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Februay 2015
Improving parasite management with annual crops

Richard Ehrhardt
Michigan State University

The health and productivity of sheep and goats in perennial pasture grazing systems are often limited by a combination of forage quality and gastrointestinal nematode (GIN) infection. This is particularly evident in lactating dams and their offspring, as these animals are at greater risk for GIN infection due to their lower immunity relative to non-lactating adults.


Alternating the grazing episodes/bouts of these susceptible animals with either machine harvesting the forage or by grazing with less susceptible animals or species (cattle, for example) are strategies to maintain forage quality while reducing infection risk.


Another effective method is to integrate the use of annual forages into a grazing program. Annuals can provide grazing opportunities with zero to low risk for GIN infection while simultaneously providing a plane of nutrition even higher than perennial pastures, meeting the nutritional requirements of lactating dams and their offspring. 

Annual forages lower GIN infection risk mainly by lengthening the time between grazing bouts.  The rest period between the last grazing of a perennial pasture and the first grazing of an annual forage planting is typically >60 days. This rest period will reduce infectivity alone. But when combined with either tillage or herbicide suppression/eradication of the sod to allow annual forage establishment, it will create an annual pasture with close to zero infectivity potential. Herbicide suppression acts to extensively desiccate the stand, creating a dry climate not conducive to larval development. In addition, the high nutritional quality of annual forages makes susceptible animals more resilient in resisting GIN infection. 


Eliminating substantial sections of perennial pasture in order to plant to annual forages is probably not a wise plan. It introduces excessive risk that may ultimately be counter-productive to whole farm productivity if not carefully planned and considered. We have found that placing 10-20% of our perennial pastures each season into annual forages allows sufficient high quality grazing in mid- to late-summer for lactating ewes and lambs while simultaneously improving our forage base. The exact amount of pasture to put into annual forages each year will vary from farm to farm depending on their production system specific needs on a particular year.


We target perennial pastures that lag in productivity and/or quality for renovation. We start the renovation process when the perennial pasture has expressed the majority of its yearly forage yield (>65%), which in south central Michigan, happens by mid-to-late June.  At this time, perennial pasture growth is staring to slow, but the ground retains enough moisture to allow for establishment of the subsequent annual forage crop.  The lowest risk method we have found is to allow 2 grazing or combination grazing/machine harvest events during may to early June, then allow 1-2 weeks of regrowth, followed by  elimination of  the perennial stand with glyphosate herbicide. 

Strips of leafy brassica varieties and Sudan grass from the field shown in prior photo ready for mid-August grazing. The photo was taken 49 days after seeding.

A perennial pasture killed by an application of glyphosate in mid-June and seeded to strips of leafy brassicas and Sudan grass 2 weeks later. Composted manure created from the winter feeding bedding was added to improve soil fertility just prior to the no-till seeding.

We then allow a final grazing event 7-10 days following glyphosate application, followed by an application of composted manure.  Annual forages are then seeded directly with a no-till drill into the sod with top dressed compost in late June/early July. No-till seeding prevents the excessive soil moisture loss and weed growth that can occur following conventional tillage, thereby allowing for more rapid and successful annual crop establishment.  Depending on the species chosen, grazing can commence as early as the first week of August in this system. 

Annual forages species can excel not only in fiber digestibility, energy, and protein content, but in growth during warm, dry weather compared to perennial pasture species.  Examples of these species include:  Sudan grass that is low in lignin due to the influence of the brown mid rib (BMR) gene, and forage brassicas (principally leafy turnip, Chinese cabbage and leafy rape hybrids and their crosses). These varieties can be planted as monocultures, mixtures, or in strips (photo .  At MSU, we studied both leafy brassica and BMR Sudan hybrids planted in these three configurations for summer grazing.  During the recent cool, wet summer, we found that both leafy brassicas in monoculture and leafy brassica/BMR strips excelled in animal performance (weight gain of weaned lambs) expressed on both an individual and per acre basis, far exceeding that of perennial pasture. 


Caution must be taken in extrapolating these findings to every season and climate, however. In warm and dry years we have seen relatively high yields of pure stands of BMR Sudan.  Therefore, to reduce season to season risk in our region, we are currently recommending planting of mixed strips of BMR Sudan grass and leafy brassica. The strip plantings excel over mixtures because they reduce species competition due to shading while also providing forages that complement each other in nutritional profile (BMR Sudan is high in digestible fiber, leafy brassicas are high in soluble carbohydrate and crude protein). Consult with an extension forage agronomist in your region for ideas on which crops may excel in your climate for your purposes. 

An annual cropping system reduces GIN infection risk, improves forage quality, allows for greater grazing availability throughout the year, and provides an opportunity to improve soil quality.  These improvements work synergistically to positively impact both whole farm productivity and animal health.  


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