Height to withers and abdominal circumference effects on diets of grazing goats

Abstract

Diet selection in an arid rangeland of northern Mexico by short (height to withers <71 cm) and tall (>77 cm) multiparous non-pregnant, non-lactating does and the diets of multiparous non-pregnant, non-lactating does with reduced (<92 cm) and large (>101 cm) abdominal circumference is described from microhistological analysis of fecal samples. In the rainy season tall goats tended to rely more heavily (P<0.10) on shrubs than short goats (71.4% versus 63.3%), but in the dry season the diet of both groups of goats contained equal amounts of shrubs. The proportion of forbs in the goats’ diet did not vary between stature groups in either season, but during the rainy season short goats selected more (P<0.05) grasses (7.5% versus 2.0%) than tall goats. Shrubs and forbs were eaten in equal amounts by does with reduced and large abdominal circumference during both seasons, but goats with reduced abdominal circumference tended to select more (P<0.10) grasses, compared to goats with larger abdominal circumference. The mean similarity index for tall and short goats was 73, whereas this index was 77 for goats with reduced and large abdominal circumference. For all classes of goats shrubs and forbs were preferentially selected over grasses. These data indicate that a larger body size seems to confer advantages in this plant community where browse is the predominant food resource. These results also indicate that goats with reduced abdominal circumference tended to select less preferred forages than those with large abdominal circumference.