Doctoral Dissertations

Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

F. Neal Schrick

Committee Members

Christopher N. Boyer, John T. Mulliniks, Renata N. Oakes, Ky G. Pohler, Brynn H. Voy

Abstract

Three studies were conducted to determine the effects of stockpiled winter forage species and protein supplementation strategy on heifer growth, reproductive performance, nutritional status, rumen fermentation, and the economic implications of forage-based heifer development. In all three studies, spring-born, beef heifers were stratified by BW and randomly assigned to 1 of 3 stockpiled forages: (1) endophyte-infected tall fescue (TF, Schedonorus arundinaceus (Schreb.) Dumort) (2) big bluestem (Andropogon gerardi Vitman) and indiangrass (Sorghastrum nutans L.) combination (BI), or (3) switchgrass (SG, Panicum virgatum L.). Forage treatments were randomly allocated to receive 1 of 2 supplement types: (1) 0.68 kg·heifer-1·d-1 of dried distiller’s grains with solubles (DDGS) or (2) 0.22 kg·heifer-1·d-1 of blood meal and fish meal (BF), resulting in a 3 × 2 factorial arrangement of treatments. Treatments were initiated in January and concluded in April at the onset of the breeding season. In Exp. 1, BW was greater (P < 0.01) for TF heifers, resulting from an increased (P < 0.01) ADG from initiation to breeding for TF heifers. From January to April, heifers grazing SG and BI pastures had a negative ADG; however, from breeding to final pregnancy diagnosis, SG and BI heifers compensated and had greater (P < 0.01) ADG than TF heifers. Pregnancy rates at fixed timed-AI and overall pregnancy rates did not differ (P ≥ 0.38) by forage or supplement treatment. In Exp. 2, heifers grazing SG pastures had greater (P = 0.04) ruminal acetate concentrations than their counterparts. However, ruminal concentrations of propionate and butyrate were not influenced (P > 0.32) by forage species. Due to an increase in ruminal acetate concentration, ruminal acetate:propionate ratio was greater (P = 0.04) for heifers grazing SG pastures. In Exp. 3, total cost of producing a heifer’s first calf using the three forage-based systems was $1,079 to $1,149/head with tall fescue (TF) being the most expensive forage-based heifer development forage system. Overall, low-input heifer development using stockpiled warm-season forages and protein supplementation may be a viable opportunity to extend the grazing season, lower production costs, and select for more efficient replacement females in the southeastern United States.

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