Stocking rate and monensin supplemental level effects on growth performance of beef cattle consuming warm-season grasses.

The objective of this study was to evaluate the effects of monensin supplementation on animals receiving warm-season grass with limited supplementation. In Exp. 1, treatments were a factorial combination of 2 stocking rates (1.2 and 1.7 animal unit [AU] [500 kg BW]/ha) and supplementation with monensin (200 mg/d) or control (no monensin) distributed in a complete randomized design with 3 replicates. Thirty Angus × Brahman crossbred heifers (Bos taurus × Bos indicus) with initial BW of 343 ± 8 kg were randomly allocated into 12 bahiagrass (Paspalum notatum) pastures and supplemented with 0.4 kg DM of concentrate (14% CP and 78% TDN) daily for 86 d. Herbage mass (HM) and nutritive value evaluations were conducted every 14 d, and heifers were weighed every 28 d. There was no effect (P ≥ 0.97) of monensin on HM, herbage allowance (HA), and ADG; however, animals receiving monensin had greater (P = 0.03) plasma urea nitrogen (PUN) concentrations. The stocking rate treatments had similar HM in June (P = 0.20) and July (P = 0.18), but the higher stocking rate decreased (P < 0.01) HM and HA during August and September. Average daily gain was greater (P < 0.01) for the pastures with the lower stocking rate in August but not different in July and September (P ≥ 0.15). Gain per hectare tended to be greater on pastures with the higher stocking rate (P ≤ 0.06). In Exp. 2, treatments were 3 levels of monensin (125, 250, and 375 mg/animal per day) and control (no monensin) tested in a 4 × 4 Latin square with a 10-d adaptation period followed by 5 d of rumen fluid collection and total DMI evaluation. Blood samples were collected on d 4 and 5 of the collection period. Ground stargrass (Cynodon nlemfuensis) hay (11.0% CP and 52% in vitro digestible organic matter) was offered daily. The steers received the same supplementation regimen as in Exp. 1. Total DMI was not different among treatments (P = 0.64). There was a linear increase (P ≤ 0.01) in propionate and a tendency for decreased acetate (P ≤ 0.09) concentrations in the rumen with increasing levels of monensin; however, there was no effect (P ≥ 0.19) of monensin levels on ruminal pH and ruminal concentrations of butyrate and ammonia. In addition, there was no effect (P ≥ 0.73) of monensin levels on plasma concentrations of glucose, insulin, IGF-1, and PUN. In summary, monensin supplementation effects were not detected at either stocking rate and may not be effective in increasing performance of beef cattle grazing low-quality warm-season grasses with limited supplementation.

First Report of Alternaria alternata Causing Leaf Spot on Aloe vera in Louisiana.

Aloe vera (L.) Burm. f. is a perennial succulent plant that is grown worldwide mainly for medicinal and cosmetic uses. In the USA, it is mainly cultivated in some southern states to produce aloe gel for the cosmetic industry (3), and in Louisiana it is also sold commercially as an ornamental. During the summer of 2011, several A. vera plants infected with leaf spots were observed on the campus of Louisiana State University, Baton Rouge. Large, necrotic, sunken, circular to oval, dark brown spots were present on both surfaces of the leaves. Infected leaf tissue pieces were surface disinfested with 1% NaOCl solution for 1 min and plated on potato dextrose agar (PDA). Plates were incubated at 28°C in the dark for 4 days. A dark olivaceous fungus with profuse golden brown, branched, and septate hyphae was consistently isolated from the infected tissue on PDA. The fungus produced conidia with longitudinal and transverse septa, and was morphologically identified as an Alternaria sp. (4). Conidia were produced in long chains, pale to light brown, obpyriform, with a beak (6.0 µm long), one to seven transverse and up to three longitudinal septa, and measured 10 to 45 µm long × 7 to 18 µm wide. Conidiophores were straight, septate, light to olive golden brown with conidial scar, and measured 35 to 100 µm long × 2 to 5 µm wide. Genomic DNA from a single-spored isolate was extracted and the internal transcribed spacer (ITS1-5.8s-ITS2) regions were amplified and sequenced using primers ITS1 and ITS4. BLASTn analysis of a 486-bp sequence (GenBank Accession No. JQ409455) resulted in 100% homology with A. alternata strain DHMJ16 (GenBank Accession No. JN986768) from China and several other Alternaria spp. The fungus was identified as A. alternata based on mycelial and conidia characters after being grown under standard, previously described conditions (4). Pathogenicity tests were carried out by inoculating six potted aloe plants with 0.5-cm diameter discs taken from a 6-day-old culture grown on PDA. Four discs were placed on the upper surface of each of the bottom leaves of every plant. Inoculated plants were individually covered with a plastic bag and maintained in a greenhouse for 1 week at 25 ± 2°C. Six control plants received only agar plugs. Seven days after inoculation, necrotic leaf spots were observed on the inoculated plants and A. alternata was reisolated from these spots. No leaf spots were observed on control plants. To the best of our knowledge, this is the first report of leaf spot caused by A. alternata on A. vera in Louisiana. Several outbreaks of the disease have been reported in Pakistan and India as damaging aloe gel production in those countries (1,2). An outbreak of this disease in Louisiana could represent a serious issue for the state's A. vera ornamental commerce. References: (1) R. Bajwa et al. Can. J. Plant Pathol. 32:490, 2010. (2) A. Kamalakannan et al. Australas. Plant Dis. Notes 3:110, 2008. (3) T. Reynolds. Aloes: The Genus Aloe. CRC Press, Boca Raton, FL, 2004. (4) E. G. Simmons. Alternaria: An Identification Manual: Fully Illustrated and with Catalogue Raisonné 1796-2007. CBS Fungal Biodiversity Centre, Utrecht, The Netherlands, 2007.