Biological efficiency: How relevant is this concept to beef cows in a mixed livestock, seasonal pasture supply context?

S.T. Morris, I.M. Brookes, W.J. Parker, S.N. McCutcheon

Department of Animal Science, Massey University, Private Bag, Palmerston North, New Zealand.

Proceedings of the New Zealand Society of Animal Production 1994, 54: 333-336

Efficiency, defined as the ratio of output to input, can be calculated for any product, and for any of the resources employed to generate that particular product. "Weight of calf weaned per unit cow liveweight" is commonly used to measure biological efficiency in the beef cow herd, based partly on the assumption that feed intakes and hence costs are related to liveweight. A more direct measure, and the one used here, is "weight of carcass produced per unit of feed intake". The biological efficiency of the traditional beef breeding cow, determined in this manner, is low compared to that of other beef cow systems (e.g. twinning cows, once-bred heifers). This is primarily because of the relatively low reproductive rate in traditional cow herds and the high proportion of annual feed consumption used to maintain the breeding female and her replacements.

A simple output/input ratio may not, however, be appropriate for the mixed sheep and cattle systems which are widely used in New Zealand. For these systems, where a competitive or complementary relationship may exist between enterprises, a more complex efficiency ratio that contains elements of the whole farm system is likely to be more appropriate. Furthermore, in a seasonal pasture production system, where the supply of feed is likely to limit production at certain times of the year, feed does not have fixed value. Feed costs therefore become an important component of the efficiency equation. Utilisation by other livestock of a scarce resource (e.g. winter feed) is also likely to have an influence on the economic efficiency of the system. For example, if biological efficiency is ignored then output (weight of calf weaned) may be increased simply by increasing cow size but with no consideration of the extra feed inputs necessary to maintain larger cows, or the pressure that additional feed requirements may place on other components of the system at particular times of the year.

In this paper, the relevance of biological efficiency is explored by comparing both biological and economic efficiencies of four cattle systems - traditional beef cows, beef x dairy cows (with and without twinning) and once-bred heifers - alone and in mixed sheep and cattle policies. We conclude that biological efficiency is a relevant concept, primarily because its components (carcass weigh and feed consumed) are also important determinants of economic efficiency. However marked differences between systems in the value of the carcass produced and/or feed consumed can lead to a poor correlation between the efficiency ranking of systems by biological and economic criteria.

Keywords: NZSAPAB; beef breeding cows; biological efficiency; once-bred heifers; twinning; beef x dairy cross cows.

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