Effect of Starch Addition to Concentrate Supplemented at Low Levels in Forage-Finished Beef Cattle on Growth Performance, Carcass Traits, Fatty Acid Profile and Meat Quality.

ARMSTRONG-PRICE, CAITLIN THERESA. Effect of Starch Addition to Concentrate Supplemented at Low Levels in Forage-Finished Beef Cattle on Growth Performance, Carcass Traits, Fatty Acid Profile and Meat Quality. (Under the direction of Matthew H. Poore). The effect of low level starch supplementation on carcass characteristics in pasturefinished beef cattle is not currently known. An experiment was conducted to compare a fiberbased concentrate with a concentrate containing added starch from ground corn on cattle performance, carcass characteristics, and fatty acid profile. In a two year study (2015, 2016) Angus and Angus x Simmental crossbred yearling cattle (heifers n=23; steers n=40) were separated into four groups balanced by weight and sex before each group was randomly assigned to one of two treatments. Treatment 1 (TRT 1) received a concentrate pellet of 50% soybean hulls and 50% corn gluten feed while Treatment 2 (TRT 2) received a concentrate composed of 50% TRT 1 pellets and 40.5% ground corn and 8.5% soybean meal. Supplements were isonitrogenous and fed at 1% of BW (dry matter basis) which was recalculated based on body weight and adjusted every 28d. Groups were randomly allotted to predominately fescue pastures and rotationally grazed for an average of 180d in Year 1 (March to September 2015) and 245d in Year 2 (March to November 2016). The progressively heaviest 2 or 3 animals/group were selected and cattle were slaughtered on 4 dates between August to October in Year 1 and October to November in Year 2. An average of 1912.0 kg/ha biomass with 14.7 % CP and 66.7% TDN in Year 1 and 4345.6 kg/ha biomass with 11.4 % CP and 64.6 % TDN in Year 2 was available throughout the finishing periods and were statistically different (P < 0.05) between years. Hot carcass weights were recorded at slaughter and back fat, marbling score, and ribeye area were obtained between the 12 and 13 rib after 11d in Year 1 and 8d in Year 2 of dry aging. Two 2.5 cm thick longissimus muscle samples were collected from each carcass at the 13 rib, vacuum sealed, and frozen at -16°C prior to slice shear force and subcutaneous fat color analyses. One longissimus muscle sample was ground, lyophilized, and homogenized prior to performing ether extract of crude fat and fatty acid profile analysis. Data were analyzed using GLM procedures in SAS. Growth performance was significantly different (P < 0.05) by year, regardless of treatment, for time to finish and initial BCS which were greater in Year 2, average daily gain, change in BCS, serum urea nitrogen, and dressing % which were all greater in Year 1. Initial BCS was significantly higher (P < 0.05) in TRT 2 and change in BCS was significantly greater (P < 0.05) in TRT 1 regardless of year. Neither final weight, final BCS, or carcass weight were significantly different (P > 0.05) for treatment, year, or treatment*year. Carcass data collected showed increased (P < 0.05) back fat deposited in TRT 1 cattle and significantly greater a* measurement for back fat color in TRT 2 regardless of year. Other back fat color measurements, L* and b*, and longissimus muscle area were not significantly different (P > 0.10) among treatment, year, or treatment*year. Kidney, pelvic, and heart fat was increased significantly (P = 0.0003) and back fat color measurement a* was significantly less (P < 0.0001) in cattle finished in Year 2. Carcasses had an average yield grade of 2.6, marbling score of 5.5, and USDA quality grade of low choice (17.2) which in addition to meat tenderness and crude fat content were not significantly different (P > 0.10) for treatment, year, or treatment*year. Cattle finished in Year 2 had significantly higher (P < 0.05) stearic acid and margaric acid regardless of treatment where other SFA were not affected by treatment, year, or treatment*year. Most MUFA and PUFA were not significantly different (P > 0.10). Palmitoleic, vaccenic, cis-vaccenic, ALA, EPA, and DHA as well as total omega-3 fatty acid, omega-6: omega-3 ratio, and the total unidentified fatty acids were higher (P < 0.05) for cattle finished in Year 1 regardless of treatment. A significant treatment effect was observed in stearic and vaccenic being higher (P < 0.05) in TRT 2 compared to TRT 1 regardless of year. Significant treatment*year interactions (P < 0.05) were reported for vaccenic acid, ALA, DPA, total omega-3 fatty acid, and total MUFA. The presence of high quality forages for grazing during the finishing period may have a more significant impact on growth, carcass characteristics, and meat quality regardless of the addition of starch to a fiber-based concentrate. Supplementation of a fiber based concentrate without additional starch may be beneficial for creating a healthier fatty acid profile from a human health perspective. © Copyright 2017 Caitlin Theresa Armstrong-Price All Rights Reserved Effect of Starch Addition to Concentrate Supplemented at Low Levels in Forage-Finished Beef Cattle on Growth Performance, Carcass Traits, Fatty Acid Profile and Meat Quality by Caitlin Theresa Armstrong-Price A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science