Feed is the single-largest expense in milk production. Many other livestock industries use feed efficiency as a benchmark for performance; however, dairy producers have only recently started to evaluate feed efficiency. Differences in production systems prevent a straightforward comparison of feed efficiencies. The following [article] discusses how to measure and use these values.

Measuring feed efficiency
Feed efficiency (FE) can be calculated most simply as pounds of milk produced per pound of dry matter (DM) consumed. The problem with this simple approach is that the fat content of the milk is not considered. Since fat contains more energy than other components of milk, ignoring milk fat can skew FE calculations.

The best way to account for fat content is to calculate FE as pounds of 3.5 percent fat-corrected milk produced per pound of DM consumed.

Factors affecting feed efficiency
Feed efficiency can vary from 1.0 to nearly 2.0 across stages of lactation or farms. This means that a number of factors other than dry matter intake (DMI) and fat-corrected milk production must be considered when using FE as a benchmark.

Major factors

•Milk production
Higher production nearly always means higher FE. This is because maintenance requirements are diluted more with the higher intake associated with higher milk production.

•Bodyweight
Bodyweight affects maintenance requirements. At equal milk production, cows with lower bodyweights will have higher FEs.

•Bodyweight or body condition change
When nutrients are directed towards weight gain, rather than milk production, FE is reduced. This is often a desirable situation, for example, in cows replenishing body stores lost during early lactation. Conversely, cows may have very high FEs when they are losing weight. In this situation, a high FE might be a cause for concern, not celebration. In general, differences in FE may occur due to the bodyweight or body condition changes that occur over the course of lactation.

Minor factors

•Genetics
Genetics ultimately determines how nutrients are allocated for maintenance, milk production and other body functions. Genetic lines that are highly productive will have higher FEs than less productive lines.

•Changes in maintenance requirement
Any change in the maintenance requirement will affect feed efficiency. Three common factors are cold or heat stress, walking or exercise and extended standing. Increases in walking distances or standing times will lower FE. Extremes of heat or cold will also decrease FE.

•Feed digestibility
Higher feed digestibility usually increases milk production, thereby increasing FE. Common methods to increase feed digestibility include proper feed processing and improving forage quality or NDF digestibility.

•Growth or reproduction
Young cows will generally have lower FE because substantial amounts of ingested nutrients will be used for growth. Pregnant cows will have reduced FEs in late gestation because of fetal growth; this would most likely be a factor in herds using shortened dry periods.

•Nutrient imbalance
Overfeeding or underfeeding nutrients may adversely affect FE. Research has shown overfeeding protein decreases both FE and efficiency of nitrogen use.

Economics of feed efficiency
As would be guessed from the number of factors affecting it, feed efficiency can be misleading when used as the sole parameter to evaluate economic efficiency of either cows or herds.

Feed efficiency does not equal economic efficiency. At the same FE, cows producing more milk will probably also have higher incomes over feed cost. One important note: do not purposefully decrease feed intake in a herd to improve FE. This will usually decrease milk production and profitability.

Feed efficiency guidelines
1. Check intake and milk production numbers for accuracy before worrying about feed efficiency. Feed refusals must be accurately measured for meaningful calculations.

2. Target for an entire herd or mid-lactation cows (180 to 220 DIM average for the herd or group); 1.4 to 1.6 pounds fat-corrected milk (FCM) per pound DMI is normal.

3. Early lactation (less than 30 DIM)
a. 1.5 to 1.8 pounds FCM per pound DMI is good
b. FE greater than 1.8 may indicate excessive weight loss and ketosis problems
c. FE below 1.4 indicates milk production problems or erroneous feed intakes

4. Late lactation (greater than 300 DIM)
a. FE follows the lactation curve downwards after milk production peaks
b. 1.1 to 1.4 FE is normal. It may be difficult to achieve an FE of 1.0 if cows are gaining weight and are well beyond 300 DIM.

Take-home messages
Feed efficiency (FE) is the primary driver of profitability for meat-producing animals. Using FE to evaluate dairy operations where there are multiple requirements for nutrients (milk production, bodyweight changes, reproduction and growth) complicates the process, but it does not reduce its usefulness.

Because of the many factors affecting FE, no single FE value can be set as a standard or goal that would be appropriate for all cows, all stages of lactation or all herds.

Within a herd, changes in FE can be used to help determine the economic impact of feeding and management changes.

Improvements in FE can improve profit whether they result from increased milk production per pound of DMI or getting the same milk from a lower intake. PD

References omitted due to space but are available upon request.

—Excerpts from University of Minnesota Dairy Days Proceedings, 2006

James G. Linn, Professor of Dairy Nutrition, Department of Animal Science, University of Minnesota