Economic Value Of Live Weight In South African Dairy Cattle C.B. Banga 1 , F.W.C. Neser 2 , J. van der Westhuizen 1 and D.J. Garrick 3 Introduction A sound breeding objective should, of necessity, incorporate all economically relevant traits. In the past, breeding objectives for dairy cattle in most countries were focussed solely on production traits. Significant changes have, however, taken place in recent years, gradually leading to more balanced breeding objectives comprising a wider range of economically important traits (Miglior, F., Muir, B.L. and Van Doormaal, B.J. (2005)). Several studies (Groen (1989); Groen and Korver (1990); Visscher, P.M., Bowman, P.J. and Goddard, M.E. (1994); Spelman and Garrick (1997); review by Veerkamp (1998); Pe´rez-Cabal, M.A., González Santillana, R. and Alenda, R. (2006)) support the inclusion of live weight in breeding objectives, to account for increased maintenance costs of heavier cows. A few countries such as New Zealand (Spelman and Garrick (1997)), Finland (Hietanen and Ojala (1995)) and Australia (Hayes, B.J., Bowman, P.J., Chamberlain, A.J. et al. (2009)) have, accordingly, incorporated live weight in their dairy breeding objectives. In South Africa, genetic evaluation is routinely carried out and EBVs published on 23 dairy traits; however there are no scientifically developed and clearly defined breeding objectives. Genetic trends show that selection in South African dairy cattle is mainly directed at increased yield and improved type (Theron and Mostert (2004)). The objective of this study was to determine the economic value of live weight in South African dairy cattle, as part of an exercise to develop sound and broader breeding objectives. Materials and Methods Economic values were calculated separately for the two major dairy cattle breeds (Holstein and Jersey) in each of the two major dairy production systems in South Africa (intensive concentrate-fed and pasture- based systems). A bio-economic herd model, simulating an average farm (base herd) for each breed in each production system, was developed. Data collected through the National Dairy Animal Improvement Scheme were used to derive base herd parameters (Table 1). Farm economic data and milk pricing information were provided by the Milk Producers’ Organisation of South Africa (MPO (2008); Koos Coetzee (2009), personal communication; Dawie Maree (2009), personal communication) and the milk buyers (Berlo Cotsee (2009), personal communication; Pieter van Zyl (2008), personal communication)). The price of beef was obtained from the South African Meat Industry Company (SAMIC (2008)). The partial budget approach was used to compute economic values by simulating the marginal change in profit resulting from a unit increase in live weight, while all other traits remained constant. This was done by considering incomes and expenses for the base herd and a higher live weight herd. It was assumed that increased feed (energy) requirements for higher live weight were met by buying in extra feed and that non- feed costs remained constant. In the pasture-based production system, it was assumed that purchased feed is obtained at opportunity cost, defined as average revenue in the base situation, following Garrick (2002). 1 ARC Animal Production Institute, P/Bag X2, Irene 0062, South Africa 2 Department of Animal Science, UFS, P O Box 339, Bloemfontein 9300, South Africa 3 Department of Animal Science, Iowa State University, Ames, IA 50011, USA