BACKGROUND
Rhipicephalus microplus is a major cattle ectoparasite in tropical and subtropical regions and is associated with major production losses and pathogen transmission. The paper notes that ticks affect about 80% of livestock worldwide and generate losses ranging from 13.9 to 18.7 billion US dollars annually. Because chemical control has led to acaricide resistance and environmental concerns, the investigators evaluated whether pasture management could reduce tick infestation. Specifically, they studied whether rotational grazing with different pasture rest periods modifies on-animal tick burdens compared with continuous grazing. The stated objectives were to evaluate three grazing modalities—continuous grazing, rotational grazing with 30-day pasture rest, and rotational grazing with 45-day pasture rest—and to describe the population dynamics of R. microplus under these conditions in the humid tropics.
METHODS
The experiment was conducted from April 2021 to March 2022 at the Center for Teaching, Research and Extension in Tropical Livestock Production in Mexico. The design included 3 grazing treatments on 2 ha African stargrass pastures with natural tick infestation: continuous grazing (CG00), rotational grazing with 30-day recovery (RG30), and rotational grazing with 45-day recovery (RG45). RG30 used 11 paddocks of approximately 0.18 ha each with 3-day grazing and 30-day recovery periods, while RG45 used 16 paddocks of approximately 0.12 ha each with 3-day grazing and 45-day recovery periods. Thirty heifers aged 8–12 months with average live weight of 182 ± 44 kg were randomly allocated, with 10 animals per treatment. Fifteen days before the experiment, all animals were treated with albendazole and coumaphos so they began with similar tick loads. During follow-up, animals were not treated against ticks. Tick counts were performed every 14 days from 7:00 to 9:00 h, for a total of 26 counts over 1 year. Only R. microplus females larger than 4.5 mm were counted. A veterinarian counted ticks on the right side of each animal and multiplied the total by two. Climate variables were also recorded; during the experiment, environmental temperature ranged from 11.5 °C to 37.0 °C, monthly relative humidity from 67 to 85%, and monthly precipitation from 54.0 to 427.7 mm. Data were non-normally distributed, so the investigators used the Kruskal–Wallis test for comparisons and Spearman correlations for climate associations, with a 95% confidence interval and p < 0.05 considered significant.
KEY RESULTS
During the first six counts, corresponding to April, May, and June, tick burdens were low and similar among groups (p > 0.05). For example, on 02/04/2021 mean counts were 1.60 in CG00, 1.40 in RG30, and 1.00 in RG45; on 01/06/2021 they were 5.00, 2.20, and 1.40, respectively. From count 7 to count 16, corresponding to July to November, animals in RG30 had the highest tick counts (p < 0.05). Peak values in RG30 included 59.20 on 29/06/2021, 83.80 on 13/07/2021, 90.80 on 11/08/2021, 117.20 on 24/08/2021, 188.40 on 08/09/2021, 162.40 on 20/09/2021, 115.00 on 18/10/2021, and 88.00 on 03/11/2021. By contrast, RG45 remained much lower during this period, reaching 0.00 on 29/06/2021, 11.20 on 13/07/2021, 15.00 on 27/07/2021, 1.00 on 11/08/2021, 4.40 on 24/08/2021, 0.60 on 08/09/2021, 0.00 on 20/09/2021, 0.00 on 18/10/2021, and 3.20 on 03/11/2021. In the last ten samplings, covering November to March, RG45 was significantly lower than RG30 and CG00 (p < 0.05). Examples include 0.40 on 16/11/2021, 0.00 on 30/11/2021, 2.20 on 14/12/2021, 1.60 on 28/12/2021, 3.20 on 11/01/2022, 0.80 on 25/01/2022, 1.80 on 08/02/2022, 0.80 on 22/02/2022, 2.80 on 09/03/2022, and 3.40 on 23/03/2022.
Cumulative burden across the experiment was highest in RG30, with 13,352 teleogins, compared with 1882 in CG00 and 660 in RG45. The burden distribution was aggregated within groups. In RG30, 30% of animals accounted for 55% (7344/13,352) of parasite loads. In RG45, 30% of animals accounted for 57% (1073/1882). In CG00, the corresponding pattern was 42% (277/660). No animals showed health problems during the study. Population dynamics also differed by treatment. RG30 showed five infestation peaks: June and July averaging 71.5 ticks per animal; September averaging 188 ticks; October averaging 115 ticks; January averaging 31 ticks; and February averaging 48 ticks. The authors report that there was no association between tick infestation and climatic variables (p > 0.05).
CLINICAL IMPLICATIONS
This study suggests that not all rotational grazing is beneficial for tick control. Under these humid tropical conditions, a 30-day rest period appeared to worsen infestation relative to both continuous grazing and a longer rest strategy, whereas a 45-day rest period was associated with persistently lower tick loads and the lowest cumulative burden. For cattle producers, the practical implication is that rotational grazing can be used as a non-chemical tick-control tool, but the recovery interval matters. A 45-day pasture rest may help reduce dependence on acaricides and thereby potentially reduce selection pressure for resistance and chemical residues in animal products and the environment. However, the findings come from a single experimental site with 10 animals per treatment, so they are most directly applicable to similar pasture, climate, and management conditions.