Quantification of forage particle length and its effect on intake and chewing behavior in dairy cattle

A method for the quantitation of the particle length distribution in processed forage was developed, tested, and used to investigate the effect of processing method and forage type on particle length distribution. The same method was also used to investigate the effect of forage particle length on voluntary feed intake (VFI) and chewing behavior in dairy cattle. A simple vibrating tray forage particle separator (FPS) was constucted to separate forage particles on the basis of length alone. Although not completely accurate, the separator produced repeatable results in separating forage particles into six theoretical length fractions (66.0 mm). Cumulative sample weight undersize of separated orchardgrass hay was fitted by regression to a linear and two exponential equations, a lognormal distribution, and a modified Weibull function. Only the Weibull function closely fit these separation data. The median particle length (MPL) could be predicted by the inverse of the B parameter of the modified Weibull function while the use of the C parameter (named the Coefficient of Spread (CS)) was proposed as a measure of the spread of particle lengths around a given median. Alfalfa and low and high quality orchardgrass hays were hammered through a 12.7 mm screen and chopped at 3 theoretical lengths of cut (3.18, 6.35 and 9.53 mm) and separated on the FPS to determine the respective dry matter (DM), crude protein (CP) and acid detergent fiber (ADF) MPL and CS. The MPL were based on the weight of each nutrient collected in each particle length fraction on the FPS. Different forages, processed by the same method, produced significantly different (P < 0.05) DM, CP and ADF MPL, and CS. Furthermore, the differences in DM MPL and CS between forages were significantly different (P < 0.05) from those for CP and ADF. There were also significant differences (P < 0.05) between the DM and CP MPL, and the DM and ADF MPL, within each forage type. Twelve lactating Holstein cows were fed orchardgrass hay chopped to two different MPL (7.3 and 18.1 mm) at two forage to concentrate ratios (40:60 and 60:40). The particle length of the forage did not significantly affect (P > 0.05) VFI or chewing behavior. Increasing the forage to concentrate ratio significantly (P < 0.05) decreased voluntary feed intake, increased the time spent chewing per kg of feed intake during eating and rumination and increased the number of boli regurgitated per kg of feed intake during rumination. When dairy steers were fed timothy-brome hay chopped to 4 MPL (5.2, 9.0, 13.3 and 20.0 mm) at a 60:40 forage to concentrate ratio, an increase in the MPL of the forage in the diet significantly (P < 0.05) decreased the time spent idle, increased the time spent ruminating and the total time spent chewing (eating plus rumination), and increased the number of boli regurgitated per kg of feed intake. These effects of forage MPL on chewing behavior were directly related to the logarithm of the forage MPL. Increasing the MPL of the forage significantly decreased (P < 0.05) the time spent chewing per bolus regurgitated during rumination.Land and Food Systems, Faculty ofGraduat