Pasture crops provide about 70% of the feed consumed by livestock. As expected, the importance of each kind of feed varies with the type of livestock.
Sheep and goats obtain greater than 80 percent of their nutrition from forage, while 73 percent of beef cattle nutrition is from forages.
New and changing management practices in the dairy industry allow forage to be anywhere from 20 to 80 percent of a cow’s diet at any time in her life.
Lengthening the grazing season by using practices such as stockpiling forage or planting annuals for forage can greatly reduce production costs for a wide variety of livestock species.
To be profitable, dairy farmers have an increased dependency on forages, grazing and pastures. Pastures can be a useful source of forage on land that is unsuitable for other crops. The amount of pasture needed depends on pasture quality, animal size and type, season and species of forage in the pasture.
During the rainy season like now, plenty of lush, green pastures are available for livestock.
However, these lush pastures are often very high in moisture; therefore, diluting their nutrients. The result is that animals have a difficult time consuming enough to meet all of their nutrient requirements. Two unrelated, but equally important problems are commonly seen during the early grazing season – grass tetany and pasture bloat.
Grass tetany
Grass tetany, commonly referred to as ‘grass staggers’, is a metabolic disorder caused by a deficiency in magnesium. Livestock are most susceptible to grass tetany during early lactation, when milk production is at its highest, or when they are older and less capable of mobilizing Magnesium reserves in their bones.
The greatest risk of grass tetany is usually found in pastures grown on soils that are low in available Magnesium, but are high in potassium and nitrogen.
Clinical signs of grass tetany include: not grazing, nervousness (staring and keeping their heads and ears in an erect position, or lying down and getting up frequently), muscle twitching and ‘staggering’ while walking.
An affected animal may go down on its side and experience muscle spasms (periodic foreleg paddling, twitching of the eyes and ears) and convulsions. An affected animal usually dies during or after a convulsion unless treatment is given.
Treatment
Treatment should be given in the early stages of grass tetany. Cattle or goats that are down longer than 12-14 hours have a slim to no chance of survival.
A 20 percent magnesium sulfate (Epsom salt) solution can be given subcutaneously (under the skin) treatment. Blood Magnesium levels can be increased within 15 minutes by intravenously administering 500 ml of calcium borogluconate solution with 5% magnesium hypophosphate. The solution must be administered slowly, and heart and respiratory rates should be monitored closely during administration.
The best treatment for grass tetany, however, is prevention. Pastures grown in soils that are low in both Magnesium and pH (the acidity or alkalinity of a solution) should be limed with dolomitic lime, which contains high levels of Magnesium. Legumes (for example: clovers, lespedezas) often contain high levels of Magnesium naturally and may help reduce the risk of grass tetany when included in forage programs.
However, the most reliable method of prevention is supplemental feeding of Magnesium and calcium one month prior to and during grass tetany season. Look for mineral mixes that include 2.5-3.5% Magnesium to add to feed rations.
Pasture bloat
Bloat is a digestive disorder characterised by an accumulation of gas in the first two compartments of a ruminant’s (cattle, sheep, and goats) stomach. Gas is a natural by-product of ruminants’ digestion, and is usually relieved by eructation (belching).
Pasture, or ‘frothy’, bloat, results from the production of a stable foam that impairs the animal’s ability to relieve these gasses, thus causing the rumen to expand and compress the lungs. Once this happens, the oxygen supply will be cut off and the animal will suffocate, sometimes in as little as an hour.
Bloat can be caused by grazing animals on lush pastures – typically pastures or small grains – that are low in fiber and highly digestible, but bloat is most commonly seen in animals grazing on immature legume pastures, specifically clover and alfalfa.
Other legumes, such as arrowleaf clover, berseem clover, sericea lespedeza, annual lespedeza, and crown vetch, contain leaf tannins that help to break up foam.
However, some animals, such as ‘aggressive-feeders’, are more susceptible to bloat than others.
Clinical signs of bloat include: rapid swelling on the left side and signs of discomfort, such as kicking at their bellies.
Catching bloat in its early stages often yields the best results. Bloat can occur in as little as 15 minutes to an hour; however, there is usually a 24 to 48-hour lag before bloating occurs. Immediately remove a bloating animal from the bloat-inducing pasture and offer them dry hay. This will reduce the bloat problem in all animals that will eat.
Forcing bloated animals to walk can increase belching. Remember to handle bloated animals gently since their breathing is impaired.
If this does not lessen the bloating, then you can try to manually release the gas by:
1) stomach tubing – this involves restraining the animal and passing a rubber hose down the esophagus.
2) Trocar – this is a device that punctures the rumen from the outside and is a rapid and effective means of releasing the gas.
This should be used as a last resort as animals treated with a trocar will require antibiotics to prevent peritonitis (a potentially deadly inflammation of the abdominal lining).
Just like with grass tetany, prevention is the best treatment for bloat. If your pasture is predominantly legumes, like clover, consider over-seeding your pasture with a pasture grass. Bloat has very rarely occurred in pastures that are a 50/50 mixture of grasses and legumes.
Do not turn out hungry animals on lush legume or small grains pastures without feeding them hay or supplemental grain. Finally, invest in anti-bloat products with poloxalene in them. Poloxalene is an anti-foaming agent that prevents bloat for 12 hours by breaking down stable foam.
A good, easy-to-use source of poloxalene is a salt molasses block – there are 30 grams of poloxalene per pound of block. To use, remove other sources of salt, and replace with poloxalene blocks – about 14 kgs per 4-5 animals (cattle) – at least 3 days before placing animals in pastures with significant bloat risk.
