Agriculture Reference
In-Depth Information
low in cobalt, or where high levels of iron or manganese reduce the avail-
ability of cobalt to plants. Excesses of iron or zinc can interact to reduce
the absorbance of each other [43]. Selenium is required for the enzyme
glutathione peroxidase, and a defi ciency of selenium can result in exces-
sive lipid peroxidation, called white muscle disease, which can be fatal in
young sheep and cattle. Excessive selenium can also be deadly: most lo-
coweed plants are selenium accumulators, and their consumption can pro-
duce acute selenium toxicity, leading to rapid death; chronic consumption
of selenium accumulator plants can lead to blindness or infertility [27].
4.3.2 VITAMINS AND MINERALS IN ORGANIC CATTLE
SYSTEMS
Vitamins and minerals are provided to dairy cows in a non-organic system
by including them in the total mixed ration (TMR). By mixing vitamins
and minerals in a formulated ration, the animals cannot choose to con-
sume more or less of a specific ingredient and selective feeding is limited.
The practices of organic dairy producers can include a similar vitamin and
mineral supplement using allowed ingredients, but may be more varied in
regard to delivering vitamins and minerals. Organic dairy feeding systems
range from large scale organic dairies (more common in the western US),
where a mixed ration (partial TMR) is used along with required pasture,
to small-scale exclusively pasture-based dairies (dominant in the upper
Midwest and the northeastern US). When TMRs are not used, vitamin
and minerals may be provided for free-choice consumption by animals.
Additionally, providing individual minerals (cafeteria style) to allow for a
truly free-choice selection instead of mixing or including them in a TMR
has been suggested as a way to allow individual animal selection to meet
nutritional requirements when forage quality is variable [44]. Beef cattle
on pasture and rangeland may be provided free-choice access to mixed
vitamin and minerals, a practice that is similar in non-organic and organic
beef cow-calf systems. Mixed organic swards containing plants of white
clover, chicory and plantain have been found to have greater mineral con-
centrations compared to perennial ryegrass or timothy [45], as do weeds
such as dandelion, dock and chickweed [27]. Soder et al. [46] reported that
