29 Mar The rationale for the recent USDA introduction of dentition as a measure of carcass maturity; and how this compares to current Australian MSA protocols
US Trip Report by Bridie Luers
Tenderness is a significant driver of consumer purchasing decisions for beef as it has a major impact on eating quality (Mateescu et al., 2016). Tenderness may be affected by a number of intrinsic carcass properties and one of the main drivers of beef tenderness is the development of collagen crosslinking within muscle (Weston et al., 2002). Increased collagen crosslinking occurs as the physiological maturity of the carcass increases, which is affected by age, use of hormones, nutrition and stress (Maltin et al., 2003). Increasing maturity is a well-established cause of a reduction in the tenderness of the meat, resulting in tougher beef (Shorthose and Harris, 1990).
Ossification and Dentition as predictors of physiological maturity and age
The Meat Standards Australia (MSA) grading system in Australia currently uses skeletal ossification as one of the carcass inputs to predict carcass physiological maturity and subsequent eating quality (Polkinghorne et al., 2008). This grading system has been developed, through the use of over 86,000 untrained consumers over eight countries, by determining the factors which affect eating quality and establishing their direct and indirect effects on it (MLA, 2011). This assessment follows the USDA guidelines, measuring ossification in the thoracic, lumbar, and sacral vertebrae in increments of 10 from 100-590 (AUS-MEAT, 2016). Bonny et al. (2015) found in low maturity cattle (ossification score <200, or aged ≤987 days) that animal age had no influence on the eating quality. In this category of cattle, ossification had a significant effect on eating quality, making it a more appropriate measure of maturity for most commercial beef carcasses, such as steers, heifers and young bulls. Ossification also provides a prediction of eating quality on a continuous scale, compared with dentition which cannot discriminate between carcasses within the same category (Thompson, 2016).
In Australia, the assessment of dentition is used to assign carcasses into alternative categories such as YG (Young beef, 2-tooth) YP (Young prime beef, 4-tooth) and PR (Prime beef, 7-tooth) (AUS-MEAT, 2016). Dentition influences the rates on price grids for carcasses sold on a carcass-weight basis as it was believed that these age differentials were associated with a variation in carcass value due to associated differences in eating quality (Toohey and Hopkins, 2015). However, recent changes to grading systems include the shift away from utilising dentition to grade carcasses as it has been found to be an inaccurate method of predicting the eating quality of cuts within a carcass.
A recent recommendation by the Australian Beef Language Review White Paper has seen the launch of a new Eating Quality Graded (EQG) cipher for MSA-graded carcasses (Biddle et al., 2016). The industry has chosen to support this recommendation to replace dentition and sex categories on a voluntary basis (MLA, 2016). This change suggests the phasing out of dentition ciphers (MLA, 2016), which would mean producers would not have to send their cattle to slaughter early in an attempt to avoid carcass deductions associated with cattle cutting their teeth. The EQG cipher aims to provide an outcomes-based product description underpinned by Meat Standards Australia grading system which can be easily conveyed to customers and the quality of that product guaranteed (MLA, 2017).
Up until recently, the USDA grading system also utilised a similar protocol for determining carcass physiological maturity and assigning an eating quality grade. The USDA has five maturity grades, from A through to E, with ‘A’ representing the youngest cattle, usually 9-30 months of age (USDA, 2016). Until recently, the maturity of a carcass was only determined by assessing ossification along the vertebral column, and combining this with an assessment of the lean colour in the loin eye muscle. Producers are paid according to the maturity; and the subsequent eligibility for different USDA quality grades can be determined (NCBA, 2015).
Recent changes to the USDA beef grading system
As of December 2017, the USDA has announced that the USDA beef grading system includes dentition, and documentation of actual age, as alternative methods of classifying carcass maturity.
Recent research funded by the United States Beef Checkoff Program has been the catalyst behind the acceptance of dentition as an indicator of carcass maturity, in preference to skeletal ossification. These studies have shown that the differences in chronological age and physiological age are not accurately reflected through evaluation of skeletal maturity (Acheson et al., 2014; Tatum, 2015). Pre-mature vertebral ossification contributes to these inaccuracies, with cattle as young as 14 months old having been found to be classified as ‘B’ maturity or older according to the USDA quality grading system (O’Connor et al., 2007). Skeletal maturity is influenced by factors such as diet, hormones and health status, which can lead to an altered rate of ossification (MLA, 2011). This means the carcass quality grade can be reduced and unnecessarily devalued because of the process in which maturity is being assessed (Tatum, 2011).
Each maturity category (A through to E) is meant to reflect an increase in physiological maturity and hence a decline in tenderness and eating quality. This logic is reflected in the processors price grid, with each subsequent category delivering the producers a price penalty. According to dentition, cattle with less than 3 permanent incisors are classified as <30 months of age. Whereas cattle with ≥3 permanent incisors are classified as ≥30 months of age. In studies involving fed steers and heifers classed as less than 30 months of age it was found that both trained panellists and Warner-Bratzler shear force instrumental measures could not detect any significant difference in tenderness between those categorised as ‘A’ maturity versus ‘B’ or ‘C’ (Acheson et al. 2014). The solubility of the collagen, which affects cooking, also did not differ between ‘A’ and ‘B’ or ‘C’ maturity carcasses in feedlot cattle classed as less than 30 months of age (Tatum, 2013). These findings indicate the meat produced from grain-finished cattle classified as less than 30 months of age at slaughter had similar shear force measurements and trained sensory attributes despite which USDA maturity grade they were assigned (Tatum, 2015). Hence discounting these carcasses based on the skeletal maturity is not justified as it has no bearing on eating quality (Tatum, 2015).
The acceptance of dentition as an alternative option for assessing carcass maturity is also of greater convenience to some processors. Since 2004, all carcasses processed in a federally inspected beef plant are already divided into two age groups, less than 30 months of age and greater than or equal to 30 months of age, based on dentition (FSIS, 2004). The purpose of this is to prevent exposure of humans to tissue which could potentially be infected with Bovine Spongiform Encephalopathy (Tatum, 2011). Many export partners of the United States already require verification of age via dentition assessment of cattle, meaning beef destined for domestic markets will mainly be affected (NCBA, 2015).
The National Cattleman’s Beef Association (2015) estimated the economic impact of allowing dentition to be used to assess carcass maturity in a study involving over 15.5 million head from May 2014 to April 2015. It was found that this change would shift 1% of the total number of grain-finished cattle to become eligible for graded beef programs. This represented greater than $42.8 million in income for beef producers per annum due to less producer revenue lost as a result of unnecessary reduction in carcass value on the basis of skeletal maturity classifications.
Beef tenderness has been shown to reduce with increasing cattle age and physiological maturity. Current MSA and USDA grading systems utilise skeletal ossification to assess maturity. Based on recent findings the USDA grading system has just introduced dentition as an alternative option for assessing physiological maturity in US beef plants. Evidence of pre-mature skeletal ossification in cattle less than 30 months of age and a lack of difference in eating quality between carcasses graded ‘A’ versus ‘B’ or ‘C’ maturity, have been the major rationale behind this decision. Meanwhile, under Australian standards, industry is set to move away from dentition assessment with research showing that it has no bearing on eating quality. These differences in industry direction reflect the differences in industry supply chain structure and research outcomes. It is unclear how changes to the USDA grading system may influence the Australian beef industry. However, ongoing research and development utilising untrained consumer eating quality data is essential to underpin the robustness and strength of the MSA grading system for beef.
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