- Hay is the basis for a healthy diet in small herbivores, and should make up a significant proportion of the diet.
- Hay serves as a source of long-stem fiber.
- Indigestible or insoluble fiber stimulates gut motility and maintains healthy gut flora.
- Alfalfa hay is generally recommended for growing small mammals.
- Most adults benefit from a diet based on grass hays.
Why is hay important?
Hays are harvested, dried forages that are often fed to popular small mammals like the rabbit (Oryctolagus cuniculus), guinea pig (Cavia porcellus), and chinchilla (Chinchilla lanigera) (Fig 1). In these small herbivores, hay serves as a source of long-stem fiber. Indigestible fiber or lignin moves through the colon and is excreted as hard feces or “day feces”.Fiber is needed to stimulate gut motility and maintain healthy gut flora. When small herbivores are fed a low fiber, high carbohydrate diet they are at greater risk for bacterial enteritis, particularly very young rabbits. Enterotoxemia is caused by overgrowth of Clostridium spiriforme, C. difficile, or C. perfringens. The gastroprotective effects of dietary fiber have been well documented. Small herbivores on high fiber (i.e. hay-based) diets are more resistant to stress-induced gastrointestinal stasis. Gastroprotection is especially important in rabbits because of their particularly complex and relatively fragile gastrointestinal tract.
Grasses and other fibrous foods also contain abrasive phytoliths. Phytoliths are silica bodies produced by plants that may help to wear down the open-rooted teeth of rabbits and rodents. Small herbivores are adapted for rapid wear. Tooth wear is approximately 10 times faster in the rabbit when compared to the horse. A lack of adequate dietary attrition can lead to dental changes within days putting small herbivores at increased risk for dental overgrowth and malocclusion.
Practical feeding strategies
Offer hay free choice. Alfalfa hay (see Types of Hay below) is a great dietary source of protein and calcium. Alfalfa is generally recommended for young, growing animals or individuals that need extra calories such as frail, geriatric animals or lactating does. The high protein, high calorie content of alfalfa-based diets may predispose adult animals to obesity. Therefore adults on a maintenance diet may be offered unlimited grass hay, oat hay and straw instead (see below).
There is another reason to replace alfalfa hay with grass hay in the rabbit. Rabbits are unique among mammals in that the kidneys excrete all dietary calcium. Excess dietary calcium ingested with alfalfa hay may lead to hypercalcuria or excessive calcium in the urine. Hypercalcuria can manifest as calcium sand or sludge in the bladder or even urinary stones. This is another reason alfalfa hay is primarily recommended for the young, growing rabbit and not the adult maintenance diet.
Types of hays
There are many types of hay or forage. Alfalfa is an important forage crop throughout much of the world, and it serves as a great source of dietary protein and calcium. Grass hays include a group of plants such as timothy, wheat, rye, oat, orchard grass and tall fescue. Timothy hay is one of the most commonly available grass hays.
Hay is not homogeneous forage. The nutrient composition of hay varies with the plant species, the stage of maturity or growth at cutting, and the method of handling and curing or drying (Table 1). Hay harvested at an advanced stage of growth (“late cut”) has a relatively high fiber content and low levels of protein and energy. Early cut hay is lower in fiber and higher in protein and energy.
Table 1. Concentrations of fiber, protein, and minerals in hay and straw
|Hay||Stage of maturity||Neutral detergent fiber (%)b||Acid detergent fiber (%)c||Lignin (%)||Crude protein (%)||Ca (%)||P (%)|
|Orchard grass||Early bloom||60||34||5c||12.8||0.27||0.34|
|Orchard grass||Late bloom||65||38||9||8.4||0.26||0.3|
|n/a: not available
a: All parameters are reported as a percentage of dry matter composition.
b: Neutral Detergent Fiber or NDF is a popular common measure of fiber in feed analysis that represents a collection of compounds including lignin, hemicellulose and cellulose, but not pectin.
c: Acid detergent fiber or ADF is the percentage of highly indigestible plant material.
d: Mean values from selected straws (barley, oat, and wheat) commonly fed to dairy cattle (Anderson 2006)
How to evaluate hay
With the exception of zoo personnel, most veterinary staff obtain hay from the pet store in small, portable bags. When feeding larger numbers of small mammals it is more economical to buy square bales from local feed stores or hay brokers. The analysis of hay listed below is limited to a basic, visual inspection, but most packaged hay in pet stores contains a quality analysis on the bag.
Visual evaluation of hay
- Odor and condition
- Foreign material
Hay harvested at an advanced stage of maturity is coarse and “stemmy” (see “leafiness” below) while early cut hay is relatively fine-stemmed and leafy.
The ratio of leaves to stems is an excellent indicator of hay quality. High quality hay has a greater proportion of leaves to stems. Stemmy grass hay is defined as large, coarse stems and a low leaf content. Stemmy alfalfa hay tends to have a high proportion of broken or shattered leaves that are often lost during feeding.
Hay can range from bright green to yellow or brown in color. Color can be a deceiving parameter to evaluate since it is a poor indicator of digestibility. For instance, yellow early cut, rain damaged hay can have higher nutritive value than bright green, late cut hay. In addition to light rain damage, hay can also appear yellow due to maturation or sun bleaching. Sun-bleached hay tends to be a light golden yellow color. Yellowing due to maturation may be distinguished from sun bleaching because all of the plants, rather than just those on the outside, have the same yellow tinge. Hay that has been exposed to rain, heavy dew, or fog has a characteristic dark brown or black appearance, which can indicate mold growth. Slight discolorations from sun bleaching, dew, or moderate heating during baling are not as serious as the loss of green color from maturity, rain damage, or excessive heating and molding in the bale.
Odor and condition
The smell of fresh mown hay is the standard by which all hay is judged. Hay should not be musty, moldy, or dusty. Mildew or mustiness indicates weather damage or insufficient drying before baling.
Obviously hay containing injurious foreign material should not be fed to animals.
Detailed, technical analysis is indicated whenever large quantities of hay are purchased. Twelve to 15 core sample are removed from hay bales with the use of a bale corer and an electric drill. A final sample size of 1 quart to 1 gallon (0.9- 3.8 liters) is sufficient for most laboratories.
Indigestible or insoluble fiber plays a critical role in maintaining gastrointestinal health. Long-stem, insoluble fiber stimulates gut motility and maintains healthy gut flora. The gastroprotective effects of fiber reduce the risk of gastrointestinal stasis in stressed patients. Feed small herbivores unlimited amounts of hay. Alfalfa is recommended for young, growing animals while adults on a maintenance diet benefit from grass hays.
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