|WHITE, ROBIN - Virginia Tech|
|Hall, Mary Beth|
|FIRKINS, JEFFREY - The Ohio State University|
|KONONOFF, PAUL - University Of Nebraska|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2017
Publication Date: 12/1/2017
Citation: White, R.R., Hall, M., Firkins, J.L., Kononoff, P.J. 2017. Physically adjusted NDF (paNDF) system for lactating dairy cow rations. II: Development of feeding recommendations. Journal of Dairy Science. 100:9569-9584. doi.org/10.3168/jds.2017-12766.
Interpretive Summary: Maintaining a healthy ruminal pH is essential for keeping dairy cows healthy and productive. However, many different dietary physical and chemical characteristics, as well as animal behavior, affect ruminal pH and must be considered when formulating diets. Using equations to predict rumen pH, feed intake, and rumination time, we created a workable diet formulation calculator to give guidelines as to what diet characteristics were needed to maintain the rumen at a healthy pH. The tool could be used by nutritionists on specific diets they formulate for lactating dairy cows. The calculator incorporated various measures that nutritionists can obtain through feed analysis and on-farm measurements, such as dietary particle size, forage amount, fiber, starch, and other dietary chemical and digestibility characteristics. This tool is an improvement over options currently used to formulate diets that maintain ruminal health. It has great potential to ensure or improve animal health, productivity, and welfare.
Technical Abstract: The objective of this work was to leverage equations derived in a meta-analysis into an ensemble modeling system for predicting dietary physical and chemical characteristics required to maintain desired rumen conditions in lactating dairy cattle. Given the availability of the data, responsiveness of ruminal pH to animal behaviors, and the chemical composition and physical form of the diet, mean ruminal pH was chosen as the primary rumen environment indicator. Physically effective neutral detergent fiber (peNDF) is defined as the fraction of NDF that stimulates chewing activity and contributes to the floating mat of large particles in the rumen. The peNDF of individual feedstuffs is estimated by multiplying the NDF content of a feed by a physical measure, resulting in an estimated index of effectiveness. We hypothesized that the utility of peNDF can be expanded and improved by dissociating NDF and particle size and considering other dietary factors, all integrated into a physically adjusted fiber (paNDF) system that can be used to estimate minimum particle sizes of total mixed ration (TMR) and diet compositions needed to maintain varying ruminal pH targets. Particle size measures of TMR were limited to the Penn State Particle Separator (PSPS). The system employed an ensemble of models that were integrated using a variable mixture-of-experts approach to generate more robust recommendations for the percentage of dietary dry matter (DM) material that should be retained on the 8-mm sieve of a PSPS, given a specific diet characteristics. Additional and notable continuous variables also integrated in the paNDF system include the proportion of material (DM basis) retained on the 19- and 8-mm sieves of the PSPS, mean particle size, the proportion of forage, proportion of forage NDF, the diet concentration of starch, diet concentration of NDF, rumen degraded starch and rumen degraded NDF. The system was able to predict that the minimum proportion of material (DM basis) retained on the 8-mm sieve should increase with decreasing forage NDF or dietary NDF. Additionally, the minimum proportion of DM material on the 8-mm sieve should increase within increasing dietary starch. Results of this study confirmed the interrelationships between the chemical and physical form of diets fed to dairy cows, and they quantified the links between NDF intake, diet particle size, and rumen pH. Feeding recommendations can be interpolated from this work.