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Variation in browse nutrient content in western Oklahoma throughout the growing season

R. C. Merkel1, A. L. Goetsch1, M. Moseley2, R. Blackwell3, and T. Curtis4

1E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK
2USDA NRCS, Stillwater, OK
3U.S. Forest Service, USDA/Black Kettle National Grassland, Cheyenne, OK
4USDA NRCS, Taloga, OK

Leaves of browse species were sampled from May to September in west central (WC) and western OK (W) to determine changes in chemical composition throughout a growing season. Shinnery oak (SH, Quercus havardi) and sumac (SU, Rhus copallina) were sampled at each site. Blackjack oak (BK, Q. marilandica) and post oak (PK, Q. stellata) were sampled in WC and locust (LC, Gleditsia triacanthos), sand plum (SP, Prunus angustifolia), and skunkbush (SK, R. aromatica) in W. Sites were divided into three areas for sampling with three replications taken of each species in each area, frozen, and freeze dried. Samples were analyzed for DM, ash, N, NDF, ADF, ADL, and true IVDMD (NDF as end-point measure). The DM percentage tended to increase throughout the growing season (P < 0.01). There was a species by date interaction (S x D) in ash concentration (P < 0.01), with level increasing through mid-summer and then stabilizing or declining slightly. There was no difference in N level among WC species (P > 0.05), and N level was lowest in August (S x D; P < 0.01). In W, LC had higher N (P < 0.01) compared with other species. In WC, oak species had higher NDF, ADF, and ADL throughout the growing season compared with SU (P < 0.05), while in W NDF concentrations ranked SH > LC > SU, SK, and SP (P < 0.05). NDF in WC was highest in July and decreased thereafter, whereas in W, NDF concentration tended to increase throughout the growing season (S x D; P < 0.01). IVDMD of oak species in WC was lower (P < 0.05) than in SU throughout the collection period. Exceptionally high IVDMD, over 90%, was recorded for SU in both WC and W. Trends in nutrient content found over a 5- month sampling period indicate that, in general, tree leaves decrease in N concentration and increase in fiber and lignin contents.


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