Don’t get caught by grass tetany this spring

Spring calving has now commenced on most livestock farms, with ICBF figures indicating a significant shift towards earlier calving, with this being especially evident on dairy farms. This move can bring its own challenges however, as returning cows to early spring grass can be difficult, if not impossible, as spring 2020 is proving.

Flexibility will now be key for February grazing, tweaking of strategies and embracing on-off grazing will be a necessity. Detailed knowledge of average farm covers, grass growth rates and paddock ground conditions will aid farmers in deciding on rotations. Where possible, grazing should commence in paddocks of lower grass covers with good infrastructure that are close to the farm yard. Depending on ground conditions, the target should be to have 30% of the farm grazed by March 1st on light early farms (mid-March for heavy farms), with 65% grazed by March 17th (April 1st for heavy farms) and aim to be starting the second rotation in early April (mid-April for heavy farms). Hitting these dates, will give a 40-60 day paddock recovery period, and should allow for 1000kg grass cover at the beginning of the second grazing rotation.    

Due to the inclement weather, cows will be returning to paddocks of lush grass with low fibre and dry matter (DM) content. Due to early fertiliser and slurry applications, these pastures, will contain high nitrogen (N) and potash (K) levels which can negatively impact on magnesium (Mg) uptake within the soil. When combined, all these factors can have an adverse effect on the already low (Mg) adsorption rates in the grazing animal’s rumen, thus, opening the door for the onset of metabolic diseases, especially hypomagnesaemia. Moreover, heightened cow stress levels from calving, returning to lactation and dietary and environmental changes can all have additional negative impacts on animal health.

Ruminants have a poor capacity to retain (Mg), with roughly 70% of the animal’s reserves found in the skeleton and the remainder distributed in the soft tissues and fluids. Absorption occurs throughout the digestive tract but is mainly confined to the reticulorumen, once the mineral is readily soluble. Hypomagnesaemia, or more commonly known as grass tetany/staggers occurs when (Mg) levels in the blood are reduced below 1.1mg/100ml. Higher yielding, older dairy and beef cows are most prone to the disease, as high levels of (Mg) are excreted through the urine and in milk especially in early lactation.

Symptoms occur quite rapidly with severe muscle contractions, irregular heartbeat, unnecessary bellowing and convulsions all being clinical signs. Due to the short duration of the symptoms, affected animals are often found dead with the ground routed and disturbed around them due to thrashing from muscle spasms. However, early warning signs can be detected, reductions in milk yield, loss of body condition and changes in temperament can all be evident in the days prior to convulsions occurring.

A number of different management techniques can help prevent the onset of grass tetany. Feeding high (Mg) concentrate, offering high (Mg) molasses based licks or blocks, (Mg) dusting of pastures, supplementing (Mg) into the water supply and incorporating hay or straw into the diet to slow down digestion and allow for increased (Mg) absorption are all options. However consistency of (Mg) uptake can be an issue with some of these preventative measures, especially in periods of high rainfall.

Supplementing (Mg) through a molasses based liquid feed is a very effective preventative measure that can be used. Introducing Premier Ultra-Mag to the diet at a rate of 1kg/head/day will provide 25g of (Mg), therefore, suppling most cow’s daily (Mg) requirement in normal weather conditions. In adverse weather, inclusion levels should be increased to 1.5kg/head/day for periods of moderate risk and 1.5-2.0kg/head/day in high risk periods. Its liquid form, leaves it ideal for feeding through liquid feeding systems on robotic milking machines or via liquid feed milking parlours. Additionally Premier Ultra-Mag can be topped dressed on forages, mixed with dry feeds, or fed in a diet feeder as part of the TMR. It is important however, to ensure that uniform mixing of Premier Ultra-Mag and other ingredients occurs prior to feeding out. Its versatility also allows it to be fed free access through lick wheels or ball feeders.