Date of Graduation

8-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Animal Science (PhD)

Degree Level

Graduate

Department

Animal Science

Advisor/Mentor

Rosenkrans, Charles F. Jr.

Committee Member

Looper, Michael L.

Second Committee Member

Rorie, Rick W.

Third Committee Member

Kreider, David L.

Fourth Committee Member

Anthony, Nicholas B.

Keywords

Biological sciences; Beef heifers; Fescue; Grazing

Abstract

Eighty Brahman-influenced cows (5.6 BCS) were assigned to graze common bermudagrass (CB) or toxic tall fescue (E+) during a 60-d breeding season. Body condition (BC) was assessed at d 0, 30, and 60 of breeding season. Cows were managed to achieve marginal (4.2 BCS) or good (6.3 BCS) BC during last trimester. Heifer birth and weaning (WW; 7 to 8 mo) weights were recorded. The Angus sired heifers were weighed and randomly assigned to E+ or non-toxic (Novel) tall fescue at 9 to 10 mo of age for 190d. Heifer weight, growth data, and antral follicle count (AFC) were collected at yearling (11 to 12 mo) and prebreeding (13 to 14 mo). Pasture was experimental unit and heifer age as covariate. Main effects were cow conception forage (ConFor), conception BC (ConBC), last trimester BC (LateBC), and heifer fescue grazed during development (Hfes). Cows grazing E+ ConFor had heifers that weighed less at birth than heifers from cows grazing CB (33.3 vs. 35.2 kg). Cow ConFor x LateBC interaction affected heifer weight and pelvic area. Heifers developed on E+ from marginal-ConBC, E+ ConFor, and marginal-LateBC cows had the lowest ADG. Novel heifer AFC from good-ConBC, CB ConFor, and marginal-LateBC cows was greater than E+ AFC from marginal-ConBC, CB ConFor, and good-LateBC cows (25.1 vs. 3.8 follicles). Cow LateBC x Hfes affected heifer pregnancy rate (90.3, 69.6, 50.0, and 43.8 percent, Novel heifers from good-LateBC cows, Novel heifers from marginal-LateBC cows, E+ heifers from good-LateBC cows, and E+ heifers from marginal-LateBC cows, respectively). Ensuring adequate conception and late-gestation BC and developing heifers on Novel fescue will increase pelvic growth, number of antral follicles, and pregnancy rates of heifer offspring. Industry applicable tools such as monitoring cow BCS, using skeletal growth indicators, and grazing Novel fescue could be beneficial in selecting replacement heifers.

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