كليدواژه :
يونجه , جرم حجمي لحظه اي , Dairy cow , Physically effective NDF , Functional specific gravity , دامپروري , اندازه ذرات , ديواره سلولي موثر فيزيكي , Particle size , گاو شيرده هلشتاين
چكيده لاتين :
Two experiments were carried out to test the effects of alfalfa particle size and functional specific gravity on chewing activity, digestibility, rumen kinetics, and production of lactating dairy cows fed corn silage based rations. En experiment 1, using the in vitro method, water-holding capacity, insoluble dry matter, hydration rate, and functional specific gravity changes were determined in alfalfa hay (varying in particle size) and corn silage. Reduction of particle size increased bulk density, functional specific gravity, and the rate of hydration and decreased water-holding capacity of alfalfa. En experiment 2, nine mid lactation Holstein dairy cows fed total mixed rations, containing three sizes of alfalfa hay (with geometric mean 7.83, 4.04 and 1.14 mm) were used in a replicated 3 x 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, barely, soybean meal, beet pulp, wheat bran, DCP, vitamin premix and salt, respectively. The geometric means of rations were 3.34, 2.47 and 1.66 mm in long, medium and fine alfalfa treatments, respectively. Reduction of particle size increased daily NDF intake (kg), but decreased the proportion of physically effective factor and physically effective NDF in the ingested rations. Reduction of particle size increased the functional specific gravity of rations, intake of DM, but reduced digestibility of NDF and ash. Reduction of particle size decreased ruminal mean retention time, but increased the ruminal particulate passage rate. Milk and FCM yield was not affected by treatments. The rumen pH, total chewing activity, rumination, eating time and milk fat were reduced as particle size decreased, but milk protein increased. This study showed that reduction of forage particle size increased bulk density, functional specific gravity, hydration rate of alfalfa hay and was the most influential factor affecting DM!, milk composition and chewing activity but had minimal impact on digestibility and milk production.
