Accurate measurements of the digestible amino-acid contents of raw materials are desirable for least-cost formulations of diets. Due to the lack of information, in the past digestible amino-acid values for ostriches were also derived from fowl. A study was conducted to compare apparent and true digestibility of amino acids
Table 5.5. Comparison between calculated and determined TMEnvalues (MJ kg –1)
for an experimental diet in male domestic fowl (adults) and ostriches (8 months of
age), showing that determined TMEnvalues were additive and assigned to ingredi-
ents independently of its inclusion level in a complete diet. Data from Cilliers et al. (1998b).
Calculated value by cumulative Determined value by
Source calculating individual values balance method
Ostriches 11.69 11.25
Domestic fowl 8.28 8.02
in a high-protein (209 g kg–1) diet between immature ostriches (7 months) and
adult fowl (Cilliers et al., 1997). Amino-acid digestibilities were calculated by the regression method and yielded a mean value for true digestibility of 0.837 (range 0.780–0.862 as a proportion of 1) for ostriches whilst a value of 0.795 (range 0.723–0.825) was measured for fowl. Individual digestibilities are summarized in Table 5.6. True retention of dietary protein was higher for ostriches than in fowl, but the reverse was true for lipid retention (Table 5.6). Again the ostrich is better able to digest amino acids than the fowl, thus using digestibility values from poultry in diet formulation for ostriches will slightly underestimate the true amino-acid content. Results presented in Table 5.6 emphasize the importance of an assessment of amino-acid digestibilities for individual ingredients.
Determination of metabolizable energy and amino-acid requirements for maintenance and growth
According to Ferguson et al. (1994) the use of prediction equations to model growth and production is one of the best approaches to estimating nutrient requirements for poultry. There is no reason why the same principles cannot be applied to ostriches, provided the nutritional constants are known whereby ani- mal requirements are converted to feed requirements.
Cilliers (1994) and Cilliers et al. (1998d) estimated the efficiency of conver- sion of feed energy and amino acids for maintenance and growth. To obtain these factors a comparative slaughter technique was applied, where an initial group of 7-month-old growing ostriches was slaughtered and growth measured as retained carcass energy and carcass protein (amino acids) in the remainder. Birds were fed a balanced diet of which the TMEn and true amino-acid availability was also
determined by the balance method. Retained energy (RE) during the trial period (MJ kg–0.75
body mass) was regressed against TMEnintake according to the fol-
lowing model: RE (kg0.75
)=a1b3MEintakekg 0.75
the efficiency of TMEnutilization for RE (kpf) in growing birds and a3b
–1predicts
daily requirements for maintenance energy (TMEn) per kg
0.75 body mass
(Chwalibog, 1991). The same procedure was applied to estimate amino-acid requirements for maintenance and to calculate the efficiency of amino-acid uti- lization for carcass protein synthesis.
Retained carcass energy was also regressed on effective energy (EE), the unit proposed by Oldham and Emmans (1990) to correct TMEnfor differences
in heat loss of fats, carbohydrates and protein during metabolism: EE=TMEn–4.673digested protein–3.83faecal organic matter1123digested N-
free extract. Maintenance energy requirement (EEm) was also calculated accord-
ing to a formula proposed by Emmans and Fisher (1986) in which maintenance requirement was based on the protein content of the carcass (Table 5.7). The determined TMEn and amino-acid availability results were used to calculate
actual amino acid and energy intake from feed fed to experimental groups.
Table 5.6. True digestibilities (as proportion of 1) of various amino acids in a
balanced high protein diet. Data from Cilliers et al. (1997).
Nutrient Ostriches Domestic fowl
Threonine 0.831 0.804 Serine 0.849 0.823 Alanine 0.937 0.919 Valine 0.862 0.810 Methionine 0.816 0.776 Phenylalanine 0.809 0.723 Histidine 0.854 0.806 Lysine 0.832 0.755 Isoleucine 0.829 0.817 Tyrosine 0.816 0.764 Arginine 0.780 0.736 Cysteine 0.806 0.781 Leucine 0.859 0.825 Protein 0.646 0.609 Lipid 0.870 0.892
Regression equations relating retained energy on energy consumption are given in Table 5.7.
Regressions were highly significant and the efficiency with which TMEnwas
converted to carcass energy (slope of the regression line) amounted to 0.414 and 0.443 for RE expressed per kg0.75
or as MJ day–1
, respectively. TMEnrequirement
for maintenance was 0.425 MJ day–0.75
(i.e. 0.176/0.414) or 7.964 MJ day–0.75
(i.e. 3.528/0.443). The daily EE requirement for maintenance, based on carcass pro- tein content (Emmans and Fisher, 1986), amounted to 8.90 MJ day–1
(Table 5.7). Although substantially different, these two values, 7.96 and 8.90, can at least be regarded as being of the same order.
Net efficiency of amino-acid utilization
Results on daily maintenance requirements (mg kg–1
gain day–1
) and the net effi- ciency of utilization for the various amino acids are listed in Table 5.8. These val- ues were calculated with feather growth included, i.e. for the whole bird. The net efficiency of amino-acid utilization varied between 0.569 (leucine) and 0.968 (alanine). For lysine and methionine, amino acids often limiting in those materi- als available for ostrich diets, the values amounted to 0.733 and 0.780, respec- tively, which correspond well to equivalent values reported for the fowl (0.7 and 0.8, respectively; Boorman and Burgess, 1986).
Retention in various body components was separately measured in feathers,
Table 5.7. Relationship between carcass energy retention and energy intake in
ostriches in a TMEnsystem (Cilliers, 1998).
Efficiency of
RE Intercept SD Slope SD R utilization (kpf)
In the TMEnsystem
kgBM0.75 –0.176 0.018 0.414 0.022 0.97 0.414
MJ day–1 –3.528 1.011 0.443 0.056 0.862 0.443
In effective energy system1
RE –0.176 0.010 0.568 0.031 0.95 0.568
1Effective energy (Emmans, 1989) for maintenance, using carcass protein content:
EEm(MJ day
–1) = P
m
–0.2731.63P = 20.66–0.27312.48 (60.363)31.63 = 8.98060.227 MJ
day–1(Mean for 12 birds) where P
m= mature protein mass (kg), value used was for
mature birds weighing 120 kg and protein content of 17.2%; P = current protein mass of a bird, the value used was for a 65 kg animal with a carcass protein content of 19.2%.
hide, legs and skeleton (Cilliers et al., 1998d). These data were proportionally pooled and combined as total growth and retention. During the latter part of this study it was noticed that the ratio of hide to body mass increased with age in con- trast with ratios of other components, e.g. legs and feathers, which remained con- stant. Future research should therefore be directed at defining differences in growth rate and difference in the conversion of feed amino acids to the different body components.
Predicted energy and amino-acid requirements for ostriches
Results on carcass characteristics (Cilliers, 1994; Cilliers et al., 1996, 1998d) were used to estimate nutrient requirements for ostriches at different ages. A Gompertz growth curve constructed for ostriches reared from 1 day old to 520
Table 5.8. Result of maintenance needs and retention (mg kg–1EBM day–1), and
net efficiency of utilization for protein and amino acids in ostriches (calculated according to mean empty body mass of 65 kg for the period). Data from Cilliers et al. (1997).
Nutrient Maintenance Retention rates Net efficiency
Protein 678 3276 – Threonine 57 60 0.710 Serine 53 56 0.615 Alanine 86 02 0.968 Valine 65 72 0.702 Methionine 38 33 0.780 Phenylalanine 68 74 0.654 Histidine 47 45 0.877 Lysine 91 109 0.733 Isoleucine 60 63 0.682 Tyrosine 51 51 0.904 Arginine 96 118 0.948 Cysteine 21 19 0.569 Leucine 91 111 0.569
days old (Cilliers et al., 1995) was used as the basis for these predictions. It is fully realized that figures in Table 5.9 assume a constant body composition during the period of prediction, i.e. that of a 7-month-old bird, and this cannot be correct for energy contents for birds of all ages, although it may represent typical amino- acid profiles and total protein levels. Nutrient requirements in Table 5.9 must thus be seen as a first attempt to furnish guidelines in a field where scientific knowledge on nutrient requirements is almost non-existent. It was also assumed that the efficiency of nutrient utilization is constant for different age groups. Further research will be needed to test these assumptions for ostriches of differ- ent ages, and it is expected that these values will be refined.
It should be noted that figures presented in the Gompertz curve used in cal- culations were based on data collected over years on the experimental farm at Oudtshoorn, South Africa (Cilliers et al., 1995). Although conditions at the time of determination were seen as optimal, this study did not take into account feed- ing of diets to attain maximum rate of growth. Diets fed to birds during the growth period to establish potential growth curves differed substantially from what is used today. Hence a substantial improvement in rate of maturing would now be possible. As requirements were estimated per unit gain, requirements should remain unchanged.
Despite the potential of possible errors due to assumptions, requirement estimates (Table 5.9) were remarkably similar to estimates made from the Emmans (1989) formula, which uses mature protein content and the protein content of the body at a particular stage to determine energy and amino-acid needs for maintenance and growth. In Table 5.9 values are given for a TMEn
requirement of 10.4 and 19.36 MJ day–1 for 90 and 300 days of age. The corre-
sponding Emmans’ values are in close agreement and amounted to 9.3 and 19.3 MJ day–1, respectively (Cilliers, 1994).
Future work will have to establish whether energy to amino-acid ratios remain constant per unit body mass and whether the ratio of hide to carcass to legs to feathers is constant during the different phases. Cilliers et al. (1998d) found that the ratio of hide to empty body mass changed from 48.5 to 55.6 g kg–1 during the
experimental period. It will be essential to determine whether the efficiency of nutrient utilization remains constant for different age groups. Efforts should be directed towards quantifying the relative growth of the different body components and the relationship between nutrient intake and product output and composition.