Advisor

Macoon, Bisoondat

Committee Member

Lang, David J.

Committee Member

Reddy, K. Raja

Committee Member

Vann, Rhonda C.

Committee Member

Ward, Stephanie H.

Date of Degree

1-1-2013

Document Type

Dissertation - Open Access

Major

Agricultural Science (Agronomy)

Degree Name

Doctor of Philosophy

College

College of Agriculture and Life Sciences

Department

Department of Plant and Soil Sciences

Abstract

Incremental gains in productivity from new forages are likely to be very small in developed countries like the USA where forage research is highly advanced, thus animals must be used in determining their value. Three experiments were conducted. Experiment I evaluated grazing preference of cattle and its relationship with morphological and chemical characteristics. Treatments were two diploid cultivars ‘Marshall’ and ‘Gulf’ and two tetraploid cultivars ‘Maximus’ and ‘Nelson’ arranged in a 4 × 4 Latin square design experiment. Animal preference was based on herbage disappearance, the Chesson-Manly index, and animal grazing time. Both herbage disappearance (1400 vs. 890 kg ha-1) and Chesson-Manly index (8.1 vs. 5.8%) were greater for tetraploid than diploid cultivars. Experiment II quantified forage and animal response of a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass. Three stocking rates (SR), 3.75, 5, or 7.5 animals ha-1, were imposed on the two cultivars in a 3 × 2 factorial of a CRD experiment with two replications. Angus cross-bred heifers (initial BW = 240 kg) were used. There was no cultivar effect or any interactions on ADG or herbage mass (HM). Both ADG (1.22 kg d-1 at low SR to 0.98 kg d-1 at high SR) and HM (3.8 Mg ha-1 at low SR to 2.5 Mg ha-1 at high SR) had a linear response to SR. Experiment III quantified forage production, morphological characteristics, and nutritive value between a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass cultivar harvested at three different leaf stages 2-, 3-, and 4-leaves tiller-1 and two stubble heights 5 and 10 cm. Treatments were arranged in a 3 × 2 × 2 factorial of a RCBD experiment with four replications. In 2011, there was a linear increase in forage harvested from 2-leaf (7.3 Mg DM ha-1) to 4-leaf stage (8.8 Mg DM ha-1) and in 2012 the response was quadratic with the highest forage harvested at 2- and 4-leaf stages (7.6 Mg DM ha-1). These results indicate that cultivars of annual ryegrass varied in their responses to grazing preference, grazing management, and defoliation management based on leaf stage.

URI

https://hdl.handle.net/11668/19883

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