Editor’s note: Second in a two-part transition immunology series.
Calving and dystocia-management pens should be bedded and bedding removed between calvings to remove contamination.
Unfortunately, the cow isn’t that good at tipping us off to impending immune suppression caused by these transition diseases. “Right now we have no way to look at a cow and decide she is immunosuppressed,” explains Jesse Goff, DVM, PhD, of the USDA’s National Animal Disease Center, Ames, Iowa. “We have laboratory blood tests that are quite good — but they cost hundreds of dollars to perform and are currently only useful for research.”
From a practical standpoint, the immune suppression and opportunistic diseases such as metritis are more common in those cows that go off feed in the days just before calving. These are easily picked out in a stanchion barn or where cows are individually fed in research trials but difficult for today’s typical dairy to find.
However, there are some other clues. “Overly fat cows tend to fall into this category of not eating well, so controlling body condition is a good step,” Goff suggests. “The problem is that by the time I decide she is a fat cow there isn’t much to be done for her.”
Cortisol and immunity
There is a large one-to-two-day spike in cortisol at calving which probably contributes to immune suppression. Part of this cortisol spike is necessary and inevitable — cortisol is the signal from the fetus that it has matured and calving should start. Cortisol levels go from baseline resting levels of 2-4 ng/ml to 6- 10 ng/ml. “This seems to be necessary to develop fetal lungs and get the uterus ready for calving,” Goff says. “However, when animals are stressed by diseases such as milk fever, dystocia or giving birth to twins, the level of cortisol is often much higher than these physiologic levels.”
For instance, Goff notes, a cow with milk fever will typically have blood cortisol levels that are about 25 ng/ml. “At this point I think the level has crossed over from physiological to pathological — actually contributing to further disease in the animal because of its immunosuppressive effects.”
Not much work has been done to look at the effects of social stresses on cortisol levels directly in the transition period. However, frequent moves and introduction of cows to new herdmates and new systems for feeding (self-locking head catches, for instance) seem to take several days to get over, Goff says. “Each time feed intake is the cost of such a move. We are learning that any disruption in feed intake around the time of calving is associated with a poorly functioning immune system. The number one problem on real farms in my opinion is overcrowding and the effects this has on ‘stressing’ a cow and reducing feed intake.”
Stephen LeBlanc, DVM, DVSc, University of Guelph, adds that more generally, stress-associated hormones contribute to other metabolic problems. For example, epinephrine (adrenaline) enhances breakdown of fat and contributes, in part, to increased NEFA concentrations.
Prevent metabolic disease
Since metabolic diseases seem to be detrimental to the immune system, we need to work hard to prevent them. “Milk fever should not be a concern on dairies,” Goff states. “We know how to prevent most milk fever cases by keeping potassium low in the diet, bringing in anions to acidify the cow using palatable anions such as hydrochloric acid-based products and adding enough magnesium to the diet to allow calcium metabolism to proceed normally.”
LeBlanc says cows with retained placenta (RP) are probably two to eight times more likely to have metritis. “At this point we don’t have drugs or other interventions that can effectively turn around immune function and push the cow back into better health quickly,” he says. “We can now do a decent job of monitoring groups and even identifying high-risk individuals as much as two weeks before calving, but we don’t yet have good interventions to short-circuit disease or ‘fix’ these cows.”
However, he adds, we do have good general ideas of how to prevent a fair amount of the risk factors associated with immune suppression and transition disease. “This underlines the importance of consistently implementing best practices for transition. The good news is that it’s largely the same list for RP, metritis, mastitis, displaced abomasum, etc.”
Good nutrition is one of the biggest factors in disease prevention. Steady feed intake seems critical in the days around calving. Goff and LeBlanc offer this advice for avoiding feed intake decline:
Prevent overconditioning. Have body condition score of 3.5.
Separate heifers from cows to avoid the bullying-at-the-bunk problems.
Do not overcrowd cows in the pre-fresh and post-fresh pens. Allow 30 inches of bunk space per cow, and no more than 85% stocking density.
Avoid very high-energy, low-fiber diets pre-calving. These diets may increase risk of DA and there is growing evidence that they may be associated with a dramatic decline in dry matter intake just before calving — even though overall feed intake across the close-up period might actually be enhanced by these diets.
Diets must not allow sorting. The forages should be of the highest quality. These are not the cows to give poorly ensiled feeds to.
Avoid unnecessary or excessive group changes/pen moves.
Use heat abatement practices when the temperature-humidity index is greater than 72.
Have two water sources per pen.
Keep feed in front of cows at all times and feed every day.
Have large enough free stalls with sand bedding (if possible).
Have dry cows at body condition score of 3.25 to 3.5.
Priming the immune system
In general diseases such as metritis and endometritis are the result of poorly functioning neutrophils, which are part of the innate immune system. It is hard to teach them to recognize one type of bacteria over another through vaccination. The key is to make sure neutrophils are functioning well during this transition period. “You can, however, teach lymphocytes to produce antibodies and other factors that might be of aid to the neutrophils as they encounter bacteria in the uterus or mammary gland,” Goff explains.
Vaccination usually is to develop an immune response against specific bacteria or viruses. In general, much of the mastitis and metritis seen in early lactation is due to opportunistic environmental bacteria entering the mammary gland or uterus. A strong immune system will clear out these infections; a weak one will allow the bacteria to multiply to the point of causing clinical disease.
“The J-5-based coliform mastitis vaccines are of some aid since many of these infections in early lactation are caused by Gram-negative coliform bacteria,” says Goff. “If antibodies are present against these bacteria it can help the neutrophils bind to the coliform bacteria to better kill them. However, these vaccines require a priming dose and two boosters to be effective and need to be given well before the cow becomes immune suppressed to be of help against these disorders.”
Proper prepartum management and nutrition are your best bet to help the immune system perform optimally during transition. Le-Blanc found that in animals with sub-optimum circulating vitamin E in the last week prepartum, injection of 3000 IU — tocopherol SC or IM one week before expected calving reduced the risk of RP. “However,” he adds, “there is no simple way to identify individuals or herds that may benefit from this treatment.”
The bottom line, LeBlanc says, is to do everything possible to keep cows comfortable and eating and to supplement with at least 1000 IU vitamin E (2000 may help), and 0.3 ppm Se (consider organic source). “Injectable supplementation may be a useful tool if the RP rate is still unacceptably high despite optimization of the abovementioned strategies.”