CuTr2) if present. The side seam, representing the thickness of the intermuscular fat, was calculated as the difference between the side thickness and the side subcutaneous. With the belly laid flat and skin-side down, the length was measured from the anterior end to the posterior end using a measuring tape. The belly width was measured at the belly bend site on the skin side, from the last exposed rib to the caudal edge of the belly. Regarding the belly bend angle (°), the procedure described by Uttaro et al. (2024) was followed using the objective Belly Bender Version 2 (BB.V2) with the bending point for measurements standardized at 24 cm.

Figure 1.

Measurement locations along the pork belly as per Uttaro et al. (2020). CuTr1, cutaneous trunci thickness at the anterior end; CuTr2, cutaneous trunci thickness at the midpoint.

Statistical analysis

To ensure a balanced dataset by sex while minimizing bias due to liveweight, animals (n = 2308; 1055 females and 1253 males) were initially divided into 2 liveweight classes (weight 1 and weight 2) using the median liveweight (121.5 kg) as the threshold. The number of females within each category was determined using PROC SQL, and an equal number of males were randomly selected within each weight category using PROC SURVEYSELECT with stratified simple random sampling. The selected males were combined with all females using a DATA step to generate a final dataset of 1055 males and 1055 females with equal representation across weight groups. The final distribution by sex and weight group was confirmed using PROC FREQ.

Data were analyzed using the PROC MIXED procedure in SAS 9.4 (SAS Institute Inc., Cary, NC) with SW, sex, and their interaction included as fixed effects, and the slaughter date treated as a random effect. The individual pig was considered the experimental unit. Prior to analysis, data distribution was assessed using PROC UNIVARIATE to confirm normality. After model fitting, residuals were evaluated to ensure that the assumptions of normality and homoscedasticity were met. Potential outliers were examined using studentized residuals (> |3|) and removed only when biologically implausible. Least-squares means were compared using the LSMEANS statement with Tukey–Kramer adjustment to control for type I error. A mixed model analysis of variance was selected because SW was treated as a categorical factor based on practical, industry-relevant thresholds, and the goal was to compare group means rather than model a continuous trend. Statistical significance was consistently declared at P < .05.

Results and Discussion

Table 1 summarizes carcass and belly quality traits. While the focus is on belly quality, carcass traits were included to clarify interrelationships. This approach follows Uttaro and Zawadski (2010), who identified noninvasive sites predictive of belly fatness. As expected, the majority of the carcass and belly traits were consistent and uniform across the population, but some traits showed greater variability than others. This minimal variation observed in the study was primarily due to the controlled experimental design, where pigs of the same genotype were raised in the same environment and fed a similar diet throughout their growth phases. In support, Arkfeld et al. (2017) reported that genetic and management uniformity significantly reduces variability in carcass traits. The PLMY was consistent, while total lean and total fat percentages showed moderate variability, with total fat percentage being more variable than total lean percentage. This reflects the higher sensitivity of fat deposition to environmental and genetic factors (Arkfeld et al., 2017). For carcass traits, only total fat and IMF exhibited more than 10% variations. In similar larger population studies, more than 25% of variations were recorded for fat depth and marbling score (Arkfeld et al., 2016; Arkfeld et al., 2017), which are components of fat tissue. The higher IMF variability may reflect wide variation in marbling within the population. This aligns with the findings of Lo Fiego et al. (2010), where IMF content and composition varied significantly with age and other biological factors, even when overall fat content remained stable. However, the current study did not report the influence of age on carcass traits. Unlike the IMF, IV, which indicates fat unsaturation, remained consistent in terms of variability, with the range aligning with a previous report (Prieto et al., 2018).

Table 1.

Summary statistics for pork carcass and belly quality traits

Traits	N	Mean	SD	CV	Minimum	Maximum
Carcass traits
Slaughter wt, kg	2110	121.52	8.33	6.86	95.00	146.50
Hot carcass wt, kg	2110	100.82	7.24	7.18	79.14	121.96
PLMY,¹ %	2107	59.47	1.79	3.01	54.20	65.73
Total lean,² %	1688	58.37	3.49	5.98	45.78	71.06
Total fat,² %	1688	31.97	3.71	11.60	19.13	46.22
IMF, %	1903	3.63	1.22	27.71	1.81	9.99
IV³	2106	59.51	2.71	4.56	51.99	70.72
Belly traits
Belly wt, kg	2108	18.61	1.17	6.30	15.36	31.15
Belly lean,² %	1688	66.18	3.98	6.01	52.78	80.88
Belly fat,² %	1688	33.14	4.01	12.09	18.28	46.57
Length, cm	2108	68.81	2.58	3.75	34.50	78.00
Width, cm	2059	24.89	1.64	6.58	18.50	31.00
Side lean, cm	903	2.20	0.24	11.10	1.42	3.08
Side fat, cm	2110	2.62	0.46	17.67	1.20	4.80
Side thickness, cm	903	3.75	0.60	16.08	2.01	5.87
Side seam, cm	903	2.13	0.58	27.45	0.40	4.51
Side subcutaneous, cm	2110	1.39	0.24	17.05	0.50	2.50
Belly bend angle,⁴ °	1655	146.12	19.96	13.66	70.67	180.00

AOCS, American Oil Chemists’ Society; BB.V2, Belly Bender Version 2; CV, coefficient of variation; DEXA, dual-energy X-ray absorptiometry; IMF, intramuscular fat; IV, iodine value; PLMY, predicted lean meat yield; SD, standard deviation.
PLMY was determined using a Viewtrak PG-309.
The total lean, total fat, belly lean, and belly fat percentages were measured using DEXA (encore 2011, version 13.60.033, GE Lunar, General Electric, Madison, WI, USA).
IV AOCS = [16:1] × 0.95 + [18:1] × 0.86 + [18:2] × 1.732 + [18:3] × 2.616 + [20:1] × 0.785 + [22:1] × 0.723 (AOCS, 1998).
Belly bend angle was measured using the objective BB.V2 (Uttaro et al., 2024).

Belly traits, including weight, lean, and dimensions like length and width, were quite uniform, which was reflected in their coefficient of variation (CV; <7%). The uniformity is consistent with findings from Knecht et al. (2018), which emphasized the importance of measurement location in evaluating belly quality. However, like carcass fat traits, belly fat traits (i.e., belly fat and side: fat, thickness, seam, and cutaneous) were more variable (CV > 12%) than belly lean. The belly bend angle was measured using the BB.V2 device (Uttaro et al., 2024), a rapid and portable tool suitable for large-scale evaluations. The belly bend angle, an indicator of belly firmness, had a mean of 146.1°. A similar average angle of 149.4° for nonflattened bellies at time 0, with a manual conveyor angle matching the present study, was reported by Uttaro et al. (2020). However, the moving speed in the latter study was 6.8 cm/sec compared to 4 s in the current study.

Slaughter weight class and sex interactions on key carcass and belly traits

There were significant interaction effects between SWC and sex for most carcass traits (P < .05; Table 2), except PLMY and IV. SW was higher in weight 2 for both sexes (P = .04). HCW also increased with SWC, with gilts being slightly heavier than barrows at the same SWC (P = .03), indicating that heavier pigs produce heavier carcasses. The findings contrast with Bohrer et al. (2023), who reported no significant sex × HCW quartile interactions for HCW, and with Oh et al. (2022), who also found no significant interaction between SWC and sex for SW and HCW. This discrepancy may be due to our larger sample size (n = 2110) and different selection criteria. However, the nonsignificant interaction result for PLMY in the present study was aligned with the findings of Bohrer et al. (2023). The total lean percentage was greater in gilts compared to barrows and decreased as weight increased (P = .04), suggesting that gilts are leaner and that total lean percentage decreases with heavier pigs. Conversely, the total fat percentage was greatest in weight 2 barrows (34.2%) and lowest in weight 1 gilts (29.7%; P = .04). Similarly, the IMF was greatest in both weight 1 and weight 2 barrows (4.1%) and lowest in weight 1 gilts (3.6%; P = .04). These results are not consistent with Bohrer et al. (2023) and Oh et al. (2022), who reported no significant interaction between sex and SW for overall carcass composition and IMF. The reason is likely due to various factors, including diet and genetics.

Table 2.

Interactive effects of slaughter weight class and sex on pork carcass and belly characteristics¹

	Barrows		Gilts		SEM²	P Value
	Weight 1	Weight 2	Weight 1	Weight 2	SEM²	P Value
Carcass traits
Slaughter wt, kg	114.76^b	128.23^a	115.30^b	127.97^a	0.39	.04
Hot carcass wt, kg	95.02^c	106.42^a	95.80^b	106.44^a	0.35	.03
PLMY,³ %	59.07	58.64	60.37	59.70	0.10	.09
Total lean,⁴ %	57.43^c	56.33^d	60.44^a	58.74^b	0.21	.04
Total fat,⁴ %	32.86^b	34.23^a	29.65^d	31.67^c	0.22	.04
IMF, %	4.10^a	4.11^a	3.55^c	3.78^b	0.08	.04
IV⁵	59.27	58.30	60.69	59.64	0.16	.74
Belly traits
Belly wt, kg	18.59	18.83	18.40	18.72	0.07	.44
Belly lean,⁴ %	65.49^c	64.52^d	67.88^a	66.05^b	0.27	.01
Belly fat,⁴ %	33.83^b	34.83^a	31.39^d	33.26^c	0.27	.01
Length, cm	67.61^c	69.74^a	68.18^b	69.85^a	0.14	.02
Width, cm	23.91	24.92	24.81	25.93	0.08	.40
Side lean, cm	2.13^b	2.20^a	2.23^a	2.22^a	0.03	.03
Side fat, cm	2.60	2.88	2.35	2.65	0.02	.56
Side thickness, cm	3.94	4.27	3.48	3.80	0.07	.99
Side seam, cm	2.29	2.53	1.92	2.14	0.07	.84
Side subcutaneous, cm	1.38	1.53	1.25	1.37	0.01	.06
Belly bend angle,⁶ °	143.76	152.25	140.81	146.36	1.79	.10

AOCS, American Oil Chemists’ Society; BB.V2, Belly Bender Version 2; DEXA, dual-energy X-ray absorptiometry; IMF, intramuscular fat; IV, iodine value; PLMY, predicted lean meat yield; SEM, standard error of mean; SWC, slaughter weight class.
Pigs were grouped into 2 SWC: weight 1 (114.7 kg) and weight 2 (128.1 kg).
Greatest SEM occurring between sexes was reported.
PLMY was determined using a Viewtrak PG-309.
The total lean, total fat, belly lean, and belly fat percentages were measured using DEXA (encore 2011, version 13.60.033, GE Lunar, General Electric, Madison, WI, USA).
IV AOCS = [16:1] × 0.95 + [18:1] × 0.86 + [18:2] × 1.732 + [18:3] × 2.616 + [20:1] × 0.785 + [22:1] × 0.723 (AOCS, 1998).
Belly bend angle was measured using the objective BB.V2 (Uttaro et al., 2024).
Means within a row with different superscripts significantly differed at P < .05.

For belly traits, no significant interactions were found between SWC and sex, except for belly lean percentage, fat percentage, length, and side lean (P > .05; Table 2). Specifically, the belly lean percentage was higher in gilts compared to barrows, and it decreased with increasing SWC (P = .01). This trend suggests that the advantage of gilts’ leanness diminishes at higher weights. In contrast, barrows had a higher belly fat percentage than gilts, which increased with SWC (P = .01). Previous studies did not find the SWC × sex interaction observed in this study for belly lean percentage (Bohrer et al., 2023) and belly fat percentage (Oh et al., 2022). However, the nonsignificant interaction observed between SWC and sex concerning belly weight is consistent with findings from the literature (Oh et al., 2022; Bohrer et al., 2023). This discrepancy may result from differences in population, diet, and genetic background. Belly length increased with weight and was slightly longer in gilts than barrows (P = .02). The side lean also increased slightly with weight, with gilts being marginally leaner than barrows (P = .03).

The effect of sex

Sex is known to influence pork carcass and belly traits, affecting both the quantitative and qualitative aspects of pork production. Prior studies have evaluated the effect of sex on pork carcass and selected belly traits (Correa et al., 2008; Overholt et al., 2016; Bohrer et al., 2023; Font-i-Furnols et al., 2023); however, no studies have assessed sex effects on pork belly dimensions. In the present study, all carcass and belly trait means were significantly different (P < .05) for barrows and gilts, except SW (Table 3). At the same SW, carcasses from gilts recorded approximately 1.2 U greater PLMY (P < .01) than carcasses from barrows, resulting in 2.9 and 0.4 U lesser (P < .01) total fat percentage and IMF, respectively. In line with Overholt et al. (2016), the tendency of gilts to have less total fat and IMF content than barrows is also associated with a greater proportion of unsaturated fatty acids in adipose tissue, which contributes to the 1.4 U greater IV (P < .01; Table 3) observed in gilt carcasses than barrows in the present study.

Table 3.

Effects of sex on pork carcass and belly characteristics

Traits	Sex		SEM¹	P Value
Traits	Barrows	Gilts	SEM¹	P Value
Carcass traits
Slaughter wt, kg	121.50	121.63	0.36	.49
Hot carcass wt, kg	100.72^a	101.12^a	0.33	.03
PLMY,² %	58.85^b	60.03^a	0.08	<.01
Total lean,³ %	56.88^b	59.59^a	0.18	<.01
Total fat,³ %	33.54^a	30.66^b	0.19	<.01
IMF, %	4.11^a	3.67^b	0.07	<.01
IV⁴	58.78^b	60.16^a	0.14	<.01
Belly traits
Belly wt, kg	18.71^a	18.56^b	0.06	.02
Belly lean,³ %	65.00^b	66.96^a	0.24	<.01
Belly fat,³ %	34.33^a	32.33^b	0.24	<.01
Length, cm	68.68^b	69.01^a	0.12	.01
Width, cm	24.42^b	25.37^a	0.07	<.01
Side lean, cm	2.17^b	2.22^a	0.02	.04
Side fat, cm	2.74^a	2.50^b	0.02	<.01
Side thickness, cm	4.10^a	3.64^b	0.06	<.01
Side seam, cm	2.41^a	2.03^b	0.05	<.01
Side subcutaneous, cm	1.46^a	1.31^b	0.01	<.01
Belly bend angle,⁵ °	148.00^a	143.58^b	1.59	<.01

AOCS, American Oil Chemists’ Society; BB.V2, Belly Bender Version 2; DEXA, dual-energy X-ray absorptiometry; IMF, intramuscular fat; IV, iodine value; PLMY, predicted lean meat yield; SEM, standard error of mean.
Greatest SEM occurring between sexes was reported.
PLMY was determined using a Viewtrak PG-309.
The total lean, total fat, belly lean, and belly fat percentages were measured using DEXA (encore 2011, version 13.60.033, GE Lunar, General Electric, Madison, WI, USA).
IV AOCS = [16:1] × 0.95 + [18:1] × 0.86 + [18:2] × 1.732 + [18:3] × 2.616 + [20:1] × 0.785 + [22:1] × 0.723 (AOCS, 1998).
Belly bend angle was measured using the objective BB.V2 (Uttaro et al., 2024).
Means within a row with different superscripts significantly differed at P < .05.

The current experiment evaluated the dimensional parameter differences in pork belly between barrows and gilts. Bellies of gilts were 0.15 kg lighter and 0.95 cm wider compared with barrows (P < .05; Table 3). For belly weight, Overholt et al. (2016) also reported a similar observation with bellies from barrows being heavier than gilts. Arkfeld et al. (2017) established a 4.1% variation in pork belly attributable to sex. Conversely, other researchers found no difference in belly weight between gilts and barrows (Bohrer et al., 2023; Font-i-Furnols et al., 2023), possibly due to the smaller sample size and genotype.

As earlier stated, to the best of our knowledge, no studies have evaluated sex differences in pork belly dimensional parameters, as reported in this paper. Barrows recorded greater belly dimensions (side fat, side thickness, side seam, and side subcutaneous) than gilts, except side lean (P < .05; Table 3). For side thickness, Overholt et al. (2016) calculated average belly depth (thickness) by taking the mean of measurements recorded at 25%, 50%, and 75% of the belly’s length from anterior to posterior. The authors noted that barrows were thicker than gilts, which agrees with our current study, where side thickness (measured from below the rib to the skin, including the cutaneous trunci [CuTr2] if present) was greater in barrows than in gilts. In contrast, when the average belly thickness was calculated with measurements from the center of the cranial, caudal, dorsal, and ventral sections, no difference was observed between sexes (Font-i-Furnols et al., 2023). Regarding belly firmness, various objective and subjective methods have been utilized in the literature for measurement (Overholt et al., 2016; Soladoye et al., 2017; Knecht et al., 2018; Uttaro et al., 2020; Albano-Gaglio et al., 2024). However, a new objective and standardized method for determining the firmness of intact pork bellies, as described by Uttaro et al. (2024), was employed. Belly bend angle was 4.42° units greater in barrows than gilts (P < .01; Table 3) in the current study. Soladoye et al. (2017) established a moderate to strong positive correlation between belly-flop angle and dimensional traits related to fat layers of the belly (side: fat, thickness, seam, and subcutaneous). Accordingly, higher total fat percentage, IMF, belly fat percentage, and side thickness observed in the present study for barrows confirmed the increased belly bend angle, which resulted in firmer bellies. In addition, the increased belly fat deposition and thickness in the barrows contributed to a higher belly angle, resulting in firmer bellies compared to gilts. Consequently, the increased softness (i.e., lower belly bend angle) in the gilts can be linked to higher leanness and less fat components in the belly, rather than to the sex itself (Correa et al., 2006; Correa et al., 2008).

The effect of slaughter weight class

Generally, all carcass and belly traits, except side lean, were significantly influenced by SWC (P < .05; Table 4). The PLMY was influenced by SWC, with higher SW generally associated with increased total fat percentage and decreased total lean percentage (P < .01). Correspondingly, Metz et al. (2024a) reported that an increase in HCW led to an increase in 10th rib back fat and a decrease in standardized fat-free lean when different carcass weight categories were compared. The increased total fat percentage and IMF for weight 2 corresponded to a 1.01-U decrease in IV taken from the shoulder (P < .01). This result confirms the greater degree of saturation found in shoulder adipose tissue as HCW increases (Harsh et al., 2017b). In contrast, when a near-infrared spectroscopic instrument was used on-line to predict IV at the clear plate, carcasses with greater IV were associated with heavier weight (Zhou et al., 2021). The discrepancy could be ascribed to the uncontrolled production factors such as sex, genetics, and nutritional strategies that were not considered in the latter study. Nevertheless, other previous literature findings were inconsistent with our results when IV was assessed on belly adipose tissue (Correa et al., 2008; Metz et al., 2024b).

Table 4.

Effects of slaughter weight class on pork carcass and belly characteristics

Traits	SWC¹		SEM²	P Value
Traits	Weight 1	Weight 2	SEM²	P Value
Carcass traits
Slaughter wt, kg	114.70^b	128.10^a	0.16	<.01
Hot carcass wt, kg	95.41^b	106.43^a	0.33	<.01
PLMY,³ %	59.72^a	59.17^b	0.09	<.01
Total lean,⁴ %	58.94^a	57.54^b	0.18	<.01
Total fat,⁴ %	31.25^b	32.95^a	0.19	<.01
IMF, %	3.83^b	3.95^a	0.07	.03
IV⁵	59.98^a	58.97^b	0.14	<.01
Belly traits
Belly wt, kg	18.49^b	18.78^a	0.06	<.01
Belly lean,⁴ %	66.68^a	65.28^b	0.24	<.01
Belly fat,⁴ %	32.61^b	34.05^a	0.24	<.01
Length, cm	67.89^b	69.80^a	0.12	<.01
Width, cm	24.36^b	25.42^a	0.07	<.01
Side lean, cm	2.18	2.21	0.02	.18
Side fat, cm	2.48^b	2.77^a	0.02	<.01
Side thickness, cm	3.71^b	4.03^a	0.06	<.01
Side seam, cm	2.11^b	2.34^a	0.06	<.01
Side subcutaneous, cm	1.32^b	1.45^a	0.01	<.01
Belly bend angle,⁶ °	142.28^b	149.30^a	1.63	<.01

AOCS, American Oil Chemists’ Society; BB.V2, Belly Bender Version 2; DEXA, dual-energy X-ray absorptiometry; IMF, intramuscular fat; IV, iodine value; PLMY, predicted lean meat yield; SEM, standard error of mean; SWC, slaughter weight class.
Pigs were grouped into 2 SWC: weight 1 (114.7 kg) and weight 2 (128.1 kg).
Greatest SEM occurring between sexes was reported.
PLMY was determined using a Viewtrak PG-309.
The total lean, total fat, belly lean, and belly fat percentages were measured using DEXA (encore 2011, version 13.60.033, GE Lunar, General Electric, Madison, WI, USA).
IV AOCS = [16:1] × 0.95 + [18:1] × 0.86 + [18:2] × 1.732 + [18:3] × 2.616 + [20:1] × 0.785 + [22:1] × 0.723 (AOCS, 1998).
Belly bend angle was measured using the objective BB.V2 (Uttaro et al., 2024).
Means within a row with different superscripts significantly differed at P < .05.

As expected, an increase in SW from weight 1 to weight 2 increased pork belly weight (P < .01; Table 4). Similarly, Cisneros et al. (1996) reported a linear increase in belly weight with SW, and Oh et al. (2022) found a higher belly weight for the 135-kg SW group compared to the 115-kg group. Bellies from weight 2 were 1.1% wider and 0.3% thicker in side thickness than those from weight 1 (P < .01). Metz et al. (2024b) reported an increase in belly width and side thickness with increasing SW, which agrees with the findings of the current study. Measurements of other belly dimensions (i.e., side: fat, seam, and subcutaneous) were significantly greater (P < .01) in the weight 2 class, indicating fattier bellies. Notably, the belly bend angle was approximately 7.0° U higher (P < .01) in weight 2 pigs, indicating firmer bellies. With the established positive correlation between belly weight and belly-flop angle (Soladoye et al., 2017), the increase in belly bend angle could be partly due to the rise in SW. Additionally, the increased belly bend angle in weight 2 could be attributed to the increased belly fat components, width and decreased IV. In support, Soladoye et al. (2017) stated that these traits, when considered together, could be used for classification purposes. Therefore, the results from this study favor weight 2 as having firmer bellies than weight 1.

Conclusions

Increasing SW significantly affected carcass and belly traits in commercial pigs. Notably, interactive effects between SW and sex, typically undetected by traditional grading probes, were evident when using DEXA and should be considered as industry trends shift towards heavier market weights. Total belly fat content was also influenced by this interaction, with the differences between gilts and barrows diminishing at heavier weights. In contrast, belly dimensional traits, firmness, and IV were primarily driven by increased fat deposition, independent of sex. While firmer bellies may be beneficial from a processing perspective, excessive fat content may reduce product appeal for premium markets. Continued monitoring of these trends is warranted. Future research should evaluate the implications of even greater SW (e.g., 140–150 kg) and their interaction with emerging production strategies, such as immunocastration.

Conflict of Interest

The authors declare no conflicts of interest.

Acknowledgments

This study was funded by Swine Innovation Porc (SCAP-ASC-10 Swine Cluster Activity 18A “Enhancing pork belly quality across the value-chain”) and Results Driven Agriculture Research (Project # 2024F2553R “Evaluating the impact of increased pig harvest weights on carcass composition, product quality and palatability: implications for genomic selection”). Authors are also grateful for the technical support from the meat quality team at the Agriculture and Agri-Food Canada Lacombe Research and Development Centre (Alberta, Canada).

Author Contribution

Justice B. Dorleku: data curation, methodology, investigation, writing—original draft, and writing—review and editing; Tawanda Tayengwa: software, validation, formal analysis, data curation, and writing—review and editing; Benjamin M. Bohrer: writing—review and editing; Marcio S. Duarte: writing—review and editing; Philip O. Soladoye: writing—review and editing; and Manuel Juárez: conceptualization, methodology, data curation, supervision, funding acquisition, project administration, and writing—review and editing.

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