Factors that Influence Feed Efficiency in Lactating Dairy Cows
Posted: October 28, 2011
Feed efficiency is an important consideration in the nutrition and management of dairy cows. There are many factors that influence feed efficiency and understanding these can be helpful in being able to work with and improve feed efficiency.
Forages: Forages have the greatest effect on feed efficiency. Since they make up a very large component of the slowly digestible part of the diet of lactating cows, they are critical for maintaining a desired FE. They also have a large impact on FE because they are the most variable feed ingredient in terms of digestibility and nutrient composition and they comprise a greater proportion of the ration than any other feedstuff. It has been shown that FE is directly related to forage digestibility, with increased digestibility leading to increased FE. Unless concentrates are very unusual or processed incorrectly to have damaged protein or other components, they are almost always more digestible than forages. Since energy density has the same relationship with FE, much effort should be applied during harvest, storage, and feeding of forages to achieve the highest quality forage possible. Feeding forages of only the highest quality to lactating cows is of utmost importance.
Another way that forages can influence FE is through the maintenance of a desirable rumen environment. Acidosis (low rumen pH) can negatively affect FE by decreasing fiber digestibility through changes in the rumen microbial profiles. Adequate physically effective fiber (forage particle size) in the ration will maintain the proper rumen environment by stimulating chewing and ruminating, increasing saliva secretion, and improving buffering capacity of the rumen. Forage particle length is also needed to maintain the rumen environment and proper rumen motility.
Stage of Lactation: Days in milk (DIM) will have an influence on FE, because cows in early lactation will be losing body weight and using that energy for milk production. This will artificially increase FE that is calculated using only DMI and milk production. A high FE (>2.0) in early lactation can actually indicate a problem that cows are losing too much weight, possibly leading to other metabolic disorders. On the other hand, late-lactation cows will be gaining weight thus lowering their calculated FE. This lower FE should not be viewed negatively because cows need to gain body weight in late lactation so those body reserves can be utilized when the cow begins the next lactation in negative energy balance. Therefore average DIM of the herd should be taken into account when evaluating FE, and variation by stage of lactation is completely normal.
Maintenance Requirements: Changes in the maintenance requirements of lactating cattle will affect how much of their energy intake they can devote to milk production. For instance, a cow grazing pasture will have to utilize more energy walking around to consume feed than a cow in a free-stall or tie-stall barn. Other factors besides physical activity that can affect cows’ maintenance requirements are: body size, outside temperature or season of year, and stress. The larger the cow, the more maintenance requirements she will have. The more stressed the cow is beyond her thermo-neutral zone, the more energy she will expend to maintain her normal temperature. This aspect is important for cold and especially heat stress.
Lactation Number: Feed efficiency is affected by lactation number because cows in their first lactation are still growing, and a portion of their energy intake is appropriated to support that growth. After cows reach maturity they no longer have an energy requirement for growth, and they can focus their entire energy intake on maintenance and milk production.
Cow Comfort: This factor is related to maintenance requirements because an increase in stress will generally lead to an increase in energy expended for maintenance. There are many factors that can cause cows stress, several examples are: excessive heat and cold, overcrowding, disease, and cleanliness of animals.
Feed Additives: There is evidence that feeding yeast, ionophores, and direct-fed microbials to lactating dairy cows can increase feed efficiency, especially when cows are heat stressed. These additives generally increase FE by positively affecting fiber digestion; however, the gains are usually less than could be achieved by improving forage quality.
- By Daryl Maulfair, graduate student, and Dr. Jud Heinrichs, professor, Penn State Department of Dairy and Animal Science