Ewe litter size and lamb birth weight: Effects on lamb health, performance, and carcass traits.

Objective: A retrospective analysis was conducted using data from a large commercial sheep operation to determine if selection for larger litter sizes affected lamb birth weight, health, and performance.

Animals and procedure: Data on lamb health, performance, and carcass traits were collected during 2 vaccine trials conducted at a large commercial sheep operation. Data from each trial were analyzed for simple associations between ewe litter size, lamb birth weight, and lamb health, growth performance, and carcass traits.

Results: Increased litter size was associated with decreased lamb birth weight, and both were associated with higher mortality rates, including starvation and enteritis, and poorer growth performance and carcass traits.

Conclusion and clinical relevance: Increasing ewe prolificacy can reduce lamb birth weight, growth performance, and carcass traits and increase mortality losses. Veterinarians and sheep producers should consider the negative effects of selecting breeds with very large litter sizes when trying to optimize the production of lamb meat per ewe per year.