Feeding forages with reduced particle size in a total mixed ration improves feed intake, total-tract digestibility, and performance of organic dairy cows

摘要

The optimal utilization of forages is crucial in cattleproduction, especially in organic dairy systems that encourageforage-based feeding with limited concentrateamounts. Reduction of the particle size of forages isknown to improve feed intake and thus might be a viableoption to help cows cope with less nutrient-densefeeds. The main aim of this study was to evaluate theeffects of reducing forage particle size with a geometricmean of 52 mm (conventional particle size; CON) to 7mm (reduced particle size; RED) in a high-forage diet(80% of dry matter) on dairy cows’ sorting behavior,feed intake, chewing activity, and performance as wellas on total-tract nutrient digestibility. Both diets (CONand RED) consisted of 43% grass hay, 37% clover-grasssilage, and 20% concentrate and contained roughly 44%NDF, 15% CP, and 0.5% starch (dry matter basis).For CON, particle size was set by mixing all componentsfor 20 min in a vertical feed mixer. The REDdiet was treated the same, but before the mixer wasfilled, forages were chopped (theoretical length of cut= 0.5 cm) and the hay was hammer-milled (sieve size= 2 cm). Four primiparous and 16 multiparous midlactatingdairy cows were assigned according to milkyield, body weight (BW), days in milk, and parity into2 groups and fed 1 of the 2 diets for 34 d. The first 13 dwere used for diet adaption, followed by data collectionof nutrient intake, chewing activity, sorting behavior,milk production, and nutrient digestibility for the last21 d of the experiment. Seven days before the startof the experiment, data on BW, dry matter intake(DMI), chewing activity, sorting behavior, and milkproduction were collected for use as covariates. Resultsshowed that the RED diet improved DMI (+1.8 kg/d)and NDF intake (+0.46 kg/d) but decreased intake ofphysically effective NDF >8 (−3.25 kg/d). The REDfedcows increased their intake of smaller particles (<19mm), whereas CON-fed cows sorted for long particles(>19 mm). The RED cows reduced eating and ruminatingtime per kilogram of DMI by 4.8 and 1.9 min,respectively, suggesting lower mastication efforts. Inaddition, the RED diet significantly increased apparenttotal-tract digestibility of nutrients. As a consequence,RED cows’ energy-corrected milk yield was higher(27.0 vs. 29.3 kg/d) without affecting milk solids, cowBW, or feed efficiency. In conclusion, the data supporta reduction of forage particle size in high-forage diets asa measure to improve energy intake, performance, andhence forage utilization under these feeding conditions.