Potential mineral deficiencies on arid rangelands for small ruminants with special reference to Mexico

The production of milk from goats managed under extensive range grazing conditions can be affected in quantity and quality by the nutrient and especially by the mineral content of the forages on the rangeland, which in turn reflects soil and precipitation conditions. Mexico with its large dairy dual-purpose goat population and vast expanses of arid rangelands is a good model for many other countries with similar conditions. In several studies on the semiarid rangeland of northeastern Mexico the voluntary selection of brush browse, forbs and grasses by goats, and in comparison by sheep and deer was determined from observations, collections, samples from esophageally fistulated goats and sheep, and microhistological analyses of deer feces monthly for several years. The area had low annual rain precipitation often less than 400 mm and dry season from November to July. Blackbrush (Acacia sp.), Mesquite (Prosopis sp.), Palo verde (Cercidium macrum), Jujube (Ziziphus sp.), Hackberry (Celtis sp.), Pricklypear (Opuntia sp.), Cenizo (Leucophyllum sp.), Soapbrush (Porlieria sp.) were dominant brush species. Goats selected 81 ± 1.4% brush browse, 12 ± 1.2% forbs, and 7 ± 1.0% grasses throughout the year for their diet, while the botanical composition of the rangeland was 41% brush, 19% forbs, and 40% grasses. Goats preferred Acacia, Cercidium, Porlieria, and Celtis. Significant undersupplies of Mg, Cu, Mn, and Zn in the naturally selected diets of goats in relation to requirements in most months was determined. Contrary to the behavior of goats, sheep selected 95-63% grasses, 1-36% browse, and 0.1-2.2% forbs in different months of the year. Sheep had deficient diets in Ca, Mg, K, Cu, and Mn during several months. Deer appeared to select like goats 94% browse, 5% forbs, and 1% grasses. Deer had deficient diets apparently only in Zn during the 6 months of summer and autumn. Several brush browse and grass species with relatively high mineral contents during some seasons were identified as possibly helpful to alleviate mineral deficiencies, such as Hackberry (Celtis sp.), Soapbrush (Porlieria sp.), Jujube (Ziziphus sp.), Desmanthus sp., Cenizo (Leucophyllum sp.), and Huisache (Acacia sp.) brush; Hall's Panicum (Panicum sp.), and Buffelgrass (Cenchrus sp.).