Proceedings of the New Zealand Grassland Associa tion 55: f55- 159 (1993) 155 Variation in cattle liveweights at marketing R.W. WEBBY, A.B. PLEASANTS and L.A. GREAVES AgResearch, Whatawhata Research Centre, Private Bag 3089, Hamilton, New Zealand Abstract The liveweights of Friesian bulls farmed on 3 farmlets during 4 years were analysed to find how the variation in liveweight increased through time, and to review some possible farm management strategies for limiting the increase in this variation. There were 59 bulls in 1986, 66 bulls in 1987, 59 bulls in 1988 and 61 bulls in 1989. The variation in animal liveweights within a mob increased linearly through time. The small variance in the slopes of the estimates indicated that the increase in liveweight variation through time could be predicted very accurately. The rate of increase of variation through time differed in only one year (1987; P< 0.01). Variation in animal liveweight between farmlets was constant through time, and not associated with the rate of increase of within mob liveweight variation. It was shown that the ranking of animals within the frequency distrib- ution of animal liveweight changed through time. Thus the current liveweight rank of an animal was no guide to liveweight rank 5 or 6 months in the future. This suggests that minimising the increase in liveweight variation through time by dividing a mob of cattle is not feasible. The importance of control of variation in agricultural products for the operation of on-farm quality assurance schemes is discussed, and avenues for exploration of management tactics designed to minimise variation in the production of animals for slaughter suggested. Keywords: bulls, liveweight, marketing, on-farm - quality assurance Introduction A mob of cattle will have a range of liveweights at any given time despite any effort to try to produce uniformity in liveweight or any other production trait. Conspicuous variation is a characteristic of biological systems, and a factor with which all farmers will be familiar. Variation in a mob of cattle means that some animals will be ready for slaughter before others. Historically, management of this variation has not been a large problem for farmers. Typically, animals are marketed as they became ready for slaughter, and animals not ready for slaughter are retained until they are judged to be ready. Thus a farmer trades variation in animal liveweight for variation in time of slaughter. Such a marketing strategy defines commodity trading, a business that has typified New Zealand agriculture in the past and become the basis of many of the problems we face on world markets. In the future farmers need to change from commodity trading of a product to trading of products based on quality. The concept of quality in a product has been poorly defined, most people associating the concept with some subjective personal standard. However, an objective definition is possible - indeed essential - and it is based on the concept of fitness for use (Burchas 1993). This concept defines variation in the product to be the principal reason why a product may fail the expectations of the customer who wishes to use the product. A product is ‘fit for use’, and a quality product, if it performs within specifications previously laid down by a customer. Emphasising that the performance range must stay within specification tolerance limits defines product quality in terms of the variation in the product. The process of continual improvement in quality, noted as essential for access to the Japanese market by Forgie (1993), represents the application of knowledge and technology towards performance within narrower tolerances. The immediate customer of a farmer is a meat processor. The meat processor wants product from the farmer which is ‘fit for use’. That is, carcasses of a uniform weight delivered at an agreed time. This in turn enables the meat processor to satisfy their customers. Contracts between a farmer and a meat processor for the farmer to deliver animals for slaughter at a given time, and of an agreed carcass weight are the practical implications of quality trading. But such contract requirements mean that the most useful management tool a farmer has for controlling variation, that of time, is no longer available. Furthermore, contract specifications require that variation in slaughter animals be controlled or else penalties could be incurred as a result of failing the contract. The future adoption of quality assurance, in the guise of contracts to supply stock to time and carcass specifications, will demand that the influence of various factors on variation be appraised. This paper reports