The anatomy of the sheep carcass is important with respect to the muscles that are increased through the use of muscle QTL/genes. The muscles of the shoulder include the pectoralis, the latissimus dorsi, triceps brachii, and the trapzius (Swatland, 2005). All of these muscles will be part of the shoulder cut when the carcass is processed. The main muscles in the loin region consist of the longissimus dorsi, which is also known as the longissimus thoracis and lumborum, the psoas major and the gluteus medius
(McCracken, Kainer, and Spurgeon, 1 999; Swatland, 2005). The longissimus dorsi is the main muscle in the frenched rack and strip loin cuts, and it is cut approximately in half to generate the two cuts. The psoas major is the main muscle in the fi llet and is processed as pure muscle. The leg of the lamb contains many muscles some of which are the biceps femoris, semitendinosus, semimembranosus and the gluteus medius
(McCracken, Kainer, and Spurgeon, 1 999; Swatland, 2005).
The carcass of the sheep is cut into three mam sections. These sections will be processed into "cuts" depending on the market that is being targeted. A general overview of the sections can be seen in Figure 2.4. Details of carcass cuts can be found in (Anon, 200 1 ). The leg of the lamb, when it is chump on, can be processed as the boneless leg, the long leg, which consists of the part boned long leg, femur bone leg, and hind shank. When the lamb is processed so the chump is part of the middle section of lamb then the leg is processed into the part boned short leg, when this occurs the chump is processed into the chump and boneless chump.
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F RONT BR EAST
LEG
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Figure 2.4: The divisions of the lamb carcass that would be generated when the lambs are processed (Lirette et aL, 1984).
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The middle section of the carcass, chops, flanks, and fillet in Figure 2.4, is processed in many ways depending on the market that the Jamb is destined for. One way the middle of the carcass is marketed is the saddle, processed into reformed saddle cutlets. The saddle can also be processed as the chump on long lo in, or the long loin chump off. Additionally, the 1 rib short lo in, 7 rib rack, and boneless chump can be generated from the saddle. One of the most common ways to process the saddle is to generate the boneless loin, tenderloin (fillet), frenched rack cap on, or frenched rack cap off from the saddle. The flaps are always a separate cut generated from the middle section o f the carcass.
The forequarters of the carcass are processed into the either the shank, square cut shoulder and neck slices, the boneless shoulder, the 5 rib fore or the oyster shoulder. The processing of one cut will affect other cuts for example if the leg is processed into the boneless leg then the chump on long loin cannot be generated. Similarly, within a section of the carcass certain cuts have to be processed together because if the 5 rib fore is processed then neck slices cannot be produced. More detail on carcass cuts and the way the carcass is processed can be seen in (Anon, 200 1 ).
A common method of cutting carcasses is into eleven "cuts", which include the boneless leg, boneless shoulder, frenched rack, strip loin, fillet, flaps, neck fillet, muscle trim, fat
trim, leg bone and other bone. All of these cuts vary as to their muscle, fat and bone content, which can be seen in Table 2 . 3 .
Table 2 .3: Composistion o f the cuts generated b y Richmonds L td a nd used i n this study
Cut Muscle Bone S. Fat I . Fat
Boneless leg ./ X ./ ./ Boneless shoulder ./ X X ./ Frenched rack ./ X X X Strip loin ./ X X X Fillet ./ X X X Flaps ./ ./ ./ ./ Neck Fillet ./ X ./ ./ Muscle Trim ./ X ./ ./ Fat Trim ./ X ./ ./ Leg Bone2 ./ ./ X X Other Bone2 ./ ./ X X
subcutaneous fat and intermuscular fat
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2. 7
Dev elopment of Computer Models
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S imulation models are used to mimic a real situation as closely as possible, and allow changes to be made to the situation without having to perform the experiment. (Spedding, 1 998) (cited in (Dooley, 2002)) defines models as "representations of the real thing, simplified for some purpose: they include those features that are essential for the purpose and leave out those that are inessential". Models can be used in situations where the costs of performing the experiment are too high or the time that would be required to perform the experiment would not be practical. Additionally, if the situation that is being analysed does not exist then models can be used to determine the effect of the situation.
There are many types of models that can be use to simulate a situation and can include; static or dynamic models, or deterministic or stochastic models (Sorenson, 1 998). Static models, as the name implies, are constant over time, whereas dynamic models have time as a variable and will therefore change over time (Dooley, 2002) . When a stochastic model is being used, variables are represented by probability distribution, while when using a deterministic model the variables are represented by a single value, such as a mean (Dooley, 2002). As the variables in a deterministic model are represented by a single value, the outputs from the model will always be the same. Conversely, using a probability distribution to represent the variables in a stochastic model allows chance to p lay a part and the outputs will be different. As chance plays a part in a stochastic model, this model would most accurately represent an agricultural system.