Document Type

Thesis - Open Access

Award Date

2025

Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

Warren Rusche

Abstract

Recently, cattle feeders have extended days on feed (DOF) resulting in hot carcass weights (HCW) exceeding the limits of existing serial slaughter datasets. This study's goal was to determine the impact extended DOF exerts on growth performance, feed efficiency, and carcass characteristics of steers and heifers with varying proportions of Angus (AN) and Limousin (LM) genetics. In 2022, commercial AN cows from two MT ranches were artificially inseminated to 9 sires from 3 breeds (AN, LM, and Limflex (LF)) with parentage confirmed by DNA. In 2023, 216 calves (sired by 72 AN, 73 LF, and 71 LM; 105 steers and 111 heifers) were shipped to Brookings, SD and preconditioned until study initiation in January 2024. Calves were allotted to 1 of 3 pens (~72 calves/pen) and fed a common finishing diet ad libitum. Insentec nodes (12/pen) captured individual intake. Cattle were implanted on d 28 (100 mg trenbolone acetate and 14 mg estradiol benzoate; SYNOVEX Choice, Zoetis, Parsippany, NJ) and reimplanted on d 104 (200 mg trenbolone acetate and 28 mg estradiol benzoate; SYNOVEX One Feedlot, Zoetis). On d 78, Insentec nodes were designated for heifers to accommodate feeding melengestrol acetate. On day 141, cattle were assigned to one of three slaughter groups with equivalent body weights and balanced across sex, sire breed, and sire within breed. Respective groups were weighed and shipped to a commercial abattoir for slaughter on d 200, 235, and 270, respectively. Data were analyzed using PROC GLIMMIX (SAS Institute, Cary, NC) with fixed effects of sire breed, sex, and DOF. Source herd was a random effect; individual animal was the experimental unit. Percent USDA Choice and Prime exceeded 90% for all slaughter groups. A tendency for a breed x sex effect on dressing percentage was observed, with greater values for LM and LF heifers (P < 0.09). Extending DOF increased final weight (FBW) and HCW (P < 0.01), ribeye area (REA; P < 0.01), and rib fat (RF; P = 0.01). Increased DOF increased carcasses with HCW > 499 kg (P < 0.01) and increased marbling in steers (P = 0.02) but not heifers (P = 0.93). Additional DOF did not affect cumulative ADG (P = 0.24) but did worsen G:F (P < 0.01). Sire breed did not affect FBW, HCW, or ADG (P 􀋔 0.76), but increasing LM influence reduced DMI (P < 0.01), improved G:F (P < 0.01) and reduced percentage YG 4 & 5 (P = 0.04). Greater AN influence increased marbling, RF, and YG (P < 0.05). Steers were heavier and more efficient (P < 0.01) with greater REA, less RF and marbling (P < 0.05) compared to heifers. Calves sired by different breeds responded similarly to extended DOF; increasing DOF resulted in fatter, heavier carcasses with increased marbling in steers.

Library of Congress Subject Headings

Beef cattle -- Feeding and feeds. 
Beef cattle -- Growth. 
Beef cattle -- Weight. 
Beef cattle -- Carcasses. 
Beef cattle -- Feed utilization efficiency. 
Aberdeen-Angus cattle -- Genetics. 
Limousin cattle -- Genetics.      

Publisher

South Dakota State University

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Beef Science Commons

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Rights Statement

In Copyright