The effects of different feeding strategies providing different levels of vitamin A on animal performance, carcass traits, and the conversion rate of subcutaneous fat color in cull-cows

Abstract

Cull cows represent a significant percentage of revenue received from the U.S. beef industry; however, cull cows are heavily price discounted at time of slaughter. This experiment's objective is to evaluate different feeding strategies and their effects on body condition score, subcutaneous fat color, and carcass yield and quality traits in cull cows. The central hypothesis is feeding a high-energy diet, with low levels of vitamin A, for 56 d will improve animal performance, carcass yield, and quality traits in addition to capturing the point (rate) of the conversion of yellow to white subcutaneous fat. In the present experiment 98 Angus crossbreed cows were utilized. Cows were fed either low vitamin A (LVA) diet consisting of whole shelled corn, soybean hulls, soybean meal, and a mineral-vitamin supplement or high vitamin A (HVA) diet, formulated using whole shelled corn, fescue hay, dry distiller grains with soluble, and a mineral-vitamin supplement for 56 d. During the 56 d feeding period, body weights and condition scores, and subcutaneous adipose samples were collected every 14 d. On day 56, cattle were slaughtered; 48 h postmortem carcass characteristics and objective color scores (subcutaneous adipose tissue) were recorded and a sample of the longissimus dorsi lumborum was collected. Subcutaneous adipose tissue samples were utilized to record subjective color scores and then ground to be analyzed for β-carotene concentration. The longissimus dorsi lumborum samples (2.54 cm slices) were removed for Warner-Bratzler shear force (WBSF) and pH testing. Data were analyzed using the MIXED procedure of SAS. Feeding cull cows LVA resulted in differences in subcutaneous carcass fat color (P = 0.01) as well as b* values (P < 0.01) on day 56 compared with HVA. Subjective fat color scores were not different (P > 0.10) on day 0 or 14 but were different (P ≤ 0.05) on days 28, 42, and 56. Additionally, 9-cis-β-carotene concentration on day 56 were different (P = 0.05) between treatments. A trend was noticed for all-trans-β-carotene concentration (P = 0.10) on day 56 as well. Cull cow body weights were greater (P ≤ 0.04) when fed the LVA diet starting on days 14, 28, and 42; and a trend was noticed on day 56 (P = 0.09). Overall, cows fed the LVA treatment for 56 d exhibited decreased adipose yellowness and β-carotene concentrations as well as increased live weights.

Keywords: carcass characteristics; cull cow; feeding; feedlot; ground corn; performance.

Figure 1.

Least square means on the effect of days on feed on weight (kg) of cull cows fed diets formulated with low vitamin A (LVA) or high vitamin A (HVA) for 56 d. Days with * indicate significance (P ≤ 0.05), days with ** indicate P ≤ 0.01. Standard error of the mean was 42.8.

Figure 2.

Least square means on the effect of days on feed on body condition score of cull cows fed diets formulated with low vitamin A (LVA) or high vitamin A (HVA) for 56 d. Days with * indicate significance at P ≤ 0.05, days with ** indicate P ≤ 0.01. Standard error of the mean was 0.34.

Figure 3.

Least square means of subjective fat color scores of cull cows fed diets formulated with low vitamin A (LVA) or high vitamin A (HVA) for 56 d. Days with * indicate significance at P ≤ 0.05, days with ** indicate P ≤ 0.01. Standard error of the mean was 0.146.