ADJUSTMENT FACTORS AND GENETIC AND PHENOTYPIC PARAMETERS FOR GROWTH TRAITS OF BARBARINE LAMBS IN TUNISIA

Growth data on 8788 Barbarine lambs raised in central Tunisia from 1968 until 1988 were studied. Sex of lamb, type of birth, age of dam, year of birth and ram effects were important sources of variation for growth traits from birth to 3 months of age. Male and single lambs grew faster than female and multiple lambs. Means of lamb growth traits were 3.42, 9.06, 15.40 and 17.75 kg, respectively, at birth, 30, 70 and 90 d of age. Average daily gains were 183, 159 and 146 g/d between 10-30, 30-70 and 30-90 d, respectively. All growth traits were optimal when age of the dam was 5 years. Multiplicative adjustment factors were computed, taking into account sex, type of birth and age of dam. Heritability estimates were 0.26 +/- 0.04, 0.14 +/- 0.03, 0.19 +/- 0.03, 0.27 +/- 0.04 and 0.32 +/- 0.04 for weights at birth, 10, 30, 70 and 90 d, respectively. Heritabilities for average daily gains from 10-30, 30-70 and 30-90 d were 0.15 +/- 0.03, 0.24 +/- 0.04 and 0.31 +/- 0.05, respectively. Genetic and phenotypic correlations among growth traits were all positive ranging from 0.43 to 0.96 and 0.10 to 0.92, respectively. These parameters are useful information to develop genetic evaluation methods for management within-flock or cross-flock breeding programs.