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RESEARCH | |
Using breed resources to improve carcass and meat qualityPaul L. Charteris and Dorian J. Garrick New Zealand Simmental Fielday, March, 1997 The previous year has been tough for all beef producers with low international prices depressing returns for cattle. The catch phrases in the beef industry of the 90's appear to be meat quality and customer focus. Unfortunately, in New Zealand with some exceptions, few beef producers are currently rewarded for consistently producing a high quality beef product,. On-farm, meat quality can be improved through changes in feeding regime such from pasture to grain finishing, cattle management, altering selling policies and changes in breeding policy. Breeding decisions such as breed choice, crossbreeding system and selection of superior animals within a breed can all affect meat quality. 1.0 Beef cattle carcass traits Beef cattle carcass traits can be categorised as weight, yield and meat quality related. These characteristics are of primary importance to beef cattle farmers, processors and consumers respectively. Carcass yield characteristics refer to the yield of saleable meat product (meat plus specified amounts of fat) produced per carcass or per unit carcass weight. The term meat quality can be defined in terms of consumer requirements or more objectively such as chemical lean content. Meat quality may include four major areas; visual quality, eating quality, nutritional quality and safety. Some industry commentators have described the ideal carcass as yielding a maximum percentage of saleable meat, a minimum percentage of bone and enough fat to meet the market requirements. 1.1 Carcass weight With current beef cattle grading and classification, carcass weight is the strongest determinant of price received per animal and is therefore of great importance to the beef producer. However, inconsistent price signals between different carcass weight ranges create difficulties for farmers establishing target carcass weights. Unlike the farming community, carcass weight is of lesser importance for meat processors and of no importance to consumers. 1.2 Carcass yield Yield traits provide an estimate of weight or percentage of saleable beef product per carcass processed. Yield traits are important to meat processors since an increase in saleable meat yield results in more saleable product per carcass processed. A commonly used measure of yield is dressing percentage (carcass weight/live weight x 100). Since increased dressing percentage can be affected by an increase in carcass fat or bone content, it is not a good predictor of value of the carcass. Dressing percentage indiscriminately rewards the deposition of lean or fat on the carcass and may encourage producers to overfeed cattle resulting in excess fat. Carcass muscularity is defined as the thickness of muscle relative to skeletal dimensions and conformation is a visual assessment of the thickness of fat and muscle in relation to skeletal measures. Carcass conformation is an is an indirect indicator of carcass meat yield. In New Zealand, payment per carcass is determined by conformation rather than yield of saleable meat. A more accurate prediction of saleable meat yield may be obtained through equations incorporating fat depth and eye muscle area taken at the 12/13th rib intersection in addition to carcass weight. Subcutaneous fat depth is measured as the depth of subcutaneous fat over the fourth quarter of the eye muscle at the 12th rib. In practice, company graders use subcutaneous fat depth in addition to visual assessment of fat content of the whole carcass as a guide when determining fat class of a carcass. Measurement of the degree of fat cover for carcass grading and selection purposes is important since:
1.3 Meat quality Meat quality traits are important to consumers since they affect purchase (and repurchase) decisions and satisfaction of consumption. Consumers perceive that yellow fat may be associated with older animals or animals that are diseased. The chemical constituent of pasture known to cause yellowing of fat colour have been identified as carotenoid pigments, the primary pigment causing yellowing of fat colour being -carotene. Cattle finished on grain consume less carotene and so produce a non-pigmented white fat. Similarly, meat colour is an important visual trait affecting consumer purchase of a beef product which can be improved through feedlot finishing. Beef that is not a bright, attractive red colour can be perceived by consumers as not fresh, prone to spoilage or from an older animal and therefore less tender. Marbling is a term used to describe intramuscular fat content. An increase in marbling is generally associated with enhanced cooking and palatability attributes. Although there is a positive association between marbling and beef tenderness, juiciness and flavour, the association is weak. Recent US research has found that high levels of marbling required to grade USDA choice were not justified in terms of eating quality (juiciness, tenderness) of beef. In the important beef export market of Japan, the method of cooking (broiling) requires that beef has a high marbling content to avoid rapid cooking and the production of offensive odours. Consumers consider tenderness to be the most important aspect of meat eating quality. The United States beef industry task force identified increasing consistency and quality of beef product as important to improving market share, with a reduction in consumer satisfaction (primarily related to toughness) by 50% required by 1997. Marbling and connective tissue content accounted for only 20% of observed variation in tenderness, the remainder being influenced by processes occurring postmortem, including chilling, ageing and cooking procedures. Other meat quality traits include flavour and juiciness. Flavour of meat is highly influenced by environmental factors such as nutritional regime, age at slaughter and post-slaughter management. Less desirable flavour of beef from pasture finished as opposed to feedlot-finished cattle has been attributed to lower fat content, or different fatty acid composition of beef from the former group of animals. Assessment of juiciness and flavour rely on cooking meat for a specified period in a precise manner and subsequent sensory evaluation by a trained taste panel. 2.0 Sources of variation in carcass and meat quality Within any group of animals we will find variability, take a mob of calves for example, within this mob, some calves will be heavier at weaning due the genes they possess for growth, availability and quality of feed they consume (both pasture and milk supply from their dam) and their health. Now compare this mob of calves with all the beef calves weaned in New Zealand, differences in weaning weight are now due to genes in addition to differences in management between farms and between regions. Thus diffences between animals can be summarised as arising due to differences due to
When we invest in a breeding bull we are interested in his genes he transmits to his progeny. Thus for improving carcass and meat traits we would like to know what proportion of the total variation in these traits are due to genetic difference between groups of individuals. This proportion is termed heritability. Traits with a higher heritability have a higher proportion of variability accounted for by genes. Significant genetic variation exists both within and between breeds, the magnitude of this variation is generally comparable within and between breeds for most traits. Thus, significant genetic change can result from both within and between-breed selection. A United sates study (Green, 1991) showed that variation within breeds for marbling and saleable meat yield (%) was of the same magnitude as variation between breeds for the same trait. For saleable meat yield (kg), variation between breeds was greater than variation within individual breeds. Differences between breeds are more easily exploited than differences within a breed since variation between breeds is often more highly heritable. Say for example you wished to improve saleable meat yield for your Hereford herd, the quickest way to accomplish this would be to use bulls of breeds known superior for saleable meat yield such as Limousin, Charolais and Simmental rather than select for saleable meat yield from within the Hereford breed. In addition, selection within breeds for such traits is often complicated by the fact that few animals have Estimated Breeding Values (EBVs) for traits such as saleable meat yield, marbling, meat colour and fat colour. Breed differences in performance characteristics are an important genetic resource for improving efficiency of beef production and meeting market requirements. However, more time is required before definitive statements can be made regarding breed superiority for a number of meat quality traits. Research comparing breeds in the United States is summarised in Table One for which some breeds grouped into types on the basis of four criteria. Table One Breeds grouped into biological types for four criteria
(Cundiff et al. 1993).
Increasing number of X's indicate relatively higher values, thus Jersey cattle tend to be slower growing, have smaller mature size, are less lean, are younger at puberty and have higher milk production than most beef breeds. Unfortunately there are often genetic antagonisms between traits, this means that improvement in one trait can result in decreased performance in another trait. For example there is a negative genetic relationship between marbling and lean meat yield, selecting cattle for superior marbling will tend to decrease the yield of lean meat and vice versa. Average marbling scores and lean meat yield (%) across breeds is shown in Figure Two. The breed with the highest average marbling score (Jersey) also had the lowest lean meat yield, similarly for the Chianina which had the highest lean meat yield. These trade-offs confirm the statement that no one breed excels for all traits it is for this reason that we have different beef cattle breeds and utilise their genes in crossbreeding programmes. 
If Chianina breeders decided to select for marbling, eight generations (40 years) of single trait selection for this trait would be required to increase marbling in Chianina to the level of that in Angus. In the process however, due to negative genetic correlations, lean meat yield of the Chianina would decrease. Due to difficulties of measurement of marbling on the live animal, most rapid genetic improvement would occur through crossbreeding programmes where breeds with marbling superiority such as Wagyu or Jersey are utilised. An example crossbreeding programme would be to mate an early maturing dam breed known for high marbling and meat palatability to a high growth rate terminal sire breed which produces a high lean meat yield. New Zealand Beef Processor data Earlier maturing breeds have a higher fat depth and lower lean meat yield at a constant carcass weight than do late maturing breeds. In a comparison between beef cattle breeds slaughtered at Manawatu Beef Packers in New Zealand, Garrick (1994) found that British breeds had higher subcutaneous fat depth at a similar carcass weight than did Exotic x British breeds and cattle of dairy origin. The implications of this for farmers are that steers of Continental x British breeds can be finished to higher carcass weights without incurring fat depth penalties compared with steers of British or Dairy x Beef breeds. New Zealand breed comparisons Among the most comprehensive beef cattle breed evaluation in the world have been conducted in New Zealand, through AgResearch, Ruakura. In one study, 1908 steers from eleven breeds were evaluated over five years. Sires were mated to either Angus or Hereford dams. These trials were conducted through the 1970's, due to breed genetic trends the relative rankings of these breeds are likely to be different in 1997. The effect of breed of sires on carcass traits of progeny slaughtered at 31 months age and adjusted to a fixed carcass weight of 277 kg or a fat depth of 6.5 mm is shown in Table Two. Sire breeds are ranked on the average yearling weight of their progeny with highest yearling weights shown at the top of the Table. Table Two: Effect of breed of sire on carcass traits at 31 months
of age when adjusted to a fixed carcass weight of 277 kg or a fat
depth of 6.5 mm (Morris et al. 1990)
Carcass productivity (average carcass weight x calf survival from
birth to weaning) relative to a base of 100 for Hereford x Angus
cattle. Carcass weight is hot carcass weight at 20 months of age.
Summary Carcass and meat quality traits differ in importance depending on the sector of the beef industry examined and the requirements of different markets. Variation in traits arises from variability in due to both environment and genes the animals possess, however only these genetic differences can be exploited to change meat quality of animals in future generations. Cattle breeders can exploit genetic variation both within and between breeds to improve carcass and meat quality traits. However, these traits are only part of the a large complex of traits which, together with fertility, survival and growth performance all impact on farm profitability. Acknowledgments Thanks to Mr. Doug Lyneham, AFFCO, New Zealand for supplying data from Manawatu Beef Packers. Beef cattle breeding research and extension support is provided by the New Zealand Meat Research and development Council (MRDC). References Charteris, P.L. June, 1996. Breeding Matters - Beef Supplement. The New Zealand Animal Breeding Trust. Cundiff, L.V.; Szabo, F.; Gregory, K.E.; Koch, R.M.; Dikeman, M.E.; Crouse, J.D. 1993. Breed comparisons in the germplasm evaluation programme at MARC. Proceedings of the Beef Improvement federation Research Symposium and Annual Meeting, Asheville, NC. Garrick, D.J. 1994. Meeting market specifications: Exploiting breeds and crossbreeding for profitable production of beef. Proceedings of the Central districts Sheep and Beef farmers Conference, vol 3: 35-40. Morris, C.A.; Baker, R.L.; Carter, A.H.; Hickey, S.M. 1990. Evaluation of eleven cattle breeds for crossbred beef production,: carcass data from males slaughtered at two ages. Animal Production, 50: 79-92. |
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