The caprine diet must include forages such as grass and hay as well as other herbaceous materials such as leaves and twigs, which they browse. Forages and browse contain cellulose, which is a complex carbohydrate that makes up much of the structure of plants. Also referred to as fiber, structural plant material must be present in a goat’s rumen to facilitate and sustain fermentation. Microbes (mostly bacteria) in a goat’s rumen break down the cellulose through the fermentation process, which results in products called volatile fatty acids. These volatile fatty acids are the chemical precursors that finally become glucose, the primary energy source for all of the mammalian species.
Goats, as well as all ruminants, are created with the ability to consume herbaceous materials that single stomach species (monogastrics) are incapable of digesting. The rumen is "the big fermentation vat" that initially breaks down the cellulolytic or woody forage material into smaller components. The "digesta" exits the rumen and moves into other stomach chambers where continued digestion of the feed occurs in a fashion similar to that of monogastrics (e.g. humans, poultry and swine, etc).
The sources of dietary energy for monogastrics is primarily fats, sugars and starches that are absorbed into the blood stream by way of the small intestine. Ruminants such as goats make little use of fats, sugars, and starches as direct sources of metabolizable energy. Energy metabolism in ruminants must occur as the result of the fermentation of feedstuffs in the rumen, producing the volatile fatty acids, which are absorbed in the small intestine and converted to glucose in the liver.
All plants vary in their potential to supply energy for ruminants depending on the complexity of the cellulose they contain. The more woody or "stemmy" a plant is, the more chemically bound together the cellulose is and the more difficult it is for microbes to get at it and break it down.
Forage quality is defined as the amount of fiber that it contains. The more a plant matures, the more fibrous it becomes in order for it to stand upright as it grows and either flowers or seeds. Both energy potential and protein content in forages are inversely related to maturity. Immature forages such as early season pasture grasses are generally higher in protein and lower in cellulose. The cellulose in younger plants (early vegetative stage), is generally more digestible because rumen microbes are able to more quickly and more completely break it down and ferment it which results in more volatile fatty acids and, ultimately, more blood glucose.
Both milk production and growth rates in goats are directly affected by blood glucose levels. Even though grains (corn, barley) and commodity by-products (wheat midds, sugar beet pulp) are routinely fed to goats to augment energy levels, their rumens, in order to function efficiently and remain healthy, must always contain fiber from plants. The greater the digestibility and fermentability of a forage or browse is, the more energy it will supply. Even though goats love to go out into the pastures and woods to browse, given the choice when offered a sweetly cured, fine bale of grassy hay, they’ll stick around the barn and consume the hay and then stand around and complain when it’s all gone.
Protein in goat diets must also be considered. Generally, protein in a lactating goat diet should average around 17-18% crude protein (CP). The protein content in the forage being offered will dictate how much protein must be supplemented. Early season pastures can test well over 20% CP which is more than enough protein for a lactating goat diet and grain supplements don’t need to be over 16% CP. As pastures mature (grasses have gone to seed) or if the hay available is of poorer quality and full of stemmy weeds, then CP and energy levels in the grain supplements must be adjusted upward to reach the targeted average 17-18% CP for the total diet.
Goats, of course, have been created to be talented browsers. They can find the most nutritious parts of a bush or weed when needed. However, bear in mind that maturity and woodiness generally equate to less energy and protein. Goat owners and managers need to be aware of the conditions and quality of pasture and browse, especially if milk production is expected to be maintained.
Lactating goat diets consisting of larger proportions of higher quality forages nearly always result in more milk production compared to diets of lower quality forageeven if they’re supplemented with more expensive grains supplements. That’s because the rumen does a more efficient job of fermenting fibrous feedstuffs as opposed to starchy feedstuffs. High starch levels in the rumen will often result in higher acid levels, which lowers the pH level (acid-base balance). Fiber fermenting bacteria work best in a pH environment of 6.0 to 7.0. As pH drops below 6.0, those fiber fermenting bacteria will be harmed, decreasing the rate of fermentation.
As with all ruminants, the amount of energy provided in a diet is a direct function of how much fermentation occurs in the rumen in a given time period and how rapidly digesta moves through the stomachs to be absorbed in the small intestine. This is not to say that goat diets shouldn’t be supplemented with grains or by-products. Grains and by-products also provide fermentable components that microbes can use as well as other combinations of amino acids, vitamins and minerals that may not be provided in forages alone.
Forages for ruminant diets are quickly and easily analyzed by forage testing laboratories and the cost of a forage analysis is reasonable. With the recent and continuing escalation of feed costs, proper balancing of lactating diets is becoming a necessity. Especially when maximizing milk production, a diet cannot be balanced properly and cost effectively without knowing what the quality of the forage is. Most forage testing labs will provide more information than goat owners will ever need. The basics, however, should include:
- Dry matter/moisture content
- Crude Protein
- Net Energy-Lactation (NEL) measured in megacalories per pound (mcals/lb.)
- NDF (Neutral Detergent Fiber)
Forages with NDF levels over 65% (dry matter basis) don’t have the energy because there’s "too much fiber" and the digestibility of that fiber is diminished. Likewise, crude protein levels that drop below 12% indicate more mature forages and protein in the ration must be supplemented to meet protein requirements for high producing does. Calcium (Ca) and phosphorus (P) must be balanced, too. The Ca:P ratio must be kept around 2:1. Legumes (alfalfa) hay tend to have higher Ca levels compared to a grass hay. A grain supplement must be balanced so that Ca is not overfed and that the Ca:P ratio is never inverted, with more P being in the diet than Ca.
It’s very difficult to compensate for poor forage and it always costs more money. Even if hay is pricey, it may wind up producing more milk and being more profitable than a less expensive alternative.
Forage is the foundation for all ruminant diets. When goats are fed a diet, the rumen microbes are also being fed. To a certain degree, the rumen microbes are more important than the goat. Without rumen microbes, rumen function ceases and nothing is digested. When the rumen isn’t healthy, the goat won’t be healthy, either. Whether goats are pastured or confined, learning how to balance diets based on the quality of forages will result in a healthy and productive herd of goats.