weight at 08:00 hours and 17:00 hours for maintenance purposes. Mineral licks and water were provided adlibitum. This
was done so as to maintain a stable rumen environment before the rumen liqour was collected. Collected rumen liqour
was strained through four layers of cheese cloth into a pre-warmed, vacuum flask and kept at 39oC under CO2
atmosphere. About 0.2g of 1mm ground samples (WN, PN, DhN and DfS) were weighed into the glass syringes. A mixture
of 30ml of rumen liquor and buffer in the ratio of 1:2 was added into each of the 100ml calibrated glass syringes that
were pre-warmed to 39oC. Oil was applied to the pistons to facilitate ease of movement and prevent gas escape. Two
blank syringes with rumen liquor without a feed sample were included as controls. All syringes were incubated in a water
bath maintained at 39oC and shook periodically. Gas production readings were recorded at 0 and after 3, 9, 12, 24, 48,
72 and 96 hours of incubation.
The gas production characteristics were computed by fitting the mean gas volumes to the exponential equation of
ꢀ ꢁ ꢂ ꢃꢄꢅ ꢆꢇꢈꢉꢊꢋ
ꢌ
(1)
Where: Y is gas production (ml/0.2g) at time t, a is gas production (ml) from immediately soluble fraction, b is gas
production (ml) from insoluble fraction, a+b is gas production from potential degradable fraction, c is the rate constant of
gas production per hour (h), t is the incubation time in hours and e is the exponential constant (2.718).
In vitro gas production parameters were used to estimate organic matter digestibility (OMD), metabolisable energy
(ME), Dry Matter intake (DMI) and short chain fatty acids (SCFA) using the models presented in Equations 2 to 5.
ꢄ
ꢌ
ꢍꢎꢏ ꢐ ꢀ ꢅꢑꢒꢓꢓ ꢂ ꢔꢒꢓꢓꢕꢇꢖꢗ ꢂ ꢔꢒꢑꢘꢇꢙꢚ ꢂ ꢔꢒꢔꢛꢘꢅꢇꢜꢝ
(2)
(3)
(4)
(5)
ꢎꢞ(MJ/Kg)ꢀ ꢟꢒꢟꢔ ꢂ ꢔꢒꢅꢠꢛꢇꢖꢗ ꢂ ꢔꢒꢔꢘꢡꢇꢙꢚ
ꢏꢎꢢ(kg/day)ꢀ ꢅꢒꢛꢛ ꢂ ꢔꢒꢑꢕꢁ ꢂ ꢔꢒꢔꢟꢕꢡꢃ ꢆ ꢑꢣ
ꢄ
ꢌ
ꢤꢙꢥꢝ ꢦꢦꢧꢨꢩꢪ ꢀ ꢔꢒꢔꢟꢟꢟꢇꢖꢗ ꢆ ꢔꢒꢔꢔꢑꢟꢘ
Where: GV is gas production after 24 hours, CP is crude protein and XA ash content of the processed form of croton,
a, b and c are constants as described in Equation 1.
In sacco degradation (nylon bag technique)
In sacco degradation of the various forms of croton was carried out using Nylon bag technique as described by
Ørskov (2000). Two mature fistulated Friesian steers weighing 450±25 kg live weight were used. The steers were fed on
Rhodes grass (Chloris gayana) hay and wheat bran at 90% and 10% respectively of the total ration at 3% of their body
weight at 08:00 hours and 17:00 hours for maintanance purposes. Mineral licks and water were provided adlibitum. This
was done so as to maintain a stable rumen environment. Five grams of each processed sample of croton was weighed
into duplicate nylon bags (12cm by 6cm, 50µm pore size). The bags were incubated for 0, 9, 12, 16, 24, 48 and 72 hours
in the rumen. Zero-hour washing was measured by soaking nylon bags containing the sample in water maintained at 39
oC for 1 hour. Bags from zero hour washing and those retrieved from the rumen were washed thoroughly under running
cold water for 15 minutes until the washing water was clear. The bags with the residue were then dried at 60oC for 48
hours in a forced air oven and dry matter loss determined as the difference from the original weight. Crude protein and
neutral detergent fibre (NDF) from the residue were then analysed. The DM, CP and NDF degradability characteristics were
Excel Computer program (Chen X. B., Rowett Research Institute, Aberdeen UK).
ꢚ ꢀ ꢁ ꢂ ꢃꢄꢅ ꢆꢇꢈꢉꢊꢋ
ꢌ
(6)
Where: P is the degradability of (DM, CP and NDF) incubated in the rumen at time t in hours, a is the percentage of
rapidly soluble fraction, b is the percentage of insoluble but fermentable fraction, a+b is potential percentage of
degradability, c is the rate of constant degradation per hour (h-1) and e is the exponential constant (2.718).
Effective degradability (ED) of DM, CP and NDF was calculated using Equation (7).
ꢊ
ꢞꢏ ꢀ ꢁ ꢂ ꢃꢄꢊꢫꢬꢭ
ꢌ
(McDonald, 1981)
(7)
Where: a+b is the potential degradability, c is the rate constant degradability per hour (h), kp is the ruminal outflow
rate. The following outflow rates (kp) per hour were considered (0.025, 0.05 and 0.08). Rumen undegradable protein
(RUP) was calculated by subtracting effective degradable CP% from 100%. The DM index value (IV) which denotes the
fraction of the feed that would provide nutrients to the animal for its maintenance needs was calculated using Equation 8.
A feed with an index value above 33 would provide sufficient nutrients to the animal for its maintenance needs.
ꢢꢗ ꢀ ꢁ ꢂ ꢔꢒꢑꢃ ꢂ ꢟꢔꢔꢣ
Where: a, b and c are as described in Equation 6.
Statistical analysis
Analysis of variance (ANOVA) was carried out on proximate composition, fibre fractions, minerals composition, gross
energy (GE) and phytochemicals as well as in vitro gas production and in sacco degradability parameters. The analysis
was based on completely randomized design using STATA (2017). Significant differences between the means were tested
using Tukey’s honest significance difference (THSD). The following statistical model was used
ꢮꢯꢰ ꢀ ꢱ ꢂ ꢲ ꢂ ꢈꢯꢰ
(9)
ꢯ
38
Citation: Kabochi Njoroge E, Celina Wambui C and Bwire Wasike C (2021). Nutritional composition, in vitro gas production and in sacco degradability of processed