| Summary: | 碩士 === 國立中興大學 === 畜產學系 === 93 === The purpose of this study was to understand the effect of particle size in total mixed ration (TMR) on the homogeneity of TMR, total dry matter intake, milk yield and compositions, contents of blood biochemicals, and fecal characteristics in lactating Holstein cows. In trial 1, 44 cows averaging body weight 577 ± 12 kg and milk yield 27.2 ± 6.1 kg daily were randomly assigned into two groups, which were allotted into two isonitrogenous (CP 16.3%) and isocaloric (1.61 Mcal NEL/kg DM) TMR treatments in a 2 (experimental period) × 2 (treatment) Latin square design. The particle size distributions detected with Penn. State Particle Separator of the two treatments were 19% vs. 16% long particles (longer than 1.9 cm), 30% vs. 33% medium particles (0.8 to 1.9 cm), and 51% vs. 51% short particles (shorter than 0.8 cm). The results showed that no significant differences (P > 0.05) between the two treatments were observed in total dry matter intake, milk yield, milk compositions, fecal pH value and starch content, but reducing TMR particle size significantly (P < 0.05) increased the blood albumin content. In trial 2, 30 cows averaging body weight 563 ± 29 kg and milk yield 31.1 ± 6.0 kg daily were randomly assigned into two groups in the same design as that in trial 1, except the particle size distributions of the two treatments were 21% vs. 14% long particles, 28% vs. 30% medium particles, and 51% vs. 56% short particles. The results showed that no significant differences (P > 0.05) between the two treatments were observed in total dry matter intake, milk yield, and milk protein content, but reducing TMR particle size significantly (P < 0.05) increased the yields of 4% fat corrected milk and lactose. In blood characteristics, reducing TMR particle size significant (P < 0.05) increase the blood calcium content and calcium to phosphate ratio. However, no significant differences (P > 0.05) between the two treatments were observed in other biochemicals in blood serum. In fecal characteristics, two treatments had almost the same fecal pH value and starch content. It is therefore concluded that reducing TMR particle size could not significant increase the total dry matter intake and milk protein content, but the yields of 4% fat corrected milk and lactose were increased when the particle size distributions were 14% long particle, 30% medium particle, and 56% short particles instead of 21%, 28%, and 51%, respectively.
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