The relationship between plasma and saliva urea nitrogen in grazing red deer calves : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor with Honours at Lincoln University

Abstract

I evaluated the relationship between saliva urea N (SUN) and plasma urea N (PUN) in red deer calves (n = 23) over five months, with the objective of creating an easy tool to quickly evaluate circulating urea nitrogen concentrations. The experimental design was a 2x2 factorial arrangement different seasonality phenotype (High and Low) and two different forage based diets, a medium-quality diverse treatment (Diverse) or a low-quality perennial ryegrass-white clover treatment (PRG) offered ad libitum. Blood and saliva samples for determination of PUN and SUN were evaluated monthly at civil dawn between April and September of 2022. A moderately strong relationship between PUN and SUN was identified by simple linear regression (R2 = 0.65, P < 0.001). The interaction between diet and date of sampling had a significant effect on the relationship between SUN and PUN (P < 0.001). This interaction is likely explained by the seasonal variation of crude protein (CP) content of the diet. The use of a mixed model procedure improved the model fit increasing the adjust R2 by 0.12 and reducing the root mean square error by 0.341. There was no effect of seasonality on prediction estimates of PUN from SUN although a tendency for sex by seasonality interaction was observed (P = 0.09). Therefore, evaluation of the diet and date of sampling can be used to improve reliability of the prediction estimates of PUN from SUN in red deer calves. Further investigation into the effects of significant factors on this relationship is required to improve the reliability of the model, before SUN can be used to predict PUN.