THE CONVENTIONAL CARCASS EVALUATION AND THE CARCASS DISSECTION ANALYSIS OF PIGS

The information provided by conventional carcass evaluation concerning the carcass quality established by analyses of dissection was investigated on progeny testing pigs (n = 153). After conventional carcass evaluation, the left half of the carcass was cut up. In the most valuable part of the half carcass (ham + carri -f back + fore back -(shoulder -f-kidney fat) the skin -(fat component was separated from the meat -| bone component. The material was processed by stepwise multiple regression analysis. It was possible by means of the results of conventional carcass evaluation to explain 69 % of the variation in the weight of the skin + fat component and 64 % of the variation in its percentage, 61 % of the variation in the weight of the meat -fbone component and 56 % of the variation in its percentage, 59 % of the variation in the weight of the most valuable part of the carcass and 17 % of the variation in its percentage. The estimations calculated for the skin + fat component and its percentage had the same characteristics in conventional carcass evaluation as explanatory variables. The estimations calculated for the meat + bone component and its percentages differed from each other. The estimations calculated for the most valuable part of the carcass and its components also explained the shoulder, back and ham, as follows: a) the shoulder, most weakly, b) the skin + fat of the back, best by the skin + fat estimations (56 % of the variation), c) the meat + bone of the ham, best by the meat + bone estimations (58 % of the variation). The length of the carcass and of the side did not occur in the estimations. In carcass evaluation by litter testing there has occurred a switch from a system of subjective evaluation by a points scale to a system of objective measurements. There has also been a concurrent increase in the application of various degrees of cutting and dissection of the carcass in order to clarify its anatomical composition and to compare various methods of measurement (e.g. Rittler el al. 1965, Blendl 1966 a and b, Fewson et al. 1967, Stouffer & Burgkart 1967, Pedersen 1968, and Cupka 1968). In 1967—1968 pigs at the Pohjanmaa litter testing station were evaluated not only by cutting and dissection but also by conventional litter testing. It is thus possible in the present study to analyse methods of measuring carcass quality on the basis of domestic material. The purpose of the study is to examine the information provided by traditional carcass evaluation concerning the most valuable part of the carcass, its skin -)fat and meat + bone components, and the ham, back parts and shoulders.

most valuable part of the half carcass (ham + carri -f back + fore back -(-shoulder -f--kidney fat) the skin -(-fat component was separated from the meat -| bone component.
The material was processed by stepwise multiple regression analysis.
It was possible by means of the results of conventional carcass evaluation to explain 69 % of the variation in the weight of the skin + fat component and 64 % of the variation in its percentage, 61 % of the variation in the weight of the meat -f-bone component and 56 % of the variation in its percentage, 59 % of the variation in the weight of the most valuable part of the carcass and 17 % of the variation in its percentage.
The estimations calculated for the skin + fat component and its percentage had the same characteristics in conventional carcass evaluation as explanatory variables.The estimations calculated for the meat + bone component and its percentages differed from each other.The estimations calculated for the most valuable part of the carcass and its components also explained the shoulder, back and ham, as follows: a) the shoulder, most weakly, b) the skin + fat of the back, best by the skin + fat estimations (56 % of the varia- tion), c) the meat + bone of the ham, best by the meat + bone estimations (58 % of the variation).
The length of the carcass and of the side did not occur in the estimations.
In carcass evaluation by litter testing there has occurred a switch from a system of subjective evaluation by a points scale to a system of objective measurements.There has also been a concurrent increase in the application of various degrees of cutting and dis- section of the carcass in order to clarify its anatomical composition and to compare vari- ous methods of measurement (e.g.Rittler el al. 1965, Blendl 1966 a and b, Fewson et al. 1967, Stouffer & Burgkart 1967, Pedersen 1968, andCupka 1968).
In 1967-1968 pigs at the Pohjanmaa litter testing station were evaluated not only by cutting and dissection but also by conventional litter testing.It is thus possible in the present study to analyse methods of measuring carcass quality on the basis of domestic material.The purpose of the study is to examine the information provided by traditional carcass evaluation concerning the most valuable part of the carcass, its skin -)-fat and meat + bone components, and the ham, back parts and shoulders.

Material
The material consists of a total of 153 Landrace and Yorkshire pigs.This is part of a material gathered for genetical analysis.The pigs were received at the testing station in 1967 and the first half of 1968.The feeding was the standard-mixture normally supplied at litter testing stations (Partanen 1969).The pigs were slaughtered at a live weight of approximately 90 kg (average 89.66, standard deviation 2.44).Conventional carcass analysis was performed 24 hours after slaughter, and the left side of the carcass was cut immediately thereafter in the manner presented by Uusisalmi (1969 a and b).
In the cutting and dissection analysis, attention was paid chiefly to the most valuable part of the half carcass ( = ham + carre + back -(-fore back + shoulder -(-kidney fat) and to its skin + fat and meat + bone components.The carcass was also weighed, and the weight of its left half was calculated as the aggregate weight of the parts obtained by cutting.
Mention should be made of the following linear measurements and area measurements in conventional carcass evaluation: thickness of back fat, thickness of side fat, i.e. of 5.0.1.,length of carcass, length of side, area of cross-section of musculus longissimus dorsi, fat/ meat ratio (Fig. 1).
Further, a points scale of 9-15 was used to evaluate the characteristics: distribution of back fat, hams, quality of belly, meatiness, shoulder region, fineness of skin and bacon type.Of these, the hams, the shoulder region and the fineness of the skin were evaluated sensorily.Apart from the above characteristics expressing anatomical composition, eval- uation was also made of the meat quality by the intensity of colour (scale I-7) and of the quality of the fat by its firmness (scale 9-15).Among the characteristics expressing feed consumption and weight growth, the most important are the following, which were calculated by litter group: feed consumption, feed units per day per pig, daily gain per pig.
The bases for the calculations of the progeny test index (the »old» index) are: thickness of back fat, area of m. long, dorsi, length of side, daily gain and hams (graded in points).
The index is based on the results obtained by Varo (1962) with factor analysis.Processing of the material By means of stepwise multiple regression analysis (State Computer Centre 1966) estimations were calculated for the most valuable part of the carcass, for its skin + fat component and for its meat -)-bone component and the percentages of these.Each of the above was treated in turn as the dominant function and the others as ordinary functions together with the other results ofcutting and dissection.The optional explanatory variables were a total of 30 results of conventional carcass evaluation.
The programme of the stepwise multiple regression analysis proceeds stepwise, adding or subtracting one factor at a time.In the processing of the material, use was made of a free model in which the factor most improving the correlation coefficient is selected as the new factor at each step.The F-test (F S? 4.000) was used as the criterion for the factor to be added or subtracted.In addition to the estimations, the analysis produced the means, the standard deviations, a correlation matrix and regression coefficients.This study did not proceed to detailed explanation of the partial regression coefficients, for several of the optional explanatory variables were correlated to each other.

Results
Table 1 shows the means, standard deviations and coefficients of variation of the characteristics (a total of 50 characteristics) describing carcass quality and capacities of growth and feed consumption.The results show that the skin -(-fat component of the most valuable part of the half carcass is 17.26 per cent of the half carcass, and its meat + bone component 46.48 per cent, and that the most valuable part of the half carcass amounts to 63.74 per cent of the half carcass. The coefficient of variation for the live weight is only 2.72 per cent.It should be remem- bered in this context that the intention is to slaughter the animals at the same live weight, but that slaughtering was done at intervals of one week.For the sake of comparison it may be mentioned that the coefficient of variation for the carcass weight is 3.66, for the half carcass weight 4.16, for the most valuable part of the carcass 5.06 and for the meat + bone component of the most valuable part 6.31 and for the skin -f-fat component thereof 11.64.The coefficients of variation for individual parts of the carcass, such as shoulder, ham and back parts, are greater than the coefficient of variation for the most valuable part of the carcass.It may be mentioned that the coefficients of variation for the back fat and the 5.0.1.fat according to conventional carcass evaluation (v-% 14.53 and 21.38) are higher than the variation coefficient of the skin + fat component of the most valuable part of the carcass.
The variation of visual scores for such characteristics as hams, belly, shoulder region and fineness of skin is smaller than the variation of the characteristics in which the points value was also affected by objective measurement.
Table 2 shows the phenotypical correlation of the results of the cutting and dis- section with the results of conventional carcass evaluation.The correlation coefficient between live weight and half carcass is 0.71, that between carcass weight and half carcass is 0.71, that between carcass weight and half carcass 0.76, and that between carcass weight and the most valuable part of the half carcass 0.72.
Table 2. Phenotypical correlation of the dissection data with the results of conventional carcass evaluation (see Table 1).n = 153.
The meat + bone component.Table 5 shows the estimations for the meat + bone component of the most valuable part of the carcass and for its percentage.
The meat + bone model includes the characteristics; meatiness, weight at 25 % slaughter loss, distribution of back fat, hams and skin quality.R 2 amounted to 0.608.The final model calculated for the percentage of the meat -(-bone component includes the bacon type, 5.0.1.,skin quality, slaughter loss percentage, area of m.long.dorsi and firmness of fat.It might be mentioned that meatiness was included at the second step but dropped at the seventh step.R 2 amounted to 0.563. The multiple correlation coefficients between each of the 20 dissection results and the estimations of the meat + bone component (in g and in %) are shown in Table 6.
The most valuable part.Table 7 shows the estimations for the most valuable part of the carcass and its percentage.The final estimation for the most valuable part of the carcass includes the area ofm.long.dorsi, live weight, slaughter loss percentage, point ofham, s.o.L, and meat colour.R 2 amounted to 0.593.The weight with 25 per cent slaughter loss was included in the first step but dropped from the model at the fourth step, when the live weight was included.The slaughter weight was dropped from the model at the eighth step, when the slaughter loss percentage was included.The 5.0.1.was included in the estimation at the third step, dropped at the seventh and re-included at the eleventh.In the model for the precentage of the most valuable part of the carcass the characteristics included were the average number of feed units per animal per day, the slaughter loss percentage, the age at a weight of 20 kg and the area of the m.long.dorsi.The coefficient of multiple determination was low (R 2 = 0.168).
The multiple correlation coefficients between each of the 20 dissection results and the estimations of the most valuable part (in g and in %) of the carcass are shown in Table 8.

Discussion
The carcass quality of pigs is chiefly dependent on the anatomical composition of the carcass, which, in the measurements of carcass quality, is understood to be a) the amounts of meat and fat and the ratio between these, b) the sizes of the different parts and the relationships between these.The basic units adopted for measurement in the present study were, consequently, the most valuable part of the carcass, its skin + fat component and meat -f-bone component and the percentages of these.It was also possible to note informa- tion on shoulder, back parts and ham.
Owing to economic reasons, dissection of the left half only was performed.On an average, the left half amounted to 49.85 per cent of the carcass weight (45.62 % -53.58 %, observations on 109 pigs).Thus splitting of the carcass brings in a factor of error, which mainly affects the back parts.The carcasses were weighed to an accuracy of about 100 g, and the parts of the left side of the carcass to an accuracy of 10-20 g.Another difficulty in dissection was the comparability of the separations of shoulder from fore back.Likewise, the separation of the skin + fat and meat + bone components was difficult to per- form on the shoulder as accurately as on the ham and back parts, for the fat layers on the shoulder pene- trated the meat layers.It is partly for this reason that the coefficients of variation of the shoulder and its components are greater than the respective coefficients of variation for the ham and the back parts.Cla- rification of the shoulder was desired on account of »shoulderham».
Concerning the ratios between carcass weight, the half carcass and the most valuable part of the half carcass, it should be remembered that the correlation between the carcass weight and the half carcass (r = 0.76) is only slightly greater than the correlation between the carcass weight and the most valuable part of the half carcass (r = 0.72).
The skin + fat component.It can be seen from Table 4 that the estima- tions for the skin + fat component of the most valuable part (R = 0.83) and its percen- tage (R = 0.80) calculated from the results of conventional carcass evaluation measured best the respective characteristics, although the skin + fat model measured the half carcass equally well (R = 0.83).This phenomenon is probably explained by the presence of live weight and slaughter loss percentage in the model.The two models were almost identical (see Table 3).Thickness of 5.0.1.occupied first place in both models, but the distribution of back fat and the test index were also common variables.A closer examina- tion shows that the meatiness points appearing in the skin + fat model are replaced by the area of the m.long.dorsi in the model expressing percentage.It should be remembered that the meatiness points are chiefly determined on the basis of the area of the m.long.

dorsi.
The meat + bone component.It can be seen from Table 6 that the estimation calculated for the meat + bone component of the most valuable part of the carcass meas- ures the meat -(-bone component (R = 0.78) best, and, thereafter, the most valuable part of the carcass and the half carcass (R = 0.73).The model calculated for the percentage of the meat -(-bone component measures best the percentage of the skin + fat component (R = 0.80), next best the skin -)-fat component (R = 0.76) and third best the percentage of the meat + bone component (R = 0.75).The models measuring the meat + bone component and its percentage also show characteristics in common, such as meatiness and skin quality.The final coefficients of multiple determination of the estimations cal- culated for the meat + bone component (in g and in %) are slightly smaller than the final coefficients of multiple determination of the models calculated for the skin T fat component (in g and in %).It can be concluded from this that it is not possible by means of conventional carcass evaluation to measure as accurately the meatiness of the carcass as its fattiness (Fig. 2).
The most valuable part.The model calculated for the most valuable part of the carcass (see Table 8) measures best the weight of the half carcass (R = 0.84) and next best the skin + fat component of the most valuable part of the carcass (R = 0.79) and third best the most valuable part of the carcass (R = 0.77).When it is remem- bered that the model included both the live weight and the slaughter loss percentage, it is easy to understand why the model best measures the weight of the half carcass.The coefficient of multiple determination has become as high as that of the meat + bone component of the carcass.It was not possible to estimate to any appreciable extent the percentage of the most valuable part of the carcass from the data obtained by carcass evaluation (R = 0.41, R 2 = 0.168).
Characteristics.The following characteristics of conventional carcass evalua- tion were those most commonly included in the estimations presented: the thickness of 5.0.1., in most models occupying first place in the estimations of the skin + fat component and its percentage; the back fat and the distribution of the back fat, partly replacing each other; the meatiness, in first place in the models measuring the meat + bone com- ponent and its percentage; the area of the m.long.dorsi, alternately with the previous, for instance in the skin + fat model; the live weight together with the slaughter loss percentage; replacing the carcass weight; the bacon type and the ham points as charac- teristics of meatiness.
The colour of the meat as an index of quality, and the firmness of fat as an index of fat quality, each occur once almost significantly in the estimations.
It may be mentioned that the carcass length and the side length, which affect the structure and appearance of the pig, did not occur in the models.Nor did characteristics measuring additional growth and feed consumption appear to any extent.
The shoulder, back parts and ham.The estimations calculated for the most valuable part of the carcass and its components also provide an explanation of the shoulder, the ham and the back, as follows: a) the shoulder, most weakly, b) the back, generally best by the skin -|-fat estimation, and c) the meat + bone of the ham, best by the meat + bone estimation (Tables 4, 6 and 8).

Fig. 1 .
Fig. 1.Area of musculus longissimus dorsi and area of fat.

Fig. 2 .
Fig. 2. Variation of the most valuable part of carcass and its dissection results and their per- centages explained by means of characteristics of conventional carcass evaluation.

Table 1 .
Averages and standard deviations for certain dissection data and results of conventional carcass evaluation at the Pohjanmaa litter testing station 1967-68.n = 153.

Table 3 .
Skin + fat component of the most valuable part of the carcass estimated by means of step- wise multiple regression analysis.Optional explanatory variables = 30 characteristics of conventional carcass evaluation, n = 153.

Table 4 .
The multiple correlation of the following carcass dissection results with the characteristics included in the estimate of the skin ■+■ fat component in the most valuable part, n = 153.

Table 5 .
Meat + bone component of the most valuable part of the carcass estimated by means of step- wise multiple regression analysis.Optional explanatory variables = 30 characteristics of conventional cascass evaluation, n = 153.

Table 6 .
The multiple correlation of the following carcass dissection results with the characteristics included in the estimate of the meat + bone component of the most valuable part, n = 153.
Area of m. long, dorsi Points:firmness of back fat

Table 7 .
The most valuable part of the carcass estimated by means of stepwise multiple regression ana lysis.Optional explanatory variables = 30 characteristics of conventional carcass evaluation, n = 153

Table 8 .
The multiple correlation of the following carcass dissection results with the characteristics included in the estimate of the most valuable part of the carcass, n = 153.