Hot topic: Apparent total-tract nutrient digestibilities measured commercially using 120-hour in vitro indigestible neutral detergent fiber as a marker are related to commercial dairy cattle performance

Abstract

Measuring individual feed nutrient concentration is common practice for field dairy nutritionists. However, accurately measuring nutrient digestibility and using digestion values in total digestible nutrients models is more challenging. Our objective was to determine if in vivo apparent total-tract nutrient digestibility measured with a practical approach was related to commercial milk production parameters. Total mixed ration and fecal samples were collected from high-producing cows in pens on 39 commercial dairies and analyzed at a commercial feed and forage testing laboratory for nutrient concentration and 120-h indigestible NDF (iNDF) content using the Combs-Goeser in vitro digestion technique. The 120-h iNDF was used as an internal marker to calculate in vivo apparent nutrient digestibilities. Two samples were taken from each dairy and were separated in time by at least 3 wk. Samples were targeted to be taken within 7d of Dairy Herd Improvement (DHI) herd testing. Approved DHI testers measured individual cow milk weights as well as fat and protein concentrations. Individual cow records were averaged by pen corresponding to the total mixed ration and fecal samples. Formulated diet and dry matter intake (DMI) records for each respective pen were also collected. Mixed model regression analysis with dairy specified as a random effect was used to relate explanatory variables (diet nutrient concentrations, formulated DMI, in vivo apparent nutrient digestibilities, and fecal nutrient concentrations) to milk production measures. Dry matter intake, organic matter (OM) digestibility, fecal crude protein (CP) concentration, and fecal ether extract concentration were related to milk, energy-corrected milk, and fat yields. Milk protein concentration was related to CP digestibility, and milk protein yield was related to DMI, OM digestibility, CP digestibility, and ether extract digestibility. Although many studies have related DMI and OM digestibility to milk production under controlled experimental settings, very few have related practical in vivo measures to milk production. By documenting the practical OM digestibility relationship with milk production, nutritionists and scientists may have confidence in this approach for measuring diet performance and collecting nutritional data for commercial dairies.

Production responses of high producing Holstein cows to ruminally protected phenylalanine and tyrosine supplemented to diets containing high levels of canola meal

“…All samples were ground (model 4 Wiley Mill, Thomas Scientific, Swedesboro, NJ, USA) to pass a 1 mm screen. The TMR samples were assayed for crude protein (CP), fat, ash, neutral detergent fiber assayed with heat stable amylase (aNDF) and starch (Schalla et al 2012). Acid detergent fiber (ADF), lignin(sa), acid-and neutraldetergent insoluble CP (ADICP and NDICP) were assayed as described by Swanepoel et al (2015).…”

Mathematical linkage of total-tract digestion of starch and neutral detergent fiber to their fecal concentrations and the effect of site of starch digestion on extent of digestion and energetic efficiency of cattle

“…Through analysis of representative samples of the diet (TMR) and feces as well as a digestion marker, the digestibility of diet DM, starch, NDF, ADF, and nonstarch non-NDF DM (by difference) could be calculated once matched samples are assayed for the appropriate components. Conveniently, uNDF120 has been employed as an indigestible marker in some digestion trials and field studies (Schalla et al, 2012). Unfortunately, the concentration of ADL within uNDF240 present in the diet of 26 different dairy herds was related only weakly (R 2 = 0.24) to its concentration within fecal uNDF240 (Powel-Smith et al, 2015).…”

“…Balancing diets based on input alone while ignoring multiple outputs is similar to developing a budget based on income alone while ignoring expenses. Direct measurements of energy and nutrient digestibility based on feed and fecal analysis using home-grown and homeprocessed feed ingredients being fed to high producing cattle should provide appraisals of energy and nutrient availability that are more applicable locally than generalized models can provide (Schalla et al, 2012). Ideally, future models should allow incorporation of field measurements of digestibility to modulate specific prediction equations and provide checks and balances that can be used to improve model reliability and applicability.…”

Use of a direct-fed microbial product as a supplement during the transition period in dairy cattle

“…However, lignin should be used with caution in digestibility studies as it can be partially digested (Fahey and Jung, 1983), mainly in less lignified grass-based forages. Recently, a method was developed to use iNDF as an internal marker, which is quantified after 120 h of in vitro incubation in a rumen-inoculated medium (Schalla et al, 2012). Our results indicated no difference between methods in assessing total-tract digestibility, likely because of the level of lignification and (or) the ensiling process of the forages used in the current study.…”

“…Fecal and TMR samples were frozen at −20°C for further analysis. Samples were analyzed for starch, NDF, lignin, and insoluble NDF (iNDF) using the Combs-Goeser method (Schalla et al, 2012). Apparent total-tract digestibility of NDF and starch were calculated, with lignin and iNDF as internal makers, using the following equation: Apparent nutrient digestibility (%) = 100 -{100 × (TMR marker/fecal maker) × [fecal nutrient content (% of DM)/TMR nutrient content (% of DM)]}.…”