Abstract
1. Pen effects and sire x hatch interaction effects on growth rate to 8 weeks of age were estimated from family and progeny test data obtained from the application of two commercial breeding programmes for growth rate to broilers.
2. The following variance components were obtained: σ2(pen) = 255 g2, σ2(sire) = 1 260 g2, σ2(sire × hatch) = 1 997 g2,σ2(residual) = 19 708 g2.
3. It is concluded that the effectiveness of progeny testing for growth rate in broilers is severely restricted by sire x hatch interaction effects.