Why do certain prepartum diets work well on one dairy but not another? Why are anionic salts required on some dairies, while others can get by without feeding them? I don't know the answer, but I do know that there's no cookbook prepartum diet that works for all dairies. Certainly fresh cow management has a lot to with a successful transition program. Dairies that have excellent fresh cow treatment protocols, consistent feeding procedures and good cow comfort have better success.
But opinions vary when it comes to specific dietary recommendations for prefresh diets that reduce subclinical and clinical hypocalcemia and postpartum metabolic disorders (ketosis, retained placenta, displaced abomasums and even mastitis). Steam up grain mixes, controlled energy dry cow rations with straw, low potassium, low calcium, high calcium with or without anionic salts; take your pick. You and your nutritionist need to figure out what works best on your dairy.
So what are some recommendations that most of us can agree on? First, avoid fat dry cows. Whatever dietary strategy you use to keep cows in shape in late lactation and during the dry period, transitioning fat dry cows is a challenge. Second, reduce potassium as much as possible in pre-fresh diets (< 1.3% if possible). Third, feed adequate magnesium (.4%). Magnesium sulfate is the preferred source in prepartum diets.
In my personal experience, urine pH is the best indicator of whether supplemental anions are needed in addition to reducing cations (potassium and sodium). Cows experience fewer transition metabolic disorders when pre-calving urine pH is 6-7. In addition to feeding magnesium sulfate, I like to use a chloride based anionic supplement because I can easily vary the amount of anions based on urine pH, without significantly affecting mineral concentrations. I also agree with Cornell University recommendations of keeping prepartum calcium levels at about 1%, although opinions vary on this. New data from Cornell indicates that feeding anionic supplements increases blood phosphorus levels. Low blood phosphorus can also lead to post calving downer cow problems. However, prepartum ration phosphorus over .4% may increase the risk of milk fever.
Reference: New Concepts in Nutritional Management of Transition Dairy Cows, Thomas Overton, et al., 2008 California Nutrition Conference Proceedings.
--Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. You can contact him at firstname.lastname@example.org.
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