A novel approach to determine synchronization index oflactating dairy cow diets with minimal sensitivity to random variations

Abstract

tRuminal synchronization of energy and protein supply is a strategy suggested by nutrition-ists to increase the efficiency of ruminant metabolic processes such as microbial proteinsynthesis and to decrease the environmental excretion of nutrients. A so-called synchro-nization index (SI), formulated as a function of the ratio of nitrogen to organic matter releasein the rumen, is widely used to quantify and evaluate ruminal synchronization. A main con-cern is that SI values obtained from the in situ experimental method are influenced by manyrandom factors and therefore SI value, calculated by the currently-used formula, may notrepresent actual degree of synchronization. Therefore, in this paper, we comprehensivelyexamine sensitivity of SI to random variations (unwanted measurement errors) due to theexperimental conditions variability. Evaluations were performed by means of in situ experi-ments on 3 ruminally fistulated Holstein lactating dairy cows, where 18 different diets werestudied. The diets (g/kg DM) were formulated to a range of CP (150–190), NFC (300–400),NDF (310–410), and ADF (169–246). Based on measured data, a set of synthetic data werealso generated to study a range of random variations and their effect on SI values. Ourresults indicated that SI values are quite sensitive to the random variations (i.e., signifi-cantly decrease as random variations increase). This fact revealed that the currently usedSI depends not only on degree of synchronization, but also on degree of random variationsdue to the inevitable experimental conditions variability. Therefore, the original SI is notfully representative of the actual synchronization when having a high degree of variability.To resolve this problem, we propose a novel approach to calculating SI based on a regressionanalysis on measured data of nitrogen and organic matter release followed by an analyticalderivation of SI based on the regression results. The SI values obtained from the new methodshowed minimal sensitivity to the random variations. The original method yielded a muchlower SI than the new method (0.64 vs. 0.92) for our optimum diet (g/kg DM) (NFC = 350, NDF = 330, ADF = 183, and CP = 165), showing some degrees of asynchrony for this diet.Therefore, we conclude that the new method provides more reliable SI values for deter-mining and quantifying ruminal synchronization.