PSIV-A-6 - The effects of botanical composition of pasture on fecal egg counts in grazing sheep

Abstract: Grazing sheep are prone to harboring gastrointestinal parasites that often impact animal health and productivity. The objective of this study was to evaluate the effect of botanical composition of pasture on parasitic fecal egg counts in grazing sheep. Dorset × Suffolk crossbred ewes (n=34; BW=75.3 kg) and their offspring (n=57; BW=23 kg) were used. Four weeks prior to the start of the study, all ewes were orally dewormed with cydectin. Ewes were stratified by weight and assigned (with their lambs) to one of two pastures mixes: GM (Grass Mix, 47% orchard grass, 30% white clover 13% ryegrass, 10% bromegrass) or LM (Legume Mix, 45 % ryegrass, 28% red clover, 27% white clover). Each 0.30-hectare pasture was subsequently divided into four grazing paddocks through which each group was rotationally grazed. Sheep rotated between paddocks every 4-5 d to prevent over grazing. Forage samples, collected prior to sheep entering a new paddock, were analyzed for crude protein (CP), total digestible nutrients (TDN), acid detergent fiber (ADF), neutral detergent fiber (NDF), and mineral content. At the end of the 22-d-grazing period, fecal egg counts (FEC) were conducted on ewes and lambs to quantify stomach worm, coccidia, and nematodirus, burden using the McMaster method. Differences were identified in forage quality. CP and copper levels were higher in LM pastures (P< 0.01), NDF was lower in LM pastures (P≤0.001), and manganese was higher in GM (P≤0.001). There were no differences in TDN, ADF, or zinc content. Stomach worms, coccidia, and nematodirus were identified in sheep in both pasture mixes. FEC for stomach worms was 1537 and 4347 epg for the GM and LM pastures, respectively (P=0.1872). Coccidia load in sheep in the GM pastures averaged 3315 epg while those in LM pastures averaged 4568 epg (P >0.05). The Nemotadirus load averaged 35 epg (GM) and 8 epg (LM; P> 0.05). The FEC for stomach worms was 1537 and 4347 epg for the GM and LM pastures, respectively (P >0.05). When separated by age, there were no differences in stomach worms or nematodirus among ewes on GM or LM (P>0.01), however, ewes on GM had fewer coccidia (P=0.02). There were no differences in FEC in lambs on GM or LM pasture for any of the parasites evaluated (P>0.05). The percentage of sheep above 1,000 epg was calculated for each of the parasites; no differences were observed due to pasture mix. The proportion of sheep with a burden greater than 1,000 epg was 36% (GM) and 48% (LM) and 55% (GM) and 58% (LM), for stomach worms and coccidia, respectively. No sheep had a nematodirus burden greater than 1,000 epg. Data from the current study indicates that botanical composition does not significantly impact parasite burden in sheep.