The "Transition Period" from the dry period to lactation is commonly defined as three (3) weeks before calving to three (3) weeks after calving. This six-week period is critically important to the health, production and profitability of dairy cows. The challenge faced by cows is the sudden and marked increase in nutrient requirements for milk production at a time when feed intake, and thus nutrient intake, lags far behind. The research literature indicates that from one (1) month before calving to four (4) days after calving there is an approximate tripling (3X) of demand for glucose, a doubling (2X) of demand for amino acids, and nearly a five-fold (5X) increase in demand for fatty acids. Milk fever, ketosis, retained fetal membranes, metritis, and displaced abomasum primarily impact cows during the transition period. The immune system is also suppressed during this time, leading to increased susceptibility to mastitis.
A Body Condition Score (BCS) of 3.25 to 3.75 ( 1 = Thin and 5 = Obese) for close-up dry cows is best. BCS's of less than 3.25 do not provide enough body reserve to offset normally depressed feed intake after freshening in satisfying the nutrient demands for milk production. However, over-conditioned cows (BCS greater than 3.75) almost always have more severely depressed feed intakes prior to and after calving, and thus pull excessive amounts of fat from their body stores to supply the energy needed to produce milk. This high level of mobilized fat can easily overwhelm the liver and lead to a "fatty liver." Excessive mobilization of fat from the body stores is associated with greater incidences of all kinds of health problems during the transition period.
The liver is one of the most metabolically active tissues in the dairy cow, utilizing about 25% of the whole body oxygen consumption while accounting for only about 2% of whole body weight. Essentially all nutrients absorbed from the gastrointestinal tract pass through the liver before they go to other tissues and organs, such as the mammary gland. An impaired liver has difficulty converting ammonia (which is toxic) to non-toxic urea. Normal liver tissue converts propionic acid, amino acids and glycogen to glucose which is used throughout the body for energy and also for the synthesis of lactose. A compromised liver has difficulty breaking down fat to CO2, water and energy, thus ketone bodies build up and the cow is prone to develop "Ketosis." It is estimated that each metabolic disease occurrence reduces lactation milk yield by close to 2,000 lbs.
The bottom line is to manage the cows so that they have a BCS of 3.25 to 3.75 at dry-off and maintain that BCS during the dry period. Keep the cows eating the "specially formulated close-up ration" 3 to 4 weeks before calving (a double dose of yeast culture stimulates appetite). The close-up ration should contain enough effective fiber to maintain a functioning "rumen mat" which really helps reduce the incidence of LDA's. Use anionic salts or other management tools to prevent milk fever. Reduce cow stress as much as possible by providing a clean and ample sized maternity area and sufficient manger space. Adjust cows slowly to the fresh cow ration (an ideal close-up ration should contain most of these same ingredients).©