The following is from an article by Jud Heinrichs, professor of dairy science at Penn State University, which appeared on the DAIReXNET learning network.
Q: What are we learning about precision feeding of dairy heifers?
A: Much of the recent heifer nutrition research has evaluated precision feeding of highly digestible diets to dairy heifers for improving feed efficiency and reducing manure. Feed represents the largest component of the total cost of heifer production, and it clearly represents the major way to control heifer costs. Diet type and the amount fed can be large factors that affect feed efficiency and are the major aspects that we use in precision-feeding heifers. Ration digestibility is also obviously important. The more digestible the feedstuffs used in the ration, the more efficient the heifer will be.
Based on published research for precision-fed dairy Holstein heifers, nutrient specifications as currently understood are as follows:
- Protein: Balance primarily for crude and soluble protein.
- 14% to 15% CP for pre-pubertal heifers based on DMI of 2.15% BW/day.
- 13% to 14% CP for post-pubertal heifers based on DMI of 1.65% BW/day.
- Maintain at least 30% to 35% soluble CP in the rations at all times to allow for optimal rumen microbial protein production.
- Rumen undegradable CP levels in excess of 25% to 30% of the CP are not required; use only standard feed sources based on price and availability and not feeds specifically designed for high bypass protein values.
- Soluble protein (SP) and rumen degradable protein (RDP) are efficiently utilized by dairy heifers.
- Energy: The energy requirement of the heifer will be influenced by BW, growth rate, and the environment in which the heifer is being raised. Diets can be formulated at a fixed (generally higher) energy content and precision-fed to specifically meet the heifers’ energy requirement for growth.
- Fiber: Traditionally, high levels of fiber or low-quality forage are fed to dairy heifers to control dietary energy intake; however, precision-feeding high-concentrate, low-fiber diets effectively accomplishes the same goal. Economics and the mix of forages available to a farm usually drive the forage level to feed. Research has revealed that the ratio of forage to concentrates can be extremely wide, from 95% forage to 25% forage.
- Vitamins and minerals: In precision-feeding systems, it is important to balance diets to current National Research Council (NRC) specifications for vitamins and minerals. With limited newer data, there are no indications to suggest vitamin and mineral requirements are altered when heifers are precision-fed.
Monitor heifer weight
Weighing heifers is a relatively simple means to monitor animal performance, and this practice is a must for precision-feeding dairy heifers successfully. With a precision-feeding system, heifers must be weighed to allow one to know what amount of feeding is required, while maintaining the growth rates needed for breeding at a given age or for calving at a given BW. Scales or weight tapes can be used for heifers with equal success.
- Weigh heifers at the same time of day (relative to feeding); otherwise, alterations in gut fill can impact average daily gain (ADG) calculations.
- Weighing heifers once per month is best, but once the system is stable, less frequent weighing can work as long as body condition is observed regularly.
- It is best to weigh all heifers; however, on some farms, it may not be realistic, as heifer numbers may be labor prohibitive. In this case, weighing a representative group (10% to 25%) of the heifers in a pen each time will suffice. It is important to be sure that this group is representative of the entire group.
- Monitor individual heifer and group gains against benchmark weights, and alter management, specifically feed intake strategies, as needed.
In any group-housed heifer facility, minimizing variation in size and age of heifers in each group is important, and it remains important in managing a precision-feeding system. Typically, beyond 4 months of age, heifers should be housed with other heifers as close to the same age as possible and always in groups with less than 200 pounds (90 kg) of BW variation within the group. Often, this means having groups with 2 to 4 months of age variation at the most. Post-breeding, this number can be increased to 300 pounds (136 kg) of BW spread between animals within a group.
In precision-feeding systems, heifers will need adequate bunk space, often 14 to 24 inches of feed bunk space per heifer as they progress from 4 months of age to pre-calving or 22 months of age. Precision-fed heifers will not have access to feed available at all times of day; thus, all heifers in a pen must have access to the feed bunk at the same time. Overly aggressive and timid heifers are very susceptible to over- or under-nutrition when feed bunk space is limited. If precision-fed heifers on a high-forage diet have feed available 12 to 16 hours/day, feed bunk space is often not an issue. If heifers are fed 30% to 40% concentrate diets and feed access is limited to 6 to 8 hours/day, feed bunk space can become an issue. Use common sense to see if all heifers are satisfied and are growing uniformly when using these feeding systems.
Two strategies can be used when feed bunk space is limited. The first is simply grouping animals with peers of similar BW. The second strategy is to provide impediments to free motion at the feed bunk, such as headlocks or closely placed divider posts. This will likely be effective to some degree but not completely. Feeding twice daily is not recommended as this has been shown to increase heifer competition and weight gain variability within a pen.
At the initial implementation of the precision-feeding protocol, heifers will likely vocalize immediately prior to feeding, with the frequency and magnitude increasing toward the next feeding. Experiences are that this behavior will diminish and virtually disappear 10 to 14 days after the implementation of the precision-feeding strategy. This is not unlike the transition that calves have from milk at weaning time. As long as the heifers are growing according to the ADG goals of your operation and receiving a correctly balanced ration, they are being adequately fed.
Precision-feeding heifers until 30 to 45 days before calving has had no adverse effects on calf birth weight, dystocia, metabolic problems, DMI of cows in early lactation, or first-lactation milk production. Any changes in rumen and gut volume when using this feeding system late in gestation have been shown to occur rapidly and do not limit postpartum DMI; therefore, milk production is the same for these heifers as compared to conventionally fed heifers.