Effects of Alfalfa Particle Size and Soybean Oil on Digestibility, Chewing Activity, ‎Milk Yield and Compositions of Early Lactating Holstein Cows

. Eight Holstein cows in early lactating stage were used in a 4×4 change-over design within 4 periods of 21-d to determine the effects of alfalfa hay particle size and soybean oil supplementation on intake, digestibility, ruminal and blood metabolites, chewing activity, milk yield and compositions. Four total mixed rations containing 20, 20 and 60% corn silage, alfalfa hay and concentrate respectively were fed to cows twice daily at 0800 and 2000 h. The rations were prepared based on differences in percentage of soybean oil in the concentrate and particle size of alfalfa hay: 1) 0% soybean oil, long-cut alfalfa; 2) 4% soybean oil, long-cut alfalfa; 3) 4% soybean oil, alfalfa powder; 3) 4) 4% soybean, alfalfa powder. Soybean oil had no effect on DMI, but digestibility of NDF, ADF, EE and ash decreased and crude protein digestibility was increased. Reduction of hay particle size, increased DM, and OM intake but decreased the digestibility of DM, OM, NDF, ADF, EE and ash. Milk yield was increased, but milk fat and protein percentage decreased with addition of soybean oil. Reduction of particle size and addition of soybean oil, decreased time spent ruminating and total chewing activity. The addition of soybean oil to fine alfalfa had a synergism effect on decrease of intake time, rumination time and total chewing activity. Decreased particle size and addition of soybean oil declined rumen NH3-N concentration. Reduction of particle size significantly increased ruminal particulate passage rate, and decreased ruminal mean retention time, however, oil supplementation had no significant effect on passage rate, and ruminal mean retention time. Oil supplementation significantly increased milk yield, but decreased its fat and protein content. When particle size of hay decreased, with no effect on milk fat and protein content, milk yield significantly increased in treatments those contained oil supplementation. The oil supplementation in rations not only did not increase fat of milk, but also significantly decreased NDF digestion and consequently milk fat content