Clinical milk fever is a particular insidious metabolic disease in freshened dairy cows. I have witnessed on some dairies, it’s not a significant problem, while next-door neighbours are plagued with downer cows one calving after another.
In other dairies, milk fever doesn’t show up for months and then it shows up with a vengeance. From years of experience, I have concluded that milk fever, hypocalcaemia or calcium-deficient status exists in some form in all fresh cows at different levels. Its reduction in problematic herds comes down to implementing a milk fever protection plan.
In my last case with milk fever, I received a phone call from a dairy producer who milks about 200 dairy cows, who hasn’t seen a clinical case in more than a year and then within a few weeks has three vet-confirmed cases. All were fourth-plus lactation cows. Two of these downer cows responded to Ca-Mg infusion and were put on the milk line, while the last one never got up and died.
On any given day, the dairy producer feeds about 18 to 20 close-up dry cows on their own straw pack, segregated away from the faraway dry cows and lactating cows. They are feed 21 days prior to calving a transition diet consisting of 15 lbs. of lactation diet refusal, eight lbs. of a 16 per cent transition cow pellet (my formulation) and the remainder, good-quality grass hay. He does not implement any post-calving oral calcium treatments. In the last few months, a string of 25-28 dairy cows have been in the close-up group.
Plan of action
In order to take corrective action, I took a few minutes to review my own working knowledge of calcium metabolism in transition dairy cows. Namely, a pregnant dairy cow just prior to calving requires large amounts of calcium for the production of about 10 litres of colostrum, which literarily drains her blood of calcium. The lowest concentration of blood calcium occurs within 12 to 24 hours before calving and usually returns to normal within two to three days after calving.
During this critical time, most fresh cows cannot absorb enough dietary calcium from their small intestine, so they must rely upon bone mobilization in order to elevate calcium levels into their bloodstream. This calcium-resorption ability of the close-up dry cow is regulated by her parathyroid hormones (PTH), which must be primed a few days ahead of calving, otherwise she is a candidate for milk fever.
Although the natural incidence of clinical milk fever has been shown to be about five per cent in most herds, it does not affect all fresh cows within a given herd, equally. Research has shown that first-calf dairy heifers rarely get milk fever (less than one per cent), because they have lower colostrum and early milk production; thus, lower calcium requirements compared to mature cows (fifth lactation, as high as 10 per cent). These young heifers also have a higher level of PTH, which seems to prepare them for rapid bone mobilization of calcium.
With this science background, I can continue with my investigation to discover the probable cause of these triple milk fevers to appear after a year of absence. A list of substantial milk fever risk factors found were:
- Modest amounts of dietary calcium — A planned calcium deficiency in close-up dairy cows often causes PTH to be released and stimulate bone mobilization to release adequate calcium. University studies demonstrate that feeding less than 10 g/head/d calcium (a dry cow requires 40 g/head/d for maintenance) is effective in preventing milk fever. However, this producer was feeding a substantial amount of haylage and may have short-circuited this process.
- Dietary potassium levels were significant — Potassium contributes to alkaline blood that suppresses bone calcium mobilization. Keeping dietary potassium levels to less than 0.65 per cent for close-up dairy cows has been shown to control milk fever and other fresh cow problems. Although, forages in this case were not tested, it is plausible that high levels of potassium were provided from haylage and even from the large amounts of grass hay being fed.
- Low feed intake issues — There is about a 30 per cent natural decline in dry matter intake from the start of the faraway dry period to calving. During my barn walk, it did seem the close-up dry cow pen was a bit crowded with limited bunk space. It is reasonable to speculate with this recent influx of close-up dry cows, there would be competition for fresh feed and some of the cows maybe forced to eat leftovers — lactation diet/grass hay without any close-up pellets.
From these points of milk fever predisposition, I made three recommendations. First, the producers should sample and then analyze the entire transition diet for calcium and potassium, so I can make necessary adjustments to their close-up dry cow feeding program. Second, the producer should give each fresh cow a tube of calcium oral gel/paste (containing calcium carbonate, calcium chloride and other bioavailable calcium) after calving. It is my understanding that cows can absorb an effective amount within 30 minutes of supplementation. Last, I recommend if the number of close-up cows remain high, the producer might consider splitting up his sole close-ups into two groups to allow more loafing room and bunkspace.
As a dairy nutritionist, I have taken a serious and conservative approach to this case and others concerning clinical milk fever. My final concessions encompass a milk fever protection plan rather than prevention plan. That’s because the incidence of clinical milk fever is often baffling; caused by dietary and management factors and even when corrected doesn’t eliminate milk fever in its entirety. I believe my approach “works” when the incidence of milk fever in a particular dairy herd is reduced or in the above examination doesn’t happen again for a long time.