Season and sex influences on botanical composition of cattle diets in southern New Mexico.

Abstract

We conducted a study in southern New Mexico to determine seasonal variation in botanical diet composition of cattle and to compare cow and steer diets. The climate and vegetation is typical of semidesert grassland. Fecal samples were obtained from a group of cows and steers during spring, summer, fall, 1989; winter and summer, 1990. Results showed that cattle diets were highest in grass content during spring (57%), summer (78%), and winter (54%), while fortes comprised the highest proportion of cattle diets during the fall (47%). Shrubs were moderately important during winter (18%). Dropseeds (Sporobolus spp.), black grama (Bouteloua eriopoda [Torr.] Torr.), threeawn species (Aristida spp.), and leatherweed croton (Croton pottsii [Klotzch] Muell. Arg.) were key forage species for cattle. The importance of these species varied with season, availability, physiological stage, and presence of other species. Differences between cow and steer diets varied with season. The relative similarity ranged from 70% (fall) to 90% (summer). The lower fall similarity compared to that in the summer might be related to physiological variation or past differences in grazing experience between cows and steers. For practical purposes, steer diets might generally be used to represent cow diets, but caution should be exercised during periods of low forage quality.