Comparison of grazing systems
Researchers evaluated the effects of two different types of grazing systems of sheep (intensive cell grazing versus conventional rotational grazing) on gastrointestinal nematode (GIN) infections over two years on a farm located in a temperate region of Western France.
The mean grazing periods in the cell grazing system did not exceed 3 days. The average was 0.5 days in 2016 and around one day in 2017 and 2018. By contrast, the mean grazing periods in the rotational grazing system were 6 days in 2016, 2017 and 2018. Mean rest periods for the cell grazing system were stable, between 45 and 47 days; whereas, rest periods fluctuated more in the rotational grazing system, from 35.3 days (2018) to 44.6 days (2016).
Grass heights varied greatly from one season to another. Similar seasonal patterns were observed in both systems; however, ewes in the cell grazing system grazed during winter (excepted during the month after lambing - March) whereas ewes in the rotational grazing system were kept indoors from January to end of March. As a result, ewes in cell grazing system grazed six months when grass height was below 4 cm (1.8 in) while ewes in the rotational grazing system grazed only two months under these conditions.
When considering the whole study, the type of grazing system did not significantly influence the intensity of egg excretions of adult ewes even when the proportion of ewes excreting high numbers (>500 or >1000) of GIN eggs was higher in the cell grazing system than rotational grazing system. Lambs born in the rotational grazing system excreted significantly more eggs than lambs born in the cell grazing system. Packed cell volume did not differ by grazing system, whereas ewes in the cell grazing system had lower body condition scores.
The most striking result was the effect of grazing system on the GIN species composition harbored by ewes and their lambs: with time, the proportions of Haemonchus contortus infections were lower in cell grazing system than in rotational grazing system. In the beginning of the study, Teladorsagia circumcincta was the dominate worm species in both grazing systems. By the end of the study H. contortus was present in the cell grazing system (50%) but in lower proportion than in rotational grazing system: 55 vs. 88%.