Validating intrinsic markers and optimizing spot sampling frequency to estimate fecal outputs

Abstract

Indirect methods of spot sampling with intrinsic markers to estimate fecal output and nutrient digestibility often have been used in dairy nutrition research as alternatives to total collection of feces (TC) because of labor and expense. However, fecal output and nutrient digestibility estimated from the indirect method must be accurate regardless of altering dietary conditions. This experiment was designed to validate the accuracy of using indigestible neutral detergent fiber (iNDF) or acid-insoluble ash (AIA) as intrinsic markers to estimate fecal outputs and nutrient digestibility compared with TC and to determine the optimal number of spot sampling events to accurately determine fecal output and then nutrient excretion. The experiment used 12 multiparous lactating Holstein cows in a randomized complete block design. Cows were blocked by days in milk and milk yield and randomly assigned to 1 of 2 diets: a diet containing about 49% corn silage on a dry matter basis and a diet containing about 48% alfalfa silage with high by-product (soyhulls) and supplemental K. During the final 3 d of 21-d periods, TC was performed, and 12 spot samples were collected for the same 3 d to represent every 2 h in a 24-h cycle. Fecal outputs and nutrient digestibility of dry matter, organic matter, or nitrogen estimated with iNDF or AIA as an intrinsic marker were compared with TC. Overall, fecal outputs and digestibility estimated with iNDF were similar to that estimated with TC, whereas AIA overestimated fecal output by 44 to 61% and underestimated nutrient digestibilities by 16 to 32%. However, potential differences in statistical inference of dietary effects between iNDF and TC were found. Data from individual spot samples were aggregated to represent spot sampling frequencies of 12 (SP12), 6 (SP6), 4 (SP4), or 2 (SP2) evenly spaced events starting at feeding time. Compared with TC, SP12 produced similar fecal content of iNDF, organic matter, and nitrogen, but fecal AIA content was greater. Furthermore, compared with SP12, SP6 produced similar fecal content of all nutrients, whereas marker and nutrient concentrations in SP4 and SP2 were different. In this experiment, iNDF was a better fecal marker than AIA, and a spot sampling frequency of at least 6 events was necessary. However, interpretation of dietary effects could be confounded when iNDF was used to estimate fecal outputs.

Effects of ensiling time on corn silage neutral detergent fiber degradability and relationship between laboratory fiber analyses and in vivo digestibility

“…Indigestible NDF has been recommended as an intrinsic digestibility marker (Huhtanen et al, 1994;Lee and Hristov. 2013;Morris et al, 2018), and 120-h IV iNDF has been shown to predict well nutrient digestibility and lactational performance of dairy cows in commercial farm settings (Schalla et al, 2012). Grass silage ash-free iNDF288 concentration was closely related to in vivo ATTD of OM, determined by total fecal collection, for 86 silages (Huhtanen et al, 2005).…”

Estimation of between-Cow Variability in Nutrient Digestion of Lactating Dairy Cows Fed Corn-Based Diets

“…Although the total collection of feces is the most accurate procedure in quantifying nutrient digestibility [ 49 ], we adapted the spot sampling technique to overcome practical difficulties such as sampling from large no of cows, time, special facilities and the high cost associated with the total collection. As marker concentration of feces is highly variable throughout a day [ 15 , 50 ] a proper representation of diurnal variation in fecal marker concentration should be achieved by sampling at multiple time points. The use of different spot sampling frequencies in a 24-h cycle has been well documented in the literature in estimating total-tract digestibility [ 18 , 51 , 52 ].…”

“…The use of different spot sampling frequencies in a 24-h cycle has been well documented in the literature in estimating total-tract digestibility [ 18 , 51 , 52 ]. However, findings of a recent study suggested that six sampling events (every 4 h in a 24 h cycle) as the minimum adequate fecal spot sampling frequency to use iNDF as an internal marker when estimating total tract nutrient digestibility [ 15 ].…”

“…During the feeding trial, TMR samples (500 g each) and orts (200 g) were collected daily (frozen at −20 °C) and composited weekly. Six fecal grab samples (~200 g of feces each) from each cow were collected twice daily to cover 0400, 0800, 1200, 1600, 2000, and 2400 h time points over final 3 days as previously described [ 14 , 15 ] and composited by wet weight for each cow over three days.…”

Production and nitrogen metabolism in lactating dairy cows fed finely ground field pea plus soybean meal or canola meal with or without rumen-protected methionine supplementation

“…It should be noted that this sampling protocol did not cover a diurnal feeding cycle, and 2 d was likely too short to account for the variability in DMI. Recent research revealed that approximatively 6 time points appear to be required for estimating fecal output of DM and urinary volume when using the fecal grab and spot urine sampling protocols, respectively, in dairy cows (Morris et al, 2018;Lee et al, 2019). Therefore, our apparent total-tract digestibility and urinary excretion data should be interpreted cautiously.…”