Dosing and fecal sample collection effects on the estimates of intake using n-alkanes as markers

Authors: Jaramillo, David; Bauman, Lisa; Ogden, Robin; Akins, Matthew; Kalscheur, Kenneth

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Obtaining accurate estimates of intakes in situations where individual animal feeding cannot be measured is challenging, especially under grazing. Alkanes are naturally occurring plant cuticular waxes and have been used as external makers for intake estimations, especially dotriacontane, C32 alkane. This study sought to evaluate the accuracy of alkanes to estimate intake from heifers consuming a haylage or a total mixed ration, by dosing once or twice daily with an alkane bolus and comparing the intake predictions from an intensive and less-intensive fecal sampling schedule. The results indicate that C31:C32 alkane pairs provide better estimate than C32:C33 alkane pairs. Strategies for dosing either once or twice daily were both accurate, as long as animals receive equal dose of the marker. There was no discernable advantage for an intensive fecal grab sampling regimen; twice daily, morning and afternoon, fecal sampling provided adequate intake estimates with either once or twice-daily dosing regimens. This study is beneficial for researchers conducting studies evaluating intake using alkane markers. The results indicate it may be recommended to adopt once-daily dosing regimen with twice-daily fecal sampling schedules. This reduces labor requirements, while not sacrificing accuracy of intake predictions.

Technical Abstract: The use of markers continues to be among the best tools available for estimating dry matter intake (DMI) in situations where individual animal feeding cannot be feasibly measured. The constant animal handling required for dosing markers and subsequent fecal sample collection required are often limiting, especially under grazing or when animal handling facilities are not accessible. Identifying strategies for more efficient use of labor while not sacrificing the accuracy of estimates are important for further application of these techniques. The objectives of this study were to: 1) Test potential diet and dosing effects of C32 n-alkane for intake estimates; 2) Compare intake estimates from two contrasting (i.e., intensive vs. less intensive) fecal sampling regimes; and 3) Determine whether intake estimates differ when two different n-alkane pairs (C31:C32 or C32:C33) are used. The study was laid out using a 2×2×2 factorial arrangement in a randomized complete block design. Treatments were the factorial arrangement of two diets, two n-alkane marker dosing regimens, and two fecal sampling regimens. The two diets were grass haylage (HLG) and a total mixed ration (TMR). Daily intakes were recorded using Calan gates. The two alkane dosing regimens were once (1X) or twice (2X) daily dosing of a gelatin bolus containing dotriacontane (C32) n-alkane. The 1X treatments received two capsules every morning, while the 2X treatments received one capsule in the morning and one in the afternoon, both receiving 933 mg C32/d. Fecal samples were either taken three times daily over four days with times shifted each day (4x3), or twice daily at the same times each day (AMPM). The results indicate the use of C32:C33 n-alkane pairs were not accurate for predicting DMI (Lin’s Concordance Correlation Coefficient [CCC] all < 0.5). The C31:C32 n-alkane pairs provided accurate estimates of DMI, having adequate agreement (CCC >0.6) between predicted and observe DMI estimates. Strategies for dosing either 1X or 2X daily were both accurate, within the confines of the present experiment. In terms of fecal sampling, there was no discernable advantage for the intensive (4×3) fecal sampling regimen; twice daily (AMPM) fecal sampling provided adequate intake estimates with either 1X or 2X dosing regimens. For studies conducted under similar conditions, it may be suitable to adopt 1X dosing regimen with twice-daily fecal sampling schedules. Further studies are warranted to understand the use of different alkane pairs for intake predictions.