Targeted pre-breeding nutrition improves reproductive performance in an accelerated lambing system

Lamb production is hindered by seasonal supply and low productivity. Systems that decrease birth interval, known as accelerated systems, can overcome these constraints. To improve the nutritional management of these systems we examined the impact of altering energy intake during the pre-breeding period on reproductive outcomes. Ewes were randomly allocated to one of three 21-day pre-breeding nutritional treatments immediately following weaning: underfed (UF), control (C), or overfed (OF). This design was repeated over two seasons: short-day (Dec 2-22, n = 81) and long-day (April 3-23, n = 99). Vasectomized rams were introduced during days 7-21 of this period. During the subsequent 34-day breeding period, ewes were fed a common diet (120% of maintenance energy). During the pre-breeding period over both seasons, UF, C and OF ewes consumed 63%, 121%, and 222% of maintenance energy requirements, respectively. These treatments resulted in consistent changes in maternal energy status, including body weight, body condition score, and plasma NEFA concentration (P < 0.001 for all), during both seasons. The reproductive rate was higher in OF ewes compared to C and UF ewes (P < 0.05) in both short (22%) and long (43%) seasons, driven by a modest increase in conception rate (10%) and a larger increase in litter size (20%). Litter size, but not conception rate, was elevated in the short-day season. No differences in reproductive outcomes were observed between C and UF ewes. We conclude that energy excess during the pre-breeding period improves reproductive performance and minimizes its seasonal deficit in ewes in an accelerated system.