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

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 16:30 hours, 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 (2.15 mg kg-1, below normal values) showed a sampling time x breed interaction (P<0.05) with a quadratic trend (P<0.02). Iron blood levels (337.48 mg kg-1) showed a sampling time x age 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 (86 micrograms kg-1) initial levels than Suffolk sheep (61.14 micrograms kg-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 (0.46 mg kg-1) than in Rambouillets (0.35 mg kg-1). Suffolk sheep had higher Zn (P<0.01) and Cu (P<0.05; below normal values) levels in wool (146.63 and 2.16 mg kg-1, respectively) than Rambouillet sheep (141.34 and 1.72 mg kg-1, respectively). No effect was found in Fe wool levels (291.22 mg kg-1), and Se concentration in wool (204.7 micrograms kg-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.