The Relationship Between Acid Detergent Insoluble Nitrogen and Nitrogen Digestibility in Lactating Dairy Cattle

Five trials (19 treatments) conducted at the University of Nebraska-Lincoln (UNL) on lactating dairy cattle were analyzed to determine how the concentration of ADIN in the ration affects total tract N digestibility. Additionally, 6 published studies (13 treatments) were included to expand the data set. Results from the UNL trials showed that as the concentration of ADIN in the ration increased, the digestibility of ADIN also increased. However, the relationship was poor (r2 = 0.29). To account for random effects among trials, a meta-analysis was conducted. In the UNL trials, as the ration concentration of ADIN increased, total tract N digestibility decreased; this relationship was moderate (r2 = 0.55). A meta-analysis of the published studies illustrated similar results with a moderate correlation (r2 = 0.44). All data were combined for a meta-analysis, and similar results illustrated a moderate relationship (r2 = 0.58). There was positive relationship between ADF and the concentration of ADIN in the UNL trials; however, the relationship was poor (r2 = 0.19). Additionally, a poor, negative relationship (r2 = 0.14) was observed between ADF and N digestibility in the UNL trials. Milk yield (31.9 ± 3.1 kg/d) in the UNL trials was unaffected (r2 = 0.01) by the concentration of ADIN in the ration. These data suggest ADIN is partially digestible, N digestibility is moderately influenced by ADIN concentration in rations, there is a poor relationship between ADF and the concentration of ADIN, and milk yield is unaffected by the concentration of ADIN.