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PRODUCTION PAPER

Canopy Height and Nitrogen Supplementation Effects on Performance of Heifers Grazing Limpograss

^a Agron. Dep., P.O. Box 110300, Univ. of Florida, Gainesville, FL 32611-0300
^b Dep. of Anim. Sci., P.O. Box 110910, Univ. of Florida, Gainesville, FL 32611-0910

* Corresponding author (les{at}mail.ifas.ufl.edu)

Received for publication December 10, 2001. Leaf percentage and herbage crude protein (CP) are greater in the upper than lower half of limpograss [Hemarthria altissima (Poir.) Stapf & Hubb.] canopies; thus, canopy height may affect N status and cattle (Bos spp.) weight gain. Average daily gain (ADG) of beef heifers and sward characteristics were measured on continuously stocked limpograss pastures grazed to heights of 20, 40, and 60 cm, with cattle receiving 0 or 0.8 kg d^-1 of a 44% CP corn (Zea mays L.)–urea mixture. Cattle grazing 20- and 60-cm pastures increased ADG by 200 g when supplemented (to 590 g); however, cattle grazing 40-cm pastures tended to have greater ADG when not supplemented (644 g) vs. when supplemented (536 g). Herbage mass and allowance increased with increasing canopy height, partially explaining greater ADG of unsupplemented cattle grazing 40- vs. 20-cm swards. The 40-cm canopies also had lower herbage bulk density, allowing greater opportunity for selection of leaf than in 20-cm canopies. Stocking rate increased linearly (5.9–8.5 head ha^-1) as canopy height decreased from 60 to 20 cm, and gain per hectare increased linearly with decreasing canopy height for both unsupplemented (161–352 kg) and supplemented (273–378 kg) treatments. Data suggest stubble height is an important determinant of heifer performance. A 40-cm canopy height may be near optimum because of greater herbage allowance and opportunity to select leaf than in dense 20-cm canopies and less trampling and greater leaf proportion and accessibility than in 60-cm swards.

Abbreviations: ADG, average daily gain • BUN, blood urea nitrogen • CP, crude protein • DOM, digestible organic matter • DM, dry matter • HA, herbage allowance • HM, herbage mass • IVOMD, in vitro organic matter digestibility

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