Effect of Inbreeding on Pre-Weaning Growth Traits of Barki and Rahmani Lambs تأثير التربية الداخلية على صفات النمو قبل الفطام للحملان البرقى والرحمانى

 
Data on 704 Barki and 732 Rahmani lambs born at Alexandria University Experimental Station between 1991 and 2014 were utilized in this investigation to evaluate the effects of inbreeding of lambs and ewes on birth weight (BW), weaning weight (WW) and average daily gain (ADG) from birth to weaning.  Inbreeding coefficients of lambs and ewes were estimated using Wombat program by fitting a univariate animal model for each breed separately. Least squares analysis of variance indicated that means of BW, WW and ADG of Barki lambs were 3.69 and 20.53 kg and 139.71 g, respectively. The respective values for Rahmani lambs were 3.54 and 20.09 kg and 137.81 g.The means of lamb and ewe inbreeding coefficients were 0.0616 and 0.0434 for Barki and 0.0845 and 0.0552 for Rahmani.The effects of season and year of birth, sex of lamb, type of birth and parity on all studied traits of both breeds were significant (P<0.01 or P<0.05) except the effect of year of birth on BW and effects of parity on WW and ADG of Barki lambs which were not significant. Linear regression coefficients of studied traits on inbreeding of lambs were not significant for both breeds except that of ADG of Rahmani lambs which was significant (P<0.05). On the other hand, linear regression coefficients of lambs studied traits on their ewes inbreeding were significant (P<0.01) for Barki breed. The corresponding coefficients for Rahmani breed were significant (P<0.01) for WW and ADG but not for BW. The regression coefficients of Barki lambs BW, WW and ADG on lambs inbreeding coefficients were -0.0032 and 0.0275 kg and 0.2107 g, and were 0.0031 and -0.0384 kg and -0.3906 g for Rahmani, respectively. The corresponding estimates of Barki BW, WW and ADG on ewes inbreeding coefficients were -0.0182 and -0. 2104 kg and -1.6110 g and those for Rahmani were -0.0035 and -0.1041 kg and -0.8329 g, respectively. In General, the current results indicated that inbreeding level of ewes had greater detrimental effects than that of lambs on lambs' growth traits especially for Barki breed. Therefore, inbreeding should be avoided in this flock of Barki and Rahmani sheep through utilizing planned mating or introducing breeding rams from other sheep flocks.