Dosing frequency, fecal sampling, and digestibility method influence titanium dioxide-based intake estimates in dairy heifers.

Indigestible markers continue to be among the best tools available for estimating intake, especially when individual animal feeding cannot be feasibly measured. Titanium dioxide (TiO2) is a commonly used external marker for estimating fecal output. Estimates of digestibility are still required to estimate intake, which can be obtained through feed chemical analysis or by using internal markers. The objectives were: 1) test potential diet and dosing effects of TiO2 for intake estimates; 2) compare intake estimates from two fecal sampling regimes (i.e., intensive vs. less intensive); and 3) determine accuracy of intake estimates using TiO2 as a fecal output marker and different in vitro or in vivo methods of estimating diet digestibility. In vitro methods to determine digestibility included in vitro DM digestibility and in vitro OM digestibility. In vivo methods to determine digestibility included indigestible neutral detergent fiber (iNDF) and acid detergent insoluble ash (ADIA). Treatment were arranged as a 2 × 2 × 2 factorial in a randomized complete block design. Treatments included 2 diets, 2 TiO2 dosing schemes, and 2 fecal sampling regimens. Diets were grass haylage (HLG) and a total mixed ration (TMR). Dosing was once (1×) or twice (2×) daily administration of bolus containing TiO2. The 1× treatments received 2 capsules every morning, while the 2× received 1 capsule in the morning and 1 in the afternoon, both receiving 10 g of TiO2/d. Fecal samples were collected either 3 times daily over 4 d with times shifted each day (4 × 3), or twice daily at the same times each day (AMPM). Intake for TMR was overestimated by up to 4 kg/d using iNDF as an internal marker, independent of the dosing scheme and fecal composite type. For HLG, intake was underpredicted by up to 2.6 kg/d. Increasing dosing regimen, along with an intensive fecal collection period did not improve the accuracy of the intake estimates. Coupling fecal excretion estimates from TiO2 with in vitro methods for diet digestibility can provide accurate intake estimates. Both iNDF and ADIA provided accurate intake estimates. Using ADIA may be preferable due to it not requiring cannulated cattle and needing less labor than iNDF. Reasonably accurate intake estimates can be obtained under the evaluated conditions using less intensive dosing and sampling strategies, provided that digestibility estimation methods are appropriately selected and validated.