Sequence grazing systems on the southern plains

Abstract

Eastern gamagrass (Tripsacum dactyloides (L.) L.) is a perennial warm-season bunchgrass that starts growth earlier in the spring than most other warm-season grasses. This suggests that combining eastern gamagrass with other warm-season grasses in a sequence grazing system could lengthen the period of rapid livestock gain. We studied sequence grazing systems consisting of eastern gamagrass and Old World bluestem (Bothriochloa ischaemum L.) (EG-OWB) as compared to native mixed prairie and Old World bluestem (Native-OWB) from 1993 to 1997. Crossbred beef steers averaging 239 kg grazed eastern gamagrass or native pasture from early May to early June and again from late July through August. Old World bluestem was grazed in mid season. We measured forage yield and nutritive value and steer gain. Standing forage of eastern gamagrass above a 15-cm stubble height averaged 895 kg ha-1 at the start of the first grazing period and 2,430 kg ha-1 at the start of the second grazing period. Dry, cold winter and spring weather reduced this amount to 80 kg ha-1 in May 1996 and precluded grazing the eastern gamagrass that season. Crude protein content of eastern gamagrass was greater than 14% and in vitro dry matter disappearance (IVDMD) was greater than 65% in May. By August, crude protein content had dropped to 5-8% and IVDMD was 45-50%. Peak standing crop of Old World bluestem averaged 4,580 kg ha-1 over years. Steer gain over the entire grazing season, 103 days, did not differ between forage systems, averaging 1.02 kg head-1 day-1 in both systems. Steer gain was higher on native pasture than eastern gamagrass in the late grazing season (0.91 versus 0.60 kg head-1 d-1, p=0.02). As a result of higher stocking rates, steer gain was 257 kg ha-1 for the EG-OWB system and 103 kg ha-1 for the Native-OWB system (p<0.01).