ECONOMICS OF GASTROINTESTINAL PARASITISM OF CATTLE

Understandably, cattle are raised for profit, as beef and/or dairy. An ything that negates that equation results in a loss to the producer an d to the livestock economy. Thus, parasites negatively affect the econ omy of the industry. Worldwide, gastrointestinal nematode parasites, e specially Ostertagia ostertagi, and those of the respiratory tract (Di ctyocaulus viviparus) have a potentially major impact on herd health. In the past 10-15 years, anthelmintic (AH) drug development and the st rategic 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 p asture management, are also being developed to enhance herd health and the cattle economy. The determination of the economic impact of paras itism has thus become less apparent, to the extent that measures, such as performance parameters, must be used to measure differences betwee n treated and untreated animals or herds. These include weight gain, r eproduction, lactation and forage use. To determine the effectiveness of control measures, field trials are designed to measure these parame ters by the demonstration of improved performance. Because these trial s are conducted in a competitive mode, results are often debated by co mpetitors and by the scientific community because of study design. Var iables 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 h as been reduced to subclinical levels. Thus, we are now in the process of fine-tuning the positive effect of these control measures for enha nced production. Understandably, beef and dairy producers have 'produc tion of high quality commodities' at a cost-effective level as a commo n goal. Successful cattlemen calculate expenditures and income by line item including veterinary expenses and cost and labor in administrati on of AH. Return is based on performance. Again, nematode parasites ca n disturb the equation enough to make production less profitable or ev en unprofitable. Most USA beef cattle producers believe that worm para sites do have an effect on cattle health and production so that 77% us e AH and the market impact is that AH have become integrated into catt le 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 provid e 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 whic h are more reliable and convenient in terms of delivery and labor. Con trol measures must also include better pasture management with less im pact on the environment and to justify investment in land. In addition , successful producers are better educated, more cost-conscious, consu mer-oriented, sensitive to the environment and attuned to the economic s of parasitism. (C) 1997 Elsevier Science B.V.