Effects of Alfalfa Particle Size and Specific Gravity on Chewing Activity, Digestibility, and Performance of Holstein Dairy Cows

Abstract

Two experiments were carried out to test the effects of alfalfa particle size and functional specific gravity (FSG) on chewing activity, digestibility, rumen kinet- ics, and production of lactating dairy cows fed corn silage based rations. In experiment 1, water-holding capacity (WHC), insoluble dry matter, hydration rate, andFSGchangesweredeterminedinalfalfahay(vary- ing in particle size) and corn silage. Reduction of parti- cle size increased bulk density, FSG, and the rate of hydration, and decreased WHC of alfalfa. In experi- ment 2, 9 midlactation Holstein dairy cows fed total mixed rations containing 3 sizes of alfalfa hay (with geometric mean 7.83, 4.04, and 1.14 mm) were used in a replicated 3 × 3 Latin square design. The diets contained 20, 20, 35, 7, 7.5, 10, 0.3, 0.1, and 0.1% of DM alfalfa, corn silage, barley, soybean meal, beet pulp, wheat bran, dicalcium phosphate, vitamin pre- mix, and salt, respectively. The geometric means (GM) of rations were 3.34, 2.47, and 1.66 mm in long, me- dium, and fine alfalfa treatments, respectively. Reduc- tion of particle size increased daily NDF intake (kg), but decreased the proportion of physically effective factor (pef) and physically effective NDF (peNDF) in the ingested rations. Reduction of particle size in- creased the FSG of rations and intake of DM but re- duced digestibility of NDF and ash. Reduction of parti- cle size decreased ruminal mean retention time (RMRT), but increased the ruminal particulate pas- sage rate. Milk and FCM yield were not affected by treatments. The rumen pH, total chewing activity, ru- mination, eating time, and milk fat were reduced as