Minimizing the duration and level of negative energy balance (NEBAL) is an important nutritional aspect of managing dairy cows during the transition period. The transition period spans from three weeks before calving to three weeks after calving. Not only does NEBAL affect milk yield, but it also can have a significant influence on reproductive performance.

Negative energy balance occurs when the daily energy requirement for a cow cannot be met by the energy she consumes in a day. Typically a cow’s dry matter intake (DMI) will decline about one week before calving beginning the period of NEBAL during the transition period. After the cow calves, the magnitude of NEBAL increases because her DMI lags behind energy required for the rapid increase in milk yield.

Cows with excessive NEBAL tend to have poor fertility. NEBAL can be monitored by observing body condition scores (BCS) following calving. Excessive BCS loss during the first 30 days in milk is associated with delayed ovulation. Body condition score should be at 3.25 - 3.5 at dry off and maintained throughout the dry period.

The goal is to keep BCS loss during early lactation (0- 30 days in milk) at less than 0.5 units BCS. Research by Ronald Butler of Cornell University evaluated timing of first ovulation based on level of BCS loss during the first 30 days in milk.

BCS loss

First ovulation after calving

< 0.5 unit

30 days

0.5 to 1.0 unit

36 days

>1.0 unit

50 days

Cows that have first ovulation delayed past 50 days in milk have a significantly lower probability of becoming pregnant.

The impact of BCS loss on days open was summarized by Lopez-Gatius and co-workers who reviewed 11 research studies. Results indicated that cows with body condition loss of 0.5 to 1.0 units BCS had 3.5 more days open than cows that lost less condition. Days open increased by 11.0 days for cows that had greater than 1.0 unit BCS loss. Butler also reported that a number of studies have shown conception rate decreases as the amount of BCS loss increases in early lactation.

Negative energy balance is a major nutritional factor affecting reproductive performance. When excessive BCS loss occurs, first ovulation after calving is delayed, conception rates decline and days open increase. Dairy producers must strive to optimize DMI and energy intake for cows throughout the transition period to minimize the level and duration of NEBAL and BCS loss during early lactation.

Richard Pursley, professor of animal science and Michigan State University Extension reproductive management specialist, recommends monitoring BCS three weeks before, at time of, and three weeks after calving to identify potential problem cows. Goals for BCS should be 3.25-3.5 prior to and at calving, and 3.0 at three weeks post-calving. Herd veterinarians and nutrition consultants can help develop strategies to resolve the problem of significant BCS loss during the transition period.