First, let us understand what is feed efficiency (FE). Feed efficiency is a measure of converting feed nutrients into milk or milk components in lactating cows. In simplest term, it is the pounds of milk produced per pound of feed dry matter (DM) consumed by the cow.
Feed is the single largest expense (40 - 50% of production cost) associated with milk production. Hence, in order to increase the profitability of a farm, it is important to improve the conversion of feed nutrients into milk either by 1) Increase milk yield with same dry matter intake 2) decreasing the dry matter intake but maintaining the same milk yield.
Measuring Feed Efficiency
One simple way to measure the feed efficiency (FE) is quantity of milk produced per quantity of dry matter (DM) consumed. The calculation based on a cow would be: kilograms of daily milk produced divided by kilograms of feed DM consumed:
(kg of daily milk produced)/(Feed Fed - Feed Refused) x DM % of feed
An example would be:
(36 kg of milk produced per day)/ ((50 kg Feed Fed - 2.8 kg feed refused) x 50% DM) of the ration = 1.53 FE.
There is however a problem with this way of measuring the FE as it does not consider the fat content of milk. The production of milk fat requires a lot of energy from the cow. Hence, FE needs to be standardised by using Energy-Corrected Milk (ECM) yield. This would allow for comparison across different breeds of dairy cows with different milk composition. The formula below is used to convert to ECM yield.
There are other important factors to consider when measuring feed efficiency.
One such factor is the use of actual Dry Matter Intake (DMI). Using accurate DMI figure is important for accurate estimates of FE. DMI means weighing not only what was fed but also the refusals.
Another important factor to consider is the DM of ration components. It is essential to measure the DM content of the TMR and the forages used in the ration in order to obtain a more accurate FE estimates.
Factors Affecting Feed Efficiency
Feed efficiency varies from around 1.0 to 2.0 during lactation phase of a cow. There are several factors that will affect the feed efficiency of a cow.
1)Forages - By far the biggest effect on feed efficiency is forages. They make up a very large component of the slowly digestible part of a diet of lactating cows and are essential in maintaining a desired FE. Another reason why they play a big role on FE is because they are the most variable feed ingredient in terms of digestibility as well as nutrient composition. They also make up a large proportion of the ration than other feedstuff. Research shows that FE is directly related to the forage digestibility. The better the digestibility, the higher the FE. Therefore, it should be the priority of farmers to feed high quality forages to lactating cows in order to maintain a high FE.
2) Body Weight (BW) of Cows - The BW of a cow is important when trying to evaluate the FE between cows of different lactation stages or breeds. In general cows with lower BW have a higher FE. For example, comparing two cows with equal milk production, the cow with 25% less BW have a 10 - 12% higher FE.
3)Milk Production - In general, a high producing cow will be more energetically efficient as more of the consumed energy will be used for production rather than maintenance. Since maintenance will be a smaller proportion of total energy intake, there will be more product output per unit of energy intake involved, hence, this increases the FE.
4) Pregnancy - Pregnancy will reduce the FE as the fetus requirement increases during late gestation. However, this impact will be small
5)Age - Generally, the FE for younger cows will be lower as compared to matured cows. This is because younger cows tend to divert their nutrients to growth during mid and late lactation stage.
6)Feed Additives - It has been suggested that feeding yeast, ionophores, and direct-fed microbials to lactating dairy cows will be able to help increase the feed efficiency. This is especially true when cows are heat stressed. These additives will help with the fibre digestion although the gains will usually be less than could be achieved by feeding quality forages.
7) Days in Milk (DIM) - DIM will have an impact on FE as cows in early lactation stage will be losing body weight and using that energy for milk production instead.
In early lactation stage, a high FE (>1.8) would indicate that a significant amount of BW are being mobilised to support milk production. This will cause the cow to become ketotic and the body reserves will be depleted to a point where the milk production as well as reproduction will be negatively affected. On the other hand, a low FE (<1.2) in early lactation stage would indicate that there could be potential health problems such as acidosis.
A good target would be 1.5 - 1.6 FE for cows 150 to 200 DIM. As for cows greater than 250 DIM, a FE below 1.4 is normally expected. The lower FE is due to lower energy diets being fed and the shifting of nutrient intake from milk production to body weight gain, replenishment of body condition and pregnancy. The decrease in FE during late stage lactation is usually caused by a decrease in milk production but without a proportional decrease in feed intake.
8) Genetics - Genetics will ultimately determines how the nutrients will be partitioned between maintenance, milk production and other metabolic functions. According to Gibson (1986), high milk production genetic lines were more efficient in converting feed to milk as compared to low milk production genetic lines. With that being said, high genetic lines lost more BW during lactation as compared to low genetic lines.
9) Feed Digestibility - Increasing the feed digestibility will cause more nutrients to be available for milk production. There are a few ways to help increase the feed digestibility such as proper processing of corn silage and grain or feeding very high quality forages.
10) Environmental Factors - Research shows that cool weather favours feed efficiency (1.40) as compared to warmer conditions (1.31).
11) Changes in Maintenance Requirements - The higher the maintenance requirements, the lower the FE. For example, cows on pasture or cows that required to walk long distance to and from a parlor will have lower FE compared to tie stall housed cows.
Economical Feed Efficiency
Using feed efficiency as a tool to monitor herd performance is good but it should never be used as the sole parameter to evaluate economic efficiency of cows or herds. From Table 1 below, it is observed that Herd A and Herd B have the same FE - 1.50. In this case, the herd with higher milk production per cow per day returned the most income. Therefore, unless the feed prices increased substantially relative to milk prices, the herd with higher milk production per cow per day will be more profitable at equal feed efficiencies.
Table 1. Annual Impacts of milk production on profitability of two herds with same feed efficiency (1000 cows each), milk price $17/cwt.
On the other hand, by improving the feed efficiency, the feed cost to produce same amount of milk will be lower as shown in Table 2.
Table 2. Impacts of feed efficiency on the milk production costs of two herds with different feed efficiency (1000 cows each), milk price $17/cwt.