Little work has been done to determine the prevalence of gastrointestinal nematodes (GIN) in Ontario cow–calf herds. A prospective single cohort study was conducted during the grazing seasons of 2014 and 2015. Twenty-four crossbred cows were randomly assigned to one of six rotationally grazed fields each year, blocked by calving date and parity (n = 48). Feces were collected and weight and body condition score (cows) recorded at approximately 28 d intervals. Fecal egg counts (FEC) were performed using the Wisconsin method. No clinical signs of GIN parasitism were observed. Cow FEC stayed relatively low throughout both pasture seasons [mean 8 ± 20.02 eggs per gram (epg) of feces, n = 301]. Most calf FEC were also low throughout both seasons (mean 42 ± 86.20 epg, n = 268). The sample time [a proxy for days on pasture (DOP)] had a significant effect on cow epg (P < 0.001) and calf epg (P < 0.001). Cow and calf FEC peaked at the fourth sample, after 55–72 DOP; 4 epg (95% CI 2.57, 6.32) and 24 epg (95% CI 15.82, 37.19) for cows and calves, respectively. Mean calf FEC did not have a significant effect on calf weaning weight (P = 0.9).