How to calculate the UFL ?
To calculate the UFL, it is used a system of equations applied in estimating the net energy of forages.
Gross energy (EB) is determined indirectly based on the chemical composition:
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where PB, GB, CelB, SEN (g/kg DM) represents protein, fat, cellulose and extractive non-azotated substances resulted from the chemical analyzes and Ct = constant (depending on forage).
Digestible energy (ED) is determined by using the relationship:
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dE = energy digestibility
dE = 1.0087 dSO – 0.0377 (forages)
dE = dSO – 0.015 (concentrates)
dE = dSO – 0.020 (meal)
dE = dSO – 0.013 (cereals)
dSO = organic matter digestibility
Metabolizable energy (EM) is estimated by the relationship:
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CelBo = crude fiber (g / kg organic substance)
PBo = crude protein (g / kg organic substance)
NA = alimentation level which is given by the ratio between EM and EM needed for maintenance (1.7)
For determining the use efficiency of metabolizable energy for the milk production it is calculated the concentration of metabolizable energy of the forage.
q = EM/EB
Therefore, the efficiency for milk production is:
kl = 0.463 + 0.24 x q
The milk net energy (ENL) is calculated by applying the efficiency to the metabolizable energy.
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The energy content of forages, expressed in feed units for milk is:
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The amount of protein can be expressed in percentages or g of crude protein and digestible protein per kg of forage or kg of dry matter. Moreover, for ruminants the amount of protein is expressed in g digestible protein in the intestine per kg of DM and per kg of forage.
The amount of protein can be expressed in crude protein (PB) resulted after the chemical analysis, based on which it can be determined the digestible protein (PD) using the apparent digestibility coefficients (CD).
PD% = PB% x CD%
Protein value of forages used in dairy cows feed can be calculated using the PDI system (digested protein in the intestine).
It is now well recognized that crude protein or digestible crude protein are neither adequate or biologically sensible measures of the value of dietary protein for ruminants. The French protein (PDI) system is based on this concept and estimates the quantity of amino acids absorbed in the small intestine from the dietary protein undergraded in the rumen and microbial protein synthesized in the rumen.
The PDI system provides values for feedstuffs which reflects the true protein absorbed in the small intestine and it aims to balance the nitrogen and energy available in the rumen for microbial protein synthesis. This system, like other modern protein rationing systems, requires accurate measurement of the characteristics of feed protein degradation in the rumen.
The PDI system quantifies the two major factions of the protein reached in the small intestine:
1. PDIA – actually digestible protein in the intestine of food origin, which comes from the proteins in forages that were not digested in the rumen;
2. PDIM – actually digestible protein in the intestine of microbial origin.
Considering the two limiting factors of protein synthesis, the fermentable energy and the degradable protein, can distinguish two values of PDIM:
- PDIME – digestible protein in the intestine permitted by the fermentable energy content;
- PDIMN – digestible protein in the intestine allowed by the available degradable nitrogen content.
Feedstuffs are assigned two values, PDIN and PDIE.
- PDIE = true protein absorbable in the small intestine when rumen fermentable energy (organic matter) is limiting microbial protein synthesis in the rumen.
- PDIN = true protein absorbable in the small intestine when degradable N is limiting microbial protein synthesis in the rumen.
1. PDIN (g/kg DM) = PDIA + PDIMN
a) PDIA (g/kg DM) = PB (1 – DT) x 1.11 x dr
where: PB – crude protein (g/kg DM);
DT - protein theoretical degradability in the rumen (at concentrates 25-90%, at forages 60-80%);
1.11 –the proportion of the actual undigested nitrogen substances in the rumen, compared to the calculated one starting from DT;
dr - true digestibility of alimentary origin amino acids in the small intestine (on average, 80%, considering that the microbial protein is made in a proportion of about 80% from amino acids and about 20% from nucleic acids, and other nitrogen-based products, practically indigestible).
b) PDIMN (g/kg DM) = PB x [1 + 1.11 (1 – DT)] x 0.9 x 0.8 x 0.8
It is thought that microorganisms can capture about 90% of the alimentary degradable nitrogen, which serves to the manufacture of rumen microbial protein, that about 80% of it arrives in the intestines and has a true digestibility of 80%.
2. PDIE (g/kg DM) = PDIA + PDIME
PDIME (g/kg DM) = SOF x 0.145 x 0.8 x 0.8
SOF (g/kg DM) = SOD – PB (1 – DT) – GB - PF
where: SOF – fermentable organic matter (g/kg DM);
SOD – digestible organic matter (g/kg DM); (SO x CD) / 100; SO – organic matter (%); CD – digestibility coefficient (%);
GB – crude fat (g/kg DM);
PF – fermentation products from silages (g/kg DM).
It is thought that microorganisms synthesize, on average, 145 g of protein per kg of fermentable organic substance, with 80% content of amino acids and with 80% digestibility.
The mineral value is expressed by the content in main macroelements (g of calcium and phosphorus per kg of forage) and microelements (ppm).
The amount of vitamins is recommended to be expressed through the content of carotene (mg / kg) or through the vitamins A, D, E (international units).
