Control of Gastrointestinal Nematodes in Dairy Cattle Under Intensive Rotational Grazing Management
1. Determine the dynamics of gastrointestinal nematode transmission in dairy cattle on a farm which has been forced to increase the frequency of anthelmintic treatment since adopting an intensive rotational grazing system.
2. Based upon the seasonal transmission of gastrointestinal nematodes on the study farm, devise a strategic treatment protocol that both minimizes economic losses and drug input. Assess effect of strategic treatment protocol upon subsequent parasite transmission.
3. Assess the extent of similar parasite problems in Northeastern farms practicing intensive rotational grazing.
Results to Date
Intensive rotational grazing systems are becoming more prevalent in the US because of the necessity of using existing land resources in a more efficient and environmentally friendly way. One potential problem with intensive grazing systems is the possibility that this more intensive use of the pastures will lead to problems with gastrointestinal nematode parasites whose transmission can be greatly increased under such conditions. This can result in an over-utilization and overdependence on anthelmintic drugs, and long-term problems for the producer.
A study was initiated on a working dairy farm that had converted to a intensive rotational grazing program. The producer had noticed that after several years of intensive rotational grazing, he was required to use anthelmintics, in a therapeutic manner, with increasing frequency to maintain milk production at acceptable levels. The overall goals of this project are to define the magnitude of the parasite problem, develop strategic treatment programs that make more efficient use of the drugs, and minimize their usage, and to assess the impact of these parasites in intensive grazing systems in the Northeastern US.
In the past year we have used tracer calves to assess the transmission patterns of the parasites in the dairy herd under study. The results indicate that the herd does have significant levels of parasite transmission in both the replacement heifer and mature milking cow groups.
The predominant parasite encountered is the pathogenic stomach worm Ostertagia ostertagi. The source of the parasites in the spring, when animals are turned-out onto the pastures, is larvae on the pastures that have survived the preceding winter. There is little or no arrested development in the host as has been reported in Northern Europe. These results indicate that strategic control programs should be focused on cleaning up the pastures in a way that both reduces pasture burdens in the fall, and retards build-up of larvae in the spring. Such a program has been devised at will be tested in the coming year.
In addition, a questionnaire to assess perceived parasite problems in intensive grazers in the Northeast was developed and sent to several thousand prospective clients. Two mailings were done to attempt to acquire maximal feedback. The respondent questionnaires were screened to determine if they met the criteria of the study, and the appropriate respondents were then entered in a data base for statistical analyses. This has resulted in several hundred usable responses that are now ready for analyses to be completed in the coming year.