Effects of the Naked Gene on Postweaning Performance and Thermotolerance Characters in Fryer Rabbits

This investigation quantified the effects of the naked gene on postweaning and thermotolerance characters in rabbit fryers during 42-d growth trials in summer of 2002 in subtropical south Texas. In 1999, a rare naked rabbit was mated to commercial New Zealand White does, resulting in 16 F1 litters and 113 offspring, all of which had normal fur coats. To expose the recessive naked gene in the homozygous state, F1 X F1 inter se matings were made between half-siblings to create an F2 generation. Based on the expected 3:1 phenotypic ratio (furred to naked), in the F2 generation, 192 rabbits had normal fur coats and 48 rabbits were naked, supporting the single recessive gene hypothesis (χ = 2.94; P>0.05). Weaned fryers were randomly assigned to growing pens containing either two or three furred or naked non-littermates. Individual fryer traits included initial and final body weights and ADG, as well as respiratory rate and rectal body temperature. Pen traits included feed and water intake. For individual traits, data were blocked for random effects of fraternal-litter and pen (nested within treatment), and fixed effects of treatment (naked and furred groups), age batch, gender, fixed effect interactions, and initial age of fryer (linear covariate). Results revealed (P<0.001) that naked compared to furred fryers had heavier final weights (1996 versus 1784 g) and more rapid ADG (27.3 versus 24.0 g/d). Pens of naked compared to furred fryers, on average, had higher feed intake by 28 g/d per fryer (P<0.001), but pen feed efficiency (total gain/total feed intake) was poorer for naked than for furred rabbits (0.230 and 0.279; P<0.001). Daily water intake was similar (199 and 188 ml), on average, between pens of naked and furred fryers. However, furred compared to naked fryers had a higher free water-to-feed intake ratio (2.13 and 1.72 ml/g; P<0.01). At 1400 hr, naked fryers had lower rectal temperatures (38.9 and 39.7 oC) and lower respiratory rates (120 and 161 breaths per minute) compared to furred rabbits, respectively. Our results suggest that naked rabbits had better heat tolerance and(or) a higher critical body temperature zone than furred rabbits, and hence better growth performance. This preliminary experiment yielded promising results in favor of naked rabbits, but additional trials are needed to confirm these results.