Selection for muscularity	cerned than any other part of the live animal.
Certainly they should receive the major em-
Most swine producers know about pork phasis in any visual appraisal. In order that carcass evaluation procedures. Breeders	fat not be confused for muscularity, the ap-
supplying stock for commercial use realize	praisals should be made in the period before
that their sales cannot be based solely on the	the laying down of fat becomes prominent,
genetic ability of their stock to grow rapidly.	Furthermore, in making	such judgments, one
There is an increasing demand for them to	should recognize the extraneous factors
present evidence that their animals will pro- which influence muscularity but have no induce lean carcasses of high quality as well.	fluence upon the breeding value of the animal
The breeder or producer must decide how	such as management, season, and so forth,
much time he can devote to obtaining the W measurements and then choose the method	Backfat thickness
I which is most suitable for him. Several
1 methods are available, all of which may be	Backfat thickness measurements can be
used singly or in combination.	obtained relatively quickly and easily by
means of the probe. It, like most of the
Muscularity refers to the lean portions	carcass traits,	is highly heritable. Conse-
of the carcass included in the ham, loin,	quently rapid progress can be made through
picnic, Boston butt and bacon cuts. Since the	selection against backfat	thickness. Research
ham and loin make up about 70 per cent of the	has shown it to be highly	related to other car-
lean cut weight of the carcass, plus the fact cass and production traits as well. As back-they are the highest valued cuts, their per- fat has been reduced by selection, decreases centage of the total can be used as an efficient in feed utilization and increases in average measure of muscularity. The inclusion of	daily gain, per cent lean cuts, per cent ham
other cuts often introduces error stemming and loin, and loin eye area have resulted si-from cutting variations. The greatest diffi-	multaneously.	Thus, this trait measured on
culty is obtaining live animal measurements	the live animal	offers the breeder and pro-
which accurately reflect muscularity.	ducer one of the quickest, most accurate,
and most profitable methods of herd improve-

Visual appraisal	ment.
This is the oldest and most frequently	Loin eye area
used method of assessing muscularity. But
v to use if effectively one must be certain that	The relationships between loin eye area
he concentrates only on the points which ac- and carcass and production traits are not as curately indicate muscle mass. The muscu- great as they are in the case of backfat thick -larity of hams and loins is more easily dis- ness. Therefore, selection solely for this
AS-374 Sept. 1967
Selection for Pork Carcass Improvement
V. A. Garwood and M. D. Judge, Animal Sciences Department
Pigs to Pork  selection