Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Animal and Nutritional Sciences

Committee Chair

Eugene Felton

Committee Co-Chair

Scott Bowdridge

Committee Member

Kevin Shaffer


Dietary cation-anion modification in cattle has effects on productivity through various means. Alterations of dietary cation-anion balances has been shown to affect plasma osmolarity. Plasma osmolarity is directly related to renal function and metabolism in all animals. In a feeding operation with a single diet fed to a similar population of animals, plasma osmolarity should fall within a somewhat normal range (approximately 270-310 mOsm). However, subtle, yet very distinguishable differences will exist between animals. In theory, variances in osmolarity may reflect differences in metabolism and as such, efficiency of feed utilization. Many researchers believe that utilizing residual feed intake (RFI) expressed in a population as a selection tool will lead to improved production efficiency in beef cattle. Residual feed intake is normally distributed. Like osmolarity, RFI will have subtle, yet very distinguishable differences existing between animals. The objective of this study is to determine if there are any detectable relationships between plasma osmolarity measurements and RFI within a controlled test population and to further determine how this information may be used in improving the utility of RFI measurements. In this study (77d), intake, BW, and ultrasound measurements of yearling heifers were observed. Frozen (-60oC) plasma samples were thawed at room temperature and osmolarity determined. Plasma samples (n=67, n=70) were analyzed to determine osmolarity. All data were analyzed using the CORR procedures of SAS. Plasma osmolarity measured on day 70 demonstrated a weak relationship to RFI (r = 0.226; P = 0.0); no other correlations existed ( P > 0.10) in this data set. There were little to no relationships between osmolarity and ultrasound rump fat (P > 0.90), rib fat (P > 0.98) and intramuscular fat (P > 0.13). Only days 21 and 35 had relationships between ribeye area and osmolarity. (P = 0.04; P = 0.0002). There were also minimal detectable relationships of osmolarity with metabolic body size ( P > 0.06) or intake (P > 0.08). However, osmolarity values fluctuated over the nine (year 1) or ten (year 2) different time points, thus plasma osmolarity measurements taken during or shortly after dietary adaptation may not directly correlate to an animal's RFI value. However, analysis of how animals establish a cation-anion balance may have some relationship to the animals RFI phenotype.