Updated Nutrient Specifications for the Dairy Herd

Author: Charles C. Stallings, Extension Dairy Scientist, Nutrition, Virginia Tech

Publication Number 404-105, June 1996


Table of Contents

Introduction
Growing Dairy Heifers
Dry Cows
Lactating Cows

Introduction

Nutrient requirements are periodically updated as new information becomes available. The last NRC publication for dairy cattle was printed in 1989. That publication did a good job of addressing some of the previous criticism about appropriateness of requirements under field conditions. With a few exceptions, what was proposed in 1989 is still acceptable today. However, some modification may be appropriate.

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Growing Dairy Heifers

We have been stressing the desirability of having first calf heifers calve at less than 26 months of age. Some dairymen have been resistant to this because they felt that young heifers did not do well during their first lactation relative to older heifers. One of the keys to making the system work is getting the heifer to calve at an acceptable size (at least 1200 lbs. for large breed heifers and 800 for small breeds). This is weight after the calf is born. Heifers that reach this size generally do well and have the ability to peak at 70 or more lbs. of milk per day. In order to do this, Holsteins must average about 1.7 lbs. gain/day and Jerseys 1.2 lbs. after weaning.

Table 1 contains requirements for three ages of heifers. The 3-6 month group needs more nutrients per pound of feed than the 6-12 and 12 and older groups. Younger heifers consume less feed, so the nutrient density needs to be higher. Protein required drops from 16% for the young calf to 12% for the older heifers. Virginia Tech research suggests that energy content of diets for a given rate of gain should be adjusted according to housing and environmental conditions. Heifers reared in confinement housing, such as the Virginia Countersloped barn, require 10-20% less energy. Adjust pounds of grain fed per day based on observed gain. Notice that calcium and phosphorus concentration declines as the heifer gets older, but the other minerals do not change with age. Part of this is due to a lack of information about the requirements for some of these nutrients, especially the microminerals. The vitamins are expressed as amounts (International Units) and not concentration, and they actually increase as the heifer gets older. This would be true for all of the other nutrients if actual quantity was expressed instead of concentration. These tables of nutrient requirements for heifer growth are suggestions and represent nutrients required under optimal conditions. During cold, wet weather, energy requirements increase. Similarly, heifers heavily infected with intestinal parasites require higher levels of nutrients.

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Dry Cows

Dry cow requirements are to maintain the cow plus fetal growth plus some weight gain. The range in energy is to accommodate situations where some body condition restoration is needed during the dry period. Indications are that .25 to .5 body condition units can be put on during the dry period with little adverse effect. The requirements for energy are higher than NRC in an attempt to ensure acceptable condition at calving. The other nutrients are similar to NRC except vitamin E, which has a range up to 1000 IU's, a level that has been associated with improved udder health and reduced somatic cell counts. Close-up dry cows, cows in the last 2 to 3 weeks of the dry period, usually are placed on a transition ration that contains more nutrients than would be in a ration for the far-off cows. Energy would be at the upper end of the suggested range and fiber at the lower end. Sometimes protein is also increased as more supplement is fed. If anionic salts are fed calcium is many times increased to levels greater than suggested in the table. Calcium at 1.4% of the dry matter ration has been proposed as desirable when anionic salts are fed to the close-up dry cows. Care should be taken when using these salts because of palatability problems and the elevated calcium.

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Lactating Cows

The lactating cows are categorized by production group within the herd. The high production group would be those top producers in the herd plus most cows less than 90 days in milk. A range is given in order to adjust for production of the herd. Lower producing herds wouldn't need as much as higher producing herds, because cows are not milking at as high a level. The higher producers will many times be fed fat and, therefore, the calcium should be .9-1% and magnesium .30%. Requirements for potassium, sulfur, iron, copper, manganese, and zinc have been increased above NRC for the top production group.

First calf heifers should be given special consideration and remain in the top group to a lower production level than older cows. In other words, if older cows are moved out of the top group at 80 lbs. of milk, first calf heifers might be moved at 70 lbs. because body weight is less and they have less ability to consume feed. Therefore, they need a more nutrient dense ration. Not too many herds in Virginia contain three production groups. Most usually have two groups. In this case, the middle group specifications would be appropriate for the low group. The low group's specifications would only be appropriate with cows in the final few months of gestation, producing less than 50 lbs. of milk. Herds that are capable of having three groups will often have a high production group composed only of older cows and a separate heifer group. Both groups would be fed the high group ration. The third group would be compatible with the middle group specs. The goal is to prevent extreme changes in nutrient concentration when switching groups. This minimizes the reduction in milk when switching groups.

Table 2 contains some terms nutritionists consider when attempting to balance the ration for rumen available carbohydrates and protein. Nonfiber carbohydrates are our best indication of the carbohydrates that are available for fermentation in the rumen. In most rations much of this fraction would be starch, primarily from grains and corn silage. Notice that the table is broken into three columns by days in milk. This corresponds to production groups similar to those in Table 1 . At the nonfiber carbohydrate levels indicated, there should be adequate energy for the rumen to produce adequate microbial protein.

Protein is divided into that which is undegradable and degradable in the rumen. These two must add up to 100%. Generally, higher production warrants higher concentration of undegradable protein. Not all the research supports this idea and it is still uncertain when a response is expected. However, many nutritionists are recommending a source of rumen resistant protein in rations for high producing cows. Neither undegradable or degradable protein can be measured with a laboratory test. Therefore, book or average values are used, making this aspect of nutrition as much art as science. A recommendation is to have half of the degradable protein as soluble. Soluble protein indicates the amount of degradable protein that is rapidly degraded in the rumen and is easily mesured in the laboratory.

Recommendations will certainly change as we learn more. Also, as cows increase in production, requirements will be modified. A recent list in The Virginia Dairyman had six Virginia herds above 25,000 lbs. milk per cow. Certainly, they are pushing our ability to provide requirements appropriate for their level of production.

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