The efficiency of converting feed to milk matters on farms because it has a major influence on farm profitability and environmental stewardship in the dairy industry. Dairy feed efficiency in North America has doubled in the past 50 years, largely as a byproduct of selecting and managing cows for increased productivity.

Increasing productivity results in a greater percentage of total feed intake being used for milk instead of cow maintenance. Elite dairy cattle currently partition three times more feed energy toward milk than toward maintenance.

We are not likely to continue to make major advances in feed efficiency simply by increasing milk per cow. Instead, we also must focus on how to get more milk from each unit of feed.

The simplest way to define feed efficiency is milk per unit of feed, but this does not give adequate consideration to energy density of different feeds in a diet and the composition of milk, nor to gains or losses in body energy.

Thus, I prefer to discuss the efficiency of converting feed energy to the energy of milk and body tissues.

Feed energy is lost in two major ways. Feed energy is lost as feed chemicals are processed to the net energy (NE) of a feed with energy lost as feces, gases, urine and heat.

Some feed NE is captured as milk or body tissue, but some is lost as heat for maintenance, which is necessary for the survival of the cow. Energetic efficiency is the energy captured in products divided by the energy consumed.

Feed efficiency should be considered at the farm level and thus must account for feed wastage and the salability of products, as well as the economic value of feed and milk components, over a cow’s lifetime. For this article, however, I will mostly discuss efficiency per cow.

The major factors that affect feed efficiency on farms include milk energy yield per cow, cow bodyweight (which correlates with her maintenance requirement), longevity and the percentage of lifetime a cow is lactating, nutritional accuracy in feeding and the efficiency of converting feed energy to NE.

A cow’s maintenance requirement is considered to be constant and related to its bodyweight. The typical Holstein cow has a maintenance requirement of about 10 Mcal of NE per day. If a cow eats at 1X maintenance and produces no milk, feed efficiency is 0 percent. As she eats more feed and produces milk, some of the feed energy is captured as milk.

However, the marginal increase in efficiency with each unit of milk diminishes; thus, the increase in efficiency is less going from 20 to 30 kg (44 to 66 pounds) milk per day than going from 10 to 20 kg (22 to 44 pounds).

In addition, as cows eat more feed, digestibility is depressed, and eventually feed efficiency will plateau or even decline as intake continues to increase. We don’t really know the optimal level of production relative to bodyweight, but elite cows (greater than 15,000 kg or 33,069 pounds per 305-day lactation) may already be near the optimal level of production for maximum efficiency.

Management to improve feed efficiency

At the farm level, we can increase efficiency by increasing milk production per day of life. Increasing cow longevity from three to four lactations, reducing the age at first calving from 26 to 22 months or reducing calving intervals from 14 to 12.5 months could achieve similar improvements in lifetime efficiency as a 10 percent increase in daily milk production.

One often-overlooked management aspect of feed efficiency is feed management. To minimize feed wastage requires an annual evaluation of procedures for harvesting, transporting and storing feeds, mixing diets and managing bunks.

However, when managing bunks, it is important to remember that maximizing feed intake for lactating cows generally increases milk per cow and efficiency. Feeding to maximize intake while minimizing waste is a balancing act that takes commitment.

Feeding cows for greater feed efficiency

Nutrient requirements vary as lactation progresses, and the optimal diet for maximum efficiency and profitability changes as well. Unfortunately, many farms feed a single TMR throughout lactation. A single TMR usually has less starch and protein than optimal for high-producing cows but more starch and protein than optimal for cows in later lactation.

Based on feeding goals and cow biology, I recommend at least three rations for the lactating cows on a farm (Figure 1).

Fresh cows should be fed for optimal health, and expensive supplements are warranted. Cows in peak lactation should be fed for maximum milk; because their intake is limited by rumen fill, they should be fed minimum-fiber diets with plenty of digestible starch to maximize energy intake.

Cows in later lactation with body condition score greater than 3 should be fed less fermentable starch and more fermentable fiber to promote partitioning of nutrients toward milk instead of body tissues and thus minimize fattening.

Nutritional grouping or computer feeders can improve production and profits in the high cows and cut feed costs and improve health in late-lactation cows. The farm team should strategize how to feed for stage of lactation.

Selecting cows for greater feed efficiency

In the past, genetic selection has relied heavily on quantification of the phenotype in daughters of young sires. The science of genomics has changed this. We are now able to select for new traits, like feed efficiency, for which daughter information is not available. One way to select for feed efficiency is to select for high milk production while selecting against feed intake.

Residual feed intake (RFI) is a measure of actual versus predicted intake for an individual cow or, in other words, RFI is the feed a cow consumes that cannot be justified based on its production.

The heritability of RFI in lactating cows is about 0.17, and it is repeatable across diets, lactations, stages within a lactation and stages of life. The use of genomics in selection against RFI is already beginning in Australia, where it is part of an index for “Feed Saved,” which selects against body size and against RFI while also selecting for the yield of milk components.

Eventually this will happen in North America, but until then, selection against body size is another way to select for efficiency.

Unfortunately, over the past 50 years, we have been selecting Holsteins for greater body size. It is time to quit showing them favoritism – they are making our industry less efficient.

This larger size might be acceptable if it resulted in greater milk. However, we found no genetic correlation between bodyweight and milk energy output and a negative genetic correlation between bodyweight and feed efficiency.

Thus, in concurrence with research in 2000 and on the basis of enhancing feed efficiency, profitability, animal welfare and sustainability, the U.S. dairy industry should stop selecting for larger cows and instead use an index that favors greater milk production and components, smaller cow size and negative RFI.

Conclusion and implications

We have made major gains in feed efficiency in the past 50 years as a byproduct of selecting, feeding and managing cows for increased productivity. By increasing efficiency, we have increased profitability and environmental sustainability.

Someday we will also be able to select cows against feed intake. In the meantime, it is reasonable to continue selecting for greater milk production, but we should also select for modest reductions in body size.

In addition, we need to do a better job of feeding cows according to their nutritional needs through nutritional grouping or computer feeding; this will improve efficiency and profitability.

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