Rory Lewandowski, OSU Extension Educator, Athens County
Raising sheep within a pasture based production system presents the manager with two challenges; internal parasite control and summer slump production of cool season pastures. The use of a warm season annual like sudangrass may offer the pasture based sheep producer a parasite control option while at the same time filling in the forage production slump demonstrated by cool season pastures during the hot summer months. In this article, I’ll draw on some of the results and lessons learned using sudangrass during the summer of 2007 on the Curt Cline farm in Athens County.
The internal parasite of major concern to pasture based sheep producers is the barber pole worm, Haemonchus contortus. Resistance to all classes of chemical de-wormer currently on the market has been documented in Haemonchus contortus populations in various farms around Ohio. The prudent sheep producer will therefore limit the use of chemical de-wormers and place emphasis on controlling parasite infections through a better understanding of parasite biology and corresponding pasture management. A key concept is the use of safe pastures. A safe pasture contains no, or very low levels of, infective Haemonchus contortus larvae. This can be achieved by keeping sheep off a pasture for a period of time so that there is minimal survival of parasite larvae, or by planting an annual forage where larvae do not survive.
Under typical cool season pasture conditions the population of infective Haemonchus contortus larvae continues to build from the start of spring grazing. By mid to late summer, after several rotations through pasture paddocks, levels of infective larvae can be extremely high and grazing lambs and milking ewes can quickly pick up levels that at best suppress production and gain, and at worst, can be fatal. At the same time that lambs and ewes are under stress from parasite infection, pasture quality and quantity is decreasing. In this situation a warm season annual forage like sudangrass can make a real difference. In addition to acting as a safe pasture where parasite burdens are not increased, under hot summer conditions these forages will continue to grow and produce a high quality feedstuff.
In 2007, as part of an on-farm study investigating the use of alternative forages as a control option for internal parasites, a brown mid-rib (BMR) sudangrass from Ampac Seed Company was planted on the Curt Cline farm in Athens County. BMR sudangrass is more palatable and produces a higher quality forage compared to a non-BMR sudangrass. Trials in other states had shown very good animal gains on this forage.
The field was seeded on June 1 at a rate of 25 lbs/acre. Since our 2007 trial, I have spoken with Ampac seed representatives and they are currently recommending a seeding rate for grazing conditions of 35 lbs/acre. The field had been in winter rye and was tilled using a chisel plow and disk. Seed was applied with a broadcast seeder mounted on a 4-wheeler and then cultipacked. The seedbed was very dry. Soil fertility on this field was at low to moderate levels with a soil pH slightly below 6.0. According to the Ohio Agronomy Guide, soil fertility levels should be similar to what is needed to produce a 100-to 150-bushels/acre-corn crop. This translates into a critical soil phosphorus level of 15 ppm and a soil potassium level of 100 ppm at a cation exchange capacity of 10. Following a grass sod, nitrogen requirements range from 60 lbs/acre for a 3-4 ton yield goal to 100 lbs/acre for a 5-6 ton yield goal. Seed should be planted one-half to one inch deep on a firm seedbed. Recommended planting time is from late May until the end of June. Soil temperature should be in the 60 to 65 degree F range.
Rain was in short supply in 2007 and the prepared seedbed was too dry initially for the BMR sudangrass seed to germinate. On June 4 a quarter inch of rainfall provided enough moisture for seed germination. Fortunately, an isolated thunderstorm brought 1.3 inches of rain to the farm on June 9-10. From this point on the BMR sudangrass made rapid growth. On July 12, several days before the first grazing pass with lambs was begun, random samples were collected from the field, and a dry matter yield was calculated at 3000 lbs/acre. By the time the lambs were turned into the field several days later, some additional growth had occurred and the field averaged about 40 inches in height. We recognized that grazing should have begun earlier, but due to other conditions of the study, this was when lambs had to start the grazing pass. According to both the Ohio Agronomy Guide and the Ampac Seed literature, grazing should start at between 24 to 30 inches in height, and be grazed down to a 6 to 8 inch stubble.
Even though lambs began grazing the BMR sudangrass later than recommended, quality samples collected on July 16, the day the lambs entered the field, came back from the lab with an analysis of 20% crude protein and 68% TDN. This quantity and quality of forage was produced during a period with limited rainfall and daytime temperatures in the 90’s. During this same period cool season grass pastures were shutting down, recording low levels of dry matter accumulation.
Something that producers need to consider regarding a warm season annual like sudangrass is how to best utilize the production capacity of the forage. Since the forage grows rapidly, it is similar to managing the spring flush of cool season pasture growth. It is very easy for the forage to get ahead of animal consumption, leaving a field of mature, declining quality forage. This happened to us at the Cline farm, and half the BMR sudangrass field was fenced off and cut for hay when it became apparent that there was more forage than could be consumed in a timely manner by the number of livestock available to graze.
The Ohio Agronomy Guide says that when a 6-8 inch stubble is left, plants should re-grow to the 24 to 30 inch grazing height in 2 to 3 weeks. This is consistent with what was observed on the Cline farm. So, getting back to a management strategy to best utilize the forage quantity being produced, while also taking advantage of the high quality that is possible, the producer may want to consider staggered plantings of the sudangrass at 2 week intervals, or plan to do a cutting for hay or silage on part of the acreage. A sample planning calculation might look something like this: Sudangrass at 24-30 inches of height producing 2500 lbs of dry matter (DM)/acre. Ewes at 170 lbs consuming 3% of body weight per day need 5.1 lbs of DM. If the field is strip grazed, forage utilization should be at least 70%, so 2500 lbs of DM x .70 = 1750 lbs of DM available. If we want a 2 week grazing period, this will allot 125 lbs of DM / day, so we could graze 25 ewes/acre for 14 days. If 70-pound lambs were the grazing animals, and we figure dry matter consumption at 4% of body weight, then 45 lambs could be grazed on this acre for 2 weeks. If we had staggered planted a second acre of sudangrass 2 weeks after the first, or harvested the second acre as stored forage when grazing started, it would now be ready for a grazing pass. In reality, because the sudangrass will continue to grow and add dry matter from the time the grazing pass is begun, more animals will be needed to keep ahead of forage growth. However, this example illustrates the potential available during a time when forage is generally in short supply.
In addition to the forage production supplied by the BMR sudangrass, it also provides a safe pasture free from infective parasite larvae. The process involved in establishing the sudangrass destroys any larvae that might have been present if a previously grazed sod is used. Based on the experience at the Cline farm, even if infected sheep/lambs are moved on to the sudangrass, the shed eggs and resulting infective larvae are unlikely to add to the worm burden of grazing animals in subsequent grazing passes because: 1) leaving a 6 to 8 inch stubble insures no, or very few larvae will be ingested as typically infective larvae are found on the first 3 inches of grass plants, and 2) the structure and spacing of sudangrass stems will make it difficult for larvae that hatch from eggs in the feces to cover the distance needed to crawl up stems.
During the course of the study on the Cline farm it was found that while lambs were grazing with their mothers they had developed high levels of parasites. It was later discovered that the parasite population on the farm had resistance to all chemical de-wormers except for Cydectin. This was not documented until late in the season, shortly before beginning the second grazing pass on the BMR sudangrass on August 21. As a result, lambs maintained high parasite numbers for most of the project. While many of the lambs demonstrated resilience to these high parasite numbers as indicated by FAMACHA eyelid scores of 1 and 2, performance still suffered. As an example, just before the lambs entered the BMR sudangrass on August 21, lambs scoring a 3 or higher on the FAMACHA eyelid scorecard were de-wormed using Cydectin as a rescue treatment. This amounted to 7 lambs out of the 20-lamb study group. The remaining 13 lambs were not treated. At the end of a 3-week grazing pass on the BMR sudangrass, the untreated lambs had gained 0.19 lbs/day, while the treated lambs had gained 0.42 lbs/day.
There are several lessons here. One is that early season pasture management is critical to avoid loading up ewes and lambs with high parasite burdens. Two, make sure you know what chemical de-wormers really work in your flock. Finally, a warm season annual like sudangrass can provide a high quality forage when cool season pastures are declining, but that quality is put to best use in terms of animal performance when heavy parasite loads do not stress animals.
In summary, a warm season annual like BMR sudangrass can be used to provide a safe pasture while producing good tonnage and good quality during a time cool season pastures have little growth. To most effectively utilize this forage, a producer must have a plan to manage the rapid growth, including adequate animal numbers, strip grazing, staggered plantings and/or the capacity to harvest surplus growth.