Effect of breed and age on the voluntary intake and the micromineral status of non-pregnant sheep. 1. Estimation of voluntary intake.

Twenty-four sheep were used to test breed and age differences in voluntary intake (VI). The sheep were divided into four groups of six animals each: Suffolk mature ewes (SM), Suffolk yearlings (SY), Rambouillet mature ewes (RM), and Rambouillet yearlings (RY). The animals grazed alternatively two mixed pastures containing Trifolium repens latum, Lolium perenne and Pennisetum clandestinum from 07:00 to 16:30 hours and remained penned overnight. Voluntary intake was estimated using chromic sesquioxide (1g per sheep) as an external marker, administered in two gelatin capsules, one before and one after grazing, during 65 days. Faecal grab samples were collected directly from each animal for three consecutive days beginning on Day 7 of the experiment and at 14-day intervals until Day 65 (sampling times=5). Hand-plucked samples of forage were used to estimate in vitro dry matter digestibilities (IVDMD), which were used with estimates of fecal output to calculate intakes (per animal and per kg of metabolic body weight (kg(0.75))). The data were analyzed as a completely randomized design in a factorial arrangement with repeated measurements. Voluntary intake, expressed both per animal and per kg(0.75), showed a breedxage interaction (P<0.001). Suffolk mature ewes had the greatest daily VI (1.88 versus 1.26kgDM/animal for the other three groups) because they were the heaviest animals, but their VI/kg(0.75) (0.071kgDM/day) was not different (P>0.05) from that of RY (0.063kgDM/day), which were smaller, younger animals. Suffolk yearlings and RM had similar VI/kg(0.75) (0.057 and 0.051kgDM/day, respectively), not different from that of the RY. Intakes showed a cubic trend (P<0.001) with time, possibly because of changes in IVDMD and climatic conditions. The lower intake, yet better gains of RM and RY indicate a greater ability to thrive under conditions of average pasture quality. High forage availability did not result in greater forage consumption. The information on VI was later used to assess the micromineral status of the sheep in the experiment.