Effect of divergent selection for the volume of muscle on the hind

The evaluation is based on the experiment which was published by Szendrő et al. (2012).

Objective of the experiment

The objective of the study was to analyze the effects of divergent selection for CT measured thigh muscle volume (TMV). This section focuses on evaluating the economic values at the farm and slaughterhouse levels.

Material and methods

TMV was measured by CT in PWhite growing rabbits at 10.5 weeks of age.

Rabbits were selected to increase (PP) or decrease (MM) their TMV during two generations. Production performance, slaughter traits and economic values of their offspring were compared.

Economic evaluation Natural indicators

Selection had no effect on daily weight gain and body weight at the age of 10 weeks (Table 18). Due to a lower amount of fat tissues (fat depot), the PP group had lower feed intake and better feed conversion ratio than MM rabbits. This is explained by the fact that the energy requirement for building fat into the body is higher than that of the muscle (protein). This is why PP rabbits consumed less feed to achieve the same weight gain. A favorable side effect of the CT aided selection is the improvement of feed conversion rate. These results were confirmed when different crossbred rabbits were compared (Szendrő et al., 2010).

73 Table 18

Effect of divergent selection for thigh muscle volume on productive performance of growing rabbits

MM: progeny of the minus-selected parents of the second generation;

PP: progeny of the plus-selected parents of the second generation

Significant differences were found in TMV, weight of hind part, hind leg and meat on hind leg, with higher values in the PP group. Opposite differences were found in kidneys, and perirenal and scapular fat weights (Table 19).

Table 19

Effect of divergent selection for thigh muscle volume (cm³) on carcass traits (g)

Traits Second selected generation

SE Prob.

MM PP

CT measured thigh muscle volume 309 336 21.2 0.004

Body weight at slaughter 2454 2445 211 0.863

Skin 350 353 22.7 0.657

Head 116 118 4.81 0.957

Full gastrointestinal 440 410 47.7 0.432

Hot carcass 1485 1504 43.6 0.362

MM: progeny of the minus-selected parents of the second generation;

PP: progeny of the plus-selected parents of the second generation

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The ratio of the full gastrointestinal tract compared to body weight was higher for the MM rabbits (Table 20).

Table 20

Effect of divergent selection for thigh muscle volume on ratios of carcass and carcass parts

Traits Second selected generation

SE Prob.

MM PP

Percentage of body weight at slaughter, %

Skin 14.2 14.5 0.93 0.576

MM: progeny of the minus-selected parents of the second generation;

PP: progeny of the plus-selected parents of the second generation

Compared to the reference carcass, ratios of the fore part, perirenal fat and scapular fat were higher in the MM group, while ratios of the hind part and hind leg meat were higher in PP rabbits. Previously, the efficiency of selection for the L-value was shown by genetic analysis, genetic trend estimation and a divergent selection experiment. The difference between the plus and minus selected groups was 5.8% for the L-value and 5.1% for the weight of the mid part (Szendrő et al., 1996). Breeding values of CT

measured animals increased during the three years (Specify Years), studied: 0.12, 0.35 and 0.78, respectively) (Szendrő et al., 2004). The

estimated genetic correlation between the L-value and dressing out percentage was 0.47 (Nagy et al., 2006). The effectiveness of selection for

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TMV was also demonstrated by Gyovai et al. (2008) using the data from the routine breeding. At the same time the volume of fat depots and feed intake decreased while the feed conversion ratio improved.

Financial indicators

Cost of production at the farm level, the price of slaughter rabbits, the revenue (from whole carcasses and from different carcass parts) at the slaughterhouse level, as well as profitability indicators on both the farm and slaughterhouse levels of rabbits selected divergently for decreasing (MM) and increasing (PP) their TMV are shown in Table 21.

At farm level

In the progenies of the second generation of divergent selection for increasing TMV (PP) had lower feed consumption (Table 18) than that of rabbits selected for decreasing thigh muscle volume (MM). Thus cost of feeding decreased by 7% in PP compared to the MM group. Negligible costs of mortality were found in both cases. The difference between the price at slaughter (which is considered as revenue for the farmer) was only 0.01

€/rabbit, in favor of the MM group. Based on low, medium and high feed prices, the profit of MM was 0.45, 0.33 and 0.22 €/rabbit, while PP rabbits achieved profits of 0.47, 0.35 and 0.25 €/rabbit, respectively. Differences show that PP rabbits achieve at least 8,300 € more income for a farmer producing 50,000 rabbits yearly on a farm. When the calculation was made on high price feed instead of low feed price, profit in the MM group decreased by 52.6%, while the decline was 47.3% in the PP rabbits. In each feed price category, the cost to revenue of MM group exceeded that of PP rabbits. With increasing feed price, the difference between the MM and PP

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groups also increased, the differences in ratios were 0.47, 0.73 and 0.84%

for low, medium and high feed prices, respectively, in favor of PP rabbits.

Table 21

Profitability of divergent selection for thigh muscle volume (TMV) at the farm and slaughterhouse levels

Notes: Low, Med and High: low, medium and high price of pellets (at farm level) or selling price (at slaughterhouse level); €/r= €/rabbit; SH= slaughterhouse; numbers in bold represent values higher than average; *Cost of slaughtering was not identified at the slaughterhouse level, thus, the differences among the groups are reasonable

At slaughterhouse level

From the slaughterhouse’s point of view, the difference in revenue from rabbit products was between 0.31 and 0.39 €/rabbit, in favor of PP rabbits, depending on the selling price. MM rabbits could achieve profitability ratios above the average only when selling rabbit products on well-paying markets

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(i.e. at high selling prices), while PP rabbits were profitable even at a medium price. The difference between the revenues from carcass parts was remarkable (1.45 €/rabbit). The highest profit (4.34 €/rabbit) was achieved by PP rabbits, while the lowest value (2.90 €/rabbit) was found with the MM group. Consequently, PP rabbits may achieve 50% higher profit than MM rabbits at the slaughterhouse level, depending on the selling price.

Concerning cost to revenue, profit to cost and cost efficiency, the differences were between 2.50-2.72, 8.95-11.07 and 0.09-0.11%, respectively, in favor of the PP group.

All of the values showed that the selection for improving muscle on hind legs by CT had significant economic benefits for both the farmer and the slaughterhouse, but higher profits for the slaughterhouse.