PSX-A-15 Late-Breaking: Use of a rumen-protected fatty acid supplement on growth performance in feedlot heifers

The objective of this experiment was to evaluate the of use different doses of a rumen protected fatty acid supplement in feedlot heifers. Seventy-two (cross bread) heifers were blocked by body weight and animals within each block were randomly allotted to a pen. Each pen had 4 heifers, and there were 6 pens per treatment. All animals were fed a basal diet of 14% corn silage, 73% dry rolled corn, 10% cracked soybeans, 1% urea, and 2% mineral vitamin mix for 83 days. Each treatment received different dose of a rumen-protected fatty acid supplement (RPFA), which contained 40% flaxseed oil, 55% treated soy lecithin, and 5% dextrose; processed using the procedure described in the patent (pending: US 2020/0197346 A1). Treatments were T1: 125 g RPFA; T2: 250 g of RPFA, and T3: 375 g of RPFA. Treatments were daily top dressed. Heifers were weighted on days 0, 50, and 83. Longissimus dorsi muscle (LMA) and back fat (BF) at the 13 rib were measured using ultrasound day 0 and 83, before the animals were sent to slaughter. Dry matter offered per day and refusal collected twice a week were used to estimate dry matter intake (DMI). Data were analyzed as a randomized complete block design, with treatment as a fixed variable and block as a random variable. Means were separated using a polynomial contrast. There were no differences (P ≥ 0.16; Table 1) on final body weight, average daily gain (ADG), DMI, gain to DMI ratio, or dressing percentage. There where quadratic tendencies (P ≤ 0.1; Table 1) for hot carcass weight (HCW), LMA, and BF. Based in the results from the current experiment, feeding 100 g of flaxseed oil (250 g of RPFA) improves HCW and LMA but also BF, without affecting growth and DMI.