An experiment on two exotic breeds of New Zealand White (NZW) and Californian (CAL) rabbits was carried out to evaluate genetically post-weaning growth performance of these two breeds raised under adverse hot conditions. Data on 2291 of NZW and 1628 of CAL rabbits were used. Post-weaning growth traits investigated were body weight (at 5,6,8,10 and 12 weeks) and daily gains and livabilities (at the age intervals of 5-6, 6-8, 8-10 and 10-12 weeks). Variance components and sire heritabilities were estimated for these traits by using Henderson's method (HM) and Restricted Maximum Likelihood (REML). Sire transmitting abilities (STA) for these traits were estimated using a single-trait Animal Model (AM).
For most growth traits of both breeds, estimates of the sire component of variance obtained using either HM or REML were low or somewhat moderate. The percentages of variation due to sire for growth traits estimated using HM or REML in NZW and CAL rabbits ranged from 0.0 to 12.5% for body weight, 1.7 to 13.1% for daily gain and 12.7 to 13.5% for livability. For most growth traits, estimates of sire component of variance in NZW rabbits obtained when using HM were generally smaller than those obtained when using REML, while inconsistent trend was observed for CAL rabbits. Although all estimates in both breeds were generally low, heritability estimated by using HM and REML in NZW rabbits were higher than those corresponding estimates in CAL rabbits. These estimates ranged from 0.049 to 0.501 in NZW vs 0.0 to 0.256 in CAL for body weight, 0.142 to 0.518 in NZW vs 0.070 to 0.184 in CAL for daily again and 0.106 to 0.502 in NZW vs 0.021 to 0.154 in CAL for livability. The differences between minimum and maximum values of STA for post-weaning growth traits and livabilities were low or somewhat moderate. For body weight at different ages, there were about 81 to 85% of the sires in NZW (47 sires out of 59) and 77 to 80% in CAL (30 sires out of 39) representing an absolute difference of less than 40 grams. For daily gains in both breeds, the largest number of sires was found in the class with the smallest absolute difference in STA and the smallest number of sires was found in the class with the largest absolute difference. Among all growth traits, percentages of positive estimates of STA were nearly similar in both breeds and they ranged from 50.6 to 61.0% for body weights, 46.2 to 55.9 % for daily gains and 51.3 to 66.1 % for livability.
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