Balancing Dairy Diet Around Forage Quality

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2/11/2014 Dairy Goat Journal. | raising goats | goat business

http://www.dairygoatjournal.com/90-6/balancing_caprine_diet_around_forage_quality/

Balancing Caprine Diet

Around Forage Quality

By John Hibma

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 dependingon 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 toaugment 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 canfind 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 forage—even if they’re supplemented with more

expensive grains supplements. That’s because the rumen does a moreefficient 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)

Calcium

Phosphorus

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 ratiomust 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.

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Balancing Dairy Diet Around Forage Quality