Introduction

    A recent audit sponsored by the National Cattlemen’s Beef Association (Boleman et al., 1998) reported that approximately 25% of beef carcasses were fed too long as demonstrated by back fat measurements greater than 15 mm. Conversely the same audit reported that 25% were marketed too early and not fed long enough. This variation in the body composition of represents inefficient allocation of resources and missed opportunity. Beef feedlot management systems should aim for consistency in meat quality that requires all animals to be harvested at a target body composition. Although this difference in genetic potential cannot be observed upon arrival into the feedlot, identifying genetic factors associated with growth performance allows producers to maximize carcass value.

Description of QMP (Quantum Management Protocol)
A major factor of this difference is believed to be a result of leptin genotypes.

    As cc cattle begin to fatten:
  • Higher leptin concentration is recognized by leptin receptors in the hypothalamus
  • Signals are sent to suppress appetite
  • Metabolism is modulated to draw on stored energy (fat)
  • Fat tissue is regulated to reduce fat deposition
    As tt cattle begin to fatten:
  • Circulating leptin concentration is less well-recognized by the leptin receptors
  • The animal continues to act in a hunger mode – eating and storing fat, including intramuscular fat (marbling)
  • Additional fat tissue means more leptin production, but again it is largely unrecognized
The figure below illustrates how leptin genotype is used to identify animals if the tt genotype and on average may fatten 14 + 3 days sooner than animals of the cc genotype and 7 + 3 days sooner than animals of the ct genotype


Your Results
Table 1. The effect of leptin genotype on body weight and backfat estimates.



Choosing a Market Date
    An effective beef feedlot system aims to maximize animal productivity while ensuring consistency in meat quality that requires all animals to be harvested at a target body composition. Instrumental in this approach is the ability to identify genetic variation within animal the animal population and the ability to predict the rate of growth through the use of bioinformatics.

Attached to this document are the following:
  1. Three Frequency Tables, one for each leptin genotype. Using exponential growth of back fat, we estimated days on feed (DOF) for each required to reach an optimal level of fatness. The Tables below illustrate the proportion of animals that are estimated to be at 12-mm at 7-day intervals. This information can then be used to determine how the days on feed are required to hit a target point (i.e. 75%, 85%, 95% etc. carcasses with back fat > 12-mm).
  2. Individual Animal Data. An outline of individual animal Genotype, and associated body weight and estimated back fat level. This data will allow you to identify outliers that will hamper your ability to ship a uniform lot.