PSIV-3 - Quantifying free choice mineral intake in a lamb feedlot setting: implications for cost of mineral supplementation

Abstract: The objectives of this study were to assess mineral consumption in feedlot lambs on a pen basis, comparing estimated intakes with the manufacturer’s specified target intake and examining potential influences of environmental variables on free-choice mineral intake. Ninety-three lambs (initial BW = 45.68 kg ± 1.51) were evaluated as part of the “Lamb-A-Year” producer discovery program at the University of Wyoming – Laramie Research and Extension Center (Laramie, WY). There were wethers (n = 68) and ewe lambs (n = 25) of diverse breed types (Western white-faced n = 47, black-faced n = 4, crossbred n = 42) sourced from 24 regional sheep producers. Upon arrival, lambs were allocated to eight pens (10-12 lambs/pen) and provided ad libitum access to a custom textured ration over a 24 d testing period. Each pen received 1.81 kg of a custom granularized mix containing specified levels of Ca, P, NaCl, Se, vitamin A, and vitamin D daily. Mineral intake was determined by subtracting residual mineral from the 1.81 kg administered the previous day. Individual consumption was calculated by dividing total mineral intake by the number of lambs in each pen. The difference between actual intake and target intake was computed per pen to estimate cost per head based on a $1,440 metric ton (t). A least squares regression analysis was employed to examine the effects of average daily temperature range, minimum temperature, and maximum temperature on mineral intake. Across the 24-d period, mean intake was 46.26 ± 1.9 g/head/d with an upper 95% mean of 50.24 g/head/d and a lower 95% mean of 42.28 g/head/d. The study found that the mean difference between observed mineral intake and the manufacturer's target intake was 22.4 ± 1.9 g/head/d, with intake exceeding target intake on 23 d out of 24 d. This overconsumption translated to an increased cost of $0.04/head/d. Statistical analysis revealed that neither the average daily temperature range (P = 0.06), minimum temperature (P = 0.36), nor maximum temperature (P = 0.60) adequately explained the variability in mineral intake. These results underscore the importance of addressing overconsumption of free-choice mineral in housed lamb feeding settings, where intake was roughly double the manufacturer's target. Furthermore, there is a clear need for additional research to quantify the variability in mineral intake in grazing sheep production systems.