*By Hamna Vahab, Ipseeta Nanda, lalrohlui, Anand TS and S. Talukder
The part of the food animal body that remains after commercial dressing procedures is popularly called carcass. Evaluation and constant maintenance of carcass quality is the measure of output which paves the way for upbringing trade in meat sector which in turn pays the efforts of farmers and uplifts their living standards. According to Polkinghorne et al. (2010) carcass classification affects the price determination and is responsible for meeting the consumer expectations, which is a concept called “consumer grading system”. It helps the farmer to recognize quality of animal which they are producing and hence can have improved and better planning to have high grade animals and carcasses. In addition, it can certify their animals and carcasses for class, quality and condition through authorized agencies. It also helps the meat processing sector to select the different meat grades on the basis of market and consumer demands. The classification depends upon the description of carcasses using specifically defined anatomic features which are simultaneously important to the sellers as well as buyers (Sather et al., 1991). Thorough knowledge, how this grading system can help in upbringing the output of meat sector in upgrading quality as well as for meeting consumer demands is very much necessary.
Evaluation of carcass simply means to evaluate all those factors which determine the average value per unit weight of carcass (Purchas, 2012). Evaluation of carcass primarily depends on the carcass weight, dressing out percentage and the composition of carcass. According to Jones (1989), evaluation of carcass has at two significant functions; that are evaluation of carcass composition as a part of scientific experiments and a system for evaluation of commercial carcasses based on lean meat content.
The evaluation of potential carcass qualities in live animal is an important requirement in case of breeding males since they can have a greater population characteristic influence in comparison to females. Carcass evaluation is an important aspect of grading and classification of carcass. With grade or class there can be some similar characters in common and with that classification becomes a comparatively easier process, but with different grades one may be superior or inferior to another while classes are just different (Kempster et al.,1982). In some instances, the carcass evaluation can be done mainly for research purpose (Purchas, 2012).
The carcass weight and dressing out percentage along with carcass composition chiefly determines the value of carcass.Carcass weight or hot carcass weight can be defined as the hot or un-chilled weight of carcass after removing head, hides, internal viscera and gastrointestinal tract. Carcass confirmation and length of the carcass are significant in increasing the weight of it. Carcass with a good confirmation tends to have a thicker appearance and well-defined muscles. If the level of fatness remains the same, well confirmed animal tends to have more lean meat (Warris, 2001). Carcass length is a straight line from the forward edge of the first rib to the forward edge of the aitch bone. If all other factors influencing the composition remain the same, carcass with more weight tends to have an increased carcass value.
The dressing percentage can be simply defined as the carcass weight as a percentage of live weight immediately prior to slaughter or in other words, the live weight multiplied by the dressing percentage gives the carcass weight (Coyne et al., 2019). Dressing percentage is directly depended on the live weight. According to Coyne et al. (2019), dressing percentage is influenced by both genetic and non-genetic factors. The animal factors influencing dressing percentage include sex, age, fatness, muscularity and pregnancy status. Factors affecting live weight such as gut fill and carcass weight such as bruising or decoction for shrink influence dressing percentage. The dressing percentage increases as the live weight of the carcass decreases (McKiernan et al., 2007).
Purchas (2012) illustrated that carcass composition is determined primarily by the lean meat yield percentage which in turn is determined by the carcass fat percentage and the muscle to bone ratio. The lean meat quality depends on external factors which involve mainly the processing of meat and intrinsic factors which include palatability factors (viz., odour, juiciness, flavour etc.); appearance (viz., colour, texture etc.); nutritive value, safety, wholesome characters and the processing properties. Carcass composition is also influenced by the distribution of lean and fat and the carcass shape. Yet another study states that the carcass composition is highly determined by genetic factors, age of the animal status of nutrition, hormonalbalance, environmental condition and the changes can even occur during pre-slaughter handling. Dry firm and dry condition in beef and Pale soft exudative condition in pigs are the commonly encountered carcass conditions (Irshad et al., 2013).
Polkinghorne et al. (2010) defined carcass classification as a set of terms describing characteristics of the carcassthat are helpful to thosewho are involved in trading of carcasses. Grading is the placing of different values on the carcasses for the pricing purposes, depending upon the requirements of traders and market.It is a systematic way to express value and quality of carcass by sorting in to groups according to selected characteristics. Grading plays a very significant role in marketing and merchandising of carcass. The animals which score high, fetches higher grades in carcass too. Different countries have their specific grading patters to suit their consumers and market patterns. The most popular among them is the system developed by United States department of Agriculture, popularly called the USDA system or Federal system of carcass grading. Grading is done so that it helps the farmer to recognize their quality of animal and for better planning to improve program and produce high grade animals and carcasses.It helps the producer to certify their animals and carcasses for class, quality and condition through authorized agencies and it helps meat processing sector to select a required type according to the needs of market and consumers.
Existing grading systems in different countries
The marketing of meat has several challenges and each with its own set of pros and cons.Less market transparency, imprecise description of the product at the point selling and inadequate feedback about the consumer requirements are some factors which negatively impact market status (Farmer and Farrell, 2018). The main purpose of descriptions systems is to smoothen the trade by describing commercially important attributes of meat (Price, 1995).
Miller (1976) conducted a study about the consumer acceptability of USDA system, states that the consumer shall be made more aware of the quality parameters. Important factors to be considered included carcassweight, age and maturity of the animal, sex, fat cover, colour, conformation and freedom from bruising and blemishes. Depending upon the country marbling and lean colour and texture of the meat are often considered.The Canadian grading system mainly utilises maturity of the animal and marbling in assigning grades of carcass. The systems of standards were adjusted with bulls in such a manner that bulls were allowed in top grades earlier but had eventually been replaced (Price, 1995). In 1992 it was further improved and in 1996 marbling of the meat was incorporated as in USDA.
As per Canadian system there are 4 quality grades for cattle; Prime, AAA, AA and A complemented by maturecattle grades.Canadian grades exclude carcasses having fat with yellow colour and require better muscle and lean texture. Maturity is assessed as youthful or mature on the basis of skeletal development of the animal.Rib eye region that is the area of longissimus dorsi is looked after for noting the meat colour usually between the 12th and 13th ribs. Fat is also assessed together with meat texture and carcass confirmation with minimum standards for evaluating each as character of youthful grades. The yield grades are Canada 1, Canada 2 and Canada 3. (Polkinghorne et al., 2010).
In Australia initially quarters were graded on the basis of conformation, age and fat cover as first, second and third grade of evaluation. This system was replaced in 1987 by the AUS-MEAT language exposing a deliberate change from subjective quality assessment to strict specification which enabled a carcass to be described in respective ofsex, dentition and weight without quality connotation (Polkinghorne et al., 2010). Later based on USDA grades, eating quality predictors and refined factors were added to grading which include ossification and marbling.
In Japan carcass evaluation system has five quality grades. In 1971, “Tokusan” that is the premium grade. Meat quality grade parameters were assessed by quartering between the 5th and 6th ribs. Marbling is assessed by a unique twelve beef marbling score (BMS) from 1 to 12. The BMS scores is related to five beef marbling grades like, excellent (BMS 8–12), good (BMS 5–7), average (BMS 3–4), below average (BMS 2) and poor (BMS 1). There are five beef brightness and colour and grades such as very good, good, average, below average and inferior. The marbling, meat colour, firmness, meat colour and texture and fat colour, lustre and quality grades are thenconsidered as the factors in assigning the carcass quality grades. With the lowestresult determining the quality grades being 1 and the complete designation goes from 1 to 5. Japanese yield grades are determined by applying regression equation on ribeye or the loin eye area, rib thickness that is a measured muscle thickness above the rib, cold left side weight and subcutaneous fat thickness. All measurements were taken at the level of 6th or 7th rib. Yield grades are designated A (72% and above which is a cut yield above average), B (69–72% the averageyield) or C (under 69% and is below average range (Polkinghorne et al., 2010.). Korea included quality and yield grades, having 5 & 3 levels and, giving a total of 15 categories in grading (Kim and Lee, 2003)
USDA grading system
The most establishedand widely known example is the USDA Grading System which is issued by the US department of Agriculture. USDA system is popularly called the Federal system.It describes carcasses in terms of eight quality grades as Prime, Choice, Select,Standard, Commercial, Utility, Cutter and Canner and yield grades of 1 to 5 as Prime, Choice, Good, Standard, Utilityand Cull (Smith et al., 2008). The tentative US standards for beef grades were formulated in 1916, which was revised from time to time (Miller, 1976). The standards were reprinted with amendments in 2017.Confirmation refers to the morphology of the animal such as build,shape contour and its different prime cuts, quality which denotes the characteristics oflean meat and finish which is meant by the fatness of the animal are basic parameters taken care of in grading. Quality is the characteristic of muscle which is more accurately determined by the lean meat and marbling content. Finish refers to the fatness of the animal.
There are two types of grading in USDA system (i) Quality grade (ii) Yield grade. The quality grade is determined by the amount of fat and its distribution, muscling, maturity, marbling, refinement of hair, hide, bone, smoothness and symmetry of the body (Fig 1). Five USDA maturity grades and 8-9 degrees of marbling grades are followed. Fourmajor factors are considered for assessing yield grades which include the hot carcass weight, back fat thickness, percentage of kidney, pelvic and heart fat (KPH) and the rib eye area. Hot carcass weight is the weight just after harvest after the removal of hide, head, gastrointestinal tract and other internal organs. Rib eye area indicates amount of lean muscle associated with carcass. Just like Canadian system it is determined between 12th and 13th ribs. Optimum range is 11-15 sq inches. Back fat thickness is the most important determinant of retail yield which is measured at the 12th rib (in case of cattle) or 7th rib (in case of pig) and it ranges from 0.15 to 0.8 inches. As the back fat thickness increases, cuttability and percentage of retail products decreases, resulting in less desirable product yield.Kidney pelvic and heart fat is usually expressed as percentage of weight of hot carcass. Internal fat or KPH increases, then the retail product of yield decreases (Lu and Tan, 2004). There are 8 yield grades viz., prime, choice, good, standard, commercial, utility, cutter and canner based on the maturity and marbling level. Stags are graded prime while cows are not.
USDA chart for grading on the basis of maturity and marbling
(Source: US Standards for Grading Beef Carcass, effective from Dec 18, 2017)
The US prime has highest quality and intramuscular fat, but has a limited supply. The US Choice is of high quality which is widely available in foods service industry and retail markets. The difference between Choice and Prime is due to the fat content in the beef. Prime typically has a higher fat content, typically well distributed marbling than the US Choice. The US Select formerly known as US Good is lowest grade commonly sold at retail. It is acceptable quality, but is less juicy and tender due to leanness. The US Standard is again lower quality, yet economical. It is lacking marbling. The US Commercial is further low quality, lacking tenderness, produced from older animals. The Utility, Cutter and Canner are of least quality. For Veal and claves, the quality grades are Prime, Choice, Good, Standard, Utility and Cull (United States Standards for Grades of Carcass Beef, 2017). Apart from beef, USDA system also classifies pork, lamb, sheep, and so on into various grades. There are 5 levels of maturity such as A 9-30 months, B 30-42months, C 43-72 months, D 73-96 months, and E greater than 97 months.
According to Bureau of Indian standards (BIS) –IS:2537, which came into existence in 1995,there are six standards in India based on conformation, finish and quality. They are Prime, Choice, Good, Commercial, Utility, Cutter and Canner. Likewise, lamb and poultry are also classified.
Fabrication of carcass
Cutting procedure or fabrication of carcasses of food animals refers to the method of separating a chilled carcass into different commercial parts. The fabricated cut up parts fetch an improved price range in the market compared to a whole carcass. Fabrication also helps in proper cooking of different cut up parts each fetching a different value. Fabrication is more or less same for all slaughter animals except pigs.
Novel upcoming grading strategies
At present, majority of the on-line evaluation of carcass uses back fat thickness and depth of the muscle to determine the overall yield and this technique seems to reach its maximum potentiality and accuracy.
The novel strategies for improvement need to be sorted out since dissection of carcass is time consuming, expensive and subjected to biases, newer methodologies using magnetic resonance imaging (MRI), X-Ray technologies are on research. Certainly, future evaluation and grading system will be based on weight of commercial cuts, its economic market value and the ration of lean and fat it contains. Colour, marbling which deals the aesthetic quality will also be given much importance (Kerry, 2009). Video Image Analysis (VIA) systems using electronic camera technology, and with computer-based digital image analysis techniques, to derive the significant features from multiple images of carcasses and which estimates of various carcass attributes including carcass composition and yield will be soon coming into existence. VIA can be effectively utilized to get direct measures of fat cover, eye muscle size, and dimension to infer composition and yield (Fig 2) (Craigie et al., 2012).
Variations within the carcass are to be understood by the buyers and it shall be reflected by cuts or even with muscle description. Researches has been constantly upbringing the variable relationship between thepalatability of cuts when overlaid with breed, carcass hangingand hormonal growth promoters (Thompson, 2002; Thompson et al., 2008). Optical method for evaluating meat quality is an upcoming trend in carcass evaluation. Spectroscopic methods are used to define the freshness of meat which is supposed to be an integral part of grading system in the upcoming days (Prieto et al., 2009).
Novel methodologies are being developed in field on carcass evaluation and grading. Researchers are more focussing on imaging techniques to determine the grades without opening the carcass which can save a lot of money and man power. Consumer’s preferences can be attributed to variables other than the direct examination of the carcass during classification. There are major difficulties in designing consumer-based grading schemes and in developing consumer-based grading schemesachieving a country-to-country and industry-to-industry coordinationinside each nation. Advances in carcass classification, grading, and market grading will also continue to make value-based grading of beef more economically feasible. To increase the value of grading, beef grading schemes that rely on customer results must be created. With more people becoming health-conscious, we are optimistic that the next era will be one of quality over quantity. The concept of consumer grading system must be upheld and at the same time, technologies should be focus on developing easiest and least time-consuming methods for evaluation of carcass without compromising the quality parameters.
Bureau of Indian Standards (1995). Meat and meat products-beef and buffalo meat-fresh, chilled and frozen-technical requirements (IS: 2537). Government of India. https://law.resource.org/pub/in/bis/S06/is.2537.1995.pdf.
Coyne, J. M., Evans, R. D., and Berry, D. P. (2019). Dressing percentage and the differential between live weight and carcass weight in cattle are influenced by both genetic and non-genetic factors. Journal of animal science, 97(4): 1501-1512.
Craigie, C. R., Navajas, E. A., Purchas, R. W., Maltin, C. A., Bunger, L., Hoskin, S. O., and Roehe, R. (2012). A review of the development and use of video image analysis (VIA) for beef carcass evaluation as an alternative to the current EUROP system and other subjective systems. Meat science, 92(4): 307-318.
Farmer, L.J., and Farrell, D.T. (2018). Beef-eating quality: a European journey. Animal, 12(11): 2424-2433.
*Division of LPT, ICAR-IVRI, Izatnagar, Bareilly, UP-243122