Angus and Hereford cattle are particularly susceptible to low magnesium and cows four years or older have higher milk production and higher risk.
BEEF cows are often not considered a major issue for low calcium (milk fever) or low magnesium (grass staggers) on traditional sheep and beef farming systems. But as some of you may have experienced, they can have major problems before, or at, calving with low magnesium or calcium levels, which can affect one or many cows at once. This is fairly dramatic and not easily forgotten, but another lesser-known issue with magnesium is caused by chronic magnesium deficiency. SINISTER Chronic magnesium deficiency is more sinister and often leads to chronic inappetence, slower calving (high rates of dead calves born) and poorer colostrum and milk production. Udder oedema and milk fever are other more obvious signs of deficiency. As you can imagine, this is extremely detrimental to the cow and to calf survival. Cows with chronic magnesium deficiency can also become anaemic (reduction in red blood cells and oxygen carrying capacity) which can lead to abortions, deaths, and poor performance in your cows. This is much like the syndrome seen with theileria, where vulva and other membranes can be sheet white or yellow, with a lethargic and exercise intolerant cow. Risk factors include: • low magnesium intake due to rapidly growing pasture with low DM %. Pasture is lowest in magnesium content availability in winter and early spring; • reduced feed intake due to inclement weather, yarding or low magnesium; • interference from other minerals is a big problem, for example if your soils are high in molybdenum; • high levels of potassium and nitrogen in pasture leads to inability to absorb available magnesium; • recent fertiliser application with potash and nitrogen can cause issues; • rapid transit of feed from the rumen due to lush pasture reduces absorption of magnesium. SUSCEPTIBLE Angus and Hereford cattle are particularly susceptible to low magnesium and cows four years or older have higher milk production and higher risk. Very thin and overfat cows are at higher risk due to metabolic inefficiency leading to less magnesium utilisation. We underestimate the effects of good farming practices and its effect on mineral balance in pasture, particularly in fast growing periods such as in spring (and to lesser degree autumn). Good grazing management of pasture and good fertiliser practice (particularly to enhance clover proportion and production) has led to much more lush pasture at calving for beef cows, leading to higher rates of issues. Calving later in spring can help balance this, but only to a small degree. There are many options for supplementation and quick and cheap blood testing can identify issues in beef cows and prevention also depends on your farm infrastructure and willingness with labour inputs and farm machinery. Please give us a call if you think this may be an issue on your farm, it is well worth investigating.
