Forage Intake and Ingestive Behavior of Cattle Grazing Old World Bluestems

Abstract

AbstractMany native and introduced warm‐season grasses are being seeded as a consequence of crop reduction programs; however, little is known about the intake and ingestive behavior of cattle (Bos taurus L.) grazing such grasses. The influence of differences in herbage mass, sward height, and morphological composition of old world bluestem (Bothriochloa spp.) pastures on herbage intake and ingestive behavior of steers were examined over the course of two grazing seasons at El Reno, OK. Soils were fine‐silty Pachic Haplustolls of the Dale series. Swards of ‘Caucasian’ [B. caucasica (Trin.) C.E. Hubb.] and ‘Plains’ [B. ischaemum (Hack.) Celarier & Harlan var. ischaemum (L.) Keng.] old world bluestem were maintained within the range of 0.5 to 5 Mg ha−1 by continuous variable stocking. Five grazing trials were conducted using a total of 20 swards over the 2 yr. In both years, pastures were grazed from mid‐May to late September by steers with an initial weight of ≈250 kg. Results showed that changes in sward height had little influence on organic matter intake or ingestive behavior, but changes in herbage mass, green mass, total green leaf proportion, and leaf proportion had more effect. Diet digestibility was most influenced by the proportion of green leaf in the sward. Organic matter intake increased with increasing green leaf mass to 1.07 Mg ha−1 and then decreased. Intake per bite and grazing time also increased as proportion of green leaf and herbage mass increased, respectively. These two measures of ingestive behavior were highly influential on intake. Management of old world bluestems should aim to maintain swards with a high proportion of green leaf.