Economics of gastrointestinal parasitism of cattle.

Understandably, cattle are raised for profit, as beef and/or dairy. Anything that negates that equation results in a loss to the producer and to the livestock economy. Thus, parasites negatively affect the economy of the industry. Worldwide, gastrointestinal nematode parasites, especially Ostertagia ostertagi, and those of the respiratory tract (Dictyocaulus viviparus) have a potentially major impact on herd health. In the past 10-15 years, anthelmintic (AH) drug development and the strategic use of AH have positively balanced the economic equation, so that overall, parasitism in cattle is often observed or determined to be subclinical or economical. Other control measures, such as better pasture management, are also being developed to enhance herd health and the cattle economy. The determination of the economic impact of parasitism has thus become less apparent, to the extent that measures, such as performance parameters, must be used to measure differences between treated and untreated animals or herds. These include weight gain, reproduction, lactation and forage use. To determine the effectiveness of control measures, field trials are designed to measure these parameters by the demonstration of improved performance. Because these trials are conducted in a competitive mode, results are often debated by competitors and by the scientific community because of study design. Variables must then be taken into consideration in the interpretation of results. It is now well known that, with the generation of new AH and appropriately-timed administration, parasitism of well-managed herds has been reduced to subclinical levels. Thus, we are now in the process of fine-tuning the positive effect of these control measures for enhanced production. Understandably, beef and dairy producers have 'production of high quality commodities' at a cost-effective level as a common goal. Successful cattlemen calculate expenditures and income by line item including veterinary expenses and cost and labor in administration of AH. Return is based on performance. Again, nematode parasites can disturb the equation enough to make production less profitable or even unprofitable. Most USA beef cattle producers believe that worm parasites do have an effect on cattle health and production so that 77% use AH and the market impact is that AH have become integrated into cattle herd health programs. However, to be most cost-effective, programs must be strategic but flexible with scheduling tailored for the region and the cattle operation. Other technologies should eventually provide rapid identification of worm populations by species and numbers and recognition of individual animal response to parasites and inheritance of that trait by their progeny. Computerized programs for analysis of seasonality of the epidemiology of gastrointestinal parasites and of herd performance could predict appropriate timing and cost benefit for control measures. Modes of AH administration are being developed which are more reliable and convenient in terms of delivery and labor. Control measures must also include better pasture management with less impact on the environment and to justify investment in land. In addition, successful producers are better educated, more cost-conscious, consumer-oriented, sensitive to the environment and attuned to the economics of parasitism.