Abstract:
This study investigated if there is any confounding effect of stocking rate on the use of
internal markers to determine and predict the dietary ingredient composition, dry matter intake
(DMI) and digestibility of diets consumed by sheep. Fifteen sheep were randomly allocated to
stocking rate treatments of one (SR1), two (SR2), four (SR4) and eight (SR8) sheep per pen (space
allowance: 31.04 m2
, 15.52 m2
, 7.76 m2 and 3.88 m2 per sheep, respectively) and fed ad libitum maize
stover, sorghum stover and veld hay by supplying 110% of previous day’s intake. Sheep were rotated
across the treatments in four periods of 10 days. The proportion of feeds selected and total DMI
were similar across all stocking rate treatments. However, diets selected by sheep in SR2 had the
highest digestibility compared to other treatments. The prediction of the effective degradability of
dry matter using acid detergent fibre content achieved an accuracy of 84.6%. A combination of crude
protein and neutral detergent fibre contents achieved 63% accuracy in the prediction of the rate of degradation of feeds. The use of acid insoluble ash (AIA) as an internal marker to predict nutrient
intake, digestibility, DMI and dietary ingredient intake accounted for 84.3%, 81.2%, 53.0% and 64.1%
of the variation, respectively. The predictions of dietary feed proportions and nutrient quality selected
obtained with least squares procedure using a combination of modified acid detergent fibre (MADF),
acid detergent lignin (ADL) and AIA accounted for 81.0% and 72.4% of the variation, respectively.
In conclusion, regardless of the different stocking rate tested in this study, a combination of MADF,
ADL and AIA as internal markers can be used to estimate diet and nutrient selection by sheep using
the least squares procedure. Hence, these markers can be used to predict ingredient composition of
diet, diet and nutrient selection, nutrient intake and digestibility in free ranging animals.
