Fattening performance and carcass characteristics were evaluated in 202 lambs sired by D’man (D), Timahdite (T) and terminal sires of the Ile-de-France (IF), Lacaune (L), and Mérinos Précoce (MP) breeds. Previous results had suggested that the three latter improved breeds had relatively similar growth and carcass performance in crossbreeding. They were, therefore, pooled in this study into one meat group breed (M) to facilitate comparisons between the five genotypes of interest: two purebreds (T, D), two single crosses (D ✕ T (DT), M ✕ T), and one three-breed cross (M ✕ DT). Results showed important improvements of performance in crossbred lambs especially those sired by meat breed rams. M ✕ T and M ✕ DT lambs grew fastest (238 and 256 g/day, respectively) and showed the best food conversion ratio. D purebred lambs realized the lowest fattening gains (196 g/day) while, T and D ✕ T lambs were intermediate (209 and 218 g/day, respectively). The D lambs deposited relatively more internal fat and relatively less subcutaneous backfat, and their carcasses had the lowest conformation score and smallest longissimus muscle area (11·23 cm2). The carcasses of M ✕ T and M ✕ DT crossbred lambs had larger longissimus muscle areas 13·97 and 13·88 cm2, respectively, thicker subcutaneous fat cover and better conformation scores than other genotypes. The effects of M as a terminal sire breed were favourable for the majority of fattening and carcass characteristics. The absence of differences between M ✕ T and M ✕ DT genotypes on post-weaning growth, food conversion ratio and on objective and subjective measurements of carcass conformation indicated that the infusion of 25% of D genes in M ✕ DT lambs did not affect post-weaning growth and carcass traits. The results on the use of M sires and DT dams, which have above average reproductive rates, in M ✕ DT crossbreeding indicate that a two-stage crossbreeding system could enhance the quantity and the quality of meat sheep production in Morocco.

A crossbreeding experiment involving Timahdit (T), D'man (D) and improved sire breeds (M) was conducted to compare lamb production in five crossbreeding types: D ✕ D, T ✕ T, D ✕ T (DT), M ✕ T, and M ✕ DT lambs. Reproductive and production traits were analysed in 1187 litters, 1586 lambs born and 1346 lambs weaned, progeny of 605 ewes. Effects of crossbreeding type, year of birth, sex of lamb, age of dam, and type of birth were significant on the majority of traits studied. The D ✕ D and M ✕ DT crossbreeding system showed the highest litter sizes at lambing and at weaning with respective values in D ✕ D (2·17, 1·34) and M ✕ DT (1·72, 1·39). Ewes bearing the M ✕ DT cross lambs showed the highest (P < 0·05) litter weight at weaning (28·28 kg) followed by those with M ✕ T (23·14 kg), and D ✕ D (22·53 kg) lambs. M ✕ DT and M ✕ T lambs were heavier and grew faster than the other lambs. On the other hand, lamb survival rates and growth traits were the lowest in D ✕ D but those in T ✕ T and D ✕ T genetic types of lamb were intermediate. Results showed that D as a dam breed had a favourable effect on litter size (P < 0·01) but unfavourable effect on lamb survival and birth weight. The reproductive performance of DT crossbred ewes, due to their high prolificacy and lamb survival, associated with the favourable effect of an improved terminal sire (M) for growth traits, indicated that the three breed cross (M ✕ DT) could enhance lamb production in Morocco.