Dr. Jesse Goff, DVM, a featured speaker at the 2020 KVVMA sponsored NE Ohio annual dairy conference, spoke extensively on transition cows. His two morning sessions covered hypocalcemia prevention and general immune suppression within dry cows.
It can be easy to neglect dry cows because they are not producing a sellable product. Relate the dry season to preparing for a marathon. No one wakes up and (successfully) runs 26 miles without preparation (training, nutrition, rest). Can we expect a neglected dairy cow to perform well? Transition cow diets (training) should start at least 21 days before calving.
About 2 weeks both sides of calving, cows naturally experience immune suppression resulting in higher incidence of mastitis, clinical onset of chronic disease, and retained placentas. Lymphocytes (white blood cells producing antibodies to fight specific pathogens) and neutrophils (“first defense” cells) are diminished at this time.
To boost immune response, Dr. Goff suggests increasing vitamin E supplements. In a study by Dr. Bill Weiss, dry cows fed diets with 4,000 IU vit. E daily had a 3% rate of mastitis compared to 26% when only fed 100 IU daily. This would cost less than $6 per cow (4,000 IU/day fed two weeks prior and 2,000 IU one-week post calving). Vitamin E deficiency (along with Selenium deficiency) has also been linked to retained placentas. Compared to the costs of vet calls, mastitis treatment, and lost production, $6 of prevention is inexpensive.
Dry cow rations should contain about 0.6 to 0.63 Mcal Net Energy/lb. of dry matter and 12-13% metabolizable protein. Strategies to increase DM intake and consequently energy include feeding high straw diets (chopped, but avoiding fine dust), using propylene glycol or glycerin drenches, and additives like yeast, choline, and B-vitamins.
With a suppressed immune system, vaccines are not recommended within 2 weeks before or after calving. Dr. Goff advises giving an initial mastitis vaccine 2 weeks before dry-off, a booster at dry-off, and a third 2 weeks prior to calving when using vaccines.
Hypocalcemia, (calcium deficiency or milk fever), in the herd can be costly to treat. Milk fever can also lead to increased risk for metritis, ketosis, prolapsed uterus, displaced abomasum, and lower quality colostrum. Older cows are at higher risk.
A healthy cow will have 3.5 grams of available calcium in her blood at any given time. Producing 2.5 gallons of colostrum requires 23 grams of calcium to make that initial milk. It is therefore necessary for the cow’s body to use reserves from bone tissue. This process does not work as efficiently in older cows. They have less active bone cells and their intestinal receptors for vitamin D, which aid in calcium absorption, are also diminished.
A positive DCAD value diet (relatively higher levels of positive electrolytes, sodium and potassium, compared to negatively charged chlorine and sulfur) results in slightly alkaline (pH >7) blood. Calcium is better reclaimed from bone tissue when blood pH is slightly acidic. A urine test of 6.2 pH (6 in Jersey cows) reflects adequately acidified blood for proper calcium transfer from bone to blood (to milk). Common pH urine test strips from a pharmacy are cheap and easy to use for monitoring.
Dry cows with urine pH above 6.8 should have their diets adjusted by decreasing potassium and sodium and increasing chlorine and/or sulfur to result in a slightly negative DCAD value. Changing just one electrolyte fraction at a time is challenging. Contact your nutritionist or feed mill about altering your current ration or to inquire about pre-formulated feeds for dry cows. Feeding low-potassium forages is the easiest place to start on the farm. Alfalfa is relatively high in potassium (55-70 lbs/T DM).
While seemingly counter-intuitive, Dr. Goff explained that feeding a calcium-deficient diet before calving helped to prevent milk fever! He suggests 0.85-1.3% calcium on a dry matter basis for dry cows. Transition cows may also need supplemental Magnesium in an available source such as magnesium sulfate (MgSO4) or magnesium chloride (MgCl2) pre-calving and then magnesium oxide post calving (U.S.-sourced, as foreign supplements are of lower quality!) Upon freshening, cows should immediately be given a lactating cow diet consisting of higher calcium rates for optimal production and health.
A few final thoughts. Do not offer salt blocks to dry cows. A calcium IV will help initially with milk fever but may result in subclinical conditions several days later. If using a calcium bolus, administer one at calving and another 12 hours later. Prevention requires some detail work but saves money in the long run.
Matthew Nussbaum is an OSU Extension Agriculture and Natural Resources Program Assistant and may be reached at 330-264-8722.
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