The ability of dairy cows to convert feedstuffs into products for human consumption is generally referred to as feed efficiency and is expressed as pounds of milk produced per pound of dry matter (DM) consumed. This expression represents a gross measure of feed efficiency and does not account for nutrients partitioned to reproduction, growth and tissue deposition. Thus, interpretation of the value obtained should consider stage of lactation, age and stage of gestation for the herd in question.
Feed efficiency is often used to evaluate the diet formulation, but it can be misinterpreted if environmental and management factors are ignored. The purpose of this [article] is to present an argument for the use of production efficiency, expressed as pounds of 3.5 percent fat-corrected milk (FCM) produced per pound of dry matter intake (DMI), as a management tool and discuss some of the factors that influence production efficiency.
Measuring feed efficiency
The generally accepted measure of feed efficiency (FE) is pounds of milk produced per pound DMI consumed. This method does not account for the variation in milk fat produced. Thus, it is not always a good expression of the relationship between energy input and energy output. The use of 3.5 percent FCM as calculated by the equation is preferred, because it corrects for milk fat content.
3.5 percent FCM =
(0.432 x pound of milk) +
(pound of fat x 16.23)
The use of 3.5 percent FCM is particularly important when evaluating feed efficiency in Jersey herds.
A Jersey herd I interact with produces 64 pounds of milk containing 3.9 percent true protein and 5.1 percent butterfat and consumes 48 pounds of DM daily. The unadjusted milk FE is 1.33, whereas the 3.5 percent FCM FE is 1.68. The difference in these two numbers is obvious and leads to very different conclusions on the status of the herd.
A Holstein herd I interact with produces 103 pounds of milk containing 3.2 percent true protein and 3.61 percent butterfat and consumes 60 pounds of DM daily. The unadjusted milk FE is 1.72, whereas the 3.5 percent FCM FE is 1.74. The difference in these two numbers is not obvious and leads to the same conclusion.
The most difficult part of the FE equation to obtain in a herd is DMI. Some herds:
1. use feed delivery systems capable of weighing the various diet components and the amount of total mixed ration (TMR) delivered to individual pens
2. estimate daily feed refusal
3. record daily TMR offered
Others do not accurately measure the amount of feed consumed. Estimating DMI for herds that offer hay ad libitum or utilize pasture is particularly difficult.
The milk component of the equation can be obtained from bulk tank weights and butterfat percentage from the milk plant; these values can be used to estimate daily production per cow, if an accurate count of the number of cows contributing to the total is recorded daily.
The use of daily milk shipped and daily DMI provides a reasonable estimate of FE for the whole herd. Daily milk production and feed consumed per pen provide more useful values for diagnostic purposes, particularly if cows are sorted by stage of lactation.
Feed efficiency as a diagnostic tool
The goal for FE, on a whole-herd basis, for a typical herd is 1.5 pounds or more of 3.5 percent FCM per pound of DMI. A typical herd is defined herein as consisting of 25 percent early-lactation cows, 25 percent late-lactation cows and 50 percent in between. Feed efficiency would normally average approximately 1.8 for early-lactation cows, 1.3 for late-lactation cows and 1.5 for the middle group.
Research data illustrate the importance of evaluating FE according to stage of lactation and the impact of diet formulation during early lactation on total lactation production and FE. Dietary factors that influence FE include digestibility, nutrient content and nutrient balance.
Feed efficiency is not a constant across herds or within a herd throughout the year. The dairy cow has the ability, through the neuro-endocrine system, to partition nutrients to meet physiological demands in order to maintain normal body functions. Maintenance demands usually have priority over production functions, such as lactation and reproduction; an exception appears to be mammary function during early lactation when body tissue is mobilized in support of lactation.
However, mammary priority does not trump maintenance for an extended period because if nutrient delivery is insufficient to support lactation and rebuild body tissue stores then milk production decreases to the level that nutrient intake can support and meet maintenance requirements. In these instances, DMI is maintained, milk production decreases and FE decreases.
Nutrient partitioning away from the mammary gland to support maintenance also occurs when temperature rises above or drops below the lactating cow’s thermal neutral zone. Feed efficiency during summer months is often less than that observed during the cool seasons because nutrients are partitioned to maintain normal body temperature. DMI may also be negatively impacted by elevated temperature but not in proportion to milk production.
It is important to remember that mammary function is a luxury except during early lactation; thus only nutrients supplied above maintenance are available to support milk production. Therefore, environmental and management conditions that increase maintenance will reduce milk yield and FE.
It seems logical to assume that excessive exercise, uncomfortable freestalls and other conditions that interfere with cow comfort and rest time will have a negative impact on FE.
Economic importance of feed efficiency
Feed is the largest single cost to dairy producers, and its efficient use will improve net income and reduce potentially negative impacts on the environment. The following example illustrates the economic importance of even small changes in FE.
Assumptions
•Holstein cows weighing 1,400 pounds and producing 90 pounds of milk containing 3.5 percent butterfat and consuming 58 pounds of DM daily.
•Feed cost is $3.59 per day or $0.062 per pound of DM.
•Feed efficiency, 3.5 percent FCM = 1.55.
The value of 3.5 percent FCM is $0.14 per pound. Thus, the total value of the product per day is $12.60 at a daily feed cost of $3.59 or income over feed cost of $9.01.
If feed efficiency can be increased to 1.6 then DMI per 90 pounds of milk would be 56.25 pounds at a daily cost of $3.49. Income over feed cost in this case would be $9.11 or an increase of $0.10 per cow daily.
Other examples might involve an increase in milk yield without a corresponding increase in DMI, which would likely involve an improvement in diet digestibility or a reduction in maintenance requirements.
The approval of Rumensin® for lactating dairy cows is of interest because it improves 3.5 percent FCM FE by modifying ruminal digestion favorable to milk production. The specific effect of Rumensin tends to be diet-specific, but in most cases an improvement of 2 to 3 percent in solids corrected milk efficiency is realized.
The current regulations relative to the inclusion of monensin in diets for dry and lactating dairy cows allows 11 to 22 grams per ton of total mixed ration DM (100 percent DM). Typical inclusion rates would deliver 300 milligram of monensin per head daily.
Summary
Feed efficiency can be a useful diagnostic tool in herds that can measure DMI and daily milk yield. Jersey herds should use fat-corrected milk, but Holstein herds could use unadjusted milk if butterfat content is in the range of 3.4 to 3.6 percent. The goal for 3.5 percent FCM FE should be at least 1.5 for a typical herd. The FE value for a herd is influenced by management and environmental conditions as well as diet formulation. PD
References are available upon request.
Dr. John E. Shirley
Dairy Nutrition Consultant
To contact John,
e-mail him at
jshirley@ksu.edu
