Graduate Thesis Or Dissertation

 

Heifer performance and drought and grazing effects on flood meadow vegetation Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cv43p231s

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  • Native flood meadows are important for hay production and winter feeding areas in many western states. With the introduction of meadow foxtail (A lopecurus pratensis L.) and other new species, the botanical composition of the meadows has been steadily changing. With shifting priorities occuring on public lands, these flood meadows, many of which are privately owned, will increase in their importance to the livestock industry. This study was conducted on a 23-hectare representative meadow at the Eastern Oregon Agricultural Research Center, Burns, OR. The objectives were to determine drought and grazing effects on botanical composition, yield, and forage quality of meadow foxtail plus other forage species. Also, corn supplementation effects were examined to determine the ramifications on heifer performance. Four 50 X 50 meter experimental sites were established in a meadow with half of each area fenced off to prohibit any grazing. The study was conducted over a two-year period during the late spring/early summer of 1992, a drought year, and 1993, an above normal precipitation year. Data were collected in July of both years and included total yield, percent of total yield, frequency, and basal cover. Forage categories examined included meadow foxtail, sedges, rushes, other grasses, and forbs. Forage quality of meadow foxtail was also measured and included percent organic matter, in vitro OM digestibility, and crude protein content. In 1993, 72 heifers were put on the pasture and fed 0, 0.50, 0.75, and 1.0 kgld of cracked corn in four treatment groups. The average daily gain of each group was determined by weighing the heifers biweekly. Statistical significance was inferred at P0.05 for all parameters. Total yield of meadow foxtail, sedges/rushes, other grasses, and forbs in 1992 was 257, 29, 36, and 69 kg/ha, respectively. Total yield increased significantly in 1993 to 6184, 967, 614, and 430 kg/ha, respectively. The percentage of total yield for meadow foxtail and sedges/rushes increased (68 vs. 76% and 8 vs. 12%, respectively) while that of forbs declined from 16 to 5%. Even though sedges and rushes appeared to benefit from increased precipitation in 1993, the large increase in the frequency and basal cover of rushes (6 vs. 20% and trace vs. 1%, respectively) revealed that rushes increased in number of plants and not just in increased yields while sedges only increased in terms of yield. Meadow foxtail also increased in basal cover (2 vs. 5%), appearing not to be severely affected by the drought and recovering well. Grazing in 1993 favored meadow foxtail as the frequency (53 vs. 82%) increased with no decrease in basal cover. All other forage classes were unchanged. The drought increased forage quality of meadow foxtail although yield was severely depressed. In vitro OM digestibility (58.8 vs. 83.4%) and crude protein (5.0 vs. 27.1%) were decidedly lower in 1993 than in 1992, but organic matter (89.6 vs. 87.5%) was increased. A dilution effect in the wet year of 1993 may have played a role in the large decrease in N concentration due to accelerated growth. Grazing also affected meadow foxtail by increasing protein (5.0 vs. 11.9%) and in vitro OM digestibility (58.8 vs. 67.8%) and decreasing organic matter (89.6 vs. 84.8%). Herbage removal can interrupt development, prevent maturity, and initiate regrowth, thus increasing the amount of higher quality, younger live tissue. Corn supplementation had no effect on average daily gain in any of the four treatment groups of heifers. Average gain across all groups was 1.1 kgld. Failure to increase performance was probably due to the inability to utilize any extra energy because the cattle were operating at maximum protein synthesis capacity.
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