Different grazing systems and their effect on survival of internal worms of cattle

Silvina Fernández (Guelph, ON)

(The following is an adaptation of a scientific article published in Veterinary Parasitology Volume 96, Issue 4, 2001, Pages 291-299)

This study was carried out to examine the survival of the infective larvae (L3) of Ostertagia ostertagi (the most important gastro-intestinal worm in cattle) on pasture under different simulated conditions of grazing: a) mixed grazing of cattle and nose-ringed sows, and b) grazing by cattle alone.

Cattle feces contaminated with O. ostertagi eggs were deposited on three types of herbage plots: "tall herbage (TH) plots; "short herbage (SH) plots; and "short herbage/scattered feces" (SH/SF) plots.

• The TH plots imitated a cattle-only pasture, where cattle graze, avoiding the vicinity of fecal pats. In this case, feces is found surrounded by a green turf untouched by cattle.
• The SH plots imitated the mixed grazing of cattle and sows, where sows graze everywhere regardless of the presence of cattle feces. Thus, the green turf surrounding fecal pats that are avoided by cattle is eaten without problem, by pigs.
• The SH/SF plots, where cattle feces was manually broken down 3 weeks after deposition and scattered within a small adjacent area, imitated the above mixed grazing situation, plus the rooting behaviour of co-grazing sows.

Grass samples were taken every two weeks from each plot to determine the presence and quantity of L3 that had migrated from feces onto pasture. The grass samples were taken accordingly from the immediate area (named "zone 2") surrounding the fecal pats up to 25 cm, as well as from an extended area (named "zone 3) expanding a further 25 cm, adjacent to the previous one.

The three groups followed a similar pattern during the season regarding numbers of L3 recovered from the immediately adjacent area ("zone 2"), and no clear patterns between plot types were obtained.
The presence of L3 in the far area ("zone 3") was almost negligible.

Once a month, some of the fecal pats were also collected to determine the number of L3 still presence in the feces that have not yet migrated onto pasture.

The numbers of L3 found in the fecal pats were higher in those from TH plots than in the other two groups and, furthermore, the larval counts in pats from SH plots were always higher than from SH/SF plots.

Important differences were seen throughout the study from the biological point of view; more L3 were able to survive in faeces on the TH plots, presumably reflecting a better protection from heat and desiccation provided by the green grass turf compared to those in the other plots, where there was no green turf. The overall results support the idea that mixed grazing of cattle and pigs favour the reduction of O. ostertagi larval levels on pasture. This reduction is mainly due to the grazing behaviour of pigs, which by grazing up to the very edge of the cattle faeces, will either expose the larvae in faeces to adverse environmental summer conditions or ingest cattle parasite larvae (which has no consequence at all for the pigs), or both.

Silvina Fernández (Guelph, ON)
E-mail: alsife2@aol.com