1665
Effect of Diet Particle Size on Sorting, Eating Rate, Rumen pH and Digestibility in Dairy Heifers
Eight cannulated dairy heifers (19.3 ± 0.8 mo of age and 524.51 ± 10.01 kg of BW) were fed either long (62.7mm; LCS) or short (6.1mm; SCS) cut corn silage at 1.65% BW in individual stalls to determine eating behavior and digestion parameters. Diets consisted of 70% corn silage, 11% ground corn, 8% citrus pulp, 6% canola meal, 2% soy bean hulls, 1.2% Optigen and 2% mineral/vitamin mix fed once daily. Heifers were subject to a cross over design study with 18-d periods; 14 d adaptation 4 d sampling. Particle size of theTMR was measured at 0 and 2 h after feeding. Feces were collected (d 14 to 18) to determine DM digestibility. Rumen contents were sampled (d 17 to 18) to measure pH at 0, 1, 2, 4, 8, 12, 16, 20 and 22 h after feeding. Data were analyzed with Mixed procedure of SAS 9.4. The LCS ration had an increase of 91% of long (>19 mm) feed particles 2 h after feeding with no change in feed particles on the SCS diet. Feed particles retained on the 8, 4-mm and pan sieves decreased 7, 30 and 35% respectively. The overall rate of eating was not different between treatments (2.75 vs 2.37 kg/h SCS and LCS respectively; P = 0.47). Rumen pH changed throughout the day from 7.1 to 4.7 from feeding to 8 h post feeding but was not different between treatments (P = 0.55). It is likely that these variables were not different because the heifers were fed a restricted diet (8.73 ± 0.19 kg of DMI) that was consumed by 4 h after feeding. The DM digestibility of diets (75.24 ± 2.2 %) was not different (P= 0.37). In conclusion, there are no differences in rumen pH, eating rate and DM digestiblity with different particle size diets. Differences in the TMR particle size 2h after feeding suggest that heifers sort the diets indicating selective consumption of the small particles and selective refusal for the long feed particles. This sorting could promote competition and selective consumption of feed particles by the more dominant heifers, which could lead to inappropriate and variable nutrition for heifers with group fed animals.
Keywords: Heifers, sorting, DM digestibility.