Protein Nutrition

Protein:

Crude Protein (CP)

Crude protein is defined as the basic protein content of a feed, it is calculated by determining the nitrogen content of a feed.

It is not really an accurate definition of the real protein content of that feed because it inevitably includes a proportion on Non-Protein-Nitrogen (NPN). It also assumes that the protein all contains 16% nitrogen. Therefore CP = Nitrogen content divided by 0.16 (or multiplied by 6.25).

Digestible Crude Protein (DCP)

Crude protein was never going to be a particularly reliable measurement of useful dietary protein. In some feed with low “Q” values, the digestibility of the protein was poor. In order to improve the reliability of dietary predictions the CP was multiplied by the “D” value to give the DCP.

Rumen Degradable Protein (RDP) / Undegradable Protein (UDP)

Unfortunately, the DCP measurement included a significant rogue element, Non Protein Nitrogen or NPN!

NPN can be used with variable efficiency in the rumen compared to true proteins. Rumen ammonia which is a form of NPN can give rise to high blood and milk urea’s if not managed properly.

In the 1970’s research suggested that dietary protein was:

• either broken down into ammonia (NH3) and carbon fragments in the rumen, and then used by the rumen microbes for protein synthesis. (making more rumen bugs)
• or it passed through the rumen undegraded and was then available for digestion in the abomasum and small intestines.

It took about a decade before this information could be usefully correlated into a coherent ration formulation system that truly represented an improvement on the old DCP system. Henceforth protein was either rumen degraded (RDP) or undegraded in the rumen (UDP).

The Metabolisable Protein System

Protein metabolism in the ruminant is another part of the science of animal nutrition which is still undergoing debate and change. Different countries are using different systems which is a pretty reliable indication that so far nobody has got it exactly right.

In 1992 the UK adopted the, “Metabolisable Protein” system (MP System) as a significant improvement on the older DCP and the RDP/UDP systems. 1n 2002 Feed into Milk (FiM) was launched as a further improvement to the MP system.

The reason for adopting the MP system concerned the fact that the degradability of the protein varied according to the rate at which it passed through the rumen. For example, high yielding Holsteins tended to have large intakes and more rapid throughput than low yielders and the rumen degradability of say soya protein could be as low as 40% in the high yielders but as high as 85% in the low yielders.

The method of determining a system that could be used to calculate the degradability of protein more accurately, involved dangling the food source in little porous bags made out of indigestible material, in the rumen for set periods of time.

Personally, I can’t imagine how bizarre this process would appear to the layman, but it certainly produced some very useful data indeed.

The resulting figures showed the rate at which the different proteins were being degraded.

The figures produced were tabulated originally as the A, B and C fractions but modern developments in the early part of the new millennium developed the definition of the A fraction and now we use S, A, B, and C, fractions.

S, fraction is protein which is released as soon as the feedstuff enters the rumen.

A, fraction is the protein that is not released as soon as the feed enters the rumen but is degraded before it leaves the rumen.

B, fraction is the rumen Bi-pass protein.

C, is the rumen outflow rate.

The scientists had to be able to use this data to predict animal performance from the different feedstuffs.

In order to do this, they had to work out some sort of measure of animal performance to gauge against the rumen outflow rate. They came up with “Animal Production Level” (APL).

This measurement is simply the total energy requirement of the animal divided by the energy needed for maintenance.

For example:-

The APL for the Holstein cow giving 35 Kilo’s of milk referred to on page 15, is as follows: –

Total ME requirement = 235.25 MJ

ME required for maintenance = 65.5 MJ

APL = 235.25 / 65.5 = 3.6

This figure of 3.6 can now be used to determine the relative degradability of the different protein sources in this cow. (around 8% per hour on the graph below.)

Figure 1

The relationship of APL to rumen outflow rate.

From this information it can be seen that an animal feeding at maintenance has a rumen outflow of 0.02 or 2% of its rumen contents per hour. this increases to about 10 % for dairy cows producing about 40 litres of milk. The graph is not very well supported by masses of trial work at this time, but it does seem to be a reasonably good measurement on which to base predictions.

Most of the nutrition models have used this principle but have then gone on to use their own correction factors, which explains why we don’t always get the same answers.

The RDP/UDP system assumed that the protein that was not degraded in the rumen, was digested in the small intestine, and the bit that wasn’t digested at all was a constant fraction of the protein

This system began to show its limitations when farmers found that some of the raw materials that they were using, notably Maize Gluten and Dry Distillers Grains, often failed to live up to expectation. This was because the protein had been denatured by heat during manufacture and handling and, after reacting with sugars, became insoluble, and indigestible in the small intestine.

As a rule of thumb, when purchasing products lie Maize Gluten, Distillers grains, and cereal bi-products, “The yellower, the better”.

The indigestible protein can be measured by determining the amount of Nitrogen in the Acid Detergent Fibre (or ADF for short). this is referred to as the “Acid Detergent Insoluble Nitrogen” (or ADIN for short).

ADIN can be converted into “Acid Detergent Insoluble Protein” (ADIP) quite simply. Once this has been done it is easy to see how much of the protein expressed in a feedstuff analysis will be wasted.

A graphic example of this wastage factor can be found in rape seed meal where up to about 10% of the protein can be ADIP and therefore wasted.

The MP system is more accurate than the old RDP / UDP system because it automatically deducts this ADIP from the total UDP. The remaining fraction of UDP is known as Digestible Undegradable Protein (DUDP) or (DUP).

The other main element of doubt in the RDP/UDP system was that the RDP didn’t all degrade at a constant rate. We have already seen that the protein can be split up into A, B, and C fractions.

The A fraction can vary from as low as 8% in soya to around 65% in grass silage. In the case of values as high as 65%, it is probable that the rumen microbes won’t be able to cope with all of the ammonia that is being released.

Ammonia is a very important feed nutrient for the rumen microbes. They can use it to build more microbes, as long as they have access to an energy source.

Ammonia can be absorbed into the blood stream through the rumen wall very easily, so it is important to supply enough rapidly available energy in order to use the ammonia before it is wasted.

Sugar is probably the best source of energy under theses circumstances, but it should be fed at a constant rate in order to avoid acidosis.

The resultant improvement in microbe population will serve to help animal productivity.

The yield of microbes is in effect supplying the animal with extra protein in a usable form. This is known as Microbial Protein (MCP).

Excess of ammonia, results in absorption into the blood stream as urea and is then excreted via the kidneys.

This element of waste can be very significant on high protein silages and on grass swards where animals graze soon after top dressing with nitrogen.

Good diets need to recognise this dilemma and provide the animal with better quality protein and/or, sugar to help the rumen microbes thrive in the potentially very rich nutrient source.

ERDP

There is just one last piece to the jigsaw of protein metabolism; “Effective Rumen Degradable Protein”

ERDP is a measure of the amount of RDP that is actually available for microbial metabolism and growth. The old RDP/UDP system assumed that all of the RDP was available.

In fact, some of the ammonia released from the “A” fraction of the protein, is absorbed across the rumen wall into the blood stream as urea.

This Blood Urea can be measured as “Blood Urea Nitrogen” (BUN) and has a relationship with infertility in the female ruminant. The BUN is normally filtered in the kidneys and excreted in the urine, but some is found in the milk of the lactating animal.

“Milk Urea Nitrogen” (MUN) is now commonly included on the milk data returned to the dairy farmer. High MUN levels are a good indication of dietary imbalance and potential infertility problems. Low MUN levels are usually indicative of a dietary under supply of protein.

The “S and A” protein fraction is roughly defined as: –

QDP (Quickly Degraded Protein)

SDP (Slowly Degraded Protein)

The ERDP is calculated as 80% of the QDP plus the SDP.

FiM

MPN (Metabolisable Protein from rumen Nitrogen)

This new measure effectively replaces ERDP it has to be said that it is a much improved measure since it makes a further distinction of the old ‘A’ fraction into ‘S’ and ‘A’ where S is instantly available and A is rapidly available.

There should never be more than 200 grams of MPN more than that of the MPE.

MPB (Metabolisable Protein from Bypass protein)

replaces DUP, essential in high yielding cow diets where demand increases dramatically, because the output of MPN is limiting.

If you have stuck with it so far, you have by now got a good grasp of the main elements of protein metabolism. Well done! Now go and have a break, when you come back have another look at what you have just read. Getting to grips with this bit of theory will help you with your decision making when you start to balance up your own diets.

It is important to try and understand the abbreviations because they are in extensive use in virtually all of the definitive works on the subject. Once you have got to grips with the reasoning behind the definitions, will be much easier to make sense out of diet sheets and feed analyses.

Protein Metabolism

The ruminant, like all animals, needs protein in the same way it needs energy, for Maintenance, Growth, Pregnancy, and Milk production.

As already mentioned, the FME/MPE is needed by the rumen microbes, to fix the ERDP/MPN in the form of microbial protein (MCP) and subsequently metabolisable protein (MP).

The FME/MPE content of the forage fraction of the diet, will have a direct influence over the amount and type of supplementation of energy and protein in the diet.

• Low FME/MPE forages will generally be low in ERDP/MPN and need heavy supplementation with high FME/MPE and high ERDP/MPN feedstuffs.
  In plain English, forages of poor quality with low sugar and protein, don’t supply the rumen bugs with enough fermentable nutrients to insure an optimum production of more rumen bugs. The rumen bugs are needed for digesting in the abomasum and small intestine. The bugs that are being digested are effectively the main source of nutrients (Food) for the cow, so most of the time we want to design rations that get the best possible production of rumen bugs.

High FME/MPE forages will require much less supplementation but tend to coincide with low NDF levels and, as a result may well need supplementing with fibre sources. In plain English, forages that are good quality and highly fermentable, tend to cause frenzied reproduction of the rumen bugs. A by-product of this activity is acid production. If there is too much acid being produced, the rumen can shut down while the animal cuds to produce the alkali saliva needed to neutralise the acidity. In extreme cases Rumen Acidosis can be fatal. So, we have to add some nice scratchy fibre to make sure that the animal can cud well enough to regulate the rumen acidity back up to a neutral Ph.

As a rule, Silages with high acid loading will need greater supplementation of both ERDP/MPN and FME/MPE from concentrates, (ie Soya bean meal and Sugar Beet Pulp).

Microbial Protein Synthesis.

I love this bit of ruminant nutrition because it is so critical to getting good performance out of all ruminant livestock.

Anything we do to bring about an increase in the synthesis of microbes in the rumen, effectively increases the supply of nutrients to the animal. Live and dead bugs entering the abomasum and hind gut are effectively the main proportion of nutrient supply to the animal.

The basic concept of effective ruminant nutrition necessary to supply the genetic potential of highly bred modern ruminants; relies fundamentally on optimising the fermentation output capability of the animal’s rumen.

The temptation on the part of some nutritionists to overload the animal with bypass proteins and energies in the misguided belief that they are able to some how meet the animals requirements more effectively; is frankly, an expensive way of trying to hide the inability they have to get the best performance out of the rumen.

The rules for optimising Microbial Crude Protein (MCP) output are in fact, really simple:-

If the supply of protein (Nitrogen) is too low, the MCP production = ERDP supply.

If the supply of energy is too low the MCP synthesis is proportional to the FME supply.

The yield of MCP per Megajoule of FME is called “Y”.

“Y” is variable and its value increases as production (APL) increases. (see table).

Figure 2

The relationship between APL and the yield of MCP per MJ of FME

The Metabolisable Protein (MP) System.

The AFRC 1992 concluded that the MP system should be adopted as standard practise for the UK Industry.

The representation in figure 3 below (AT Chamberlain & J M Wilkinson (1996)) is a good representation summary of how the system elements are related to each other.

Notes:-

• Q D P is 80% available to microbes.
• Q D P + S D P = ERDP.
• M C P production depends on availability of FME and the value of Y.
• Only 64% of M C P is absorbed.
• U D P consists of indigestible waste (A D I P) and digestible Bypass protein (D U P).
• D U P varies according to A P L (the higher the A P L; the faster the rumen outflow rate, the greater the D U P fraction, and the smaller the ERDP fraction of any given feedstuff).
• 90% of D U P is absorbed.
• Higher A P L = Higher F C E.
• Metabolisable protein is eventually converted into Net Protein (NP). The efficiency of conversion varies according to the final use.

Figure 3

The metabolic pathways of protein utilisation

The figures shown for each end use represent the relative efficiency of conversion of each metabolic pathway.

The Metabolisable Protein system is a big improvement on the old Digestible Crude Protein (DCP) system but, it has its limitations.

• It is not very likely that the efficiency of uptake of Q D P will always be 80%.
• Nutritional data for many feeds is still incomplete.
• ADIN tests are very easily corrupted by nitrogen from the detergent, although laboratories have improved their techniques considerably.
• FME availability is likely to vary with rumen outflow rates, so high AP levels are likely to suffer from lower than expected FME levels. I have certainly found this to be true in very high yielding herds and fast growing livestock. The assumption that FME evaluation is a fixed figure is probably wide of the mark in these situations. The FiM MPE figure seems to be much more accurate since it takes better account of relative speed of fermentation and rumen outflow rates.

These areas of concern mean that the practical use of the system is still one that is open to a deal of subjective interpretation (artistic license).

I personally favour the increase in use of sugar sources in many “complete” diets in order to get over the “normal” shortfall in FME. I also tend to lead feed energy and protein by up to 8% in high output situations.

It is difficult to imagine how we can progress much from this, or even the FiM systems of rationing when feedstuff variability and hence analytical confidence in feedstuff nutrient composition, means that any development in the accuracy of the rationing system will be diluted by the questionable nature of the data being used, so I think there is a real need to be subjective when evaluating feedstuffs. Realistic interpretation of silage analysis is especially important if we stand any chance of building a reliable ration from any of the current models in use.

Protein Requirement Tables

Note the tables 12,13, and 14; below show the ARFC 1992 standard calculated requirements for cows, (see Appendix 1 a to 1 f for sheep). The values shown are additive.

ie: – Take the values for maintenance, growth, and lactation and add the sum of these values to derive the total MP requirement.

Table 12
Protein requirements for maintenance (g/day)(AFRC, 1992)

Relationship between Weight (kg) and Protein Requirement (MP)
Kg	MP	Kg	MP	Kg	MP
400	216	550	275	650	312
410	220	520	264	650	312
420	225	530	267	660	315
430	229	540	271	670	319
440	232	560	279	680	322
450	236	570	282	690	326
460	240	580	286	700	329
470	244	590	290	710	333
480	248	600	293	720	336
490	252	610	297	730	340
500	256	620	301	740	343
510	260	630	304	750	347
		640	308

Note:-1 Values do not vary in theory, but will in practise be approximate due to the effects of “Q” values and APL.

Note:-2 Requirements for growing stock are noted in chapter 6

Table 13
Protein (MP) requirements for weight change (g/day) (AFRC, 1992)

Weight Change	MP
-1.50	– 197
-1.25	– 164
-1.00	– 131
-0.75	– 98
-0.50	– 66
-0.25	– 33
0.00	0
0.25	61
0.50	122
0.75	183
1.00	245
1.25	306
1.50	367

Table 14 shows in bold print the metabolisable protein requirements for standard 3.3% milk protein production.

Table 14
Protein (MP) requirements for lactation (g/day) (AFRC, 1992)

Milk Protein (%/L)
Yield (L)	2.8	2.9	3.0	3.1	3.2	3.3	3.4	3.5	3.6	3.7	3.8
2	80	83	85	88	91	94	97	100	103	105	108
4	160	165	171	177	182	188	194	199	205	211	217
6	239	248	256	265	274	282	291	299	308	316	325
8	319	331	342	353	365	376	387	399	410	422	433
10	399	413	427	442	456	470	484	499	527	527	541
12	479	496	513	530	547	564	581	598	615	633	650
14	558	578	598	618	638	658	678	698	718	738	758
16	638	661	684	707	729	752	775	798	821	843	866
18	718	744	769	795	821	846	872	897	923	949	974
20	798	826	855	883	912	940	969	997	1026	1054	1083
22	878	909	940	972	1003	1034	1066	1097	1128	1160	1191
24	957	992	1026	1060	1094	1128	1162	1197	1231	1265	1299
26	1037	1074	1111	1148	1185	1222	1259	1296	1333	1370	1407
28	1117	1157	1197	1237	1276	1316	1356	1396	1436	1476	1516
30	1197	1239	1282	1325	1368	1410	1453	1496	1539	1581	1624
32	1276	1322	1368	1413	1459	1504	1550	1596	1641	1687	1732
34	1356	1405	1453	1502	1550	1598	1647	1695	1744	1792	1841
36	1436	1487	1539	1590	1641	1692	1744	1795	1846	1898	1949
38	1516	1570	1624	1678	1732	1786	1841	1895	1949	2003	2057
40	1596	1653	1710	1766	1823	1880	1937	1994	2051	2108	2165
42	1675	1735	1795	1855	1915	1974	2034	2094	2154	2214	2274
44	1755	1818	1880	1943	2006	2068	2131	2194	2257	2319	2382
46	1835	1900	1966	2031	2097	2163	2228	2294	2359	2425	2490
48	1915	1983	2051	2120	2188	2257	2325	2393	2462	2530	2598
50	1994	2066	2137	2208	2279	2351	2422	2493	2564	2635	2707
52	2074	2148	2222	2296	2371	2445	2519	2593	2667	2741	2815
54	2154	2231	2308	2385	2462	2539	2616	2692	2769	2846	2923
56	2234	2314	2393	2473	2553	2633	2712	2792	2872	2952	3032
58	2314	2396	2479	2561	2644	2727	2809	2892	2975	3057	3140
60	2393	2479	2564	2650	2735	2821	2906	2992	3077	3163	3248

Balancing Protein Sources

Most feedstuffs contain some form of protein, the exception being the inorganic mineral sources.

As we have seen already, there are basically two types of protein, Effective Rumen Degradable Protein (ERDP){FiM MPN}, and Digestible rumen Undegradable Protein (DUDP){FiM MPB}(or bypass protein). Both types of protein are very important.

ERDP

ERDP/MPN is commonly sourced from forages. Spring grass, for example can contain as much as 93% of its protein as ERDP/MPN! This percentage deteriorates as the season progresses, but even mid summer grass is typically 85% ERDP/MPN.

The evolution of the rumen was designed to produce microbial protein by allowing the rumen bugs to multiply. This they do by using the ERDP/MPN from feedstuffs along with the fermentable energy from the same feeds.

It is important to make sure that diets contain enough ERDP/MPN to keep the rumen bugs reproducing at the optimum rate.

For sheep fed on grass this is not usually a problem but sometimes dairy and beef animals fed on straw, wholecrop, or maize silage based diets, may be deprived of ERDP/MPN from the basic forages.

In these cases it is very important to introduce protein feeds rich in ERDP/MPN.

This is not always easy since many protein supplements also contain good levels of DUDP/MPB, and whilst the overall supply may be good it is vital that the rumen bugs get enough ERDP/MPN and that money is not wasted by feeding more DUDP/MPB than is required.

DUDP/MPB

DUDP/MPB is usually only needed as a supplement in very high output systems. Ewes at lambing and just after, will benefit considerably from inclusions of up to 25% of their protein as DUDP/MPB.

Lamb and calf creeps should also include DUDP/MPB at around 20%.

High yielding dairy cows may need as much as 37% of their dietary protein as DUDP/MPB.

The DUDP/MPB fraction of the protein is coincidentally the portion that tends to contain the richest sources of essential, and in some cases, performance limiting amino acids. Diets may well be balance for ERDP/MPN and DUDP/MPB but sometimes they are limited in performance by lack of amino acids like lysine or methionine. Amino acid balancing, is a growing part of ruminant nutrition, especially in pedigree, high output diet situations.

Rationing Tips

• Ewes only require DUDP/MPB supplementation if they are carrying twins or triplets near to lambing and just after. The addition of 50 grams of high quality fish meal (currently banned), Prairie meal or protected soya meal, is tremendously effective. Trials at the Rowett Research Institute in the mid 1980’s showed a marked improvement in colostrum quality and milk yield from ewes that were fed on fish meal.
• The UK ban on feeding fish meal to ruminants is unfortunate since it is difficult to source equivalent products. Some fish meal replacers are getting quite close but few are as good as the real thing.
• Dry cow rations benefit from the addition of around 500 to 600 grams of protected soya meal from 3 weeks before calving. This is believed to assist the animal to mobilise some of its back fat prior to calving and improve colostrum yield and quality. It has also been shown that animals come into milk production much faster and are generally easier to get back in calf. The effect is similar to the supplementation of fish meal in sheep diets.
• Animals fed on low protein forages may be supplemented with Non Protein Nitrogen from feed grade Urea. This source of nitrogen can be converted by the rumen bugs into microbial protein, in the presence of water and a suitable energy source, like molasses. It is now possible to buy ready mixed molassed urea supplements. These supplements are a safe option because they contain a regulated slow release formula that prevents a rapid build up of ammonia in the rumen.
• Feeding urea on its own has to be done very carefully indeed since it is very easy to induce serious health problems arising from excessive absorption of ammonia into the blood stream. Sheep have died from inclusions of as little as 8.5g per day and yet others can thrive on as much as 50 g per day. Unfortunately. it is not possible to prescribe accurate limits for any animal.
• The little table below shows the desired ratios of ERDP/MPN to DUP/MPB in various ruminant diet situations expressed as percentages.

	ERDP/MPN	DUP/MPB
Ewe 6 weeks to lambing	90%	10%
Ewe 2 weeks to lambing	85%	15%
Pedigree lowland ewe 2 weeks to lambing (twins)	80%	20%
Ewe 2 weeks after lambing	80%	20%
Ewe at weaning	85%	15%
High yield dairy cow (40 litres)	65%	35%
Mid yield dairy cow (25 litres)	75%	25%
Late yield dairy cow (12 litres)	85%	15%
Dry cow 3 weeks to calving	80%	20%
Lamb or Calf 5 weeks of age	80%	20%
Heifer 15 months	85%	15%
Intensive bull beef 8 months	85%	15%

Like most raw materials, buying proteins should be very carefully undertaken. The following points should be considered:

1. How much, and what quality of protein exists in the forages that need balancing? Have you had the forages analysed?
2. Is the price of bought in protein supplements representative of good value for money? What is the cost per tonne of dry matter, of any potential supplement compared to other feeds? This helps to put the price of succulents like Brewers grains and Distillers draft into perspective.
3. What is the protein quality like? DCP, ERDP/MPN, DUP/MPB, ……..
4. Is there a particular benefit from any essential amino acids? Lysine, Methionine, Leucine….
5. How will the bought in feed need to be stored and fed?
6. Is the feedstuff traceable back to source? Modern feed systems should be able to trace all feedstuffs back to origin. This is a growing requirement of UK buyers and is true of all bought in feedstuffs not just proteins. The current UFAS approval scheme is growing in its popularity as a trade coordinated quality and traceability standard demanded by agricultural livestock product customers.