Introduction
Expression of values are used to show the nutrient requirements and nutrient values in feedstuffs. The total value of a feedstuff in practical nutrition depends on the following factors:
1. Energy content carbohydrates, fats, proteins & digestibility
2. Protein content including NPN and aspects of degradability
3. Nutrient density (digestibility) and structure value
4. Digestibility
5. Vitamin/mineral contents
6. Special aspects like keeping quality, taste, toxins, influence on milk colour/taste, availability, handling etc.
7. Physical aspects
8. Price
The expression of feed value for dairy cattle strictly speaking, however, is a measurement for energy content unit and the amount of protein, in Poland respectively in the values FUM units and gram DCP per kg (or kg DM) product *.
* Note: Recently, the Polish system for animal nutrition has been adjusted. The so-called “Jednostka Paszowa Produkcji Mleka” (JPM) is used for defining energy requirements and energy availabilities. JPM is based on the Nett Energy system and as such comparable with the FUM unit utilized in this course book.
For more information, it is referred to the book on animal nutrition (Polish edition) “_ywienie Prze_uwaczy”, published by Omnitech Press – Warsaw.
As mentioned in Chapter 1, the feed value (nutritive value) of food is contained in DM, the remainder of food being water. The DM is expressed as a percentage (%) or as gram per kg of food. For instance, the DM of grass is 15% equals 150 gram DM/kg grass. DM is very important to an animal as it is used to measure hunger or appetite (the amount of food an animal can eat per day). The daily amount of DM eaten per day is called Dry Matter Intake (DMI). The total composition of the daily ration should include all nutrients required necess- ary for maintenance and production purposes within the quantity of DM.
Throughout this paper, calculations will use expression of feed values per kg DM of a feedstuff. If one feedstuff is compared with another the same system should be applied, other- wise the results will be distorted!
3.1 Energy Content
One of the main functions of a dairy ration is to provide energy to an animal. The total energy of food coming free during combustion is called Gross Energy. Only a fraction is used for maintenance (including some milk production) and production. Utilization is reduced by losses of defecation, urination, methane gasses in the rumen and heat.
The term “energy” includes the actual physical energy an animal needs, the heat to maintain its body temperature, the energy required for production and the nutrients for laying down its own energy reserve. The constituents that provide energy are the carbohydrates, fats and possible proteins! If there is not enough energy from carbohydrates and fats in the food to meet its daily requirements, part of the available proteins is converted into energy-use.
Not all energy value fed can be utilized for production and maintenance. The portion available for maintenance and production is called Nett Energy (NE), usually expressed in Joules (KJ = 1,000 J, MJ = 1,000,000 J).
Figure 3.1 shows that the energy value is most accurate with Nett Energy. This is the energy effectively used by an animal and defined for its utilization purpose. In order to compare energy values amongst different foodstuffs, it is desirable to express the energy value in one kg (or 1,000 gram) DM (of kg) of one of the foodstuffs involved. The NE system requires precise knowledge of bodyweight, quality and quantity of feedstuffs fed and eaten by the ani- mals.
Values are expressed both on wet basis and DM basis. Care should be taken. For the purpose of calculation we use the values based on DM.
In Poland, energy requirements are expressed in FUM (Feed Units Milk)* per day:
FUM for cows is a figure indicating the amount of barley in grams which gives as much Nett Energy for milk production as 1 kg foodstuff.As a rough rule
A 600 kg cow producing 15 litre milk per day (4% fat) requires 11,913 FUM, for- maintenance 5013 FUM
– production of every 1 kg milk 460 FUM 15 * 460 = 6900 FUM
3.1.1 Major Energy Systems
The major energy systems in practical use for dairy production are:
1-Starch Equivalent
2-Total Digestible Nutrients(TDN)
3-Metabolizable Energy
4-Nett Energy
3.1.1.1 Starch Equivalent (SE)
This is an earlier system of NE utilization. The system is based on production of body fat and not on milk production. The conversion efficiency of energy varies for different feeding purposes (maintenance, growth, lactation). Therefore the SE system is outdated and not commonly used any more in dairy production.
3.1.1.2 Total Digestible Nutrients (TDN)
This system is based on an estimation of digestible energy (DE) with correction for losses in urine and methane. Calculated of TDN is as follows (in %):
TDN % = % DCP + % DCF + % DNFE + 2,25 * % DCEE with
DCP digestible crude protein
DCF digestible crude fibre
DNFE digestible nitrogen-free energy DCEE digestible crude ether extract
The TDN system is simple and practical. It works satisfactory under systems where nutrition factors are rather variable (amount, type and quality of food), body weights are roughly estimated, and milk production is below the genetic potential due to management, climate and/or infrastructure (health, breeding services). The TDN system fails to consider variation in efficiency amongst feedstuffs with which TDN is utilized (from ME to NE). It tends to over-estimate the value of low quality roughage. The TDN system is widely used in the world, special in developing countries. It is an excellent tool for providing guidelines for a sound animal nutrition policy for dairy farmers under given circumstances.
3.1.1.3 Metabolizable Energy (ME)
In some European countries, this system is replacing the previous SE system. The ME system is more accurate, but is only useful in situations where animals are producing at a maximum of their (genetic) capabilities and where all other aspects of nutrition are done very precisely with constant qualities and continuity. To determine food value is rather expensive and time consuming. Therefore, ME is frequently calculated as ME = 0.82 * DE (the factor for energy loss in urine and methane is considered to be fairly constant at 18% of DE).
3.1.1.4 Nett Energy (NE)
This system is an improvement version of the SE system. Different efficiencies for energy utilization of different purposes (maintenance, growth, lactation) are recognized. The NE system requires actual measurement per feedstuff, which is complicated and costly. The variation of 40-80% energy loss from ME into NE due to heat-increment prevents that NE values can be abstracted from TDN or ME. The NE system is very accurate and valuable in production systems where all other factors of nutrition are accurately controlled. In many dairy producing countries, Nett Energy values are adopted to units of lactation energy: USA (NE lactation), China (NND: dairy energy unit), Holland and Poland (FUM).