1624 Use of fecal starch as an indicator of starch digestibility and starter intake in preweaned dairy calves

Abstract

Fecal starch (FS) has been used as a tool to evaluate starch digestibility in lactating dairy cows and feedlot steers. Some on-farm advisors are also using FS in a similar way to evaluate solid feed digestibility in preweaned dairy calves. Our objective was to evaluate the relationship of FS with starter intake and starch digestibility in preweaned dairy calves. Male Holstein calves initially 43 ± 2.9 kg BW from a single farm (N = 35) were fed different amounts of milk replacer ranging from 0.66 to 1.1 kg DM daily (27% CP and 17% fat) and weaned by 7 wk of age. Starters contained 37% whole corn, 20% whole oats, 35% protein pellet, and 3% molasses and contained 43% starch (first set) and 38% starch (second set). Fecal grab samples were taken from calves at 3 (n = 20), 6 (n = 20), and 8 wk (n = 35) of age. Twelve fecal samples per calf were taken via rectal palpation over a 5-d period each week, frozen daily, combined on an equal wet-weight basis, and subsampled for analysis. Chromic oxide was used as an external digestibility marker at 3 and 6 wk, whereas AIA was used as an internal marker at 8 wk. Milk replacer and starter intakes (offered and refused) were recorded daily during collection. Linear regression analysis of starch digestibility (%) and dry feed intake (kg/d) vs. fecal starch (%) were determined using PROC REG of SAS. At 3 wk of age, starch digestibility increased (y = 0.69x + 40.80; R2 = 0.53, P < 0.01) and starter intake decreased (y = −0.01x + 1.32; R2 = 0.20, P = 0.05) with increasing FS. At 6 wk of age, starch digestibility (P = 0.11) and starter intake (P = 0.96) were not related to FS. At 8 wk of age after calves were weaned, starch digestibility decreased as FS increased (y = −0.62x + 99.7; R2 = 0.86, P < 0.01), whereas FS and starter intake were not related (P = 0.17), a relationship in contrast to the previously observed result in calves still consuming milk replacer. In the current study, results suggest that FS was not a good estimate of starch digestion or dry feed intake in the preweaned calf but has promise for evaluating starch digestibility in calves after weaning.