Effect of Particle Size of Forage in the Dairy Ration on Feed Intake, Production Parameters and Quantification of Manure Index (Report‪)‬

INTRODUCTION Size and shape of ingested forage particles have been reported to affect voluntary intake in sheep (Troelsen and Campbell, 1968) and rate of fermentation and retention time of digesta in growing cattle (Worrell et al., 1986) and dairy cows (Nocek and Kohn, 1988). With respect to the high genetic potential of today's dairy animals, early lactation rations require high levels of energy for peak performance. Forages provide energy as well as fiber to maintain ruminal function and normal milk fat concentration. Physically effective fiber is the fraction of the diet that stimulates chewing and is related to the physical characteristics of neutral detergent fiber (NDF) (primarily particle size) that affect chewing activity (NRC, 2001). To ensure adequate fiber, the NRC (2001) recommends the concentration of total dietary NDF be at least 25% of dietary DM for lactating cows fed diets with alfalfa or corn silage as the predominate forage and dry corn grain. The physical form of specific feeds is usually quantitatively assessed by various sieving methods (Murphy and Zhu, 1997). However, the variety of methods employed has made it difficult to compare results from different laboratories or compile such data into a form that is useful for diet formulation. Particle length of forages can impact on numerous aspects of rumen function and rumen health. A certain amount of long forage particles is important in the diet to ensure proper rumen health by promoting rumination and salivation. Diets with too many small particles may result in feed particles spending less time in the rumen, resulting in less microbial digestion. Therefore, forage particles that are too fine may actually lower feed digestibility and may cause more digestive upsets if they are heavily fed. On the other hand, evaluating the feces or manure can provide information about general health, rumen fermentation, and digestive function of cows (Norgaard, 2006; Norgaard et al., 2007). When feed is not properly fermented in the rumen, some unfermented nutrients may escape rumen digestion and reach the small intestine. Normally, these nutrients may be digested and absorbed in the intestine, but if the amount is too excessive or the rate of passage is too fast, nutrients may escape both digestion and absorption in the intestine and appear in the feces. Evaluation of manure in the barn is based on a qualitative index of manure and requires more experience by the operator. In addition, it usually is accompanied by error, especially between operators when they evaluate the same herd. The change of qualitative to a quantitative index of manure was one of the aims of the present study.