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) infections. This is particularly evident in lactating dams and their o spring, who are at greater risk of GIN infection due to their lower immunity compared to non-lactating adults. Alternating the grazing episodes/bouts of these susceptible animals with either machine-harvested forage or grazing with less susceptible animals or species (e.g., cattle) is a strategy to maintain forage quality while reducing infection risk. Another effective method is to integrate annual forages into a grazing program. Annuals can provide grazing opportunities with low to zero risk of GIN infection while simultaneously providing a plane of nutrition higher than that of perennial pastures, meeting the nutritional requirements of lactating dams and their offspring.

Annual forages lower the risk of GIN infection 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 greater than 60 days. The length of 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 desiccates the stand, creating a dry climate that is 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 counterproductive to whole farm productivity if not carefully planned and considered. We have found that allocating 10-20% of our perennial pastures to annual forages each season provides 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 in a particular year.

Michigan State University Extension recommends targeting 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 annual forage yield (>65%). At this time, perennial pasture growth is starting to slow, but the ground retains enough moisture to allow for the 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.

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 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 forage species can excel not only in fiber digestibility, energy, and protein content, but also in growth during warm, dry weather compared to perennial pasture species. Examples of these species include Sudan grass, which is low in lignin due to the brown midrib (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. At MSU, we studied both leafy brassica and BMR Sudan hybrids planted in these three configurations for summer grazing. During the 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, dry years, we have seen relatively high yields from 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. Strip plantings excel over mixtures because they reduce species competition through shading while also providing forages that complement each other in their nutritional profiles (BMR Sudan is high in digestible fiber, while leafy brassicas are high in soluble carbohydrates 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.

In summary, introducing an annual cropping system reduces the risk of GIN infection, improves forage quality, increases 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.