Dr. Joe McGrath Technical Manager Ruminants,
DSM Senior Lecturer – Ruminant Nutrition, University of New England, Australia
Death, taxes and down cows do not all have to be certainties in a dairy farmer’s life.
As dairy farmers you do not have to accept that this is a reality, and by changing your focus on farm from treating sick animals to prevention you can remove one of the ‘certainties’ from the list, making dairying more enjoyable and more profitable.
Unfortunately the acceptance of down cows being part of life is reinforced by their prevalence during springtime; downers are now so common it is like a self-fulfilling prophecy. Every farm has them, it’s just some are worse than others.
DairyNZ published that there are about 2% of cows in a herd that actually go down in New Zealand during the calving period. That is 50,000 cows within the Bay of Plenty and Waikato regions alone!
Down cows is just the tip of the iceberg. For every one that goes down, there are at least 10 times more that are sub-clinically suffering the same problem. In fact
DairyNZ suggests that 1/3 of all cows in New Zealand are affected. This results in further problems with calving, milk production, fertility and mastitis through the season.
The impact of hypocalcaemia adds up to losses the industry can ill afford.
According to Dairy NZ in 2012 Milk Fever will cost farmers about $400 million on treatments resulting from calcium deficiency; however these are treatment costs and are not prevention. Often the damage to the cow is already done.
The $400 million includes not only calcium treatments for down cows, but fertility treatments associated with retained membranes, non-cycling cows and treating cows with calving difficulties.
These are all the ‘usual’ conditions farmers have come to accept as normal demands and costs for calving time.
Furthermore, it has been conservatively estimated that poor health of dairy cows during the calving period is costing the industry as a whole over $1 billion dollars per year.
Anyone who manages a herd will appreciate the precious time lost in managing these down cows at a very busy, stressful time of year.
Why are downers happening?
There are many reasons for the high levels of hypocalceamic cows in the dairy industry. The most well acknowledged is the magnesium deficiency created in cows by excessive levels of potassium and nitrogen based molecules in our modern grasses.
This lack of magnesium means that the cow fails to regulate her own calcium homeostatic systems prior to calving and also during lactation. There are several obvious signs of this. The first is the typical pasture tetany, but the sub clinical level is agitated or fidgety cows.
I call the second class of deficiency SPOC (Slightly Pissed off Cow).
A failure to regulate calcium homeostasis by magnesium involves two distinct phases, pre-calving and during lactation. The first means that the cow fails to break down sufficient bone prior to calving to allow for available calcium at calving.
The second means that the cow is unable to absorb sufficient calcium during the lactation, which means she is unable to replace her bones. Not dissimilar to not replacing body condition score.
By pasture dusting, drenching and water dosing with magnesium prior to calving we are enabling the cow to break down her bones and use this calcium at calving. However, this is effectively “raiding the bank” when it is not necessary. It also means that we have to replace more calcium in lactation, which is likely to be already lacking.
The Channel Island breeds, most notably the Jersey, are approximately 2.5 times more likely to succumb to milk fever than say the Friesian or Holstein. Nordic breeds are also known to be highly susceptible.
Why? We don’t know. But it may be interesting to look at a couple of possibilities of why Jersey’s may be more susceptible.
- They absorb certain molecules from the diet at greater rates than Friesians. For example the carotenoid Beta-carotene in grass is absorbed at approximately double the rate (results in the yellow fat and colostrum). It is known to cause vitamin D deficiency and may result in less bone deposition.
- Very high milk solids. As calcium is associated with the solid fraction (primarily casein) this means as a proportion of body weight they need to find more calcium at calving.
- Genetic selection. Selecting for “fine bones”, “dairyness” or “angularity” would suggest that we are not selecting for a robust animal and certainly means that we are selecting for animals that would appear to have less storage sites for calcium.
- Doting owners. Could it be as simple as that Jersey owners are more caring and more likely to assist cows through milk fever periods, which keeps susceptible genetics in the herd at a greater proportion than natural selection would allow?
Without trying to make out the “sky is falling”, hypocalcaemia has now been demonstrated to be the pre-cursor for just about every major metabolic disease post calving. This includes mastitis, ketosis, retained placenta, metritis, dystocia and even prolapse.
Of course these metabolic diseases increase the loss of body weight in early lactation, reduce production and have a negative effect on fertility.
Furthermore, farmers don’t know which cows will get these diseases because it is the sub-clinical cows that will go onto have a higher incidence.
What can we do about it?
The most important thing is to feed a balanced diet all year round. This will enable cows to have a replete, or healthy skeleton prior to calving and enable to cow to draw on this reserve during calving and into lactation.
To achieve this we need to maintain the macro mineral balance (calcium, phosphorus, magnesium, potassium) and also the fat soluble vitamin balance. It is important to realise that minerals and vitamins are not feed additives, they are critical components of a cow’s diet, not unlike energy, protein and fibre. The majority of the minerals and vitamins will come from the pasture, we just have to maintain the balance.
The second part is to balance her diet immediately prior to calving, in what we call the transition period. Our research has shown it is possible to achieve this on a grass based diet by utilising highly available sources of magnesium, calcium and an advanced form of vitamin D called HyD.
HyD has been demonstrated to increase the absorption of calcium and phosphorus from the diet. It is used to enable cows to absorb more calcium and phosphorus during the milking period and to activate calcium prior to calving.
We know now how to incorporate calcium into pre calving diets, which leads to healthier cows now and into their future. But the utilisation of calcium within the cow’s diet pre and post calving should only be done as part of an advanced nutritional program as there are many other nutritional imbalances in grass diets that need to be fixed first.
Is the cost of prevention worth it?
The current methods of preventing milk fever (dusting and anionic springer diets) are antiquated and risky. It relies on the cow having a healthy skeleton prior to calving and ensuring that it is replaced during the following lactation.
It is likely that this mining of the skeleton is the reason that the incidence of Milk Fever increases as they get older, and it is worse with better producing cows.
It is estimated an effective prevention strategy using low cost calcium based supplements would be a tenth, or $40 million for the industry, of the cost of having a hypo- calcaemic herd.
If we look at it on a cow basis it is perhaps more simple. For example the cost of the Sollus nutritional system pre calving is about $8 per cow. The direct cost of milk fever per cow is around $80 for every cow (DairyNZ, 2012).
Farmers then have to weigh up the extra time, stress and loss of genetic gain with the herd. So it is safe to say that a simple return of investment is at least ten to one.
From an animal welfare point of view the cost could very well be trivial.
The farmers that have adopted balanced nutritional systems don’t fear calving – they often get to the point where a down cow is most unusual, and certainly not to be expected as a normal part of calving.
It is ironic that at calving time “pre-calving check lists” are advertised by animal health groups throughout New Zealand.
I have never seen this anywhere else in the world. They are loaded with expensive post down cow treatments but not preventative treatments. The animal health industry in New Zealand should be focusing on prevention not costly cures as the damage is largely done – even if she does get up.
After all, Hippocrates is well known for “first do no harm”, however he was also well known for “let food be thy medicine and medicine be thy food”.