Improving parasite resiliency in small ruminant production systems using protein supplementation and pasture maintenance

Dr. Brady Campbell, Assistant Professor, The Ohio State University, State Small Ruminant Extension Specialist 

Here in the Buckeye state, I think it’s safe to say that spring has finally sprung and is here to stay! With more stable weather conditions and pastures beginning to green up, anticipation is building for spring turnout. Like many producers, we’re carefully watching forage growth and soil conditions as we approach the “running of the sheep”—the long awaited move from winter housing to pasture and grazing. This is an exciting time of year. Turning livestock out to pasture marks the official start of the grazing season. But before the gates swing open, it’s important not to let spring fever derail your pasture and animal health plans for 2026. 

As grazing begins, parasite pressure isn’t far behind. Internal parasites—those “worms” we talk about all grazing season—become a greater concern once livestock return to pasture. In sheep and goats, the parasites of greatest concern are strongyle-type parasites like Haemonchus contortus (barber pole worm), Ostertagia, and Trichostrongylus. These parasites feed on blood and damage the mucosal gut lining; resulting in reduced animal growth, thriftiness, and overall performance. In severe cases, they can lead to anemia, weight loss, or death. 

Thankfully, to combat these challenges, producers and managers alike have access to a limited number of anthelmintics or de-worming products that are commonly used to eliminate parasitic infections. Unfortunately, because of continual and overuse of these products, many on today’s market are becoming less effective. The good news is that dewormers don’t have to be the only tool in the toolbox. Smart grazing and pasture management coupled with improved nutrition can go a long way in helping your stock combat parasitic infection. For example, it has been well documented that protein supplementation can improve animal growth and health when challenged with increased parasite burdens. Using this strategy in conjunction with improved pasture management may aid in reducing losses in small ruminants when challenged with parasitic infection.

To investigate this strategy, we conducted a project in 2021 that investigated the use of protein supplementation and pasture maintenance on the growth, parasite burden, and economic return of pasture-raised lambs. For this experiment, we utilized 192, 60 day old speckled faced (Hampshire/Suffolk × Dorset) crossbred lambs from the Small Ruminant Research Center in Wooster, Ohio over the course of two years. Lambs were assigned to one of four treatments: 1) new pasture without supplementation (NN); 2)  new pasture with supplementation (NS); 3) established pasture without supplementation (EN); and 4) established pasture with supplementation (ES) and grazed for 112 days. Within the context of this experiment, the new pasture was a newly sown forage seeding planted in a field that was previously in crop production for > 50 years and did not receive manure. Established pastures were those grazing areas at the research station that are grazed each year by the research flock. For supplementation, lambs were offered a ~48% crude protein custom pellet at a rate of 1% body weight/day. Forages in both pastures were predominantly Tall Fescue. Lambs were rotationally grazed, providing lambs access to each paddock for three days and allowing for a minimum of 35–40-day pasture rest period prior to returning to the same paddock for the next grazing bout.  

In terms of animal growth, there was no interaction between pasture type and supplementation status. However, there was an effect of supplementation whereas lambs that were provided supplementation, regardless of pasture, had greater body weights (89.5 lbs. vs. 69.1 lbs.) and average daily gain (0.37 lbs. vs. 0.30 lbs.) when compared to non-supplemented lambs. Furthermore, there was also an effect of pasture type, regardless of supplementation status, whereas lambs grazing on newly established pastures had greater body weights (81.0 lbs. vs. 77.9 lbs.) and average daily gain (0.37 lbs. vs. 0.30 lbs.) when compared with lambs grazing on established pastures.

The parameters of FAMACHA^© eye score, packed cell volume, and fecal egg count were used to assess lamb health and overall parasite burden. For lamb health, there were interactions between pasture type and supplementation status for lamb FAMACHA^© eye score and packed cell volume. When considering lamb FAMACHA^© eye score, lambs in the EN treatment group had the greatest FAMACHA^© eye scores (2.6) and lowest packed cell volume (23.0%) over the course of the 112-day grazing period. In general, for the FAMACHA^© eye score, a score of 1 is favorable and indicative of a healthy animal. Additionally, the average range for lamb packed cell volume is 21-45%. As shown above for those lambs in the EN treatment group, these lambs were those that were negatively impacted the greatest by parasitic infection. Lambs in the NS, ES, and NN treatment groups demonstrated similar FAMACHA^© eye scores (1.2, 1.3, 1.4; respectively). However, those lambs in the NN treatment group had lower packed cell volume when compared with those lambs in the NS and ES treatment groups (26.4% vs. 30.2% and 29.1%; respectively). Although differences were noted in lamb packed cell volume, it is important to understand that these values were still well within the average range for lambs of this size. When considering fecal egg counts, lambs grazed on newly established pasture or provided supplementation had lower fecal egg counts when compared with lambs on established pastures or not provided supplement.  

Rather than just stopping here, our team was also interested in investigating the ‘why’ behind decreased lamb growth and health. In order to do so, we selected 64 lambs to harvest to quantify parasite burden and population species and evaluate lamb gut health. Through nematode collection and evaluation, we were able to determine that approximately 80% of the parasite burden challenging our lambs in this project were Haemonchus contortus, with the remaining 20% being described as either Ostertagia or Trichostrongylus axei (Figure 2). Additionally, those lambs that were exposed to a greater concentration of parasites experienced a greater amount of abomasal tissue damage as shown in the image below (Figure 3).  

Of course, a proper management recommendation isn’t complete without some interpretation as it relates to the economic benefit of implementation, right? Luckily, we’ve got that information for you as well! In general, based upon gross margin analysis, lambs offered a protein rich supplement on pasture had a 20.5 lb. increase in lamb body weight whereas newly sown pasture had a 2.9 lb. increase in lamb body weight. At a high level, our analysis considered the body weight gain of lambs from each treatment (pasture type or supplementation status). This liveweight gain was then given a value based upon market pricing at the time of this project. This body weight gain value was then used as our based in which we deducted pasture and supplement costs from each group to give an overall net value for lambs in each treatment group. Overall, when considering supplementation, those lambs offered supplement, regardless of pasture type, were of greater value when compared with lambs not offered supplement ($21.49 vs. $4.50). When considering pasture type, regardless of supplementation status, lambs managed on newly sown pastures were of greater value when compared with lambs on established pastures ($13.69 vs. $12.67).  

Within the context of this experiment, a high protein supplement (~48%) offered to lambs grazing pastures contaminated primarily with H. contortus or placing lambs on newly sown pasture increased lamb growth and improved parasite resiliency as indicated by lamb FAMACHA^© eye score, packed cell volume, and fecal egg count. Establishing new pastures demonstrated a reduction in overall parasitic burden on pasture. However, it should be noted that pasture renovations, while not eliminating the potential for animals to acquire a parasitic infection, require a greater initial investment. Selection of parasite management strategies may be influenced by cost of production, labor resources, and market opportunities. 

Campbell, B.J., Marsh, A.E., McCutcheon, J.S., Fluharty, F.L., Parker, A.J^*. 2021. The effects of protein supplementation and pasture maintenance on the growth, parasite resilience, and  economic return of pasture-raised lambs. Translational Animal Science. Doi:10.1093/tas/txab113 

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