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

Area of Science:

• Animal Nutrition
• Digestive Physiology
• Dairy Cattle Research

Background:

• Accurate estimation of fecal output and nutrient digestibility is crucial in dairy nutrition.
• Total collection of feces (TC) is accurate but labor-intensive and expensive.
• Indirect methods using intrinsic markers offer an alternative but require validation.

Purpose of the Study:

• To validate indigestible neutral detergent fiber (iNDF) and acid-insoluble ash (AIA) as intrinsic markers for estimating fecal output and nutrient digestibility.
• To compare these markers against total collection of feces (TC).
• To determine the optimal number of spot sampling events for accurate estimation.

Main Methods:

• 12 multiparous lactating Holstein cows were used in a randomized complete block design.
• Two diets (corn silage-based and alfalfa silage with by-product) were fed.
• Total fecal collection (TC) and 12 spot samples (every 2 hours) were performed over 3 days.
• Fecal outputs and nutrient digestibilities were compared between TC, iNDF, and AIA methods.
• Spot samples were aggregated to represent frequencies of 12, 6, 4, and 2 events.

Main Results:

• iNDF provided similar fecal output and nutrient digestibility estimates compared to TC.
• AIA overestimated fecal output by 44-61% and underestimated nutrient digestibility by 16-32%.
• A spot sampling frequency of at least 6 events (SP6) yielded similar results to 12 events (SP12) for most nutrients, while SP4 and SP2 were less accurate.

Conclusions:

• Indigestible neutral detergent fiber (iNDF) is a superior intrinsic marker compared to acid-insoluble ash (AIA) for estimating fecal output and nutrient digestibility in dairy cows.
• A minimum of 6 spot sampling events is necessary for accurate estimation.
• Potential confounding of dietary effects requires careful interpretation when using iNDF.