Agriculture Reference
In-Depth Information
under certain conditions include aluminum, arsenic, boron,
chromium, fl uorine, silicon, tin, and vanadium (Underwood
and Suttle, 1999). Most minerals in excess can prove to be
toxic. Minerals whose excesses are less tolerated by
animals include fl uorine, molybdenum, lead, arsenic,
aluminum, cadmium, and mercury.
The main source of minerals is various feeds and occa-
sionally water and air. Soil also can provide minerals
directly through consumption during grazing and feeding.
Plants generally have a mineral composition characteristic
of the soil though soil pH can alter the availability of soil
minerals for plants. Acid soils lead to decreased availabil-
ity of most macrominerals but will increase the availability
of many trace minerals. Alkaline soils may increase
molybdenum or selenium availability but will decrease the
availability of most trace minerals.
Most forage is a rich source of potassium and iron but
often is defi cient in sodium, copper, selenium, and possibly
iodine. Cereal grains are defi cient in most minerals. High
protein feeds generally are richer in mineral content than
forage and cereal grains. Legume forage usually is richer
in minerals than grasses, and leaves are richer than stems.
As forage matures, protein content decreases while phy-
tates and oxalates will increase; these changes reduce
mineral content and mineral bioavailability.
Nutrient balance among minerals will alter mineral
absorption. Specifi c imbalances, induced by man through
mismanagement or natural conditions, can result in mineral
interactions and reduced mineral absorption. For example,
acid soils promote molybdenum absorption by plants, and
high molybdenum intakes may reduce copper uptake and
induce copper defi ciencies in animals. Goats given the
opportunity for browsing tend to balance their mineral
needs; however, in confi nement, defi ciencies or toxicities
can occur.
One general symptom of mineral defi ciency is “ pica. ”
Goats exhibit pica as a peculiar craving that results in
eating or chewing on wood or digging or licking soil.
Assessment of mineral status of animals can help to iden-
tify mineral excesses or defi ciencies and diagnose the
source of a pica problem. This assessment includes collec-
tive knowledge of mineral content of the feeds, water, soil,
animal fl uids and tissues, as well as clinical signs and
symptoms. Diagnosis is confi rmed when the problem is
corrected and the animal recovers.
Physiological stages of production may impact mineral
requirements and if not corrected, induce defi ciencies.
Minerals are needed for body metabolism and for all
phases of growth and production, particularly for skeletal
growth of young animals, conceptus growth of pregnant
does, and milk and fi ber production. Mineral requirements
of goats are not fully understood or investigated, and estab-
lished requirements are extrapolated largely from informa-
tion from cattle and sheep. Recent research fi ndings on
mineral requirements of goats confi rm major differences
between species and have been documented for copper
(Solaiman et al., 2001).
Vitamins
Vitamins are complex organic compounds that are needed
only in small amounts, that perform multiple physiological
functions, and that are involved in many metabolic pro-
cesses. Vitamins are generally classifi ed by their solubility
as either (1) water soluble vitamins, that include the B
complex vitamins and vitamin C, and (2) fat soluble vita-
mins, A, D, E, and K. Although fat-soluble vitamins only
have oxygen, hydrogen, and carbon in their structure,
water-soluble vitamins are more variable in composition
with some containing nitrogen, sulfur, and cobalt. Water-
soluble vitamins are synthesized in the rumen by fermenta-
tion in the presence of adequate cobalt for vitamin B
12
and
sulfur for thiamin and biotin synthesis. Although rumi-
nants may be self-suffi cient for synthesizing their own B
vitamins, supply of certain B vitamins may limit produc-
tion under some conditions. Ruminants can synthesize
vitamin C (ascorbic acid) because they have the enzyme
L-gulanolactone oxidase to convert gulanic acid to gulano-
lactone during ascorbic acid synthesis. Fat-soluble vitamin
A is present in forage as its precursor
- carotene, but
vitamin E often is added to diets. Vitamin D can be
obtained through exposure of skin to sunlight but must be
supplied when animals are indoors or have limited expo-
sure to ultraviolet arrays. Vitamin K can be produced by
rumen fermentation when the rumen is free from antivita-
min K activities (coumarin) produced by molds that grow
on white clover and produce the antivitamin dicoumarol.
Although some fat-soluble vitamins are required in the
goat's diet, research data to establish requirements are
lacking; therefore, requirements have been extrapolated
from data for cattle and some from data from sheep.
β
Water
Water is the largest single component of the animal's body
making up between 50 and 81% of total weight at various
stages of development. Water has unique properties
and functions in metabolism and physically. Water faci-
litates cellular reactions with its high dielectric constant
and hydrogen-binding property that promotes ionization
of electrolytes and allows oppositely charged ions to
move independently. Water helps in the transportation of
