Adjusting Lamb Weight for Age of Ewe, Litter Size, Sex and Age of Lamb in the Swedish Sheep Recording Scheme

Abstract

The appropriateness of the current adjustment factors for weaning weight was studied on data from the Swedish Sheep Recording Scheme for the years 1981–83 and 1986–88. The study included the four main breed groups Swedish Peltsheep (P), Swedish Landrace (L), Swedish Crossbred (X) and the imported heavy breeds (K). The adequacy of the adjustment factors was also tested within the breeds Swedish Finewool (Lf), Swedish Rya (Lr) and Crossbred group having crossbred parents (X*X). Analyses (1981–83) were based on 140681 Pelt lambs, 16785 lambs from the L-group, 25092 lambs from the X-group and 6321 lambs from the K-group. Data from 1986–88 comprised in total 11% fewer lambs.

The adjusted weights for lambs after 1- and 2-year old ewes were underestimated by previous adjustment factors in all breed groups except Peltsheep. The adjusted weights were too high for single born and single reared lambs after yearlings in Peltsheep. The previous adjustment factors for litter size generally gave adjusted weights which were too high for single lambs and too low for triplets. The earlier adjustment factors gave adjusted weights for ram lambs that were too high in comparison with ewe lambs. Finally the adjustment factors for age of lamb underestimated adjusted weights by 10% in Peltsheep and the L-group, while in the X- and K-group weights were overestimated to the same degree. A new set of adjustment factors is suggested.

Key Words:

• environmental effects
• adjustment factors