Key Findings

• As a percentage, the part–whole relationship of KPH with carcass weight likely contributes more to the prediction of subprimal yield than a direct relationship between KPH and subprimal yield.
• Future prediction models developed to improve the accuracy of yield estimation should either include a highly accurate assessment of KPH or exclude KPH altogether.

background

An estimate of kidney, pelvic, and heart (KPH) fat, expressed as a percentage of hot carcass weight (HCW), is one factor used to calculate USDA Yield Grade to predict the percentage of boneless, closely trimmed retail cuts from the round, loin, rib, and chuck. In developing the original Yield Grade equation, the researchers included estimated KPH percentage because it explained variance in yield that seemingly was not explained by external fat thickness, supposing its relationship to intermuscular fat.

Assessment of KPH fat at commercial beef processing facilities in the U.S. has traditionally occurred after chilling and at the time of official USDA grade assignment. Today, many U.S. beef processing facilities remove KPH fat at the time of harvest to speed up chilling rate and to improve carcass fabrication efficiency. 

Further, KPH fat amount has been reported to vary considerably among cattle of different biological types, namely beef and dairy breeds. Hence, a standard account of KPH fat in the payment schedule across cattle types is most certainly not representative of the non-KPH portion of HCW from which processors generate cutout value. Issues associated with KPH measurement have been suggested as a contributing factor to this inaccuracy, and evaluation of yield on a KPH-removed basis has been suggested as one solution to increasing accuracy of carcass yield prediction. Carcass yield was identified in the most recent National Beef Quality Audit as a missed opportunity for the industry; thus, the ability to more accurately predict carcass yield will be increasingly important in the future. 

The objective of this study was to evaluate absolute measures of KPH, subprimal yield (SY), and subprimal cutout value (SCO) calculated on a conventional (KPH included) and alternate (KPH removed) basis from carcasses fabricated across multiple studies within the past 15 years. 

methodology

Carcass fabrication data were obtained from multiple previously conducted studies representing a wide variety of cattle types where KPH fat (either alone or combined with multiple fat sources trimmed at harvest) was measured. Data represented one carcass side (N = 816) and included hot side weight (HSW), chilled side weight, weight of KPH fat (including kidney), weights of individual subprimals, and weights of total fat, total bone, and trimmings. Individual subprimals were generated by trained personnel in a cutout style specific to each study. Carcasses were included in the study only if cutout components (subprimals, trimmings, fat, and bone) weighed back to 98% to 101% of chilled side weight. 

findings

Subprimal yield calculated with KPH removed was 20% more variable (P < 0.01) than yield calculated with KPH included, indicating that variance in KPH does not always align with variance in hot side weight. Therefore, variance introduced to hot side weight from KPH should be accounted in models predicting carcass yield on a hot side weight basis with KPH included. Otherwise, the ability to predict the subprimal portion of hot side weight will be diminished by variance in KPH that does not align with variance in other carcass traits. Conventional and alternate calculations for subprimal yield and subprimal cutout value were not different (P > 0.05). The subprimal cutout value with KPH in this study represented about 76% of the total carcass cutout value reported by the USDA in 2023; thus, changes in subprimal cutout value would largely affect the total carcass cutout value. Values for subprimal cutout value with KPH removed were approximately 6% greater than subprimal cutout value with KPH included. Assuming a direct relationship between carcass cutout value and carcass value, a market adjustment of similar magnitude might be expected if carcasses were valued on a basis of hot side weight with KPH removed. Among carcass components, KPH was least related (R2 linear = 0.167, and R2 quadratic = 0.201) to hot side weight, and subprimal and fat, bone, and trimmings were each more directly related (R2 = 0.899 to 0.953) to hot side weight. The combination of subprimal and fat, bone, and trimmings explained nearly all (R2 = 0.994) the variance in HSW. Subprimals, and not retail cuts, were generated in this study, making it hard to discern a relationship between KPH and fat depots, like intermuscular fat, contained within subprimals. Additional research is needed to understand whether a relationship between KPH and intermuscular fat exists in modern cattle.

industry Implications

Together, these data suggest that KPH is a highly variable carcass component and shares minimal relationship with other carcass components. As a percentage, the part–whole relationship of KPH with carcass weight likely contributes more to the prediction of subprimal yield than a direct relationship between KPH and subprimal yield. While this study only evaluated the KPH component of the Yield Grade equation, it is possible that relationships of KPH with other carcass variables may provide additive predictability of carcass yield. Additionally, the original Yield Grade equation was developed to predict cutability at the retail cut level, not at the subprimal level, as was measured in this study. Nevertheless, future prediction models developed to improve the accuracy of yield estimation should either include a highly accurate assessment of KPH or exclude KPH altogether from the denominator in the calculation of carcass yield.