Fertility of ewe lambs maintained indoors year-round on an accelerated breeding program

Data from records of 330 crossbred ewe lambs mated to 142 rams over 11 breeding periods were analyzed for lambing percentage to one service. These ewe lambs in two separate flocks were reared and maintained indoors year-round and were derived from the three synthetic crossbred strains being developed at the Animal Research Centre in Ottawa, Ontario, Canada. At first exposure to rams, the ewes were 6 to 7 mo of age and had no hormonal treatments to induce or synchronize estrus. The two flocks were bred alternately in January, May or September to establish an 8 mo breeding cycle. The rams were at least 10 mo old and were maintained in one of two lighting regimens. Fifteen percent of the ewes lambed and the average prolificacy was 1.6. It appears that ewe lambs mated to rams maintained in a constant day length (10 h light: 14 h dark/24 h) environment had lower fertility than those ewe lambs mated to rams maintained in an environment such that the day length was altered between 4 mo of 10 h light: 14 h dark/24 h and 4 mo of 18 h light: 6 h dark/24 h. Although the fertility level was low, the data suggest that the breeding of ewes 6 to 7 mo of age is feasible.