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Technical Bulletins

Protein Nutrition and the Transition Diet

by Mike Bettle, BSc. Hons. Animal Physiology & Nutrition
University of Leeds, England

During the stress of late pregnancy and freshening the dairy cows metabolism finds itself having to make massive adaptations in its activity and output, with the demands of rapidly growing calf and onset of lactation. Unfortunately for the cow, and the dairy nutritionist, this is also the period of least activity of the rumen. With the growing calf imposing on rumen and the cow starting to be re-introduced to it's lactation diet, care must be taken to ensure that this transitions from pregnancy to lactation is made as smooth as possible.

One component of the diet that is often overlooked during this period. is protein, more importantly, quality of protein. it has been demonstrated in University trials that inadequate protein nutrition in the close up dry period leads to calving and postpartum problems. The source of protein here is also very important. A high bypass protein source is essential for many reasons. With rumen function being impaired, microbial protein flow to the abomasum and duodenum slows and thereare less ``rumen bugs" to capture rumen soluble protein, this protein is logically overcome with a good source of rumen bypass protein.

It has also been demontrated that excess levels of rumen soluble protein causes excess ammonia levels in the rumen and elevated pH levels. This causes calcium and magnesium ions to form insoluble complexes with phosphorus making them unavailable for absorption encouraging both hypocalcaemia and hypomagnesaema which will lead to downer cows quicker than anything. Coupled with this, the major source of soluble protein in the dry cow rations I have seen, when freshing problems are prevalent, comes from alfalfa haylage and to a lesser extent hay. These forage sources in the dry cow rations should be avoided as much as possible as they also contain high levels of calcium and potassium which also add to this mineral imbalance problem as potassium directly competes with magnesium for absorption.

When considering bypass sources, protein quality is obviously important but when appetite is naturally suppressed, as it is over this transition period, palatability is also a key point to take into account. I have found nothing better than ``SoyBEST" in providing both quality and palatability in a high bypass protein source. Trials at Kansas State University have consistently shown diets containing ``SoyBEST" encourage greater dry matter intake over those containing regular soybean meal or animal protein sources. Add a little bypass methionine to the diet and you have no better way to accomplish a successful transition and maximize feed intake and milk potential

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