Index selection in terminal sires improves lamb performance at finishing.

Area of Science:

• Animal Science
• Genetics
• Meat Science

Background:

• Consumer perception of lamb meat as fatty has led to decreased consumption.
• A lean growth index was developed in the UK to enhance carcass lean content and manage fat levels in terminal sire breeds.

Purpose of the Study:

• To assess the impact of terminal sire index selection on crossbred lamb performance at finishing.
• To determine the effectiveness of the lean growth index within different terminal sire breeds.

Main Methods:

• Crossbreeding of high and low lean growth index rams (Charollais, Suffolk, Texel) with Welsh and Scottish Mule ewes.
• Commercial rearing of 6356 crossbred lambs, with data collection on finishing body weight, ultrasonic muscle and fat depth, condition score, and conformation.
• Statistical analysis of lamb performance metrics, including log-transformed ultrasonic fat depth (logUFD).

Main Results:

• High-index-sired lambs exhibited significantly heavier finishing weights, greater ultrasonic muscle depth, and reduced ultrasonic fat depth compared to low-index sires.
• Breed differences were observed: Suffolk lambs were heaviest, Texel lambs had the thickest muscle depth, and Charollais lambs had the greatest fat depth.
• Sire index selection generally resulted in improved performance, with notable variations within specific breeds like Suffolk.

Conclusions:

• Lean growth index selection effectively produces heavier and leaner lambs at slaughter.
• The findings provide producers with valuable information for selecting terminal sires that align with their production goals and market demands.