Age and body condition score and diets of grazing goats

Abstract

Diet selection by juvenile and adult non-pregnant, non-lactating goats and the diets of adult non-productive goats with low (≤ 1.5; grading scale 0-5) and moderate (≥ 2.5) body condition score (BCS) are described by microhistological analysis of fecal samples for a Chihuahuan desert vegetation in northern Mexico. In the rainy season, adult goats utilized more (P < 0.10) shrubs than juvenile goats (70.4 vs 58.6%), but, in the dry season, the diet of both groups contained equal amounts of shrubs. The proportion of forbs and grasses in the goats' diet also tended to vary (P < 0.10) between age groups in the rainy season. Juvenile goats generally had lower consumption of plants with spines than adult goats. Goats with low BCS selected more (P < 0.10) shrubs than goats with moderate BCS in the rainy season. Forbs were eaten in larger amounts by does with moderate BCS (38% of the diet) during the rainy season compared to goats with low BCS (30.9%). Regardless of age and body reserves, grasses formed less than 5% of goat diets in both seasons. Mean similarity index for juvenile and adult goats was 75, while mean similarity index for goats with low and moderate BCS was 78. For all classes of goats, Larrea tridentata (DC.) Cov., the dominating species in the plant community, was the only plant selected at proportions below those found in ground cover in the rainy season. These data indicate that, during the rainy season, juvenile goats mixed their diets to achieve more even use of forages than adult goats. These results also indicate that high utilization of shrubs, including resinous and fibrous forages, appeared to be an adaptive foraging strategy of goats with low fat reserves, when forage was readily available.