Rangeland plant production important to livestock performance
By D. Bruce Bosley
Plant production in rangeland is a key component of livestock production. Wise ranchers know that when they sell cattle they are ultimately selling grass in a value added form. They also realize the value of leaving enough vegetation in their rangelands when they pull their herds off to promote optimum forage regrowth. The rule of thumb when managing grazing is to take half and leave half. Managing range and pasture forage grasses, forbs, and shrubs during a drought becomes especially difficult. Putting or leaving livestock on pastures when green growth is sparse can harm the land's forage base. Furthermore, allowing livestock to graze on in droughty poor growth fields can also lead to animal poisonings.
Plant poisoning can affect livestock in many ways including causing reproductive problems. These poisonings can take the form of conception failures, fetal abortions, and even developmental deformities. Poisonings that affect reproduction do not show up until months after the pregnant animal consumed the poisonous plants.
A veterinarian approached me recently regarding three instances where calves were born having developmental deformities. These calves came from three different livestock operations from different areas of northeast Colorado. Locoweed and several milkvetch species are the most likely plants to have caused these deformities. Poison Hemlock is another species that can cause reproductive deformities.
Many Milkvetch (Astragalus) species inhabit upland rangelands in the High Plains, and mountain foothills. Two forms of Locoweed (Oxytropus sp.) inhabit the same locations. Poison Hemlock is a common weedy species in sub-irrigated pastures and along riparian lands along river bottoms.
When native ranges or improved pastures have good supplies of suitable forages cattle, sheep, horses, and other livestock will normally leave many unpalatable or poisonous plants alone. However, when drought limits plant growth or when livestock have grazed off most of the suitable forage growth, grazing animals are much more likely to consume plants that they generally avoid. Plant poisoning of livestock occurs much more frequently during drought when forage resources are low to non-existent than when conditions favor plant growth and forages are plentiful.
Poisonous and other generally unpalatable plants will become more abundant in lands that have a long-term history of season-long grazing. Cattle and other livestock repeatedly graze the most palatable and beneficial grasses, forbs, and shrubs when the animals are allowed to remain in pastures for weeks or months at a time. As a result, these beneficial plants decline leaving less palatable species in their place. Ultimately, the palatable plants disappear from that landscape. This process, when repeated for many years of season-long grazing, will increase the number of plants that are too objectionable for most animals to graze on unless they are the only available forage.
The most effective solution to minimizing plant poisoning risks is in changing grazing practices and removing livestock from rangelands and pastures before the grass and other suitable forages are gone. Digging out or spraying out poisonous plants merely provides a sense of reducing the risks. At best, plant removal is a short-term solution.
Please contact me if you would like more information on this or other cropping systems topics: Sterling at 970-522-3200 extension 285, or Fort Morgan at 970-542-3542.