For example, one pound of milk at peak lactation is worth approximately 200 to 225 lbs. of milk for the entire lactation. Most of the determination of how dairy cows will approach peak milk is based upon what happens during the last third of the previous lactation, the last few weeks before calving and the first three weeks post-calving. Similarly, metabolic disorders such as milk fever, fatty liver, and ketosis tend to occur in complexes, have their roots during the transition period, and result in substantial economic losses.

Furthermore, cows that get off to excellent and healthier starts are more likely to be more successful in terms of reproductive performance. Therefore, the potential benefits of optimizing all aspects of cow management during this timeframe are substantial.

Highlights include:

• Management of transition cows as a system.

Nutritional management of transition cows is a complex system composed of many factors.

The two primary changes in the biology of dairy cows during the transition period that relate specifically to energy nutrition are: 

1. The cow's demand for glucose increases dramatically when she begins to lactate.
2. The cow mobilizes large amounts of body fat in support of lactation, with important ramifications for liver function and metabolic health.

• Source and utilization of glucose during the transition period.

The cow's demand for glucose increases tremendously immediately after calving, and probably is met in part by increased usage of amino acids (protein) for glucose synthesis by liver. Nutritional management should focus on strategies to maximize the supply of glucogenic precursors for liver glucose synthesis.

• Mobilization of body fat in support of early lactation and ramifications for liver and metabolic health.

Minimize both the height and duration of the spike in nonesterified fatty acids (NEFA) that occurs when cows mobilize body condition after calving to maintain liver health. Ample supplies of glucogenic precursors are necessary to minimize formation of ketones in liver.

• Methods to increase supply of glucogenic precursors during the transition period.

Focus on increasing feed intake by fresh cows and formulating diets to maximize ruminal fermentation rather than routine usage of glucogenic supplements. Glucogenic supplements seem to be much more effective when administered as a concentrated dose rather than mixed into the ration.

• Rumen-protected amino acids for transition cows.

There is little scientific justification for routinely providing protected methionine in diets fed to transition cows. In theory, there may be some benefit to providing additional methionine or other methyl donors on fatty acid metabolism, but these effects on metabolic health and liver function have not been evaluated.

• Specific recommendations for maximizing feed intake and supply of glucogenic precursors in support of energy needs during early lactation.

Body condition score. Aim to dry cows off at a 3.25 to 3.5 and neither gain nor lose condition score during the dry period.

General goals for feed intake of transition dairy cows:

• Mid to late dry period: 28 to 29 pounds per day of dry matter (~2% of body weight)
• 7 days in milk: 32 pounds per day of dry matter (~ 2.5% of body weight)
• 14 days in milk: 38 pounds per day of dry matter (~ 2.9% of body weight)
• 21 days in milk: 44 pounds per day of dry matter (~ 3.4% of body weight)

General goals for diet formulation for transition cows.

Formulate diets that provide sufficient rumenally fermentable carbohydrates (34 to 36% NSC for close-up cows and 35 to 40% NSC for fresh cows) and proteins (60 to 65% of CP as degradable protein) to maximize synthesis of microbial protein, with resulting production of large amounts of volatile fatty acids during ruminal fermentation.

Thomas R. Overton, Ph.D., is an assistant professor with the dairy management/nutrition, department of animal science at Cornell University. He received his Ph.D. from the University of Illinois and his research program focuses on nutritional physiology of dairy cattle during late pregnancy and early lactation.

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