Risks of grazing lucerne

Lucerne is a versatile and productive fodder plant suited to dryland, supplementary irrigated and fully irrigated pastures. It can also be successfully grown on a range of soil types from light loams to heavy clays, provided there is adequate surface to ensure water does not pond.

While lucerne pastures are nutritionally highly productive, grazing them can come with a few health risks, if some of its minerals interfere with mineral availability or absorption.

Vitamin and mineral absorption issues

Lucerne is a rich source of vitamins and minerals needed for healthy animals. 

Lucerne is rich in major and minor (trace element) minerals. Although Lucerne is a rich source of calcium, potassium and magnesium, interactions between these minerals may negatively impact on availability and absorption by grazing livestock.

Lucerne pasture and hay are good sources of vitamin A, vitamin E and vitamin D, however, lucerne can cause issues with absorption of B12.

Vitamin B12 is needed for cell growth, glucose and wool production. Cobalt (thought to stimulate appetite) is converted to B12 in the rumen. In cobalt deficient soils, young lambs (as their rumens are not fully developed), and sheep on high energy rations such as lucerne, may benefit from B12 supplementation. This is because the rate of B12 absorption is improved by slow gut flow but inhibited if rumen or small intestine is damaged (e.g. worms). Lucerne’s high digestibility tends to promote rapid gut flow with pure stands of lucerne causing the greatest concern.

Health and disease issues

Grazing lucerne can come with health and disease risks, particularly when grazing fresh lucerne.

Acidosis/Laminitis

‘Sugar’ acidosis may occur on rapidly growing pastures that are high in sugar but low in effective fibre such as Lucerne in early vegetative stages. Laminitis (similar to ‘founder’ in horses) may occur due to increasing blood flow and pressure leading to blood vessel damage and swelling within the hooves.

More on acidosis

Bloat

Bloat is found in cattle and sheep and is particularly seen in sheep on fresh lucerne. 

Bloat risk is highest:

• in winter and spring
• when Lucerne is fresh
• on immature stands
• if livestock are hungry when introduced to the stand.

Dorpers and cross bred lambs are more prone to bloat. 

More on bloat

Fertility issues

In some grazing conditions lucerne may be high in levels of coumestans which reduce the ovulation rate in ewes. High levels of coumestans are increased by plant stress due to things like:

• leaf disease
• insect damage
• moisture stress. 

Trials have shown 20%+ increases in expected lamb numbers in ewes grazing lucerne prior to joining compared to ewes on dry, mature pasture and results are likely to be due to:

• improved body condition
• increased ovulation rates
• reduced dry ewe numbers
• a potential by-pass protein effect similar to improvements found when ‘flushing’ ewes with lupins prior to joining.

Recent findings however, suggest that Lucerne may also reduce progesterone production during the first few weeks of pregnancy.

Progesterone ‘maintains’ pregnancy and there is some suggestion that single bearing ewes grazing Lucerne may abort fetuses due to a reduction in this hormone. Fortunately, twin-bearing ewes appear to produce enough progesterone to maintain the pregnancy.

Minimise the use of fresh lucerne stands by ewes during joining if possible

Photosensitisation

Stock grazing on lucerne pasture with high aphid numbers are particularly susceptible

More on photosensitisation

Prolapse

Stock grazing lucerne may be predisposed to a higher risk of rectal and/or uterine prolapse if females are overly-fat and/or in late stages of pregnancy.

Grazing high energy, high moisture feeds such as lucerne may lead to:

• constipation
• straining
• prolapse.

Provide additional fibre and limit high risk stock grazing fresh lucerne stands to minimise prolapse risk.

Pulpy kidney

Pulpy kidney occurs on lush lucerne and can result in:

• a number of dead when lambs are first put out on the paddock
• sporadic deaths when the plants are ‘freshening’ up after a fall of rain. 

The carcass inflates and starts to putrefy rapidly. 

Typically, the mob is not vaccinated or only partially vaccinated with the immunity beginning to decrease. It is easily prevented by ensuring lambs are properly vaccinated with 5in1. 

In high challenge situations a booster vaccination may need to be given every three months.

More on pulpy kidney

Red gut

Red gut most often occurs on lush, high protein, highly digestible feed such as lucerne with rapid gut flow.

The disease has similar symptoms to pulpy kidney and the process causes bowel twisting or displacement.

To prevent the disease, providing roughage in the form of palatable hay or a feeder of oats can help to some extent. However, grazing for five days then removing for two days and grazing for another five days and so on until the lucerne hardens up and is no longer 'fresh' is among best ways to prevent losses.

More on red gut

Scouring

Scouring can be caused by a number of factors other than roundworms all found in lucerne pastures including:

• acidosis
• low effective fibre (low dry matter, high moisture feeds)
• excess protein to small intestine
• excessive Mg.

Provide additional dry matter to minimise the risk and intensity of scouring if grazing lucerne stands.

Preventing health risks when grazing lucerne

1. Provide additional roughage
   During early growth (vegetative stages) Lucerne has low dry matter (DM) contents. Increasing DM intake through providing low to medium quality hays:
   • reduces the risk of bloat, nitrate poisoning, red gut and scouring
   • reduces the rate of gut flow increasing vitamin B12 absorption
   • improves Mg availability and absorption,
   • provides additional vitamin D, and
   • provides a source of ‘effective fibre’ which will stimulate cud chewing and saliva production (low saliva production may lead to a reduction in natural buffer production and acidosis).
2. Supplement
   Supplement by providing dry lick/powder supplements with salt (for sodium) and Causmag, Dolomite, Acid Buf etc (for magnesium). Supplementary grain will further improve energy intakes, growth rates and magnesium availability.
3. Vaccinate/drench
   It is important to vaccinate/drench prior to allowing stock entry to lush lucerne pastures. Producers should administer a booster of 5 in 1 or 6 in 1 vaccine (2 weeks prior to commencement of grazing), a vitamin A, D, E and consider a B12 vaccination. Controlling worms is essential to ensure good health and productivity. The use of an effective broad-spectrum drench as required, is also recommended.