A systematic review of the impact of minerals on pregnant sheep and goats and their offspring in the African continent

Abstract

The dams' physiological status (gestational stages, lactation, and dry period) is crucial in utilising minerals. The mechanisms controlling the utilisation of minerals during pregnancy are inadequately understood. Unsuitable nutrition, especially from mid to late pregnancy in ewes, affects mammary development, milk production potential, the birth weight, health and survival of the offspring. This study aimed to review knowledge from studies in Africa on mineral status intake and its impact on performance and health of pregnant ewes or does and on the health and survival of their offspring. The study aimed to establish areas where information lacks, identifying extensive management systems on minerals used to meet the needs of the pregnant dam and their offspring within African conditions. Twelve Web of Science databases were used and cohort, cross sectional, case control and analytical studies were considered. Global (4132) articles, comprising 431 African studies, were identified during the review. The number was reduced to 10, fulfilling the selection criteria indicated in a Prisma flow graph. These selected studies covered a 40-year period (1975 to 2015). The minerals investigated were: Iodine (I), selenium (Se), zinc (Zn), copper (Cu), iron (Fe), calcium (Ca), manganese (Mn), magnesium (Mg), chromium (Cr), cadmium (Cd), molybdenum (Mo) and lead (Pb). Most studies conducted globally on this topic, focused on Ca, Mg and Se, followed by Cu, I, P and Zn. Studies conducted in Africa focussed on Se and Zn. Adequate Zn, Se and Cu supplementation indicated improved survival and weight gain in the offspring. Selenium plasma levels were higher, and Zn and Cu levels were lower in pregnant ewes and does. Cu levels increased in older goats. Zn plasma levels were higher in kids, aged four to six months, than those of nine to twelve months. Supplementation of I increased lambing but not kidding rates. Half of the studies were conducted in areas with mineral deficiencies (Se and I) or holding known high soil Na levels. Previous studies investigated normal plasma levels in pregnant and lactating ewes and does. More recent studies on sheep, offered more comprehensive information, whilst those on goats mostly inclined to be significantly neglected, focussing on baseline values of minerals at various life stages. Small stock farming in Africa is mainly extensive. These African studies were predominantly conducted under intensive or semi-intensive conditions. A need for specific studies within the continent was identified. These should be based on the unique nature of each region and its influence on the dam and offspring, to adequately provide for mineral requirements in optimal growth and health of the kid and lamb. This is especially important for the significant number of goats across the African continent, as inadequate research data are available.