Ribeye Study
Using Carcass Measurements In Selection Programs
In recent years ultrasound measurement of ribeye area and fat thickness has allowed objective measurements for these important carcass traits to be used in livestock selection programs. The sheep industry is behind the swine and beef industry in the use these carcass measurements. This is not surprising as the industry has traditionally lagged behind these other two meat animal species in the adaptation of genetic merit selection programs. Another contributing factor is the lack of a value-based marketing or pricing system within the lamb meat industry. Lamb carcasses are typically sold by the pound with little price differential paid based on quality or value. The lack of a value-based marketing system provides little incentive to producers to strive to produce higher quality lambs. However, with the development of producer cooperatives such as Mountain Lamb and Dakota Lamb, this seems to be changing.
The question is that in the absence of an objective selection program for carcass quality where does our industry stand with respect to our foreign competition or consumer desires. To date, we have convinced ourselves that the relative carcass merit and in particular ribeye size is one of the traits that the US sheep industry is superior to and a traits that differentiates our industry from our foreign competition. The closet set of data I have to validate this assumption is the carcass results from the lambs in the statewide 4-H carcass program (Tables 1 & 2). This data set includes lambs from about 40 counties throughout Montana during 2002, 2003 and 2004. It is a representative subset of lambs exhibited in Montana county fairs during those three years. I must point out that it is probably safe to assume that on average the relative carcass merit of these lambs are higher than an average set of lambs within the US commercial industry. Table one summarizes the average carcass measurements of the top 10 indexing lambs for each of the respective years. These results indicate that the top lambs in our industry have very desirable carcass with ribeye area approaching 4 sq inches. The standard that the US sheep industry would like to achieve is that a large portion of the lambs having a 3 sq inch ribeye or greater.
Table 1. Montana Youth Lamb Certification Program (Top Ten Indexing Lambs)
|
2002 |
2003 |
2004 |
|
| Index | 59 |
58 |
60 |
| Weight | 120 |
121 |
125 |
| Fat Thickness | 0.14 |
0.11 |
0.15 |
| Ribeye | 3.7 |
3.7 |
3.8 |
| Ribeye / CWT (carcass weight) | 5.9 |
5.5 |
5.9 |
Table 2 summarizes the average results form all lambs measured. The average ribeye of all lambs measured was around 2.7 sq inches. Only about 1/3 of the lambs meet the standard of a 3 sq inch ribeye. This carcass quality of average lambs in this data set is certainly acceptable, but, probably not a good as expected. Given that the lambs selected for exhibition in county fairs probably represent the top tier of lambs in our industry for relative carcass merit, we must conclude that our industry may not be positioned as well as we thought.
| 2002 |
2003 |
2004 |
|
| Lambs, number | 297 |
447 |
451 |
| Carcass Weight | 62 |
66 |
66 |
| Fat Thickness | 0.15 |
0.16 |
0.17 |
| Average Ribeye | 2.7 |
2.7 |
2.8 |
| Avg. Ribeye / CWT (carcass weight) | 4.4 |
4.2 |
4.3 |
| Percent | |||
| Certified | 33 |
27 |
35 |
| 3 sq. inch rib eye or greater | 29 |
29 |
40 |
| Choice & Prime | 97 |
98 |
98 |
| Correctly Finished (fat thickness between 0.1 & 0.2) | 70 |
80 |
75 |
| Yield Grade 1 & 2 | 92 |
93 |
87 |
Proper use of ultrasound data involves understanding its limitations. Although ultrasound is far superior to visual appraisal the technology has inherent limitations. For example, the accuracy of the measurements is not definitive enough to correctly rank the top 5 rams within a contemporary group. On the other hand, ultrasound is certainly useful to distinguish which rams are in the upper third or sorted into above average or below average categories. Rams having measurements of 2.6 or 2.8 sq inches are likely not detectability different for ribeye size (accuracy of ultrasound ribeye measurement is plus or minus .3 sq inches 67% of the time). However, a person can be confident that a ram with a ribeye of 3.5 sq inches is more muscular and superior to the two previous rams (ribeye of 2.6 and 2.8). Additionally ultrasound ribeye measurements are useful in identifying extremes (extremely large or extremely small).
Realtime ultrasound allows the commercial producer to know objectively and inexpensively the carcass merit of potential herd sires and to select rams that will sire lambs with superior carcass merit. To the seedstock producers, it allows the producer to objectively evaluate their potential stud sires and replacement females for carcass merit.
The potential gain of genetic improvement in carcass characteristics to the consumer and thus the industry is large. Optimum targets for carcass traits are fairly clear – 3.0+ sq. inches of rib eye, with less than .25 inches of fat (Yield grade 2) at 140 pounds. One of the problems that has always plagued the sheep industry is a true value-based marketing system that will financially reward the lambs with more desirable carcass characteristics.
Secondly, how can we integrate a carcass trait into
our selection program without compromising the maternal
traits. This answer is clear in the case of terminal
sires where all offspring enter the slaughter channels.
But in cases where many of the female offspring return
into breeding programs, selection based on carcass merit
must be balanced against the maternal traits (e.g. number
of lambs born, livability). In these cases, carcass
merit, although still important, should probably be
secondary in importance compared to the maternal traits.
However, since carcass traits are highly heritable (a
significant portion of the differences measured in rams
or ewes for these traits should be passed on to their
progeny), directional change can be accomplished even
though selection emphasis is being placed on the maternal
traits.