Response of Tropical Grasses to Stocking Rate1

Abstract

AbstractDuring favorable growing conditions tropical stargrasses (Cynodon spp.) are highly productive, producing more forage than is utilized by cattle under normal stocking rates, and resulting in large amounts of low quality, standing residue. Therefore, grazing trials were conducted to study the effects of three stocking rates (SR) (7.5, low; 10, medium; and 15 cattle/ha, high) on forage yield, quality, utilization and animal performance of three stargrasses: ‘UF‐5’ and ‘McCaleb’ (Cynodon aethiopicus Clayton and Harlan) and ‘UF‐4’ (Cynodon nlemfuensis Vanderyst var. nlemfuensis). Additionally, the medium SR was imposed on “Transvala” digitgrass (Digitmia decumbens Stent.) and “Pensacola” bahiagrass (Paspalum notatum Flugge). The average annual dry matter (DM) yields of stargrasses at low, medium, and high SR and of digitgrass and bahiagass at medium SR were 17.0, 18.3, 20.1, 15.0, and 10.0 metric tons/ha, respectively. In 1976, the in vito organic matter digestibility of digitgrass (51%) and UF‐5 (49%) was superior to that of UF‐4 and McCaleb (46%) stargrass with bahiagrass averaging 46% and 50% in 1976 and 1977, respectively. Crude protein in all entries was similar, averaging 9.9%. Seasonal DM utilization (75 to 95%) of stargrass by cattle was directly related to SR. However, forage intake of 7.6 kg DM/animal/day at the high SR was lower than at the medium (9.3) and low SR (10.2). Forage DM consumed annually (168‐day period) at the medium SR averaged 16.7 metric tons/ha For stargrasses, 14.9 for digitgrass and 9.9 for bahiagrass. Cattle average daily gain (ADG) over seasons ranged from 0.18 to 0.56 kg/dayfor stargrasses, and was an inverse linear function of SR. The ADG measured at a 6‐week interval was a curvilinear function of grazing pressure (GP) with an optimum GP of 6 to 8 kg available forage DM/100 kg body weight/day at 7.5 cm height of cut. Seasonal (168 days) beef gains (2‐year average) on stargrasses were 470, 617, and 576 kg/ha at the high, medium, and low SR, respectively. The ADG and beef product/ha at the medium SR in 1976 on stargrass, digitgrass, and bahiagrass averaged 0.35, 0.28, 0.22, kg/day, 580, 461, and 396 kg/ha, respectively. These data indicated that although ADG is low, high yields of total beef/ha can be obtained with proper stocking rates and correct grazing pressure on stargrass pastures.