RESUMO
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.
RESUMO
Twenty-four non-pregnant sheep, divided into four groups of six animals each, were used to test breed (Suffolk and Rambouillet) and age (mature (six years old) and yearling (16 months old) ewes) differences in micromineral status. The animals grazed alternatively two mixed pastures containing Trifolium repens latum, Lolium perenne and Pennisetum clandestinum from 07:00 to 16:30hours, and remained penned overnight. Hand-plucked forage samples, blood and wool samples were collected on Days 1 (except forage), 7 (except wool), 21, 35, 49, and 63 of the experiment and assayed for Zn, Fe, Cu, Se, and Mo. Blood and wool data were analyzed as a completely randomized design in a factorial arrangement with repeated measurements. Zinc blood levels (2.15mgkg(-1), below normal values) showed a sampling timexbreed interaction (P<0.05) with a quadratic trend (P<0.02). Iron blood levels (337.48mgkg(-1)) showed a sampling timexage interaction (P<0.05), with mature ewes having higher and more variable levels than yearlings. A sampling time effect (P<0.01) with a quadratic trend (P<0.05) dependent on the breed (P<0.01) was found in Se blood levels. Rambouillet sheep had higher (86µgkg(-1)) initial levels than Suffolk sheep (61.14µgkg(-1)) and they declined linearly, whereas Se levels in Suffolks showed a quadratic trend. Copper blood concentration (below normal values) was higher (P<0.01) in Suffolks (0.46mgkg(-1)) than in Rambouillets (0.35mgkg(-1)). Suffolk sheep had higher Zn (P<0.01) and Cu (P<0.05; below normal values) levels in wool (146.63 and 2.16mgkg(-1), respectively) than Rambouillet sheep (141.34 and 1.72mgkg(-1), respectively). No effect was found in Fe wool levels (291.22mgkg(-1)), and Se concentration in wool (204.7µgkg(-1)) only showed a sampling time effect (P<0.05) with a decreasing linear trend (P<0.01). Coefficients of variations higher than 50% were found for Zn and Se in blood and Fe and Se in wool. Molybdenum could not be detected either in blood or in wool. Rambouillet sheep, in general, showed lower and less variable micromineral levels than Suffolk sheep. Because no signs of deficiency were observed nor was the animals' productivity affected after the study, it is considered that reported normal values for Zn and Cu could be more variable than suspected, depending on breed, location, feeding practices and physiological state.
