View the latest updates and emergency notifications on the COVID-19 News & Information website.
College of Agriculture

Effects of Liquid Nitrogen Fertilizers on Sheep Parasites in Irrigated Pastures

Scot A. Svejda


Twenty Polypay ewe lambs were randomly assigned to one of two treatment groups; the UN32 treatment or the non-treated control. The lambs were treated with commercial anthelmintics twice prior to the beginning of the study to ensure they were parasite free. These lambs were allowed to graze for an 8 hour period in a 12’x12’ plot of irrigated grass/legume pasture which received one of the above mentioned treatments. After a three week period immediately following the grazing period, fecal samples were taken to determine eggs per gram of feces. It was shown that there was not a significant difference (P> 0.05) in eggs per gram of feces between the treatments.



Producers that use forage produced in irrigated pastures for livestock grazing have long known that to achieve maximum forage production they must fertilize.  (Peake et. al,1990) These same producers also know that to ensure maximum performance from their grazing animals, they must be in peak  health. (Mcleod, 1995) This often means treating the animals for internal parasites.  Luginbuhl and Jirik showed that, in a lab setting, nitrogen fertilizer kills internal parasites. Death is due to dehydration and therefore it is unlikely that parasites would become resistant. The objective of this study was to determine the effect of foliar application of UN32 in field plots on the level of parasite loads developed in grazing sheep.


Twenty Polypay ewe lambs were chosen at random from the farm flock at CSU, Chico. These lambs were placed in an elevated floor barn with expanded metal floor that allows feces and urine to fall through. The lambs were treated with fenbendazol and doramectin (SAFE-GARD and DECTOMAX) respectively at seven day intervals. Fecal samples were taken seven days after the final treatment to determine parasite load. All fecal samples were analyzed using the Modified Wisconsin Sugar Floatation method.( Bliss,

Twenty 12'x12' test plots of grass-legume irrigated pasture were established at the University Farm. One lamb was randomly assigned to each test plot. Each test plot was randomly assigned to either the UN32 treatment or the no treatment control group. Prior to receiving treatment, the plots were grazed by ewes from the farm flock that were suspected of having a large parasite load. This was done to ensure the presence of parasites before treatment.

The treatment consisted of 145 ml UN32 diluted in two gallons of water. This was applied as a foliar treatment with a 2.5- gallon hand held sprayer. The rate was consistent with the recommended rate of 40 units N per acre for irrigated pasture.

After the two week "cleanout" period, the lambs were placed in their assigned pens for a period of 8 hours to graze at will. After the 8-hour period, the lambs were returned to the barn to allow growth of any parasites ingested. Three weeks later, fecal samples were again collected to determine levels of re-infestation.

All data was analyzed using Analysis of Variance to determine differences in the number of eggs per gram of feces from the two treatments.


The two treatments, foliarly applied UN32 and control, showed no significant difference (P=0.3506) in the number of eggs per gram of feces in grazing sheep. Further investigations are currently underway to determine the effects of UN32 on sheep parasite larvae in irrigated pastures.


Borjas,R.  April 1997. J.R. Simplot. Unpublished data ( personal communication)

D.C.I. Peake, R.J.K. Myers, and E.F. Henzell. 1990 Sown pasture production in relation to nitrogen fertilizer and rainfall in Southern Queensland. Tropical Grassland Society of Australia v24, pp 291-298

Mcleod, R.S.,1995, Costs of major parasites to the Australian livestock industry. J. Am. Soc. Agronomy

Luginbuhl, J.M., Howell, J. 1997 Spreading fertilizer may spread death to livestock parasites. Am. Soc. Animal Science minutes from national meeting