Feed Efficiency in Dairy Heifers
Dairy heifers represent a large expense of resources including feed, buildings, and labor, yet return no money to the dairy farm until they calve or are sold. The overall objective in raising heifers must be to minimize costs while still maximizing the returns on the costs incurred. Management practices must yield the best quality heifers with the highest potential to be productive and profitable and minimize cost to the farm and the environment without affecting heifers’ well being.
Feed represents the largest component to the cost of heifer production and is such a large proportion that it clearly represents the major way to control heifer costs. Studies have shown that heifer feed costs may represent up to 60% of heifer expenses and 12% of total farm expenses.
We are often reminded of the importance of feed efficiency (lbs milk/lb feed) for lactating dairy cows as it may affect costs and income, yet the concept is seldom mentioned for the growing heifer. We also need to remember that dairy animals spend over half of their life on most farms as a replacement animal, which means that their feed efficiency is critical to the overall farm profitability.
We measure feed efficiency for heifers in pounds of gain per pound of feed. This publication will discuss some of the many factors that can impact feed efficiency in the dairy heifer, including: genetics, forage quality (fiber and dry matter digestibility), feed intake level, growth rate or stage of growth, body condition or change in body composition, gestation, heat or cold stress (environmental stresses), and exercise level.
Genetics plays a role in feed efficiency in two aspects. First, there is a genetic component of efficiency, whereby some animals are more efficient at converting feed energy into productive energy, whether that is growth of muscle and bone or milk production. In addition, genetics in relation to body size are important since an increase in body size will increase maintenance costs for energy, protein, and most other major nutrients. The smaller the body weight of the heifer at a given age, the lower the maintenance requirements of that animal. This being said, the heifer must be large enough to cycle for breeding purposes and, more importantly, large enough to calve successfully; both at appropriate ages. Adequate body weight, body condition score, and structural height of heifers are critical for achieving the management objective of raising productive, profitable heifers. Therefore, growth at a given age cannot be compromised for the sake of improving feed efficiency.
Heifers’ ability to use feed efficiently declines with age. Before puberty, heifer growth is mainly bone and muscle, but after puberty heifers gain more fat relative to bone and muscle and are therefore less feed efficient. The case can easily be made for achieving a steady state of growth from birth to first heat, followed by a second rate of growth following breeding to achieve the desired body weight at calving. Research has shown that before puberty, Holstein heifers should grow at about 1.8 lbs/day to maximize milk production in the first lactation.
Once a heifer has reached puberty (9 to 10 months of age for Holstein heifers) the rate of growth does not affect mammary development, and the next critical control point—body weight at calving—must be considered. Again, we know from research that dairy heifers need to be at or near 85% of the body weight of mature cows in your herd at first calving. If they are not, then first-calving heifers will expend excess energy during the first lactation for growth before milk production. Heifers that are small relative to their mature size will have dramatically lower feed efficiency in their first lactation as they will be growing, not producing milk. This phenomenon is a biological response to delayed growth before calving. In addition, heifers that are in the last third of gestation will be less feed efficient as the fetus and related tissues will be drawing off more dietary energy and protein to support rapid fetal growth. Heifers that have not reached adequate size at calving are also at greater risk for having difficulty delivering their calves, which has negative consequences for both calf and cow.
Environmental stresses and exercise are additional factors that affect maintenance requirements and thus will have direct effects on heifer feed efficiency. In this case we find that any environment or housing system that includes well bedded and managed free-stalls or bedded packs will improve feed efficiency because of lower maintenance costs. However any housing that allows heifers to be dirty and wet or allows animals to be heat or cold stressed will decrease feed efficiency due to increasing the maintenance energy required to maintain a normal body temperature.
Exercise also has effects, which are often small, but they can be great if heifers are walking long distances on a regular basis. In general, since heifers on pasture expend more energy to eat, their feed efficiency will be also be somewhat decreased.
A final yet important aspect to feed efficiency is the diet; both the amount fed and the ingredients in the ration can influence feed efficiency. Greater digestibility of the diet will allow the heifer to be more feed efficient. Therefore in typical heifer diets, which are mostly forage, forage quality and fiber digestibility can greatly influence feed efficiency. In addition, replacing forage with concentrate improves feed efficiency to a point, because grains and byproducts usually have better digestibility than forages. In addition when feeds with higher digestibility are fed to heifers the amount of feed dry matter needed to meet the targeted body weight gain is lower, resulting in less maintenance energy being needed for the various digestion processes in the animal.
When animals are fed more nutrient dense diets, and therefore less total dry matter per day, the rate of passage of feedstuffs out of the rumen is reduced, allowing rumen bacteria and protozoa to have a longer time to break down fiber and organic matter. This allows highly digestible feeds and forages to be digested even more, often improving total dry matter digestibility by 4 to 6% over what would normally be expected using book values for feedstuffs.
The increase in digestibility of more nutrient dense rations fed at a lower dry matter intake has the added benefit of less manure output. This reduction is positive for the environment, and saves money and time for producers, as there is less manure to haul. Of course, any excess nitrogen or minerals fed in these diets with greater digestibility and feed efficiency will still be excreted, however nutrients in the manure will be more concentrated due to the smaller amount of feces excreted.
Typical feed efficiency values for calves and heifers (feed to gain; DMI to ADG)
- Calves on milk 2:1 to 2.5:1
- Weaned calves (25% forage) 3:1 to 4:1
- Young heifers (50% high quality forage) 4:1
- Heifers on TMR 6:1 to 7:1
- Older heifers (poor forage) 8:1 or more (has been shown to be 15:1 in some cases)
Yearling heifers on high quality feeds and forages can easily have a 5:1 ratio of feed to gain, but this can decrease to 8:1 or more for less digestible, high forage diets. One example of allowing feedstuffs to digest longer in the rumen by not having animals on full feed was demonstrated in Wisconsin research. In this study heifers fed a controlled amount, 80% of ad-lib intakes, showed a 29% improvement in feed efficiency compared to heifers that were allowed to eat as much as they wanted. In addition, heifers fed a controlled amount produced approximately 2 pounds less manure (on a dry matter basis) each day than heifers fed ad-lib.
A last point is that a few feed additives that improve rumen function and microbial digestion have been shown to improve heifer feed efficiency. These include ionophores and yeast, both of which can affect feed and/or forage digestibility.
In summary, improving feed efficiency in heifers can be accomplished by increasing diet digestibility, increasing forage fiber (NDF) digestibility, stimulating rumen microbial digestion, optimizing—not maximizing—feed intake, maintaining the animal in an adequate environment, maintaining the heifer in optimal health and management, and maintaining optimal growth rates. Finally, genetics may play an important part in feed efficiency.
Jud Heinrichs, Javier Suárez, and Coleen Jones
Reviewers: Virginia Ishler and Rebecca White, Penn State
DAS 2011-184; Published January 16, 2011