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4 of Crial 2 reflects the higher intake of highly digestible
concentrate fraction during periods 2 to 4 than in period 1 (.Robinson and Forbes (1970).
Similarly, supplementation of the basal hay (7.7$ crude protein) with the concentrate (C-j) did not significantly affect its digestibility. Campbell, Sherrod and Ishizaki (1969) found that supplementation of Kikuyu grass (Pennisoturn Clandestinum).
coefficient of hay nitrogen with energy supplementation in the present report nay he due to rapid multiplication of ruminal micro— organisms and hence slightly letter digestibility of the
• »
hay. It is however likely that with very poor quality hay supplenentation with energy would lead to increased netabolic faecal nitrogen mainly of microbial origin.
In Trial 2, the digestibility of dietary nitrogen increased with increasing levels of dietary crude protein, and also with crude protein intake. This is in agreement with the reports of Robinson and Forbes (1970) and Andrews and 0rskov (1970a) who
also reported increased digestibility of dietary crude protein with increasing levels of crude protein in the rations, and also with increasing intake of crude protein. This indicates decreasing quantitative importance of the netabolic faecal nitrogen with increasing crude protein content of the ration.
The regression equation relating digestibility coefficient of nitrogen and percent crude protein in the rations (Eq. 4.7) would give higher values for corresponding dietary crude protein, than that of French, G lo v er and Duthie (1957) shown as follow:
Y = 73.7 log X - 19.8 ... ... ...(4,25) Y = 70. 3 l o g X - 14.9 ... . . . . ( 4 , 2 6 )
for nixed food and herbage plus nixed feed respectively. Because of the costs and labour of conducting classical digestibility experi
ments, attempts have been made to derive correlations between
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digestible nutrients available to the animal and the crude dietary components from which they are derived, Such regression equation as given in the present studies has several practical applications, one being the determination of the average digestibility of crude protein of rapidly growing grasses and herbages at different stages of development, another being the evaluation of average crude
protein digestibility of single or compound feeds especially where adequate facilities are not available. It can also be used for computing maintenance find production rations. The digestibility coefficient of nitrogen is not dependent only on the crude protein
content of concentrate but also on the percentage of concentrate in the ration. It has already been shown in Equation 4.9 that total digestibility of a ration increases with increase in
percentage crude protein of supplemental concentrate but tends to decrease as the proportion of concentrate increases. The tendency for digestibility of nitrogen to decrease as percentage of
concentrate increases is due to increased metabolic faecal losses that accompany supplementation with concentrate especially at low nitrogen intake.
The lower digestibility of nitrogen in period 1 than in
periods 2, 3 end 4 may be due to lower intake of the highly digestible concentrate fraction of the ration in period 1, compared with
periods 2 to 4.
Hie values of true digestibility obtained by regression and detergent methods are in very good agreement showing that the true
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digestibility of dietary nitrogen is between 86 and 92$. The value obtained from regression equation wore between 86' and 8 9 $ and those from the detergent method were from 89 to 96%. The higher value obtained from the detergent method is as expected in view of the possibility of extracting fron tlx.- faeces other nitrogenous
materials which are neither microbial nor endogenous, but dietary, and this would tend to increase the non-dietary faecal nitrogen and hence over-estimate the true digestibility. This may be
particularly so in the case of water-soluble nitrogen. Some of the water-soluble nitrogen might in fact be of dietary origin but care assumed to be included in the non-dietary faocal fraction.
Mason (1969) hao shown that the assumption that the process of digestion in the animal does not affect the extractability of the undigested dietary nitrogen in the faeces samples n a y not bo strictl;?
true. He used the detergent method and obtained the true digesti
bility values of 91 - 92$ for ryegrass hay, end 98 - 99$ for soya bean meal-based ration and reported that the values were probably higher than the true values because some undigested dietary pigments
were extracted b y the procedures employed.
The true digestibility value of 92.9 + 2.3 obtained in the
present experiment is vers?- good agreement with Mas o n ’s (1969) values of 91 to 92$ and Singh and Mahadevan’s (1970) value of 93.4 ± 1.9$
The amount of N absorbed by thm sheep did not differ with rations A and B, but increased with increasing intake of dietary
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crude protein. This is expected since the digestibility of the rations increased with increasing intake of nitrogen. The increase in ST absorbed with increasing N intake agrees with the reports of Stobo and Hoy (1973)• Since the value of the metabolic faecal N (HEll) is relatively constant por unit DM intake, it is expected
that the preportion of N absorbed will increase with increasing dietary crude protein intake,
. 0.734.
T!ie N retained per metabolic size ) increased linearly with increasing IT intake and also with absorbed IT. About 93.9$
of absorbed N was retained by the sheep. This is to be expected since the sheep were young and laying down tissues by utilizing absorbed IT. The slope of the regression equation of retained
IT with absorbed IT is 0.939 + 0.029, and has been termed 'the Nitrogen balance index of absorbed IT' (Allison, 1965) as it demonstrates the rate at which absorbed IT fills the protein stores of the animal body; consequently, this index is a function of the biological value of the dietary IT. The high N-bnlcnce index for the N content of the rations C, D, S and F indicates the very high efficiency wit::
which these animals utilized the protein of the concentrate-based rations.
The IT balance index value of 0.959 was higher than the valuo obtained for casein (0.6 5), and for urea (0.8 3) but lower than the value of 1.05 obtained for gluten Tiy Deif, El-Shazly and Abeu Akkada
(1968).
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Hie value of 0.77 obtained as the N balance index of intake II in the present studies was higher than 0.69 obtained for casein but
less than 1.02 end 0.97 obtained for gluten and urea respectively by Deif, 31— Shazly and Abou Akkada (1968), again tending to indicate very efficient utilization of the IT contents of the rations.
It is obvious fron Table 4.2 that at the hi^iest level of IT.intake, N retained was still increasing and the value of 1.11 +_
. , 0.734
0.09 g/day/I,JjCg could not bo the maximum IT retainable by the sheep.
Black, Pearce and Tribe (1973) obtained the maximum value of IT retained
0.734 , 0.734'
per % g for lambs weighing 20,8 k g 1.05 g/day/¥k g . It is likely that, given rations higher in crude protein, the value of
0
734-1.11 g/dayAn * + obtained in tho present investigation night bo. ..
. , 0.734 excoodod. Black ot al.(l973) also obtained the value of 1.46 g/day/I'Jlcg
Since the weight range of the sheep used in the present report was 1 5 - 2 6 kg, the maxinun II-retained is more likely to ho closer
0.734 0,734
to 1.05 than to 1.46 g/day/W^g . Therefore the value of 1.11 g / d a y / \ g obtained in the present experiment would appear to have reached the maximum IT retention by this group of animals with nature weight of
20 kg. The fact that the mean difforonees within those animals were not significant (P^ 0.0 5) indicates that N retained was almost tho
sane within the weight range 15 - 26 k g of the animals used in tho present experiment.
The percent II retention increased as the IT intake and digestibi
lity of the ration. IT retention was also influenced by the stage of
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growth of the animals. In the present report, young dwarf sheep at their early maturity were used and nitrogen retention values were high, which shows that dietary IT was being utilized in the formation of tissues. Stobo and Roy (1973) reported curvilinear increase in IT retention with IT intake and this is in agreement with the report of Robinson and Forbes (1970).
The supplementation of hay with concentrate (C^) mainly cassava flour, a readily digestible form of energy, increased IT retention.
This is in agreement with the report of Fick ct al. (1973).that supplemental energy improved utilization of low quality hay.
In the present experiment, supplementation of hay with concentrate (C^) decreased urinary IT and hence increased IT retention values.
The values of metabolic faecal IT (I-IFN) obtained in the present report for lambs varied from 2.98 to 3.68 g /k g DM consumed. This is lower than the value of 5.0 g /k g DM consumed often quoted for
ruminants (Maynard and Loosli, 1962). The values are however comparable to that of Dcif ot al„(l968) who reported MFI'T value of 3.58 g /k g D M consumed, and also to that of Elliott and Topps (1963), who obtained 3.66 DM consumed but higher than those of Black ot ajl* (1973), Walker and Fouchney (1964a) and Lofgreen and Kleiber
(1953) who reported MFD values of 2.04, 2.90 and 2.70 g /k g DM intake respectively. These investigators with the lower MFI'T values usod young lambs or calves maintained on liquid diets.
A wide variation had been obtained in M M values b y some investigators. The estimate of Robinson and Forbos (1970) was
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6.5 g/fcg M intake and is higher than 5.0 g /k g DM intake while on (1969) using the detergent method obtained a range of 4.4 to 7.2 g /k g HI intake for the M M values. From this, it is
evident that a number of factors influence excretion of metabolic faoool nitrogen. The composition of feeds influences excretion
of metabolic faecal nitrogen. Most of the investigators who obtained low values for M M used highly digestible feed like solid or liquid milk (Black et a l .?\975) and those who obtained higher values used hi^iljr fibrous rations (Mason, 1969).
Schneider (1935) showed that the excretion of M M was influenced by body siao as well as by the level of feed intake, M M tending to increase with increasing live weight of animal. Blaxter and Wood (1951) showed that M M excretion increased on rations of low
TO
digestibility. Lofgreen and Kleiber (1953)» using the N:3r ratio to determine K M in young calves showed that M M increased with increasing calf weights. Walker and Faichacy (1964a) obtained a <
mean of 2.90 M M / k g DM intake using protein-free diets. However, when nitrogen-free diets are given to the ruminant animals, thoir protein metabolism is substantially altered (Waterlow, 1968) and the results obtained nay not apply under normal feeding conditions
Mason (1969) showed that the proportion of nitrogenous contents of faeces is influenced by the type of the rations.
He found that when animals were maintained on rations of hay or other roughages, the percent of undigested dietary II (uDll) ranged
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