Characteristics of parasitic egg shedding over a 1-year period in foals and their dams in 2 farms in central Saskatchewan

Abstract

The goals of this study were to report the seasonal shedding patterns of strongyle and Parascaris spp. eggs in repeated fecal samples for mares (n = 38) and foals (n = 39), and to evaluate the efficacy of ivermectin treatment in mares from 2 selected horse breeding farms in central Saskatchewan. Median strongyle fecal egg counts (FEC) peaked in July and August in adult horses. The farms differed significantly (P = 0.0005) in regard to strongyle shedding categories (< 200; 200 to 500; and > 500 eggs/g) over time, but for each individual horse (both farms combined) these categories did not differ over time (P = 0.13) on samples collected in grazing season. When evaluating 3 samples collected fall, summer and fall in 2 consecutive grazing seasons, 94% of horses that shed < 200 eggs/g on 2 initial samples, remained in the same category on the third sample. Mares on each farm didn't differ statistically in shedding categories when comparing September samples from 2 consecutive years (Farm A: P = 0.56, Farm B: P = 0.06). Peak strongyle shedding occurred late fall in the first year of life for foals on Farm A, and in July in the second year of life for foals on Farm B. Parascaris spp. FEC were greatest in foals ≤ 6 months of age, with peak observed when foals were 5 to 6 months old. Ivermectin was 100% effective at reducing strongyle FEC 2 weeks after treatment in adult horses. Horses in Saskatchewan had relatively high strongyle shedding levels, which were significantly different between the farms, and high prevalence of Oxyuris equi. Strongyle shedding consistency was observed for FECs collected from mares in grazing season (July to September).

Figure 1

Means and 95% confidence intervals of lsmeans from linear mixed effects model on log of strongyle FEC in mares. Differences between the farms are marked with asterisks and differences within the farm are marked with letters, with significance set as P < 0.05. Upper- and lowercase letter A represents Farm A, and upper- and lowercase letter B represents Farm B.

Figure 2

Shedding distribution of strongyle eggs in adult mares from each farm in September 2010 and September 2011. Black area represents low shedders (< 200 eggs/g); light gray area represents moderate shedders (200 to 500 eggs/g), and dark gray area represents high shedders (> 500 eggs/g).

Figure 3

Comparison of September 2010 and September 2011 strongyle FECs for individual mares on Farms A and B.

Figure 4

Means and 95% confidence intervals of lsmeans from linear mixed effects model on log of strongyle FEC in foals. Differences between the farms are marked with asterisks, differences within the farm are marked with letters, with significance set as P < 0.05. Upper-and lowercase letter A represents Farm A, and upper- and lowercase letter B represents Farm B.

Figure 5

Means and 95% confidence intervals of lsmeans from linear mixed effects model on log of ascarid FEC in foals. Differences within the farm (P < 0.05) are marked with letters, with significance set as P < 0.05. Upper- and lowercase letter A represents Farm A, and upper- and lowercase letter B represents Farm B. No significant difference was observed between the farms at any time point.