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

Abstract

The use of indigestible 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 when grazing or when animal handling facilities are not accessible. Identifying strategies for more efficient use of labor while not sacrificing accuracy of DMI 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 two diets, two n-alkane marker dosing regimens, and two fecal sampling regimens. Diets were grass haylage (HLG) and a total mixed ration (TMR). Daily intakes were recorded using Calan gates. Alkane dosing was once (1X) or twice (2X) daily dosing of a 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 of 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 observed DMI estimates. Strategies for dosing either 1X or 2X daily were both accurate, within the confines of the experiment. In terms of fecal sampling, there was no discernable advantage for the intensive (4×3) sampling regimen compared to the twice daily (AMPM) sampling. In addition, intake estimates were similar with either the 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.