Evaluation of vitamin A status on sera metabolites, muscle fiber type and carcass characteristics of feedlot catlle

Abstract

In this study, to evaluate the effect of vitamin A, the liver must first be depleted. Following depletion, vitamin A will be reincorporated into the diet at the standard estimated requirement and at a fivefold increase of the requirement. A control group without vitamin A supplementation will be maintained to evaluate the effects of vitamin A deficiency on vitamin A status, sera metabolites, muscle fiber type, and carcass characteristics. This study is designed in 2 phases: Phase 1: Twenty-seven yearling crossbred steers (estimated initial average BW = 300 kg) will undergo a 98 day backgrounding period with a vitamin A deficient diet to ensure vitamin A status congruency across steers. These sample days will be noted as -98, -42, and O days relative to the reincorporation of dietary vitamin A. Phase 2: Following the depletion phase steers (n = 27) will be assigned to 1 of 3 vitamin A treatments sourced by retinyl acetate. The three experimental treatments will be based on multiples of the current vitamin A requirement (2,200 IU/kg of dietary dry matter) for beef cattle and include: O lU vitamin AI kg of dietary dry matter (CON); 2,200 lU vitamin A/kg of dietary dry matter (1X); 11,000 lU vitamin A/kg of dietary dry matter (5X). During 140 days on feed, rnuscle and libver biopsies will be performed. After 140 days of initiating vitamin A supplementation, steers will be slaughtered and all carcasses will be graded for beef quality evaluations, as well as Longissimus rnuscle samples will be collect for future analysis of vitamin A concentration mRNA and satellite cells. (AU)