by Dr. Warren Bohnhoff, DVM

During the past few years nutritionists have recognized that the transition period, the time from the middle of the dry period through the first 21 days of lactation, is the most crucial phase of the lactation cycle. Factors such as milk production, cow health, reproductive performance, and calf health and performance are greatly associated with the transition period and, ultimately, the overall profitability of the dairy enterprise.

Most of the determination of how dairy cows will approach peak milk is based upon what happens during the transition period. Also, metabolic disorders such as milk fever, displaced abomasa, fatty liver and ketosis tend to have their roots during the transition period, and result in significant economic loss.

Furthermore, cows that transition well are more likely to be successful in terms of reproductive performance. Quality feeds, cow comfort, balanced nutrition, and all factors conducive to maximum dry matter intake are essential to this period.

Nutritional management of transition cows is a complex system. Management of body condition during the previous lactation and dry period combined with feeding management and ration formulation throughout the dry period and early lactation all contribute largely to the equation that underlies performance during the first few weeks of lactation.

For years, we have focused on the fact that energy balance of cows usually becomes negative during the first few weeks post calving and cows will utilize body fat to support lactation during this time. Although this concept works well when our ration formulations provide estimates of net energy for lactation, we need to remember that the products that the cow actually uses to make milk and provide fuel to support herself are compounds such as glucose (sugar), volatile fatty acids produced in the rumen, long chain fatty acids from fat digested in the small intestine, and amino acids.

The Net Energy value of the diet is simply an index of the capability of a given diet to provide the nutrition factors needed in support of energy. Although this works well during most phases of lactation, it is particularly important that we target ration formulation and feeding management during the transition period to ensure that we are providing plenty of theactual nutrients the cow requires.

The two primary changes in the biology of dairy cows during the transition period that relate specifically to energy nutrition are the following: 1) The cow's demand for glucose increases dramatically when she begins to lactate. This is why many cows have subclinical ketosis shortly after calving. Her requirements are greater than what she can obtain from related dry matter intake. 2) The cow mobilizes large amounts of body fat in support of lactation, with important ramifications for liver function and metabolic health.

Prefresh and postfresh cows transition better when higher dry matter intakes are observed. Anything you do to encourage DMI during these 6 weeks will pay big dividends! Follow ANC recommendations and find ways to implement proper rations, avoid overcrowding, and maximize cow comfort.