Thanks to Kim Cassida for this great piece. Here she focuses on practices for small ruminants, but the principles work for cattle as well.
A common question among new small ruminant producers is “which forage is best for my animals?” The answer isn’t only about nutrients, but also involves parasite management and sustainable forage production.
A key consideration for managing small ruminant pastures is that the effect of small body size on metabolic rate and digestive efficiency means that these animals require more nutrients per unit of forage eaten than cattle. Therefore, pasture management for growing or lactating animals should usually emphasize maintaining nutritional value over absolute dry matter yield. Total digestible nutrient (TDN) content of plants decreases as they get larger and more mature, and therefore nutritive quality of a pasture inevitably decreases as plants grow and yield increases. In general, legumes and other broadleaf plants (including the leaves of woody plants) are more energy-dense than grasses because they contain less fibrous cell wall.
The exact point of best compromise between quality and yield is different for every forage species. Different species in pasture mixtures grow at different rates, which makes it difficult to gauge perfect timing for grazing a mixture. A good rule of thumb is to graze grasses in the vegetative stage when they have three to five leaves per tiller. For most cool-season grasses, this will occur when the pasture herbage is 8 to 10 inches tall. Legumes like alfalfa and red clover should be grazed in late bud to early flower stage. If stocking density is low and stage of production not too demanding, sheep and goats can compensate for low nutrient density in pastures by selecting only the most nutritious parts of plants, but this strategy reduces forage utilization per acre and requires more land per animal.
A second key consideration for small ruminant pasture management is gastrointestinal nematode (GIN) parasite control. Pharmaceutical control of GIN in small ruminants is increasingly difficult because many GIN species have developed resistance to available dewormers. Therefore, we try to manage pasture to prevent infection by understanding our enemy. Production and mortality losses from GIN on pasture are especially severe for goats, whose natural adaptive strategy is to avoid infection completely by browsing high above the ground and therefore have very poor genetic tolerance of the pests.
GIN eggs that are shed in feces hatch into free-living larvae that crawl up the plants in the surface moisture film from dew or rain and are eaten along with the forage, thus reinfecting the animal. Grazing taller plants might reduce the chance of infection, but it presents a negative trade-off with the goal of grazing pastures at peak nutritive yield because taller plants are generally more mature.
As we learn more about GIN, grazing management becomes more complicated. Traditionally, we believed that almost all of the GIN larvae were found in the bottom two inches of the pasture canopy, and therefore leaving grazing residual heights of four inches should minimize reinfection. My recent research while working for USDA-ARS in West Virginia demonstrated that this generalization is not always correct. In our study, enough larvae to infect animals were detected in the canopy layer above six inches in red clover-grass, birdsfoot trefoil-grass, and chicory pastures, putting the larvae squarely in the canopy horizon recommended for optimum grazing quality. Stay tuned for more information as it becomes available.
So What’s A Small Ruminant Rancher to Do?
In many cases, the most profitable solution to run-down pastures is simply to improve management of the existing pasture rather than renovating to the newest trendy forage. Pasture renovation is expensive, requires machinery which many small producers do not have, takes pasture out of use for several months, and carries risk of failure. In contrast, soil testing (which is free through the Cooperative Extension Service in many states), following soil test recommendations for liming and fertilizer application, overseeding with legumes, and building inexpensive electric cross-fences to allow managed grazing access are less risky management options that are likely to provide large returns on investment over the long term.
Nevertheless, in areas recovering from drought, many pastures will be ideal for renovation this year. Pastures should be considered for renovation when severely stressed by drought, when desirable plant cover is less than 50% of the ground surface, or when undesirable weedy species are more prevalent than desirable species. However, keep in mind that sheep and goats will readily eat many forbs that are commonly considered weeds, such as dandelions and plantains. These plants have excellent nutritive value and are comparable to legumes. Their primary disadvantage is lower productivity than improved plants. If the livestock will eat the weed and it is not toxic, then control may not be necessary.
Would you like your livestock to eat weeds? Here’s how to get them to do that:
Very nice job on the article. Your comments relative to the importance of grazing management in GIN management are right on target.
I am interested in the work you did looking at infective larvae in the canopy of forages. Can you point me to the report/data on the web?
Professor & Specialist
Animal & Natural Resource Management
Texas A&M AgriLife Extension Service
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