Abstract:
Livestock is a key asset and a primary livelihood resource for rural households in most
parts of the world and accounts for nearly 95 per cent of family income in the Arid and
Semi-Arid Lands (ASALs) in Kenya. Despite high economic importance of livestock,
inadequate nutrition results to low livestock productivity in Kenya. Ruminant feeding in
the ASALs is mainly based on the exploitation of range feed resources. Grazing ruminants
forage on different plant species with varying levels of nutrient and toxins. Despite these
complex grazing situations, sheep can select a suitable diet and regulate intake of toxic
substances. There is therefore a need understand diet selection and its role in the nutrition
of sheep. A study to assess diet selection, intake and live weight gain of sheep fed on
different grasses was conducted at Machakos Agriculture Training Centre (ATC) in two
experiments. Five sheep housed in individual pens of size (3 x 3m) were fed in a cafeteria
system with six grasses namely Brachiaria decumbens cv. Basilisk, Chloris gayana,
Cenchrus ciliaris, Chloris roxburghiana, Enteropogon macrostachyus and Eragrostis
superba were used during experiment 1. Data on dry matter intake (DMI), feeding time
and number of visits were recorded for 5 consecutive days. Selectivity index (SI) for each
grass was calculated from intake data. The grasses were analyzed for chemical composition
according to Association of Official Analytical Chemist (AOAC) (1990). Analysis of
variance (ANOVA) was conducted using the SAS, 2000 model to determine the effect of
grass species on diet selection. Four grasses and sixteen Dorper sheep aged between 12 and
18 months and weighing between 18 and 29 Kgs were used in experiment 2. The sheep
were grouped into four groups balanced for age and weight. Each group was randomly
allocated one dietary treatment. Mineral licks and water were provided ad libitum
throughout the study. Data on intake and weight gain were computed for 42 days and
analyzed by General Linear Model (GLM) procedure of SAS 2000. Results of experiment
1 showed that number of visits, feeding time, and the selectivity index (SI) were higher
(p<0.05) in sheep fed on semi-arid grasses than in the sheep fed on humid grasses. Results
of experiment 2 showed that dry matter intake (DMI) and average daily gain (ADG) were
higher (p<0.05) in sheep fed on semi-arid grasses than in the sheep fed on humid grasses.
Crude fibre had a negative correlation with ADG (r=-0.258), SI (-0.675), DMI (r=-0.627)
and in vitro dry matter digestibility (IVDMD) (r=-0.997). Crude protein had a positive
correlation with ADG (r=991), selectivity index (r=0.792), dry matter intake (r=0.955), and
in vitro dry matter digestibility(r=0.446). The result of this study indicated that diet
selection is influenced by nutritive value and digestibility of the forage. These findings also
show that diet selection can influence intake and hence weight gain of sheep. Diet selection
studies can be used in designing feeding programmes for ruminant livestock in the tropics.
