Stocking rates and parasite load in yearling steers grazed season long in the Northern Great Plains

Abstract Text: Intestinal parasitism of grazing ruminants can result in poor performance and compromised systems, especially in younger animals.  Twelve pastures (12.9±0.8 ha) were stocked at four stocking rates: light 1.83±0.38 AUM · ha^-1, moderate 3.26±0.30 AUM· ha^-1, heavy 4.98±0.78 AUM · ha^-1, and extreme 6.18±0.68 AUM · ha^-1. Yearling steers (317±32 kg) were grazed on the pastures from mid-May to mid-September, 2015. Prior to turnout, the steers were dewormed with an injectable dewormer, as well as implanted with Revalor GTM to maximize live weight gains. The steers were also supplemented with dry distillers grains with solubles at 0.3% of body weight. Steers were weighed monthly during which time fecal grab samples were collected. Results demonstrated that initially the worming treatment before turnout proved effective in the early part of the grazing season as there was no difference (P> 0.05) among treatments in egg counts per gram (epg) in June, with corresponding low epg. However, a significant difference (P< 0.05) in epg was detected between the light and extreme treatment groups in July, with low levels in the light treatment, and higher levels in the extreme treatment. Egg counts over 35 epg, which has been proved as a performance threshold in grazing yearling cattle, were noted in individual animals on all treatments except the lightly grazed treatment in August and September. This study demonstrates an association between high stocking rates and increases in detectable parasite load, and supports the conclusion that individual yearling cattle that are susceptible to parasitism may be negatively impacted by season long systems that are stocked from moderate to extreme levels in the northern Great Plains.

Keywords: parasitism, northern Great Plains, yearling cattle, season long grazing