The application of a lean growth index in ram breeding flocks

C.J. Dodd, G.L. Bennett and R.W. Purchas

Advisory Services Division, Ministry of Agriculture and Fisheries, Hastings; Ruakura Agricultural Research Centre, Ministry of Agriculture and Fisheries, Hamilton and Animal Science Department, Massey University, Palmerston North

Proceedings of the New Zealand Society of Animal Production. 1985, 45: 77-80

Performance records, including live animal ultrasonic fat depth measurements and subjective assessments of fatness by lamb drafters were analysed on 1970 ram hoggets from 25 ram breeding flocks. The average mob live weight at assessment was 47.9 kg (range 34.2 to 60.3) associated with an average fat depth C of 3.3 mm (range 1.7 to 5.6).

The subjective assessment of live-animal fat depth has the advantages of speed and simplicity but further work is required to develop the most appropriate calibration techniques.

The extent of within-flock variability in the animal records was examined and comparisons made between 2 methods of adjusting fat depth for live weight within each flock. The calculation of within-flock fat- weight relationships for this adjustment was adopted for use in larger flocks, but a constant exponent method is preferred when flock size is small.

The wide variation in the LGI within flocks suggests considerable opportunity exists to make worthwhile genetic progress in lean growth rates.

Keywords: NZSAPAB; Sheep selection; fat depth measurement; lean growth index