- Genetic trends for profitability in three woolled sheep flocks
|Last update: November 22, 2010 12:23:07 PM|
Genetic trends for profitability in three woolled sheep flocks
M. J. Herselman
Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg, EC, 5900, South Africa
E-mail: Tino Herselman
Much progress has been made during the past two decades with regard to scientifically based genetic improvement of farm livestock and marked responses in different production traits have be achieved through selection based on performance data and the BLUP of breeding values in different sheep breeds. However, the net result of such selection is an increase in production or income per head, and not necessarily per unit of available resource. The income from an individual sheep is directly related to the level of production of that animal, whereas the income from a sheep farming enterprise is determined by the efficiency of converting available grazing material into products. Although different breed societies as well as the national small stock improvement scheme supply and use economical based indices as selection criteria, these values are also expressed as income per head and not per unit of available resource. The purpose of this paper is to illustrate the effect of production based selection on farm profit in three experimental sheep flocks. Data recorded in the Carnarvon Afrino Flock (CA), the Grootfontein Merino Stud (GM) and the Cradock Merino Stud (CM) were used. Production data of 5566 lambs born in CA from 1975 to 2001, 9268 lambs born in GM from 1968 - 2002 and 5198 lambs born from 1988 to 2002 were used for the estimation of breeding values in body weight (BWebv), clean fleece weight (CFWebv), staple length (SLebv) and fibre diameter . (FDebv) using the ASFREML programme of Gilmour et al. (1997). The estimated breeding values for individual animals were averaged within birth years. Lifetime number of lambs born from 1572 (1969 to 2000), 2716 (1968 to 2002), and 1070 (1988 to 2002) ewes were available for CA, GM and CM respectively. Breeding values for number of lambs born per year per ewe (LBebv) was also estimated with the ASFREML programme. Breeding values for farm profit (PROFITebv) were calculated using the equation of Herselman (2004) as follows:
From Figure 1 it is evident that no genetic improvement in farm profit was achieved during the pre-1990 period in all three experimental flocks. In the early 90's, decreased fibre diameter was introduced as a selection objective in these flocks, which resulted in marked increases in estimated breeding values for farm profit. The decrease in PROFITebv in CA during the 80's was the net result of an increase in BW and FD during that period. The sharp increase in profitability after 1990 of GM and CM was the result of an increase in CFW and SL and a decrease in FD. More gain in profitability could have been expected if less emphasis was placed on BW as a selection objective. It is concluded that PROFITebv should be further investigated as a possible selection criterion in sheep.