About 40,000 km(2) of the Caldenal in central semiarid Argentina are r
angelands where the most important economic activity is cow-calf opera
tions. Some information on forage species, mainly regarding taxonomy,
ecophysiology, and nutritive value, is available, but detailed studies
on composition of free-ranging cattle diets are lacking. The objectiv
e of this work was to study the botanical composition and seasonal tre
nds of cattle diets in the southern Caldenal. Diets were studied throu
gh microscopic analysis of cattle feces collected monthly in a typical
plant community during a 12-month period. Grasses were the bulk of th
e diets, except in November when more than 50% of the diet was Medicag
o minima (L.) Grufberp. Highest consumption among the grasses was of P
iptochaetium napostaense (Speg.) Hack., one of the dominants in the gr
ass layer. High consumption of Pappophorum mucronulatum Nees, one of t
he few warm-season grasses in the region, was found during the summer.
Calden (Prosopis caldenia Burk.) pods, consumed in late summer and fa
n, were the only woody fragments found in appreciable amounts. Classif
ication and ordination techniques were used to analyze seasonal trends
. In spite of a relatively high homogeneity in the diets, 2 well-defin
ed seasonal trends were detected, one in the fall-winter period and an
other in the spring. Cattle diet diversity was minimum during the cold
est months of the year.