Preparation of test ingredient
Four kg of urea dissolved in 100 litter water was carefully sprinkled on 100 kg DM of CH and thoroughly mixed together. The urea-ammoniated CH was filled into a large drum, compacted to make it air tight, sealed tightly with polyethylene sheets and overlaid with a heavy object. The ensiled CH was left unopened for three weeks after which the resulting UCH was dried on a clean concrete floor under a shade to a constant weight, milled and bagged.
Animals and treatments
Eighteen 8-month-old uncastrated Red Sokoto goats, with live weight (LW) of 13.4±0.59 kg, were randomly divided into 3 groups of similar LW. Goats, housed in individual slatted floor cages equipped with facilities for collection of faeces and urine, were treated against internal and external parasites and bacterial infection before starting the experiment.
The experimental diets comprised three levels of UCH: 0 (control), 350 and 700 g/kg, substituting 0, 500 and 1000 g/kg DBG, in low-cost rations. Treatments contained (g/kg): (700 DBG + 300 cassava peel meal (CPM), 2 (350 DBG + 350 UCH + 300 CPM) and 3 (700 UCH + 300 CPM). Goats, fed at 5% of their LW with daily allowance for 20% refusals, were randomly assigned to one of three treatments in a completely randomized design (CRD). The experiment lasted for 70 d excluding 14 d adjustment period. Feeding was twice daily (08:00 h and 16:00 h), and water was available ad libitum. Goats were weighed at the beginning of the experiment and weekly before morning feeding to adjust feed offered as the LW changed.
Digestibility, nitrogen balance and chemical analysis
During the last week of the experiment, samples of feeds, orts, faeces and urine voided were collected and weighed every morning before feeding for 7 days. Samples of the faeces and urine (10% of daily production) were pooled for each animal for the 7-d period and sub-sampled for analysis. Urinary samples were acidified with 20 ml of concentrated H2SO4 to prevent ammonia losses and frozen pending chemical analysis.
The DM of feed and faeces was determined by drying in a forced-air oven at 60 oC for 48 hr. The dried samples were ground using a Wiley mill to pass a 1-mm screen and analysed for the proximate constituents according to the AOAC (2005). Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were analysed according to the methods of Van Soest et al. (1991). Non-structural carbohydrate (NSC), organic matter (OM), hemicellulose, cellulose and metabolisable energy (ME) were calculated.
Rumen fluid collection and analysis
On the last day of the experiment, about 100 mL of rumen liquor was collected 3 h post-morning feeding from the ventral sac of each goat using a stomach tube. The pH was measured immediately using a digital pH meter. The liquor was filtered through four layers’ cheesecloth. A subsample of 5 mL was preserved in 5 mL of 0.2 M HCl for NH3-N analysis according to AOAC (2005), and another 0.8 mL subsample was mixed with 0.2 mL of a solution containing 250 g of metaphosphoric acid/L for the total volatile fatty acid (VFA) analysis by titration after steam distillation. Microbial protein synthesis (MPS) was calculated using the equations of Chen and Gomes (1992):
Microbial N yield (MN) = 32 g/kg x digestible organic matter fermented in the rumen (DOMR), where
DOMR = digestible organic matter intake × 0.65
Blood collection and analysis
On the last day of the experiment, blood samples (10 mL) were taken in the morning (4 h after feeding) from the jugular veins of all the goats using Vacutainer tubes without anticoagulants. The samples were allowed to cloth at room temperature for ≥2 h and centrifuged at 4000 × g at 4°C for 20 min. Serum was separated into 2-ml Eppendorf vials. Blood serum samples were analysed for concentrations of total protein, albumin, urea-N, creatinine, aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphate (ALP), glucose and cholesterol using specific kits (Stanbio Laboratory, Boerne, TX, USA), following the manufacturer’s instructions. Globulin concentration was calculated by subtracting albumin value from its corresponding total protein value.
Statistical analysis
Data were analysed as a CRD using SPSS Base 17 (SPSS software products, USA). Polynomial (linear and quadratic) contrasts were used to determine responses to increasing level of UCH.