Phenotypic and genetic relationships between lamb and ewe traits for the Sabi sheep of Zimbabwe

Abstract

Genetic and phenotypic correlations were estimated between lamb and ewe traits in a flock of Sabi sheep reared at the Matopos Research Station. Direct additive estimates of heritability were: 0.28 ± 0.04; 0.17 ± 0.00; 0.25 ± 0.01; 0.39 ± 0.01; 0.59 ± 0.01; 0.50 ± 0.01; 0.68 ± 0.03; 0.12 ± 0.003; 0.25 ± 0.01; 0.11 ± 0.00; 0.12 ± 0.00; for birth weight, weaning weight (120 days), 12 month weight, 18 month weight, ewe mating weight, post partum weight, ewe weight at weaning of lamb, total weight of lamb weaned, slaughter weight, hot and cold carcass weights respectively. Genetic correlations between birth weight and other weights to 18 months were high (0.75-0.85), whilst the relationship between weaning, 12 month and 18 month weight was close to unity. The genetic correlation between birth weight and ewe weights (mating, post-partum and dam weight at weaning of lamb) were moderate viz. 0.51 ± 0.08, 0.40 ± 0.09, 0.49 ± 0.07 respectively and were close to unity at 18 months of age viz. 0.96 ± 0.02, 0.92 ± 0.03, and 0.84 ± 0.03 respectively. Total weight of lamb weaned was moderately correlated to birth weight (r g = 0.46 ± 0.15) but tended to be highly correlated with 18 month weight (0.92 ± 0.10) and ewe weights (0.75 ± 0.09-0.91 ± 0.07). The genetic correlation between birth weight and slaughter and carcass weight was moderate and was high at 18 months. The heritability estimates from a univariate logit transformed analysis for fertility, prolificacy and lamb survival were 0.08 ± 0.04, 0.22 ± 0.03, and 0.01 ± 0.02 respectively. The genetic correlation between fertility and lamb weight and ewe weights was low (-0.08 ± 0.004, to 0.06 ± 0.02) and some estimates had large standard errors. The genetic correlation between prolificacy and birth weight was close to zero. The genetic correlations between prolificacy and weaning weight, 12 month weight, 18 month weight, ewe mating, post-partum and ewe weight at weaning were 0.07 ± 0.02; 0.12 ± 0.00; 0.07 ± 0.02; 0.22 ± 0.00; 0.13 ± 0.00; 0.24 ± 0.00 respectively, and that between fertility and prolificacy was negative (-0.17 ± 0.07). Genetic correlations between lamb survival and birth weight, weaning weight, 12 month weight, 18 month weight and total weight of lamb weaned were 0.18 ± 0.00, 0.26 ± 0.00, 0.15 ± 0.00, 0.15 ± 0.00, 0.13 ± 0.00 respectively. Selection for birth weight and total weight of lamb weaned have possible uses in a selection index for the Sabi flock. _______________________________________________________________________________________

Estimated variance components and breeding values for pre-weaning growth criteria in Romney sheep

“…8, 12.69±2.38, 20.72±4.33, 21.65±5.53 and 14.53±3.20 kg at weaning, in Zimbabwe Sabi lambs (Matika et al 2001), in Egyptian Farafra lambs (Mousa et al 2006), in Iranian Zandi lambs (Ghafouri-Kesbi & Eskandarinasab 2008), in Arman lambs (Farokhad et al 2011) and in Indian Malpura lambs (Gowane et al 2015), respectively. Ghafouri-Kesbi (2013) reported that statistics of Kleiber Ratio at pre-weaning period were 19.61±2.4 (CV= 12.2%) in fat-tailed Mehraban lambs.…”

“…Direct estimates of heritability in sheep breeds for LBW were 0.28±0.04 in Sabi (Matika et al 2001), 0.06 in Swedish finewool (Näsholm & Danell 1996), 0.13 in Suffolk (Yamaki 1994), 0.14-0.20 in Baluchi (Yazdi et al 1997), 0.43 in Segurena (Analla et al 1997) and 0.15±0.05 in Romney (Ibrahim 2015). Furthermore, estimates for LWW were 0.17±0.00 in Sabi (Matika et al 2001), 0.34 in Suffolk (Yamaki, 1994, 0.15 Swedish finewool (Näsholm & Danell 1996), 0.13-0.19 Baluchi (Yazdi et al 1997, 0.31 Segurena (Analla et al 1997) and 0.08±0.03 in Romney (Ibrahim 2015).…”

Heritability and Breeding Value of Sheep Fertility Estimated by Means of the Gibbs Sampling Method Using the Linear and Threshold Models

“…The ranges of both the heritability index (0.01-0.39) and repeatability index (0.090-0.670) of fertility as seen in earlier works have been large: Lee, et all, 2009, Matika, et al, 2001, Matos et al, 1997, Olesen, et al, 1994,Olivier, et al, 1998, Piwczyński, et al, 2004, Piwczyński and Mroczkowski, 2009, Rosati, et al, 2002, Sousa, et all, 2000, Vatankhah, et al, 2006. One may assume that, similarly as in the authors' own research, this is largely due to which method and the model of statistical analysis was used (Matos et al, 1997, Olesen, et al, 1994, Piwczyński and Mroczkowski, 2009, Sousa, et all, 2000, Vatankhah, et al, 2006.…”

“…Unfortunately, genetic improvement in this area is very difficult relative to other production traits characterized with lower genetic conditioning (Matika, et al, 2001, Matos et al, 1997, Piwczyński, et al, 2004, Piwczyński and Mroczkowski, 2009, Sousa, et all, 2000. Moreover, discovering the genetic conditioning of fertility is more complicated than in the case of, for instance, body weight or milk yield.…”

“…Among other methods, those used for this purpose include the REML method (Lee et al, 2009, Matika et al, 2001, Piwczyński, et al, 2004, Sousa et al, 2000, the Gibbs sampling method (Piwczyński and Mroczkowski, 2009), and also the linear (Matos, et al, 1997, Olesen, et al, 1994, Piwczyński, et al, 2004, Sousa, et all, 2000, Varona, et al, 1999, Vatankhah et al, 2006) and the threshold model (Matos, et al, 1997, Olesen, et al, 1994, Piwczyński and Mroczkowski, 2009, Sousa et all, 2000, Varona, et al, 1999, Vatankhah, et al, 2006. Previous reports in the literature present studies in which probit or logit transformations were applied first (Matika, et al, 2001, Piwczyński, et al, 2004, before estimation of binomial trait heritability. Some papers describe estimates of parameters obtained in accordance with the mean value of several consecutive ewe performance values (for instance 2 or 3) (Piwczyński, et al, 2004) , or the life performance (Lee, et all, 2009).…”