Possibilities of developing Favourable Body Fat Partition Via Selection Indexes – Application on Rabbits
Abstract. Estimates of phenotypic and genetic parameters of body fat partition and other related traits were calculated using an experimental material of 152 New Zealand White rabbits of 15 bucks and 42 adult does. To construet nine selection indexes aiming at improving fat partition, estimates of phenotypic and genetic parameters for weight and linear dimensions of the live body were also obtained. The aggregate genotype included the percentage total body fat depositing subcutaneously and intermuscularly at the marketing age of 12 weeks. The füll index included the weaning body weight, marketing body weight, body length, loin width and heart girth. The full index had the highest correlation with the true breeding value (rT| = 0.597). Comparable accuracy (rTi = 0.561) would be expected from the best-reduced index (I7 = 0.009 BW –0.988 HG) combining marketing body weight and heart girth. At each round of selection with intensity =1, such a reduced index is expected to result in developing rabbits with advantageous fat partition in terms of higher percentage total body fat depositing subcutaneously (+0.35 unit %), intermuscularly (+1.91 unit %) and intramuscularly (as reflected by 0.15 unit % increase in carcass muscle yield.
As compared with its unrestricted form, the best reduced index reduced to zero change in total body fat (I7(TBF)) would result in drastic decline in percentage total fat depositing as kidney knob and Channel fat (+0.32 vs. –0.18 unit %) with little amelioration in percentage total fat aecumulating in the other depots. Selection on I7(TBF) instead of 17 would reduce improvement in marketing body weight (+0.52 vs. +0.33 gm), carcass yield (+0.10 vs. 0.04 unit %) and carcass boneless meat yield (+0.19 vs. 0.07 unit %) with increase of gain in carcass muscle yield (+0.15 vs. 0.32 unit %).