Cattle Diet Selection during the Growing Season on Upland Sandhills Rangelands

Authors

• Alejandro Orozco-Lopez, University of Nebraska-LincolnFollow

First Advisor

Mitchell B. Stephenson

Committee Members

J. Travis Mulliniks, Jerry D. Volensky

Date of this Version

4-2022

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Agronomy

Under the supervision of Professor Mitchell B. Stephenson

Lincoln, Nebraska, April 2022

Comments

Copyright © 2022, Alejandro Orozco-Lopez. Used by permission

Abstract

The Sandhills is a diverse and complex ecosystem comprised of different topographic positions (i.e. slopes and interdunes) that influence grazing distribution, plant species composition, and cattle diet selection. The first objective of this study was to evaluate how grazing intensity influences species composition on slopes and interdunes on native rangeland within the Hillside pasture (160 ha) at the UNL Gudmundsen Sandhill’s Laboratory (GSL). The second objective of this study was to evaluate forage quality of individual species from three plant functional groups (i.e. warm-season grasses, cool-season grasses, and forbs/shrubs) on native rangeland within the Hillside pasture (160 ha) at GSL. Forage quality samples were taken from 4 warm-season grasses, 5 cool-season grasses grass, 1 forb, and 2 shrubs. Samples were collected every 7-15 days from mid-May to early August in 2020 and 2021. The third objective of the study was to evaluate diet composition of cattle grazing (n = 40) within the pasture during the growing season using fecal DNA barcoding (fDNA). Fecal samples were collected from 7-8 cows every 10-20 days from early June to late-July in 2020 and 2021. Frequency of occurrence of western ragweed was 28 percentage points greater (P =0.03) on high grazing intensity interdunes than low intensity grazing interdunes. Additionally, there was a trend (P = 0.07) for greater Kentucky bluegrass on high grazing intensity interdunes compared to low intensity grazing interdune. When averaged across the growing season, CP of forbs/shrubs was 3.3 and 2.9 percentage points greater than cool-season grasses and warm-season grasses (P < 0.05). However, there were no differences (P > 0.1) in CP between warm- and cool-season grasses or functional group x collection date interactions. Diet selection as determined by fDNA indicated that cattle obtained most of their dietary protein from cool-season grasses (43.6% ± 1.5) and forbs (29.1% ± 1.5), while shrubs (13.0% ± 1.5) and warm-season grasses (3.5% ± 1.5) contributed significantly less (P < 0.01) to the cattle diets. This research highlights the influence of grazing intensity on species composition and the influence of time during the growing season on forage quality and cattle diet selection within the Sandhills.

Advisor: Mitchell B. Stephenson