Animals and management
The study was conducted in Alage Agricultural Technical and Vocational Training College form March 15, 2015 to June 30, 2015. Twenty four males Arsi-Bale sheep with an average initial body weight of 14.05±1.12 kg (mean±SD) were used and randomized by weight assigned to four groups of six sheep each. Prior to commencement of the experiment, animals were kept for 15 days for adaptation and to observe their health status. They were housed in individual pens (1 m × 0.8 m) in a well-ventilated concrete floor barn. All animals were drenched with a broad-spectrum antihelmentic and vaccinated against anthrax, pasteuriolosis and blackleg diseases. Bole soil was collected from Shalla Lake, Oromiya region. Sheep were offered ad
libitum natural grass hay at 20% refusal rate adjusted every other week and the supplemental minerals and concentrates throughout the experiment. Four treatment groups were randomly assigned to mineral supplementation.
T1 = Natural grass hay
ad libitum + 300 g DM/d concentrate + no mineral supplement.
T2 = Natural grass hay
ad libitum + 300 g DM/d concentrate + 1% salt.
T3 = Natural grass hay
ad libitum + 300 g DM/d concentrate + 1% commercial mineral mix.
T4 = Natural grass hay
ad libitum + 300 g DM/d concentrate + 2%
bole soil.
Data of feed offered and refusals of the basal diet were recorded daily in the morning. The treatment diets were formulated on a DM basis. A randomized complete block design (RCBD) was used in the experiment.
Feed intake
Experimental sheep were fed for consecutive 90 days and offered natural grass hay free choice for
ad libitum intake at 20% refusal rate where as the concentrate supplement was offered twice a day at 8.00 and 16.00 h. The amounts of daily feed offered and refused were recorded to determine daily feed intake. Chemical composition of sub-samples of feed offered and refusal were analyzed and the results were used for calculation of daily dry matter and nutrient intake.
Live weight change and feed conversion efficiency
Data on live body weight change was taken every ten days after overnight fasting starting from the first day of the last acclimatization period using a suspended spring balance. Average daily weight gain for each sheep was determined as a difference between final and initial body weights divided by the total number of actual feeding days. Feed conversion efficiency (FCE), which is the measure of feed utilization, was determined by dividing daily average live weight gain by daily total DMI of the sheep as shown by
Brown et al., (2001).
Carcass analysis
All animals were deprived of feed and water for 14h to reduce variation in gut fill and were slaughtered to assess carcass characteristics of animals. Before slaughter, animals were weighed followed by slaughtering by cutting the jugular vein to drain blood. Esophagus was tied off close to head and the animals were suspended head down, over a container and blood was collected and weighed. The head was detached from the body and weighed without tongue when the main flow of blood ceased. Skin was flayed and weighed; forelegs and hind legs were trimmed off at carpal and tarsal joints and weighed. Entire gastrointestinal tract with contents were removed and weighed and then internal contents were emptied and the weight of the empty gut was recorded. After dressing and evisceration, carcass weight was immediately recorded to assess dressing percentage on slaughter weight and empty body weight bases. Empty body weight was calculated as slaughter weight without gut contents. Hot carcass weight was estimated after removing the weight of head, thoracic, abdominal and pelvic cavity contents as well as legs below the hock and knee joints. Rib-eye muscle area of each animal was determined by tracing the cross sectional areas between the 12
th and 13
th ribs after cutting perpendicular to the back bone (
Purchas, 1978).
Partial budget analysis
It was calculated to determine profitability of all experimental feeds to sheep based on the procedure of Upton (1979). Net income (NI) was calculated by subtracting total variable cost (TVC) from total return (TR) as NI = TR-TVC. Change in net income (DNI) was calculated as a difference between change in total return (DTR) and change in total variable cost (DTVC), as : DNI = DTR-DTVC. The marginal rate of return (MRR) measures increase in net income (DNI) associated with each additional unit of expenditure (DTVC). MRR = DNI/DTVC.
Chemical analysis of feeds
Samples of daily feed offered and refused were collected, weighed and separately stored for each animal in bags and kept in a room with adequate natural ventilation until the end of the experimental period. Then feed samples were thoroughly mixed, sub samples were taken to Hawassa University Nutrition Laboratory. The DM content of the feed was determined by drying the samples at 105°C overnight. Ash content of the sample was determined by combusting the samples at 550°C for 5h in a muffle furnace. N content was determined using the Kjeldahl method and CP was calculated as N% × 6.25 (
AOAC, 1995). NDF contents were analyzed using the method of Van
Soest et al., (1991) whereas, ADF and ADL contests were determined according to
Van Soest and Robertson (1985) using ANKOM® 200 Fiber Analyzer. All samples were analyzed in duplicates. In regard to
bole soil, mineral mix and salt were sampled and taken to the Debre Zeit laboratory. Macro minerals (Ca, P, Mg, K, Na and S) and trace minerals (Mn, Cu, Fe and Zn) were analyzed using the method of
Mehlich (1984) in Mehlich 3 soil test extractant.
Statistical analysis
Data on feed intake, body weight change and carcass parameters were analyzed by analysis of variance (ANOVA) using the general linear model procedure of statistical analysis system software version 9.1(
SAS, 2008). The treatment mean was separated by Duncan’s multiple range test (DMRT), the model used for analysis of the data was: