The transition from winter to spring poses major challenges for sheep producers in the summer rainfall regions. New growth is eagerly awaited after winter, as stored feed is usually running dry. Yet new veld growth should be grazed with caution, especially if veld has been burnt.
Annelie van Deventer, ruminant nutritionist at feed company Lavendula CC, which is part of the Agri FARMACY SA group in Potchefstroom, says new growth can lead to metabolic disorders that may result in production losses. Green grazing has certain deficiencies and imbalances require attention. New growth is usually associated with a high moisture content and low effective fibre, and both phenomena pose a set of problems that must be managed.
Too much of a good thing
“The first problem we observe when sheep are moved onto new green veld too fast and for extended grazing periods is diarrhoea. The high moisture content and highly digestible grass tend to speed up the bypass rate through the digestive tract. This high bypass rate prevents the efficient absorption of nutrients.
“In addition, fresh sprouts have a low effective fibre content, which prohibits the stomach from forming normal faecal pellets. This results in diarrhoea.”
Although fresh sprouts have a high energy and protein content, she says, the excessive amount of moisture dilutes the available nutrients, leaving the sheep unable to absorb what they need. The high moisture content causes sheep to become, as it were, sated before they are truly full.
In addition, green sprouts are extremely palatable and sheep will therefore ignore any other feed source. This causes a nutrient deficiency (low dry matter consumption) and sheep will start losing weight.
Managing sheep on green pastures
Managing the bypass rate of young, new growth is possible by gradually increasing animals’ exposure to it, Annelie explains. Have animals graze for one hour a day for the first few days, and then gradually lengthen the grazing period.
Animals must also have access to good quality hay. “Most sheep producers nowadays kraal their sheep at night. A simple solution would therefore be to leave hay in the kraals so that animals will have access to it in the morning and at night. This will also solve the problem of sheep snubbing hay while seeking out palatable new sprouts.”
Ketosis in ewes
Ewes’ nutritional requirements increase dramatically during late gestation. When these ewes are subjected to a dry-matter restriction, a metabolic disorder called ketosis (domsiekte) can occur. The energy and protein requirements of ewes carrying multiple lambs are almost double that of a dry ewe, but their consumption of feed does not necessarily follow suit.
“Low dry matter consumption due to the high moisture content of the grass will prevent the ewe from ingesting sufficient nutrients in the form of energy, causing her to start breaking down body fat. This process converts fat into ketones, but ketones are toxic to a sheep and will affect the animal’s brain.
“This is where the term domsiekte comes from. She becomes disoriented, bumps into objects or simply rests her head against a fence or wall. Ketosis can be fatal if the sheep is not immediately given a good source of high energy.”
An energy source that delivers quick results is sugar (glucose). In dairy cows, propylene glycol is used to effectively counteract a negative energy balance. This will have the same effect on ketosis-affected sheep.
“It is usually sheep in good condition, or ewes carrying multiples, that are especially susceptible to ketosis. In pregnant ewes, the multiple foetuses take up so much space in the abdominal cavity that there is little room for the rumen to expand to full capacity. If she ingests green grass that has a high moisture content on top of that, it can lead to ketosis.”
Ketosis also leads to other metabolic diseases such as milk fever. It is crucial to kickstart such a ewe’s rumen as soon as possible. Consult your flock veterinarian in this regard.
The key to preventing ketosis, she says, lies in one word: energy. A highly concentrated, balanced supplement containing sufficient energy is the most effective way of supplementing young green grass in a bid to prevent ketosis. In addition, protein, minerals and vitamins are naturally supplemented to meet the requirements of the producing ewe.
Signs of illness and treatment
According to Dr Christo Fick of Agri Farmacy Professional Services Inc, signs of ketosis include lethargy, sheep that struggle to get up or lag when the flock moves to a different spot, or that bump into objects or lean their heads against it. These sheep normally exhibit a suppressed appetite and have dull eyes. Post-mortem examinations often show an enlarged liver.
Timeous treatment, he emphasises, is essential and producers should involve the flock veterinarian without delay. Treatment strategies include injecting an intravenous glucose solution, as well as dosing glycerol or propylene glycol, vitamin B, or a solution containing half to one cup of sugar or molasses and two to three cups of water.
Prevention nevertheless remains the best solution, he says. A good nutrition programme must be in place to prevent ewes from becoming overly fat at the start of their pregnancy. Sound management practices involve ensuring that no feed shortages occur, that there is sufficient protection against severe climate conditions and that animals are not handled without good reason.
Aspects of cultivated pasture
All the principles that apply to natural grazing also apply to cultivated pastures. However, because cultivated pastures are fertilised, a ‘withdrawal period’ is required where a pasture has been fertilised with nitrogen.
Annelie’s advice is to consult a grazing expert regarding the length of the withdrawal period for the specific fertiliser used – it is usually in the range of two to three weeks. Nitrate poisoning poses a risk if sheep start grazing too early.
Another risk to guard against is prussic acid poisoning. This occurs when prussic acid levels rise in certain pastures due to stressful conditions such as frost and leaf wilting. Animals that graze these pastures may experience laboured breathing and convulsions. Affected animals will soon succumb.
“A nitrogen-free energy lick combined with a buffer and ionophores given approximately two weeks beforehand, is recommended for animals that are going to graze fertilised cultivated pasture. Fertilised cultivated pastures can contain highly soluble sugars, leading to varying degrees of acidosis due to its pH-lowering effect in the rumen.
“Make sure, however, that each individual animal consumes its quota for the day, as the lick must be present in the stomach to do its job when sheep are moved onto the fields,” she says.
Subacute ruminal acidosis
According to Dr Fick, subacute ruminal acidosis (SARA) is a significant threat when animals consume starch combined with low amounts of fibre. “The rumen of a ruminant contains micro-organisms that must first adapt to the copious amounts of starch. This can take 14 to 21 days.
“When the rumen is not adapted beforehand, the micro-organisms produce lactic acid faster than they can break it down and utilise it. This causes the rumen pH to drop, and most of the other micro-organisms to die off, except those that produce lactic acid.”
Feedlot sheep, or sheep that are moved onto maize residues without having been adapted, run the risk of developing SARA. Signs of this metabolic disorder include lower feed intake, a drop in milk production and condition, and possible development of diarrhoea.
Treatment, he explains, is largely aimed at addressing complications, once the acidosis has cleared up. Antacids such as Acid Buf (registration holder: Allied Nutrition) or magnesium oxide can be given. A vitamin B supplement must be given, as acidosis tends to cause a deficiency. Penicillin is usually given for liver abscesses that may form after acidosis.
“Prevention remains the best treatment. Remember to allow for an adjustment period (14 to 21 days), limit starch intake, and include enough fibre in the diet. Lacticon S can also be dosed.”
For more information, contact Annelie van Deventer or Dr Christo Fick on 018 297 1855, send an email to firstname.lastname@example.org or visit www.agrifarmacysa.co.za.