Determination of by-product yield values from market swine

Exports of edible pork by-products totaled approximately $170 million in 2001, accounting for 11% of the total value of pork exports (U.S. MEF, 2002a). As evidenced by the yearly increases in metric tons of pork by-products exported from 1992 to 2001, international market demand is increasing (U.S. MEF, 2002a). Although the United States Department of Agriculture (USDA), Agricultural Marketing Service (AMS) reports a number of market hog byproduct yields, not all of the glands and other by-products that have value in the current domestic and export markets are reported (USDA AMS, 2002).


Differences in sex, live weight, grade and breed have been shown to affect market hog by-product yields (Davey and Bereskin, 1978; Tess et al., 1986; Cliplef and McKay (1993), as well as diet, level of feed intake, plane of nutrition, the ambient temperature at which the animals are housed, the length of fasting period prior to slaughter and the method of processing (Koong et al., 1982, 1983; Thiele, 1985; Nienaber et al., 1987; Pearson and Dutson, 1988, Rao and McCraken, 1992; Ockermann and Hansen, 2000). Additionally, McKay et al. (1984) showed that market hog by-product yields are impacted among breeds by the leanness of the breed, the halothane status, physiological differences in the rate of passage and absorption of nutrients in the gastrointestinal tract, water balance and electrolyte regulation and size at maturity. When considered with the changes in the U.S. pork population toward a leaner, more heavily muscled animal (Hayenga, et al., 1985, Eggert et al., 2002), potentially large differences may exist in byproduct yields among previous and current market animals.


While all of these factors have been shown to affect market hog by-product yield, the pork industry does not have adequate data to understand average by-products yields using current genetics and production factors and the variation associated with these yields. Additionally, information on the effect of sex on market hog by-product yield in the current market hog population is not known.


A Pork Checkoff-funded study using hogs representative of the current U.S. pork population from both sexes and slaughtered at varying slaughter weights was conducted by the National Pork Board to support market price reporting efforts of USDA AMS. The objective of this study was to identify by-product yields from a representative sample of the current U. S. pork population and understand the variance associated with each component.


Materials and Methods


Project Description
Crossbred market barrows (n = 99) and gilts (n = 97) were selected from area producers across a range of market weights (75 to 160 kg). Several genetic types were selected to assure that the population was representative of the U.S. slaughter hog population. Animals were taken from one to four farms each slaughter day with an average of fifteen hogs sampled in one day. A total of fourteen farms were sampled during the project. A small (2 head) pilot project was completed to test collection time and methods. A second pilot project (4 head) was conducted to further refine collection methods.


By-Product Collection
Pigs were electrically stunned and exsanguinated. Blood was collected at exsanguination in a pre-weighed container for approximately 5 min. Carcasses were weighed after bleeding and prior to scalding to determine live weight (carcass weight after bleeding + blood weight = live weight).


After scalding, toenails were removed and carcasses were scraped, singed and rinsed to remove any remaining hair. Carcasses were reweighed following hair and toenail removal.


The head was removed at the occipital condyles, leaving the jowls on the carcass. The whole head, including the tongue and ears with the skin intact over the skull portion of the carcass, was weighed after removal of the eyelids. The weight of the inner ear chambers was later subtracted from the whole head weight. The ears were removed and weighed singly. Ears were first weighed with the inner ear chamber intact, after which the inner ear chamber was removed and each of the ears was weighed again. The fatty base of the ear was then removed and both the ear base and the outer ear were weighed separately. The facemask (skin and tissue covering the face) was removed, after which, the snout (including the cartilage and skin surrounding the nostrils) was removed and weighed separately. The lower lip was removed from the chin area of the head and weighed. The pate meat (lean tissue between the ears), temple meat (lean tissue at the temples near the top of the jawbones), cheek meat (lean tissue on both the inside and outside of the jaw) and head meat (lean tissue on either side of the nose) were removed and weighed. The salivary glands were removed and weighed, at which time the tongue was removed between the soft palate and root of the tongue. The entire tongue was weighed, followed by tipping (removal of 3.8 cm of the tongue tip) and reweighing. The tongue cartilage (cartilage from the trachea) was removed, trimmed, and weighed. Finally, the brain was removed by splitting the skull and both halves of the brain were weighed together.


The feet were removed, with the skin intact, prior to skinning the carcass. The fore feet were separated from the carcass at or above the upper knee joint and the hind feet were separated at or above the hock joint and weighed separately.


The carcass was then skinned, with both the skinned carcasses weight and skin weight recorded.


The tail was removed, followed by evisceration, at which time internal organs were collected.


The ureter and blood vessels were trimmed close to the point of entry of each kidney, followed by removal of the renal capsule. Kidneys were then weighed separately. The spleen was separated from other abdominal viscera, trimmed and weighed. The liver was weighed after removal of the gall bladder and bile duct. The pancreas was weighed after removal of excess fat and lymph nodes. The urinary bladder was emptied, rinsed, trimmed and weighed. Both horns of the uterus were collected from the gilts and weighed. Ovaries were separated from the female reproductive tract and weighed together. The rectum was thoroughly rinsed, trimmed and weighed. The stomach was separated from the small intestine near the pyloric valve, emptied and thoroughly rinsed. The majority of the pepsin lining was removed and both the pepsin lining and stomach were weighed separately. The small intestine was divided into lengths of approximately 61 to 91 cm, thoroughly rinsed and weighed. The large intestine was divided into lengths of approximately 30 to 61 cm, thoroughly rinsed and weighed.


The heart was separated from the pluck and the pericardium was removed. Blood vessels were trimmed close to the point of entry into the heart and the heart was rinsed thoroughly to remove any blood clots. The heart was then weighed, slashed, re-rinsed and weighed again. The lungs were separated from the trachea and aorta. The pulmonary vein and artery and bronchial tubes were trimmed close to the point of entry into the lungs and were weighed separately. The trachea and esophagus were then trimmed and weighed separately.


The diaphragm, or skirt meat, was collected by trimming remnants of lean tissue from the carcass after removal of the internal organs, trimmed of excess fat and weighed. The pillar of the diaphragm, or hanging tender, was collected by trimming remnants of lean tissue after removal of the abdominal viscera, trimmed of excess fat and weighed.


The carcasses was then washed with pressurized water and weighed. The carcass was chilled at -2 to 0 °C for 18 to 24 h and chilled carcass weight was recorded.


Statistical Analysis
Statistical analysis was conducted using SAS (1999). The mixed procedure of SAS was used, with date of collection as the random term to remove any effect of improved collection techniques that occurred over time as greater experience with the protocol was gained. The sex of the pig was included in the model as a fixed variable. Both date of collection and sex of the pig were included in the class statement. Live weight was included in the model as a covariate. The covariate was tested at the linear, quadratic, and cubic levels. The quadratic and cubic levels were eliminated from the model if they were not significant. The sex by live weight interaction was also included in the model. As the heaviest pigs were barrows, sex and live weight are likely confounded. The least squares mean for each by-product was calculated by sex.




The average live weight of the 196 hogs used in this study was 111.4 ± 13.3 kg; this is slightly below the national average slaughter weight of 118.8 kg (NPB, 2001). The live weights of the animals ranged from 75.7 kg to 160.9 kg (Figure 1), with a total of 97 female (gilt) pigs and 99 castrated males (barrows) used in this study. Eight of the live weights could not be calculated due to missing data. Live weights were normally distributed for the study (Figure 1). The live weight distribution by sex is reported in Figure 2. The distribution curve for barrows was heavier than gilts; thus, sex and live weight effects on by-product yield may have been confounded. Therefore, the sex by live weight interaction was included in the statistical model. The live weight covariate regression coefficients for each of the by-products were calculated and covariate coefficients that were not significant (P < 0.05) at the quadratic and cubic levels were removed from the model. The linear coefficients, mean weight and standard error for each byproducts are reported in Table 1. Lie weight did not affect (P < 0.05) yield for the ovaries, ear base, lower lip, pork meat, and tongue cartilage.   The least squares means for each gilts and barrows are reported in Table 2. Sex effects were found for the skin, liver, stomach, kidneys, and pate meat. Barrows had higher weights for skin, leaf fat and pork meat and lower weights for tail, pepsin lining, urinary bladed, hanging tender, head meat, cheek meat and tongue (tip-on) than gilts. The sex by live weight interaction was significant (P < 0.05) for tongue cartilage.   Discussion


The by-product yields varied. Natural variation may have been due to variation among animal, variation due to collection procedures or production practices of the various farms sampled. Additionally, variation in blood weight may have been affected by kicking and other movement of the animal during sticking and bleeding, causing some splashing outside the collection bucket. This in turn would have affected the live weight, as live weight was calculated, due to the lack of facilities and equipment for an actual live weight measurement. Tail weight may have been affected by docking practices and tail biting, although evidence of tail baiting among the pigs slaughtered was not observed. Head removal may have affected tongue cartilage and pork meat yields as either of these items may have been nicked or cut during head removal.


Economics of By-products
Prices were estimated icing information for each of the by-products collected (Table 3). The USDA AMS has not been reporting prices for all by-product items. Additionally, packers are generally reluctant to reveal the value of the by-products that they collect. Eleven major packers and a number of allied industry members were contacted to obtain by-product pricing information. One packer provided pricing and market information. Another packer could not disclose the information for confidentiality reasons. A third packer felt their information did not fit well with that collected in the study. The remaining eight packers did not respond.


By-product values vary with season and market conditions. Some by-products may be sold at limited times of the year. Also, differences in transport costs may affect by-product pricing. The prices included in Table 3 represent yearly averages or seasonal prices. Some values were obtained from the cooperative packer and others from the USDA AMS.


The USDA Beef and Pork Variety Meats Report is available on the Internet at The Hog By-product Drop Value Report is available at These reports reflect the items for which the USDA AMS regularly reports prices. This may be due to the lack of availability of a market for the by-product or a price level that would discourage the collection of a by-product. Also, prices for these by-products may not always be available since packers report sales on a voluntary basis. In addition, prices are not reported unless a minimum quantity (9091 kg) is sold.


The economic value of various by-products may be further affected by collection procedures. For example, hearts may be slashed for inspection. The extent of the slashing may vary from one plant to the next. Slashed hearts are regarded as less desirable, especially in foreign markets such as China, where whole hearts receive a greater value. Kidneys also lose value if slashed. The Chinese market also places greater value on tongues that have not been tipped and tongues that have nicks or slices on the surface will lose value. Other factors that may affect by-product value may include degree of bleaching of stomachs, tail length, and bung length.


Figure 2. Distribution of live weight and sex of hogs slaughtered for by-product collection.

Figure 2. Distribution of live weight and sex of hogs slaughtered for by-product collection.

The major markets for some of the by-products are included in Table 3. Currently, the greatest export markets for U.S. pork by-products are Mexico, Japan, and China (including Hong Kong). Other markets for pork by-products include Europe, Canada, Taiwan, South Korea, and Singapore (U.S. MEF, 2002b). Future markets for U.S. exports of pork by-products may include Thailand (U.S. MEF, 2002b). The country does have a large swineherd but cannot meet domestic demand for pork by-product items. In particular, Thailand has needs for pork liver, intestines, and feet (U.S. MEF, 2002b). Competitors for variety meat export markets include Denmark, the Netherlands, other European Union countries, Canada, and Australia. Challenges in developing variety meat export markets include educating foreign consumers about the quality and safety of U.S. pork and meeting the cutting specifications of foreign markets.


The estimated per hog by-product value is $12.63 (Table 3). This number was calculated by multiplying the value, in dollars per kg, for each by-product by the average weight of the product, in kg, to determine the average value of each by-product per pig. The total estimated value per pig was found by summing the values of all by-products collected. For some byproducts, different collection methods affect the value and a product can be collected in only one form from each pig. For example, only one heart can be collected per pig and it must be either slashed or unslashed. The total value per pig was determined using the method of collection that provides greater value, such as the unslashed heart. Other examples include the stomach without the pepsin lining and the separated pepsin lining rather than the whole stomach, the whole ear rather than the ear base and outer ear, the entire face mask versus only the snout, and the tongue with the tip on.


Literature Cited

Cliplef, R. L. and R. M. McKay. 1993. Visceral organ weights of swine selected for reduced backfat thickness and increased growth rate. Can. J. Anim. Sci. 73:201-206.
Davey, R. J. and B. Bereskin. 1978. Genetic and nutritional effects on carcass chemical composition and organ weights of market swine. J. Anim. Sci. 46:992-1000.
Eggert, J. M., F. F. S. Depreux, A. P. Schinckel, A. L. Grant and D. E. Gerrard. 2002. Myosin heavy chain isoforms account for variation in pork quality. Meat Sci. 61:117-126.
Hayenga, M. L., B. S. Grisdale, R. G. Kauffman, H. R. Cross and L. L. Christian. 1985. A carcass merit pricing system for the pork industry. Am. J. Agric. Economics. 67:315-319.
Koong, L. J., J. A. Nienaber, J. C. Pekas, and J. T. Yen. 1982. Effects of plane of nutrition on organ size and fasting heat production in pigs. J. Nutr. 112:1638-1642.
Koong, L. J., J. A. Nienaber, and H. J. Mersmann. 1983. Effects of plane of nutrition on organ size and fasting heat production in genetically obese and lean pigs. J. Nutr. 113:1626-1631.
McKay, R. M., W. E. Rempel, S. G. Cornelius, and C. E. Allen. 1984. Visceral characteristics of three breeds of swine and their crosses. Can. J. Anim. Sci. 64:9-19.
NPB. 2001. The 2001/2002 Pork Facts Book. Natl. Pork Board, Clive, IA.
Nienaber, J. A., G. L. Hahn, and J. T. Yen. 1987. Thermal environment effects on growing-finishing swine. Part II-Carcass composition and organ weights. Trans. Am. Soc. Agric. Eng. 30:1776-1779.
Ockerman, H. W. and C. L. Hansen. 2000. Animal By-product Processing and Utilization. Technomic Publishing Co., Inc., Lancaster, PA.
Pearson, A. M. and T. R. Dutson (Ed.). 1988. Edible Meat By-products. Elsevier Applied Science Publishers, Essex, U. K.
Rao, D. S. and K. J. McCracken. 1992. Energy:protein interactions in growing boars of high genetic potential for lean growth. 1. Effects on growth, carcass characteristics, and organ weights. Anim. Prod. 54:75-82.
Tess, M. W., G. E. Dickerson, J. A. Nienaber, and C. L. Ferrell. 1986. Growth, development, and body composition in three genetic stocks of swine. J. Anim. Sci. 62:968-979.
Thiele, G. L. 1985. A multivariate analysis of carcass traits from three breeds of swine and their crosses. Ph.D. Diss., Univ. of Minnesota, St. Paul.
USDA AMS. 2002. USDA By-product price report. Available: Accessed July 10, 2002.
U.S. MEF. 2002a. Export Statistics 2002. Available: Accessed July 16, 2002.
U.S. MEF. 2002b. International markets. Available: Accessed Mar. 7, 2002.


Table 1. Mean weight, standard error of the mean, and regression coefficients of by-products from market swine.

By-product Mean (kg) ± Standard Error Linear Regression Coefficient Quadratic and Cubic Regression Coefficients
Blood 4.17 ± 0.60 0.02003a  
Skin 10.70 ± 2.26 0 0.000847b
Tail 0.12 ± 0.03 0.000928a  
Fore feet 0.85 ± 0.10 0.004022a  
Hind feet 1.01 ± 0.11 0.005216a  
Trachea 0.04 ± 0.01 0.000108a  
Lungs 0.79 ± 0.18 0  
Heart, unslashed 0.42 ± 0.05 0.002239a  
Heart, slashed 0.42 ± 0.05 0.002126a  
Liver 1.63 ± 0.25 0.004482a  
Spleen 0.19 ± 0.05 0  
Pancreas 0.15 ± 0.03 0.001205a  
Esophagus 0.06 ± 0.01 0.000195a  
Stomach 0.63 ± 0.10 0.001295a  
Stomach, without pepsin lining 0.44 ± 0.08 0.000911a  
Pepsin lining 0.18 ± 0.05 0.000404a  
Small intestine 1.55 ± 0.30 0.002406a  
Large intestine 1.34 ± 0.28 0.006169a  
Bung 0.15 ± 0.03 0.000680a  
Urinary bladder 0.04 ± 0.01 0.000234a  
Uterus 0.15 ± 0.14 0  
Ovaries 0.01 ± 0.003 0  
Kidneys 0.32 ± 0.05 0.000993a  
Leaf fat 1.39 ± 0.69 0.03610a  
Skirt meat 0.29 ± 0.05 0.002579a  
Hanging tender 0.19 ± 0.03 0.001117a  
Head, without inner ear chambers 6.30 ± 0.81 0.03195a  
Ears, without inner ear chambers 0.54 ± 0.09 0.001855a  
Ear base, left and right 0.30 ± 0.07 0  
Outer ear, left and right 0.24 ± 0.04 0.000923a  
Facemask 0.88 ± 0.22 0.006959a  
Snout 0.20 ± 0.04 0.000650a  
Lower lip 0.17 ± 0.08 0  
Pate meat 0.26 ± 0.09 0.01366a  
Temple meat 0.06 ± 0.03 0.002721a  
Head meat 0.09 ± 0.02 0.000546a  
Cheek meat 0.30 ± 0.05 0.001333a  
Salivary glands 0.05 ± 0.02 0.01034a 0.0000002767c
Tongue, tip on 0.25 ± 0.04 0  
Tongue, tip off 0.24 ± 0.04 0 0.000203b
Pork meat 0.21 ± 0.09 0  
Tongue cartilage 0.02 ± 0.01 0  
Brain 0.11 ± 0.01 0.000118a  

aIndicates a significant (P < .05) linear live weight effect.
bIndicates a significant (P < .05) quadratic live weight effect.
c Indicates a significant (P < .05) cubic live weight effect.


Table 2. Least squares mean, standard error of the mean, and probability of difference of byproducts from market swine

By-product Least Squares Mean (kg) ± Standard Error Probability of Difference
gilts barrows
Blood 4.20 ± 0.07 4.14 ± 0.07 0.47
Skin 10.42 ± 0.19 10.81 ± 0.19 0.01
Tail 0.12 ± 0.01 0.11 ± 0.01 0.01
Fore feet 0.84 ± 0.01 0.85 ± 0.01 0.83
Hind feet 1.00 ± 0.02 1.01 ± 0.02 0.64
Trachea 0.04 ± 0.001 0.04 ± 0.001 0.51
Lungs 0.80 ± 0.02 0.78 ± 0.02 0.46
Heart, unslashed 0.42 ± 0.01 0.42 ± 0.01 0.92
Heart, slashed 0.42 ± 0.01 0.41 ± 0.01 0.78
Liver 1.65 ± 0.04 1.62 ± 0.04 0.30
Spleen 0.20 ± 0.01 0.19 ± 0.01 0.07
Pancreas 0.15 ± 0.01 0.15 ± 0.01 0.29
Esophagus 0.06 ± 0.002 0.06 ± 0.002 0.54
Stomach 0.63 ± 0.02 0.62 ± 0.02 0.34
Stomach, without pepsin lining 0.44 ± 0.02 0.44 ± 0.02 0.79
Pepsin lining 0.18 ± 0.01 0.17 ± 0.01 0.05
Small intestine 1.55 ± 0.05 1.53 ± 0.05 0.60
Large intestine 1.34 ± 0.05 1.34 ± 0.05 0.85
Bung 0.15 ± 0.004 0.15 ± 0.004 0.52
Urinary bladder 0.05 ± 0.001 0.04 ± 0.001 < .0001
Kidneys 0.32 ± 0.01 0.32 ± 0.01 0.96
Leaf fat 1.29 ± 0.10 1.44 ± 0.10 0.04
Skirt meat 0.30 ± 0.01 0.29 ± 0.01 0.18
Hanging tender 0.19 ± 0.003 0.18 ± 0.003 0.03
Head, without inner ear chambers 6.29 ± 0.14 6.21 ± 0.14 0.31
Ears, without inner ear chambers 0.53 ± 0.01 0.54 ± 0.01 0.46
Ear base, left and right 0.29 ± 0.01 0.30 ± 0.01 0.72
Outer ear, left and right 0.24 ± 0.01 0.24 ± 0.01 0.23
Facemask 0.88 ± 0.03 0.88 ± 0.03 0.98
Snout 0.19 ± 0.01 0.19 ± 0.01 0.94
Lower lip 0.17 ± 0.02 0.17 ± 0.02 0.97
Pate meat 0.27 ± 0.02 0.25 ± 0.02 0.25
Temple meat 0.06 ± 0.003 0.05 ± 0.003 0.03
Head meat 0.10 ± 0.003 0.09 ± 0.003 0.01
Cheek meat 0.31 ± 0.01 0.29 ± 0.01 0.01
Salivary glands 0.05 ± 0.01 0.05 ± 0.01 0.75
Tongue, tip on 0.26 ± 0.01 0.25 ± 0.01 0.05
Tongue, tip off 0.25 ± 0.01 0.24 ± 0.01 0.07
Pork meat 0.20 ± 0.02 0.23 ± 0.02 0.02
Tongue cartilage 0.02 ± 0.001 0.02 ± 0.001 0.05
Brain 0.11 ± 0.001 0.10 ± 0.001 0.10


Table 3. Mean weight and estimated economic valuea of by-products from market swine

By-product Mean Weight (lb) Packer Value USDA Value Average Value ($/cwt) Per Hog Value ($) Market
2001 2000 1999
Blood 9.20 18.00 18.00 1.66  
Skin 23.59 18.67 27.11 20.79 22.19 2.81  
Tail 0.26 22.00 24.98 40.83 26.59 28.60 0.07  
Fore feet 1.87 24.00 22.22 19.29 14.13 19.91 0.37 Korea, China
Hind feet 2.22 17.00 17.00 0.38  
Trachea 0.09  
Lungs 1.74 1 to 2.50 1.75 0.03  
Heart, unslashed 0.92 24.98 22.15 19.48 22.20 0.20 China
Heart, slashed 0.92 24.00 28.05 21.27 14.92 22.06   China, USA, Canada
Liver 3.59 16.00 22.21 13.73 11.49 15.86 0.57  
Spleen 0.42 4 to 5 4.50 0.02  
Pancreas 0.34 90.00 75 to 81 84.00 0.29  
Esophagus 0.13  
Stomach 1.39 47.00 58.63 42.94 34.99 45.89   China, Mexico
Stomach, without pepsin lining 0.97 41.50 41.50 0.40  
Pepsin lining 0.39 85.00 85 to 90 87.50 0.34  
Small intestine 3.41  
Large intestine 2.96 33.93 42.82 30.34 35.70 1.06  
Bung 0.33 77.00 77.00 0.25  
Urinary bladder 0.09 $0.20 ea. 2.22 0.002  
Uterus 0.33 79.75 68.50 47.77 65.34 0.22 Mexico
Ovaries 0.02 $0.25 ea. 12.50 0.003  
Kidneys 0.70 21.00 16.25 18.53 12.68 17.12 0.12 China
Leaf fat 3.06 9.69 8.25 10.02 9.32 0.29  
Skirt meat 0.65 46.00 46.00 0.30  
Hanging tender 0.41 26.67 26.67 0.11  
Head, without inner ear chambers 13.88 48.00 48.00    
Ears, without inner ear chambers 1.19 60.00 60.00 0.71  
Ear base, left and right 0.66 15.00 15.00    
Outer ear, left and right 0.53 90.00 92.31 65.76 79.16 81.81  
Facemask 1.94 20.00 20.00 0.39  
Snout 0.43 20.00 55.05 27.51 23.50 31.52  
Lower lip 0.38 13.00 13.00 0.05  
Pate meat 0.57 25.00 25.00 0.14  
Temple meat 0.13 71.00 71.00 0.09  
Head meat 0.21 50.00 50.00 0.11  
Cheek meat 0.66 67.00 56.73 56.97 45.44 56.54 0.37  
Salivary glands 0.12 32.00 29.34 14.59 16.56 23.12 0.03  
Tongue, tip on 0.56 57.00 79.75 43.91 39.61 55.07 0.31 China
Tongue, tip off 0.53 57.00 57.00  
Pork meat 0.47  
Tongue cartilage 0.04 2.20 2.20 0.001  
Brain 0.23 65.00 51.63 42.25 33.56 48.11 0.11 Mexico
Total estimated value per hog         $12.63  

aValues in dollars/hundredweight, which is equal to cents/lb.
— Information not available.