May 213 min read

Grass Tetany in Cattle & Sheep

By Eliza MacKereth, Graduate TRAC Ruminant Productivity Consultant

With a later break in the season and increased demand for supplementary feeding, transitioning animals to pasture based diets will be a key focus for producers to reduce input costs. Despite this urgency, it is important to consider the potential complications associated with this change, in particular, nutritional diseases.

Grass tetany is a nutritional disease often connected to low blood magnesium levels (hypomagnesemia). Sheep and cattle both require daily dietary magnesium to meet requirements for metabolic functions as well as brain & nerve function, with low levels often leading to associated issues. Magnesium is tightly bound in bone reserves of ruminants, so daily dietary supplementation of magnesium is necessary. Older and lactating animals are more susceptible to hypomagnesemia due to challenges associated with drawing magnesium supplies from older skeletons and the increased requirements during milk production.

CAUSES + SIGNS

Grass tetany is either caused due to low magnesium or high potassium in the rumen, as potassium (K) inhibits magnesium absorption. Potassium levels may increase due to a lack of sodium, pasture content, fertiliser application or diet change. Likewise, magnesium levels also vary depending on pasture stage, variety, and various other factors. Young grasses and lush cereal pastures often have both low magnesium levels and low fibre content, meaning the flow rate of the feed through the digestive tract is often too fast, therefore magnesium absorption is inadequate.

Early warning signs are challenging to identify; therefore, prevention is key. Often symptoms go unnoticed until it is too late, and death of the animal occurs. Some symptoms include: muscle spasms, excitability, paddling before death and staggering. In many cases, the animal will be asymptomatic until a stress event occurs, after which symptoms will start to rapidly appear. Grass tetany is not to be mistaken for PRGT (Perennial Ryegrass Toxicity) which is linked to the presence of toxins in ryegrass rather than low magnesium.

NUTRITION/PREVENTION

To prevent and lower the risk of grass tetany, several prevention methods can be introduced. Providing roughage with fresh pastures will assist in slowing the rumen flow rate, as fresh growth is often low in fibre and moves through the digestive tract rapidly.

Despite the urgency that producers may feel to begin grazing pastures as soon as possible to reduce input costs, it is best to graze grasses at 2.5 leaf stage or later to ensure plants have a higher fibre content, therefore slowing the flow rate. In the transition to fresh pastures, sudden dietary changes should be minimised to avoid rumen upset. It should also be noted that stress events and exposure to unfavourable weather conditions may increase the risk of grass tetany.

To keep grass tetany cases to a minimum, magnesium should be supplemented into the diet. Incorporating a loose lick mineral is best management as sprinkling magnesium on forages can be wasteful and animals will not regulate intake due to it being mixed with the feed source. Using a sodium regulated loose lick mineral such as TPM Boost H.M.A. [Hi Mag Assist] will allow animals to attain sufficient magnesium. The weather resistance of the loose mineral lick makes it an excellent, labour-saving alternative to sprinkling magnesium on hay.

Your TRAC Experts In Ruminant Productivity are here to assist you in aiding in the prevention of Grass Tetany in your herd or flock, please get in touch with your local TRAC Consultant on 08 8733 1888 or email us at info@totalresult.com.au