Effect of Management Systems on the Growth of Lambs and Development of Internal Parasitism. I. Dry Lot vs. Two Pasture Rotation Systems

Abstract

Effects of three management systems, including medication, on the development of internal parasitism in lambs and on their growth were studied. The systems included dry lot confinement (Band 1), transfer of animals to a clean pasture at biweekly intervals (Band 2), and grazing of animals on contaminated pastures (Band 3). Average levels of parasitism acquired by the lambs in Bands 1, 2, and 3 were insignificant, moderate, and high, respectively. Lambs from Band 3 acquired significant infections of Haemonchus contortus by June, which continued to rise until midsummer, and heavy infections of Strongyloides papillosus in August and September. Lambs from Band 2 acquired peak moderate infections of H. contortus by midsummer and moderate to heavy infections of S. papillosus in August and September. Clinical haemonchosis in Bands 2 and 3 was not satisfactorily controlled by supplementary therapeutic dosing with N.F. grade phenothiazine. Limited evidence suggested that this may have been due, in part, to a tolerance for the drug. Circumstances did not permit a fair evaluation of copper sulfate drenches in this regard. Average daily gains of lambs in Band 1, until weaning, were significantly greater than those of lambs in Bands 2 and 3. Effect of management and parasitism on weight gains of the lambs became more pronounced in the three Bands after weaning and reached a maximum in early August. Band 3 lost weight on the average during this period. Significant differences in grease fleece weights of the exeperimental animals also were obtained when they were yearlings; the average fleece weights of these three bands were inversely proportional to the degree of parasitism observed during the previous grazing season. Internal parasitism is the most serious problem of the sheep industry in humid areas of the United States. Losses amount to several million dollars annually and deter expansion of the sheep industry in the farm states. Much of the research concerning management practices versus parasitism has been done abroad, particularly in the British Isles and Australia. A series of reports by Spedding (1954, 1955, 1956) from England indicates that proper management exclusive of anthelmintics can greatly reduce the worm burden of sheep, resulting in greater weight gains and an increase in wool production. Gibson (1956), another English worker, concluded from a 3year experiment that the following factors favored n increase in parasitism: returning the sheep to previously grazed pastures too soon, inadequate use of anthelmintics, and weather conditions favorable to larval survival. Gordon and Turner (1946) also demonstrated that rotational grazing retarded the acquisitio of parasites by sheep under Australian conditions. Since climatic conditions have a pronounced effect on the transmission of internal parasites, management research needs to be conducted in various areas on a long-term basis. Research reported in this paper constitutes 1st-year results of a long-term project at Beltsville, Maryland, involving detailed studies on the effects of various management systems, including medication, on the development of internal parasitism in lambs. Preliminary reports of this work have been given by Kates et al. (1960), Turner et al. (1960), Enzie et al. (1960), and Lindahl et al. (1961). Received for publication 6 November 1962. * Animal Husbandry Research Division, ARS, Beltsville, Maryland. t Present address: Food and Drug Administration, Beltsville, Maryland. $ Animal Disease and Parasite Research Division, ARS, Beltsville, Maryland.