Forages in swine diets and pasture systems
Forages in the form of pasture, as part of a complete feed, or silage, can be used successfully in pork production. Prior to 1950, pasture was considered a vital component in most swine feeding programs because it provided vitamins, minerals, and unidentified growth factors.
Forages may have special applications in diets for organic swine production. Forage species, maturity, growing conditions, and grazing habits of pigs all influence the nutritional value of the forage consumed. Unfortunately, there are few data available to estimate the quantity of forage consumed by pigs and the nutritional value of that forage. Consequently, most nutritionists give little or no nutritional credit to the forage when formulating diets for pastured pigs. Stored forage used in the diet or fed as silage can be analyzed for nutrient content. Nutrient content of the forage can be considered in diet formulation realizing that digestibility of those forage nutrients generally is lower than that of grains. The Pork Information Gateway publication entitled “Forages for Swine” outlines some specifics on utilizing forages in swine diets.
Some observations from that document include:
- Due to high fiber content and low energy density, forages have only limited value for young pigs (especially those weighing less than 40 pounds) and lactating sows.
- Forages are best utilized at an early stage of maturity.
- Pigs absorb more nutrients from forages after an adaptation period of at least two months.
- If forages make up more than 25% of the total diet, the crude protein content of the complete feed should be slightly higher than typical corn-soybean meal diets due to the lower protein digestibility of forages.
- When pastures are the forage source, pasture rotation should be used to prevent heavy parasite and bacterial contamination of pigs.
- Forages can be heavily damaged by grazing swine, especially with rooting in the spring and fall. Reduced stocking density will protect pastures and support greater persistence of pasture plants. Ringing of sow snouts can reduce damage, but ringing may be considered mutilation and are not allowed under some market certification standards, such as organic.
- Hogs on pasture may grow slower and require more feed per unit of gain due to high fiber intake and increased exercise compared with confinement-raised pigs.
National Organic Standards require that livestock have access to the outdoors, which can be a dirt lot or pasture. Pastures must be certified as organic before organically-raised pigs can be allowed to graze.
Use of forages can lower costs of grain and protein supplementation. In the case of pasture systems, equipment and building costs decrease, resulting in lower fixed costs of production compared with intensive confinement production systems. If sows are bred in the late spring to farrow early in the fall, good quality forage can replace up to 50% of grain and supplement needs. One acre of good pasture can accommodate up to 8 sows for a season. During other seasons of the year, however, forage quality and availability will vary, and supplementation with grain and protein supplements will need to be adjusted to provide the necessary nutrients.
Available recommendations on stocking rates for grow-finish hogs on pasture vary considerably with soil fertility, pasture species, rainfall, and season which all impact forage availability and quality. Available recommendations for pigs weighing less than 100 pounds are 15-30 pigs per acre and 10-20 pigs per acre for pigs weighing over 100 pounds. These numbers can be increased significantly with more intensive management such as rotational grazing. Grow-finish pigs on pasture are full-fed in most instances. However, some observations suggest limit feeding can be practiced with sufficient nutrient contributions coming from the pasture. Research focusing on the nutritional contributions of pasture with current swine genetics and management is limited.
A sample pasture mix might consist of seeding for permanent, rotational, or annual pastures. The permanent pasture might contain seeding of bluegrass, white clover, orchard grass, and alfalfa. The rotational pasture may include alfalfa, red clover, ladino clover, sweet clover, alsike clover, orchard grass, brome grass, and Timothy grass. An annual or temporary pasture could be made up of brassicas, rape, soybeans, cowpeas, fababeans, Sudan grass, rye, oats, wheat, barley, field peas, and mixes of grass and legumes (Zeller, 1948). Example diets that have been presented do not assume pasture supplementation due to the wide variation in forage or pasture types used, and will therefore need to be adjusted based on nutrients provided from the pasture.