FORAGE INTAKE AND INGESTIVE BEHAVIOR OF CATTLE GRAZING OLD-WORLD BLUESTEMS

Many native and introduced warm-season grasses are being seeded as a c onsequence of crop reduction programs; however, little is known about the intake and ingestive behavior of cattle (Bos taurus L.) grazing su ch grasses. The influence of differences in herbage mass, sward height , and morphological composition of old world bluestem (Bothriochloa sp p.) pastures on herbage intake and ingestive behavior of steers were e xamined over the course of two grazing seasons at El Reno, OK. Soils w ere fine-silty Pachic Haplustolls of the Dale series. Swards of 'Cauca sian' [B. caucasica (Trin.) C.E. Hubb.] and 'Plains' [B. ischaemum (Ha ck.) Celarier & Harlan var. ischaemum (L.) Keng.] old world bluestem w ere maintained within the range of 0.5 to 5 Mg ha-1 by continuous vari able 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 almost-equal-to 250 kg. Results showed that changes in sward height had little influe nce on organic matter intake or ingestive behavior, but changes in her bage mass, green mass, total green leaf proportion, and leaf proportio n had more effect. Diet digestibility was most influenced by the propo rtion 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 ingest ive behavior were highly influential on intake. Management of old worl d bluestems should aim to maintain swards with a high proportion of gr een leaf.