The start of a new season generally coincides with lambing for the majority of livestock producers. For many producers this season with an extended dry period has led to many challenges with feed shortages. The need to maintain a productive breeding operation has been front and centre. However, keeping stock well fed and performing during the summer and autumn months may be one thing, but there are still some potential hurdles ahead. All the hard work can be unraveled, despite having green feed on hand, so with a new season upon us and hopefully one with more promise, now is not the time to take your foot off the accelerator.
With the onset of lambing, breeding ewes may be at their greatest risk of succumbing to “production diseases”. However, they are more commonly referred to as “metabolic diseases” because management of the animal is directed at production, which at its peak is beyond the capacity of that animal's metabolic reserves to sustain a particular nutrient at the required concentrations. The three most common diseases likely to be experienced are
milk fever (hypocalcaemia),
grass tetany (hypomagnesemia), and
pregnancy toxaemia & ketosis (hypoglycaemia)
All the above are induced by management practices directed toward improving and increasing production. The key message is “prevention is better than the cure”.
Milk fever is caused by a decrease in calcium intake under conditions of increased calcium requirements, usually during late gestation. It can be triggered by stress or a sudden change of feed. This results in a low serum calcium concentration, particularly in animals pregnant with multiple fetuses. Some cases are complicated by concurrent pregnancy toxaemia. Milk fever can occur at any time from 6 weeks before to 10 weeks after lambing; however, the greatest demand for calcium because of mineralization of the foetal skeleton occurs 1–3 weeks prior to lambing, particularly when multiple fetuses are present in utero.
Diets low calcium levels include cereal hays or grass dominant dry pasture, poor-quality grassy hays and pasture. Most grains also contain little calcium but additionally have high levels of phosphorus, causing an inverse calcium:phosphorus ratio, increasing dietary risk.
Characteristically, milk fever occurs in outbreaks, with most cases occurring in the last few weeks of gestation, although it is not uncommon for individual animals to be affected. The onset is sudden and often follows—within 24 hr—an abrupt change of feed, a sudden change in weather, or short periods of fasting imposed by circumstances such as shearing or transportation. Animals with milk fever become restless, suffer lost appetite, muscle tremors and staggers, and usually die if left untreated.
It is important to ensure total calcium in the diet meets the animals’ specific requirements. Calcium can be easily supplemented in the form of limestone (calcium carbonate) through provision of loose mineral licks and blocks rich in Calcium, introduction of legume forages post lambing or the inclusion of calcium to any grain supplementation. Sudden dietary changes or other stressors should be avoided during late gestation, and risk factors for pregnancy toxaemia investigated.
Grass tetany or grass staggers (hypomagnesaemia) is caused by a shortage of magnesium in the diet and an impaired ability to absorb magnesium by lactating sheep and cows. Animals with grass staggers have body tremors, walk with a stiff-legged gait, and are liable to collapse on their side kicking their legs in a paddling motion. In advanced stages, affected animals fall to the ground, convulse, and die shortly after.
Soils naturally high in potassium and those fertilized with potash and nitrogen are high-risk areas for grass tetany. Heavily fertilised (with N & K in particular) short, lush grass dominant pastures or cereal crops or paddocks containing heavy infestations of plants such as capeweed have the potential to interfere with magnesium absorption.
Magnesium must be given daily to animals at risk, because the body has no readily available stores. Daily oral supplements of magnesium oxide 10g to sheep (cattle 25-30g) should be given in the danger period. Most magnesium salts are unpalatable and must be combined with other palatable ingredients such as molasses, concentrates, or hay. Often feeding hay alone may be all that is required to prevent grass tetany in flocks which may be regarded as moderate risk. Fertilizers containing magnesium effectively increase herbage magnesium only on certain soil types.
Sheep and cattle should have access to hay, particularly when grazing either green cereal crops or pastures fertilized with potassium or nitrogen (or both) during the cooler, wetter months of the year.
Pregnancy toxaemia is the most common metabolic disease of sheep. It occurs in the weeks before lambing, and ewes carrying two or more lambs are particularly at risk. Signs include lethargy, staggering and not eating. The main cause is underfeeding in late pregnancy. The best prevention is to scan pregnant ewes and give those carrying multiples more feed near lambing.
Ewes with a poor body condition score (BCS ≤2) or that are over-conditioned (BCS ≥4) and carrying more than one foetus are most at risk of developing pregnancy toxaemia, although the condition can occur even in ideally conditioned ewes on an adequate ration. Ewes fitting these criteria may quickly shift from subclinical ketosis to clinical pregnancy toxaemia if feed intake is acutely curtailed by such events as adverse weather, transport, handling for shearing or preventive medication, or other primary disease (footrot, pneumonia, etc.) that lead to secondary pregnancy toxaemia.
Ewes should not enter the last six weeks of gestation with a BCS <2.5; this can be prevented by good feeding management, e.g. adequate feeder space for pregnant animals, sorting (based on BCS, foetal numbers, and animal size), forage analysis (for energy, neutral detergent fibre, and protein levels), and ration formulation.
These diseases are largely preventable; good advice and good management can ensure that a good season does not go ‘pear-shaped’ within your livestock business.
