A comparison of in-field techniques for estimating the feed intake of young boer goats on a Leucaena leucocephala/grass hay diet.
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Date
1997
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Abstract
Two methods of estimating the intake of a 25% leucaena : 75% grass hay diet by young male
Boer goats were assessed, (a) The purine derivative technique which uses the urinary excretion
of purine derivatives (expressed relative to creatinine concentration in the same sample) as an
index of feed intake, and (b) the conventional marker method, utilizing chromic oxide (Cr₂O₃)
contained in gelatin capsules and dosed twice daily, as the marker.
Following a prerun the two techniques were compared in three runs of an indoor experiment. In
each run 10 goats were randomly allocated to five feeding levels (500 to 1100 g fodder d ¯¹ on air
dried basis). A preliminary and an adaptation period during which goats were dosed with the
Cr₂O₃ and fed their daily feed allowance, was followed by a 4 day collection period during which
spot samples of urine were collected and analysed for allantoin and creatinine (allantoin being
used instead of total PDs) and faecal samples were collected for chromium analysis and
percentage dry matter determination. For the first two runs, two grab samples per day for each
goat were bulked and analysed for chromium content. For the last run, the total daily faecal
collection was subsampled and analysed for chromium. Work was done in metabolic crates to
determine the effect of time of collection on the ratio of allantoin : creatinine (A/C) in spot urine
samples and it was found to non-significant (P>0.05).
Linear regressions of:
(a) feed intake expressed per unit metabolic mass (g.d ¯¹.LW ¯°∙⁷⁵ (I_mmass)) against A/C ratio;
(b) faecal output (g d ¯¹) against feed intake (g d ¯¹); and
(c) faecal chromium concentration (mg kg ¯¹) against faecal output (g d ¯¹) were fitted to the
data.
During the prerun, only regression (a) was fitted and was non-significant (P>0.05), showing no
trend at all. For the first true run, the regression of I_mmass against A/C ratio was significant
and the correlation was high (P≤ 0.001, R² [A] 0.715, n = 10) but for the second and third runs, the
correlations only became significant when the apparent outliers were discarded from the data.
(Run 2: P≤ 0.001, R² [A] 0.824, n = 8; Run 3: P≤ 0.05, R²
[A] 0.430, n = 9). It was concluded that the relation between I_mmass and A/C ratio is not well enough defined to be used for predictive purposes.
When regression (b) was investigated, all the runs produced significant results (P≤0.001, P≤0.01, P≤ 0.001 for runs 1,2 and 3 respectively) however the correlations were not as high as expected
(R² [A] being 0.714, 0.565 and 0.863 respectively). For the regression of faecal Cr concentration
against faecal output (regression c), all runs showed significant relations (P< 0.001, P< 0.0001,
P:s 0.001 for runs 1,2 and 3 respectively) and the correlations were high (R²[A] being 0.836, 0.837 and 0.912 respectively).
The data from the three runs were pooled and single equations established for regressions (b) and (c) to allow for the prediction of intake from faecal chromium concentration.
Faecal output = feed intake * 0.448 + 19.341 (P≤ 0.001, r 0.853, R²
[A] 0.718, SE 25.664, n - 30) Faecal chromium concentration = faecal output * -241.547 + 1.315E+05 (Ps 0.001, r 0.904, R² [A] 0.811, SE 5603.788, n = 30).
In vitro figures were determined for a range of leucaena : hay mixes but no apparent trend was
found between percentage leucaena in the mix and the digestibility of the mix. These results
compared favourably with in vivo results obtained for a 25% leucaena : 75% hay mix.
Neither technique proved entirely satisfactory, but the external marker method was found to be more effective than the purine derivative technique. More work is required especially with respect to the latter method.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.
Keywords
Goats--Feeding and feeds., Leucaena leucocephala., Theses--Grassland science.