An alternative methodology of determining feed sorting in transition dairy cows fed glycerol

The objective of this study was to compare the standard methodologywith an alternative method to determine feed sorting in dairy cows during the transition period. Twenty-six Holstein multiparous cows were paired by expected calving date and fed diets containing either glycerol or high moisture corn from -28 through +56 days relative to calving (DRTC). Feed sorting was determined on -16, -9, +9, +15 and +51 DRTC in two different ways. Firstly, it was determinedas the actual intake of each screen of the Penn State Particle Separator (PSPS) consumed between 0-4, 4-8, 8-12 and 12-24 hours post feeding, and expressed as a percentage of the predicted intake of that correspondent screen. Secondly, by measuring the particle size distribution of feed consumed between 0-4, 4-8, 8-12 and 12-24 hours post feeding. The total mixed ration (TMR) at feeding and at each time post feeding was separated by size using the 3-screen (19, 8, and 1.18 mm) Penn State Particle Separator (PSPS) to yield long (>19 mm), medium (<19, >8 mm), short (<8, >1.18 mm), and fine particles (<1.18 mm), respectively. Adding glycerol to the prepartum diet increased (P<0.05) the proportion of DM% retained as long particles(>19 mm) and reduced (P<0.05) the proportion of DM% retained as short (<8, >1.18 mm) and fine particles (<1.18 mm), but it did not alter (P>0.05) the proportion of DM% retained as medium particles (<19, >8 mm). Cows fed prepartum glycerol increased (P<0.05) the preference for long particles (>19 mm) according to the standard methodology (77.2 vs. 101.5%, control vs. glycerol) and also in the alternative methodology (9.2 vs. 17.8%, control vs. glycerol). Cows fed prepartum glycerol discriminated against (P<0.05) short particles (<8, >1.18 mm) in the standard methodology (102.6 vs. 94.2%, control vs. glycerol) as well as in the alternative methodology (42 vs. 37.3%, control vs. glycerol). There was no response (P>0.05) of diet on feed sorting of fine particles (<1.18 mm) according to standard methodologyduring the prepartum interval, but cows fed prepartum glycerol decreased (P<0.05) the preference for fine particles (<1.18 mm) in the alternative methodology (17.9 vs. 13.6%, control vs. glycerol). Cows fed postpartum glycerol increased (P<0.05) the preference for medium particles (<19, >8 mm) according to the standard methodology (108.6 vs. 116.5%, control vs. glycerol), but did not (P>0.05) according to the alternative methodology. Cows fed postpartum glycerol discriminated against (P<0.05) short particles (<8, >1.18 mm) according to the standard methodology (100.6 vs. 96.6%, control vs. glycerol), but did not (P>0.05) according to the alternative methodology. Feeding prepartum glycerol to transition dairy cows increases the preference for the long-stem forage particles of the diet. The alternative methodology proposed in this study is more reliable than the standard methodology to determine feed sorting.