The effect of pregnancy and lactation on diet composition and dietary preference of goats in a desert rangeland

Composition of diets and dietary preference of goats in two physiological states: pregnancy and lactation, were investigated using microhistological analysis of fecal samples. The study was conducted during the growing season in a desert rangeland in northern Mexico. Non-pregnant goat diets contained a larger (P < 0.01) proportion of shrubs (70.9. ± 38.9) when compared with pregnant does (43.1 ± 31.2). On the other hand, pregnant goats utilized more (P < 0.05) forbs (48.8 ± 18.8) than non-pregnant goats (28.4% ± 12.1). Grasses made up 8% of the pregnant does diet, but this food group was avoided by non-pregnant does. Non-lactating goat diet was dominated by shrubs (71% of the total diet) and forbs (27%), while forbs occurred in greater (P < 0.05) amounts in the lactating goat diets. The similarity index for all forage species (where 0 = no dietary overlap and 100 = identical diets) was 80 for the pregnant and non-pregnant does, and 76 for lactating and non-lactating goats. This study demonstrated that both gestation and lactation accounted for some dissimilarities in food selection of goats. Increased nutrients requirements of these animals was associated with a higher utilization of native forbs and grasses, which suggests that, under harsh range conditions, goats adjust their diet selection according to their nutritional needs.