Abstract
The objective of this study was to compare the standard methodology with 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 determined as 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 methodology during 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. KEYWORDS: Biodiesel, byproduct, particle size, preference.
Highlights
Cattle have the intrinsic ability to select specific and needed nutrients when feeds are offered separately (STRICKLIN & KAUTZ-SCANAVY, 1983)
There was no response (P>0.05) to prepartum glycerol on the proportion of DM% retained as medium particles (8 mm) and no response (P>0.05) of treatments on the particle size distribution of the postpartum diets (Table 2)
The response to prepartum glycerol on the preference for long particles (>19 mm) in both methodologies can be explained by the fact that the proportion of DM retained as long particles (>19 mm) in the prepartum glycerol diet was increased compared with the prepartum control diet (Table 2)
Summary
Cattle have the intrinsic ability to select specific and needed nutrients when feeds are offered separately (STRICKLIN & KAUTZ-SCANAVY, 1983). The periparturient or transition dairy cow has been defined when the cow is between three weeks prepartum and three weeks postpartum (GRUMMER, 1995) During this period of transition from gestation to lactation the cow is at greater risk for developing metabolic and infectious diseases than at any other time during its life (DRACKLEY, 1999). Special attention must be paid when formulating diets, as well as feeding and nutritional strategies to minimize the feed sorting behavior of dairy cows, which can result in the consumption of a ration with inconsistent nutritive value (STONE, 2004) and increasing risks of developing subacute ruminal acidosis (COOK et al, 2004; STONE, 2004), when early lactating cows are fed low forage diets. The feed sorting behavior leads to variations in nutritive values of the TMR in the feed bunk with a greater interval of time post feed delivery (DEVRIES et al, 2005), especially when dominant and subordinate cows are grouped together, where feed sorting by some groups of cows is likely to impact the nutritional value of feeds available for other cows in the group, and may reduce the feeding value of the ration (KRAUSE & OETZEL, 2006)
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