Epidemiology of gastrointestinal nematode parasitism in Suffolk and Gulf Coast Native sheep with special emphasis on relative susceptibility to Haemonchus contortus infection.

An eight-year study was conducted to define the epidemiology of gastrointestinal nematode infection in Suffolk and Gulf Coast Native (Native) breeds of sheep, and to determine if the Native sheep is more resistant to infection. For the initial three years, each breed grazed separate pastures where anthelmintic treatments were administered to individual animals on a salvage basis. For the last five years, both breeds grazed concurrently; anthelmintic treatments were administered to individual animals on a salvage basis for the first three years, and to all animals, when treatment criteria were met, for the last two years. The fecal egg count (FEC) and blood packed cell volume (PCV) were monitored, and tracer lamb nematode burdens were determined. Overall, FEC for both breeds increased in the spring (periparturient rise) for most years and in the summer for all years. Under separate grazing conditions, Native ewes and lambs had consistently lower infection levels than Suffolk ewes and lambs. During the haemonchosis season (June-September) each year, Suffolk ewe and lamb PCV decreased, and Native ewe and lamb PCV remained relatively stable. The salvage treatment protocol resulted in 27 treatments for Suffolk and one for Native ewes; similarly for lambs, 13 for Suffolk and zero for Native. Tracer lambs grazed with their respective breed, and the FEC and mean total nematode burden corresponded with the pattern of infection for their respective breed. The predominant nematodes found in Suffolk and Native tracer lambs were Haemonchus contortus and Trichostrongylus spp., respectively. Under concurrent grazing conditions, the same seasonal repeatable pattern of infection was present and was exhibited by both breeds, with the Native ewes and lambs being consistently and significantly (p < or = 0.05) lower for FEC and higher for PCV. The salvage treatment protocol resulted in 57 and zero treatments for Suffolk and Native ewes, respectively; for lambs, 46 and 11. Tracer lamb nematode burdens again corresponded to their respective breed pattern of infection, with H. contortus and Trichostrongylus spp. being predominant in Suffolk and Native lambs, respectively. Data from all tracer lambs showed a relatively low level of hypobiosis (H. contortus only), and, although there was no consistent hypobiosis season, the tendency was for a higher level to occur in the fall. These results showed that the classic repeatable seasonal pattern of gastrointestinal nematode infection occurred in both breeds of sheep, and that Native sheep were more resistant to infection (specifically H. contortus) than Suffolk sheep.

Use of yellow-pigmented enterococci as a specific indicator of human and nonhuman sources of faecal pollution.

Antibiotic susceptibility tests and restriction enzyme analysis (REA) of genomic DNA were performed to characterize the relationship between sources of isolates of yellow-pigmented enterococci. Antibiotic susceptibility tests were conducted with 10 therapeutic antibiotics and 54 isolates grouped by source (wild and other) depending on their origin. In three antibiotics, cephalothin, erythromycin, and vancomycin, there was a significant (p < or = 0.05) association between susceptibility and source. Vancomycin resistance was significantly (p < or = 0.001) higher in isolates from wild sources compared with that in isolates from other sources. The REA technique was performed on genomic DNA obtained from 17 Enterococcus mundtii isolates from: human (3), dog (4), horse (4), Canada goose (4), domestic goose (1), and Enterococcus mundtii ATCC 43186. A total of 12 different DNA types (A-L) were identified. Except for type D, 11 DNA types were unique and were distributed among dog (A, B, and C), human (E), horse (F, G, and H), Canada goose (I, J, and K), and domestic goose (L). Results suggested that vancomycin-susceptibility testing of yellow-pigmented enterococci may have potential value in the identification of sources of faecal pollution, especially when combined with traditional quantitative methods.

Susceptibility of Suffolk and Gulf Coast Native suckling lambs to naturally acquired strongylate nematode infection.

Three trials compared responses to naturally-acquired strongylate nematode infection between suckling Suffolk and Gulf Coast Native (Native) lambs which grazed together. In Trial 1 (1992), infection in 14 lambs of each breed was monitored from birth to 12 weeks of age using fecal egg count (FEC) and blood packed cell volume (PCV). In Trial 2 (1993), two age-matched lambs of each breed were sacrificed at seven and ten weeks of age to estimate nematode burdens. In Trial 3 (1994), infection in 18 lambs of each breed was monitored (FEC, PCV, white blood cell count, differential leukocyte count, and anti-Haemonchus contortus immunoglobulin level) from birth to 8 weeks of age, at which time six age-matched lambs of each breed were sacrificed to estimate nematode burdens. The remaining 24 lambs were monitored until 12 weeks of age. In both Trials 1 and 3, infection in Native lambs peaked and then declined between 6-10 weeks of age. Infection in Suffolk lambs continued to increase as evidenced by increasing FEC with concomitant reduction in PCV, higher morbidity and mortality (Trial 1), and number of anthelmintic treatments required (Trial 3). In Trials 2 and 3, the principal nematode found at necropsy was H. contortus, and infection level was consistently lower (> 64%) in Native compared with Suffolk lambs. In Trial 3, there was no difference between breeds for WBC, any leukocyte type, or anti-H. contortus immunoglobulin level. These results demonstrated that suckling Native lambs developed resistance to H. contortus infection during their first exposure to infection at an age when they are considered immune incompetent and colostrally transferred anti-H. contortus immunoglobulin did not appear to be involved in the resistance.