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. (c) 2004 Elsevier B.V. All rights reserved.