CONCENTRATE SUPPLEM ENTS
2.4 DISCUSSION;
The concentration of total ruminal nitrogen in the sheep maintained on hay (7.7$ crude protein) was 40.8 + 3*8 mg/lOO ml.
This value is in very good agreement with the value of 40.6 mg/lOO ml obtained by .Elliott and Topps (
1964
) who maintained Persian wethers onUNIVERSITY OF IBADAN LIBRARY
86
a mixture of hay (8$ crude protein). Supplementation of hay with cassava flour-based concentrate significantly reduced (B-C0.05) the to.tal ruminal nitrogen to 29.9 + 2.5 mg/lOO ml. This value is jet however slightly lower than 34.4 mg/lOO ml obtained by Elliot and Topps (1964) for a cassava flour-based ration. They showed that the total ruminal nitrogen was correlated with the crude protein content of the diet. Their values of 49»9> 92.0 and 99.3 mg/lOO ml are higher than the present reported, values of 44.8, 68.4 and 78.2 mg/lOO ml in sheep maintained on rations G, D
and E, similar to their low roughage rations. Both this present report and that of Elliott and Topps (1964) showed that maximum level of
total ruminal nitrogen occurred about 1 hour after feeding. The unusually high variability associated with the N content of samples of the rumen liquor from sheep given low-roughage diets observed by Elliott and Topps (
1964
) was not observed in the present work as the mean differences were not significant within animals ( P > 0.05) or between periods (p> 0.05). No sharp increases wore observed in thetotal nitrogen concentration even in the sheep receiving the suplement of the highest crude protein content between 1 and 2 hours after
feeding, but there were sharp decreases three hours after feeding.
The concentration of ruminal protein nitrogen, 29.4 + 2.4 and 21.7 i. 1.5 for rations
A
and B respectively were higher than 19.8 andUNIVERSITY OF IBADAN LIBRARY
l~.l mg/lOO ml obtained, for
#
cassava flour-based rations by Elliott and Topps (1964) but the values of 31.5 + 4.4, 50.6 + 2.8 and 55.9 + 1.8 for rations C, D and E respectively are comparable to29.0,
59.1 and59.3 obtained by these investigators.
There seemed to be no difference in the percentage of N as protein in the rumen liquor which varied from 64.6$ with ration F to 73,1$ with ration B. These values are higher than 45 - 65$ obtained by Elliott and Topps (
1964
). They found that percentage of N as protein was negatively correlated with levels of ammonia. No such correlation was observed in the present investigation. Protein-N in the rumen may be derived from feed, bacteria or prcrfcoaoa. Weller, Gray and Pilgrim (1958) using Di-aminopimelie acid as marker for bacterial protein showed that bacterial protein formed 46$, protozoal 21$ and feed 26$ of ruminal nitrogen. Freitag et _q^L. (1970) using the same indicator showed that the amount of bacterial protein in the rumen fluid was affected by the dietary nitrogen source.Th^jShowed that bacterial protein formed 99$ of the rumen fluid protein 7 hours after feeding urea-supplemented ration, the corresponding value for cotton seed meal - supplemented diet was 71$. The rations used in the present investigation contained groundnut meal as source of protein apart from that Bupplied by the basal hay. The presence of readily fermentable carbohydrates such as cassava flour and molasses enhanced rapid microbial growth. It is therefore reasonable to assume
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88
that a greater percentage of ruminal protein-N would be microbial proteins.
The non-protein fraction (NPN) of rumen liquor is made up of amines, amino acids, ammonia and peptides (McDonald, 1948).
The concentration of Mon-protein nitrogen was highest 1 or 2 hours after feeding and declined 3 hours after. Annison (1956) showed that casein and groundnut meal were rapdily degraded in the rumen with the formation of non-protein nitrogenous substances. The failure to observe a rapid increase in non-protein nitrogen was due to the presence of readily fermentable cassava flour in the rations, which is in line with the well established observation that the utilization of Non-protein nitrogen is improved when fermentable carbohydrates are also present. Only with ration F containing the highest level of crude protein was an appreciably
lsLffa.
level of non-protein nitrogen obtained. It may be that in this ration, the rate of. proteolysis of dietary protein was greater than the rate of assimilation of the non-protein substances formed.The supplementation of hay with cassava flour caused a very significant (P 4L O.Ol) depression in ruminal ammonia -N. This is in agreement with the findings of Chalmers and Synge (1954)*- that addition of starch greatly depressed ruminal ammonia production. When rations B to F were fed to the sheep, ruminal amonia concentration increased with increasing dietary nitrogen intake and percentage of crude protein
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in the rations. This is in agreement with the results of Elliott and Topps (1964). Ruminal ammonia concentration was highly correlated (r = 0.9l) with concentration of non-protein in rumen liquor, which shows that ammonia was obtained by hydrolysis of non-protein
substances. Elliott and Topps's (
1964
) value of 5*9 mg/lOO ml. is higher than 4.7 mg/lOO ml obtained for ration A but their value of 1.3 mg/lOO ml was in very good agreement with present report of 1.2 mg/lOO ml for ration A. However, their values of 2.1, 5.2 and 9.7 mg/lOO ml are higher than the values of 1.8, 2.4 and 3*8 mg/lOO ml obtained in the present investigation. In any case, their rations contained less fermentable carbohydrate than those used in the present experiment.The highest level of ruminal ammonia nitrogen occurred 1 or 2 hours after feeding. No sharp decline was observed in their levels and this is attributable to efficient fixation of ruminal ammonia by ruminal microbial population (Chalmers and Synge, 1954). The high correlation (r = 0.99) between rumminal ammonia nitrogen and ruminal
X - amino nitrogen indicates that both metabolites are dependent and were probably formed from the non-protein nitrogen fx*action of the rumen liquor.
The relatively high levels of ammonia -N in the rumen of sheep maintained on only hay may be due to the fact that nitrogen in the
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90
form of urea and. mucoprotein was added to the rumen by the saliva and the degradation of these produced high levels of ammonia. This would tend to remain high as microbial protein synthesis would be
restricted by a deficiency of available carbohydrate in the ration.
The percentage of total nitrogen in the rumen liquor present in the ammoniacal form was very high in animals given hay (ll.7 ± 1.5)
«
and this was depressed to 3«1 + 1.5$ when cassava flour was given as supplement. For the concentrate-based rations, there were no
differences between the rations even though the tendency was for the percentage to increase with increasing crude protein intake or as total nitrogen in rumen liquor increased. These observations agree with the results of Elliott and Topps (1964). Low levels of ammonia-N
(4.39 ± 1.59) as percentage total nitrogen even on ration F showed that very little ammonia-N accummulated in the rumen which could subsequently be lost from the rumen; it indicates efficient utilization of the protein contents of the rations.
Ruminal residual nitrogen, also known as the Non— protein non-ammonia nitrogen, comprises mainly peptides and low levels of
-amino acids, and amines. Residual nitrogen was low on all rations except on ration F. The mean values for rations A and B, 6.8 and
7.1 mg/lOO ml, were lower than those obtained by Elliott and Topps (1964), which were 14.9 and 12.8 ng/100 ml respectively. Similarly,
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the values obtained for rations C, D and B which are 11.6, 15*2 and 18.7 were lower than 18.8, 27.7 and 30.3 mg/lOO ml obtained by the same investigators. Only on ration F (40.2 + 9»l) were high levels of residual nitrogen observed.
The residual nitrogen as a percentage of non-protein nitrogen was lower (52.0 +
8
.3
) with ration A than with other rations (79 -Q&/°)
although there were no significant differences ( P > 0.05). This is due to the relatively high levels of ammonia in the rumen of hay-fed animals. Elliott and Topps (
1964
) and Moore and King (1958) showed that an increase in ammonia concentration in the rumen was accompanied by a decrease in residual nitrogen.The supplementation of hay with cassava flour significantly depressed the levels ofp<-amino nitrogen in the rumen. This is in agreement with the results of Chalmers and Synge (1954)» Annison (1956) and Leibholz (1969). For concentrate-based rations, the levels of
o(-amino nitrogen increased with dietary nitrogen intake, percentage crude protein in the ration, and levels of ruminal total N and
non-protein nitrogen. This is in agreement with the reports of Annison (1956) who also showed that though proteins were almost certainly
converted into amino acids before degradation to ammonia, the concen
tration of free amino acids was usually low presumably because of their rapid uptake or degradation. There was a high correlation between ruminal ammonia and 0^-amino nitrogen (r = 0.99)# and also between
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92
Nonprotein nitrogen and 3(-amino nitrogen (r = 0*95)* These results agree with those of iinnison (1956) who showed that increases in
ammonia concentration followed similar increases in the concentration of o(-amino nitrogen. He also showed that the increase in the
concentration cf free o^-amino N in the rumen immediately after feeding were largely due to the presence of free <>(— amino N and labile amide N in the feeds.
The marked depression of ruminal ammonia observed when hay was supplemented with cassava flour was also observed in the case of blood urea nitrogen, and this is in agreement with the results of Lewis (1957) who found that changes in ruminal ammonia concentration resulted in similar changes in the blood urea levels. Increase in the concentration of blood urea was observed with increasing intake of dietary protein, and also with the increasing percentage of crude protein in rations B to F. Preston, Schnakenberg and Pfander (1965) obtained high correlation (r = 0.986) between nitrogen intake per metabolic size and blood urea nitrogen. Similarly, Wallace, Knox and Hyder (1970) obtained 0.92, 0.92 and 0.77 as the correlation coef- icients between blood urea and N intake, digestible N and retained N respectively. The value of r = 0.99 also obtained in the present experiment between blood urea and ruminal ammonia N is high and shows that the regression equation could be used to estimate the blood urea levels at varying concentrations of ruminal ammonia nitrogen
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for the rations used in the present experiment.
Preston ej; al#(l965) suggested that blood urea nitrogen levels could be used to assess protein utilization in lambs. Certain difficulties, however, make this almost impossible. From their
results, they showed that blood urea nitrogen in excess of 10 mg/lOO ml would indicate adequate protein intake in their ration. It is however, not correct to state that lower levels of blood urea nitrogen
necessarily indicate poor nitrogen intake, for factors such as
/ breed, age of animal and percentage of readily fermentable energy in the rations influence blood urea nitrogen levels. However, when the ration is defined, their suggestion could be useful. In the present report, even at the maximum N intake of 1.55 g/day/w
the level of blood urea nitrogen was still relatively low (4.9 mg/lOO ml).
Blood urea levels can be used to assess utilization of dietary protein especially of herbage. High protein herbages are likely to give rise to high levels of ruminal ammonia and subsequently high blood urea levels, which in turn would increase urinary urea excretion
(Coccimano and Lfcng, 1967). The low values of blood urea nitrogen in the present report would them be interpreted to mean that the dietary N were being efficiently utilized. This is supported by very low urinary excretion even on the ration of highest concentra
tion of crude protein. The low levels of blood urea can also show
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94
that an appreciable amount of it was being recycled to the rumen and utilized there.
The results of Weller jet al# (1958) and Freitafi\et a l v(l970) showed that appreciable amoung of nitrogen presented at the abomasum is of microbial origin. The values ranged from 74
7°
by Weller _et al.(1958) with a ration of hay to 99$ by Freitag et j^l. (1970) with urea-based ration. It is therefore essential to know the amino acid composition of microbial protein especially as dietary protein is being replaced by non-protein compounds in ruminant nutrition. The biological value of ruminal bacteria and protozoa wore 81 and 80$
respectively and true digestibility were 74 and 91$ for ruminal bacteri and protozoa respectively (McNaught et al, 1954).
The present report has shown that of the essential amino acids determined, histidine and methionine were present in very low
concentration in bacterial protein. This is similar to the report of Bergen, e_t al.(l968) who also obtained low levels of these two amino acids. However, the value of 1.95 g/lOO g amino acids obtained by these investigators for histidine is much higher than the present value of 0.79g/l00g amino acids obtained in this experiment. The lysine value of li.60g/l00g amino acid obtained in
, , in
the present studies is/jrery good agreement with that determined by Ahde King and Engel (1964) but much higher than that reported by Bergen £t al, (1968). The concentrations of tyrosine and phenylalanine
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reported in the present report were lower than those of Bergen e4 ,al*
(1968) and Abdo et al.(l964)«
Similarly for ruminal protozoal protein, the amino acids
present in lowest concentration are methionine (0»87g/l00g AA^-and histidine (l.05 g/lOOg Amino acids) and were both lower than the result of
Bergen et al (1964)- Prom these results, it appears that histidine and methionine present in least concentration might limit the
utilization of microbial protein.
The amino acid composition of microbial protein can only give an estimation of limiting amino acids but it can not -per se be assumed to limit the efficient utilization of dietary protein, Bergen e_t _gl.
(1968a) therefore used the plasma amino acid score (PAA-S) method of McLaughlan (
1964
) and the restricted feeding regimen of rats with10$ protein rations to determine the limiting amino acid of microbial protein. They found that for rumen protozoal protein, histidine was the limiting amino acid. The plasma levels of free histidine in rats fed protozoal protein-based diets for ten days were extremely low, indicating that this acid was most limiting. They found that the limiting amino acid in bacterial protein was oystine, whereas arginine and histidine were the next two least available amino acids.
Purser (1970) showed that pepsin was ineffective in releasing
arginine from protozoal and bacterial proteins, and this could account for its low concentration in the blood plasma of rats fed microbial proteins
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96
Land and Virtanen (1959) using labelled ammonium nitrate
as major source of nitrogen for lactating goats observed that histidine was very weakly labelled of the amino acids of milk.
They suggested that this may be due to the incapability of the ruminal bacteria to synthesize the imidazole ring. Cystino was also weakly labelled. Loosli and Harris (1945) suggested that the low level of methionine in microbial protein may be due to slow rate of synthesis in the rumen. Prom these results, it is likely that the limiting amino acids of microbial protein are histidine
,
oystine, methionine, and arginine.Though the present investigations are comparable to those of Bergen_et al. (1968), it must be emphasized that the method of pre
paration of bacterial and protozoal specimens may have brought about the differences observed in the results.
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3. ISOTOPIC STUDIES OF N I T R O G E N M E T A B O L I S M IN T H E WEST AFRICAN