By Richard Ehrhardt
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 of 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. 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 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 counterproductive to whole farm productivity if not carefully planned and considered. We have found that placing 10-20% of our perennial pastures into annual forages each season 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.
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 yearly forage yield (>65%), which in south central Michigan, happens by mid-to-late June. At this time, perennial pasture growth is starting 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 two 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 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.
Source : msu.edu