Evaluación de dosis diagnóstica de temefos y determinación de grados de resistencia

(mouth to small intestine) is the primary site of enzy- matic digestion of non-fibrous carbohydrates, proteins, and fat. The horse’s hindgut (cecum to rectum) con- tains an active microbial population and is the site of fermentive fiber digestion. Similar to the microbes in a cow’s rumen, a horse’s hindgut microbes utilize some non-fibrous and complex fibrous carbohydrates to pro- duce volatile fatty acids (VFA). The horse then absorbs and uses these VFAs for energy. This microbial fermen- tation is what enables horses and ruminants to effi- ciently utilize forages.

The location of microbial fermentation within the di- gestive tract makes horses and ruminants very differ- ent, however. Because its microbial digestion occurs after the small intestine, a horse is unable to utilize much microbial protein. A horse’s fermentation tract is also smaller than that of a ruminant. Thus, horses re- quire smaller, more frequent meals and diets that con- tain a relatively good-quality protein source.

FEED INTAKE AND NUTRIENT REQUIREMENTS The nutritional needs of a horse depend on several fac- tors:

• Activity level—Working horses have greater require- ments, depending on the frequency and intensity of work.

• Age—Mature horses have lower nutritional require- ments than young, actively growing horses.

• Production stage—Requirements are highest during pregnancy and lactation.

• Body size—A draft horse has greater nutrient re- quirements than a small pony.

Table 10.8 lists the daily recommended protein and en- ergy intake for various classes of horses.

We usually consider feeds on a dry matter (DM) basis (water removed). If a feedstuff is 90 percent DM, it contains 10 percent moisture. Most grass hays are around 90 to 95 percent DM. Dry matter in pastures can range from 30 percent in early spring to around 65 percent later in the growing season.

Horses normally consume 2 to 2.5 percent of their body weight in DM each day (100 percent dry). Intake can vary from 1.5 to 3 percent, however, depending on the horse’s activity level and the quality and digestibil- ity of the feedstuff. For example, an increase in work- load or exercise can increase intake. Less digestible feeds may remain in the digestive tract for a longer time, limiting the amount and frequency of feeding. As feed quality increases, nutrient density also increases and DM intake may decline.

Diets can consist primarily of forages (hay or pasture) or a combination of forage and concentrates. Horses must consume at least 1 percent of their body weight daily in forage to maintain healthy digestive function. Their remaining nutrient requirements can be met with other feedstuffs.

Table 10.8. Recommended daily energy, protein, and mineral requirements for horses at different stages of production (mature body weight of 1,100 pounds). Class of horse DMIa (lb/day) DEb (Mcal/day) TDNc (lb/day) CPd (lb/day) CPd (%) MATURE HORSE Maintenance, no work 18.0 16.7 8.4 1.4 7.8% Moderate exercise 20.0 23.0 11.5 1.7 8.5% Heavy exercise 25.0 27.0 13.5 1.0 7.6% Breeding stallion 22.0 22.0 11.0 1.7 7.7%

Early pregnancy (< 5 months) 20.0 17.0 8.5 1.4 7.0%

Late pregnancy (final 90 days) 22.0 20.0 10.0 1.0 8.6%

Early lactation (1 to 2 months) 24.0 32.0 16.0 3.4 14.2%

GROWING HORSE

6 months old 11.0 15.5 7.8 1.5 14%

12 months old 15.0 19.0 9.5 1.8 12%

Source: Adapted from National Research Council. 2007. Nutrient Requirements of Horses, 6th revised edition. National Academy Press.

a

Dry matter intake (100 percent dry basis). To convert to as-fed fresh forage basis, divide by the decimal of the feed’s percent dry matter (e.g., if the feed is 25 percent dry matter, and DMI is 18 pounds per day, the as-fed quantity is 72 pounds (18 ÷ 0.25 = 72).

b

Digestible energy

c

Total digestible nutrients, calculated as DE x (1 kg ÷ 4.4 Mcal) x 2.205 lb/kg

d

Body condition scoring (BCS) is an excellent tool for evaluating plane of nutrition. On a scale of 1 to 9, a horse in good condition has a BCS of 5 or 6.

Abrupt changes in diet, such as a large increase in the amount of grain or a change from dry hay to lush pas- ture can harm the microbial population in the digestive tract. Horse health problems may result. When chang- ing diet, do so gradually to give the microbial popula- tion time to adjust.

Feeding too much feed at one time can increase the risk of laminitis and colic. Feeding small amounts fre- quently is a good practice when supplementing diets with non-fibrous carbohydrate sources such as grain. If feeding grain, limit the amount to 0.5 percent of body weight per meal. For a 1,200-pound horse, feed no more than 6 pounds of grain at one feeding. In addition to energy and protein, horses require macro- and microminerals. Requirements for the macrominerals calcium (Ca) and phosphorus (P) are greater when tissues and bones are actively growing, as well as during lactation. The optimum Ca:P ratio is 2:1. Supply these minerals in at least a 1:1 ratio. Microminerals are needed in lesser amounts, but are very important. Feeds and forages supply much of the animal’s requirements. Take these sources into ac- count when providing a mineral supplement.

Some soils in the Northwest are deficient in copper, se- lenium, and other microminerals. In these areas, sup- plements should contain greater quantities of these minerals. Mineral excesses can also cause problems. Know the potential for deficiencies or excesses in your area and tailor your supplementation program accord- ingly.

A word of caution: ionophores, which are frequently utilized in ruminant supplementation programs, are toxic to horses.

PASTURE GRAZING

Grazing is a low-cost, healthy way to meet nutrient needs for most horses. Well-managed, actively growing pastures or good-quality hay can meet or exceed the nutritional requirements of most mature horses. (Horses that are worked or ridden often may be an ex- ception.) Grazing horses spend more time eating than nongrazing horses and typically display less behavioral problems, such as cribbing (sucking air) and wood chewing.

A horse weighing 1,100 pounds and consuming 2 per- cent of its body weight in dry forage (assuming forage is 50 percent DM) consumes about 44 pounds of forage per day (as fed). To prevent damage to the pasture and reduced pasture productivity, it is important to have adequate acreage. The acreage required to effectively graze a horse depends on land productivity (i.e., forage species, rainfall amount or irrigation availability, soil type, and soil quality). See chapter 14 for determining carrying capacity and stocking rate, and chapter 16 for methods of estimating forage production, conducting a forage inventory, and forage budgeting.

Horses prefer grass, but will consume most legumes and some forbs. Common pasture grasses for horses include Kentucky bluegrass, orchardgrass, timothy, smooth brome, meadow foxtail, and endophyte-free tall fescue.

Including clovers or other legumes in the pasture mix can benefit both the horse and the pasture. Legumes provide high-quality protein and reduce the amount of nitrogen fertilizer required. Do not use alsike clover, however, as it can cause horses to be overly sensitive to sunlight.

Contrary to popular belief, the protein from legumes does not cause kidney damage to horses. Horses that consume higher protein diets may urinate more often, however, so it is important to provide unlimited access to fresh, clean water.

Horses are more selective grazers than cattle and graze longer and more frequently. This selectivity may cause “patch” grazing, as horses graze vegetative growth and leave more mature plants. They also tend to defecate in certain areas and avoid grazing in these areas. Horses with metabolic disorders may need to be man- aged in a limited turnout grazing situation or with graz- ing muzzles. Grazing later in the evening and through the night, when soluble carbohydrate levels are lower, is another option for these horses.

For more information

Beef Cattle Nutrition Workbook. EM 8883-E. Oregon State University Extension Service (2004).

http://extension.oregonstate.edu/catalog/html/em/ em8883-e/

Body Condition Scoring of Sheep. EC 1433. Oregon State University Extension Service (1994).

http://extension.oregonstate.edu/catalog/pdf/ec/ ec1433.pdf

Idaho Forage Handbook, 3rd edition. BUL 547. University of Idaho College of Agricultural and Life Sciences (2005). http://info.ag.uidaho.edu/forage/

Mineral Tolerance of Animals, 2nd revised edition. National Research Council. National Academy Press (2005). New Mexico State University Sheep Production and Man-

agement website.

http://aces.nmsu.edu/sheep/index.html

Nutrient Requirements of Beef Cattle, 7th revised edition. National Research Council. National Academy Press (1996).

Nutrient Requirements of Dairy Cattle, 7th revised edition. National Research Council. National Academy Press (2001).

Nutrient Requirements of Small Ruminants. National Re- search Council. National Academy Press (2007).

FORAGE QUALITY, OR NUTRITIONAL VALUE, refers to the concen- trations of fiber, energy, protein, minerals, and other nutrients in for- age that impact animal performance. Pasture plants vary widely in quality, depending on their growth stage, leaf concentration, and age, as well as on environmental factors and time of year. In this chapter, we discuss plant components that determine forage quality, forage quality characteristics in pastures, factors affecting animal intake, for- age sampling, and quality considerations for stockpiled forages and crop residues.

Pasture Plant Composition