The USDA Yield Grade equation is skewed, West Texas A&M University (WTAMU) researchers conclude.

With the adoption of visual instrument grading, calculated yield grade can be used for payment to cattle producers selling on the grid pricing system. USDA beef carcass grading standards include a relationship between longissimus muscle area (LMA) and hot carcass weight (HCW), which is an important component of final yield grade.

As noted on a USDA Yield Grade LMA grid, a 600-lb. carcass requires an 11-sq.-in. LMA and a 1,000-lb. carcass requires a 15.8-sq.-in. LMA. This is a linear relationship, where required LMA= 0.171(HCW) + 24.526.

If a beef carcass has a larger LMA than required, the calculated yield grade is lowered, whereas a smaller LMA than required increases the calculated yield grade.

Researchers sought to evaluate the LMA-to-HCW relationship against data on 434,381 beef carcasses in the WTAMU Beef Carcass Research Center database. In contrast to the USDA relationship, WTAMU's data indicate a quadratic relationship between LMA and HCW: on average, a 600-lb. carcass has a 11.6-sq.-in. LMA and a 1,000-lb. carcass has a 14.9-sq.-in. LMA, indicating a different slope and different intercept than those in the USDA grading standards.

On the basis of these findings, carcasses weighing 417 lbs. to 741 lbs. have calculated yield grades that are 0.1 to 0.2 units lower than expected, whereas carcasses that weigh 833 lbs. to 1,100 lbs. have calculated yield grades that are 0.1 to 0.5 units greater than expected. Therefore, heavier carcasses are more likely to result in yield grades of 4 and 5 because their LMA per HCW ratio requirement is overestimated.

These data indicate that the USDA calculated yield grade equation favors carcasses lighter than 800 lbs. for having above-average muscling, and penalizes carcasses heavier than 800 lbs. for having below-average muscling.

Researchers conclude that if carcass weights continue to increase, there will be more instances of Yield Grade 4 and 5 carcasses because of the measurement bias that currently exists in the USDA Yield Grade equations. Correcting the LMA per HCW relationship should help recognize the actual value of carcasses.
Lawrence et al, 2008, Journal of Animal Science, 86:1434

Exposing freshly weaned, transport-stressed calves to a persistently infected bovine viral diarrhea (PI-BVD)-identified calf had little effect on feedlot performance, New Mexico State University researchers found.

A single experiment of completely randomized design was conducted to evaluate the effects of long- or short-term exposure to a calf identified as PI-BVD on feedlot performance and carcass characteristics of freshly weaned, transport-stressed beef heifers.

Two hundred eighty-eight heifers vaccinated for BVD before weaning and transport were processed and given a metaphylactic antibiotic treatment at arrival, and were fed common receiving, growing and finishing diets for a 215-day period. Treatments were designed to directly or adjacently expose the cattle to a PI-BVD heifer. Directly exposed treatments were:

  1. negative control with no PI-BVD calf exposure (control);

  2. PI-BVD calf commingled in the pen for 60 hours and then removed (short-term exposure); and

  3. PI-BVD calf commingled in the pen for the duration of the study (long-term exposure).

Spatially exposed treatments were:

  1. negative control with no PI-BVD calf exposure (adjacent pen control);

  2. PI-BVD calf commingled in the adjacent pen for 60 hours and then removed (adjacent pen short-term exposure); and

  3. PI-BVD calf commingled in the adjacent pen for the duration of the study (adjacent pen long-term exposure).

Exposure to a PI calf transiently (60 hours) or for the duration of the feeding period (215 days) did not affect final bodyweight compared with unexposed heifers. Neither period nor overall dry matter intake was affected by PI-BVD calf exposure, and no differences were observed between short- and long-term exposed heifers in the direct or spatially exposed groups. Likewise, total trial average daily gain was not affected, and overall efficiency of gain was unaffected by PI-BVD calf exposure in direct or spatially exposed groups.

The study's results suggest that exposing previously vaccinated, freshly weaned, transport-stressed beef calves to a PI-BVD calf has little, if any, marked effects on health, performance or carcass characteristics.
Elam, et al, 2008, Journal of Animal
Science, 86:1917