This experiment was conducted to investigate the effect of urea and urea-calcium hydroxide treated rice straws on feed intake, rumen fermentation and milk production in lactating dairy cows. Three multiparous Holstein crossbred dairy cows, mid-lactation with 365 ± 30 kg BW, were randomly assigned to receive three kinds of rice straw according to 3 × 3 Latin square design: untreated (T1), 2 × 2% urea-calcium hydroxide treated (T2) and 3% urea treated (T3). Based on the present findings, urea-calcium hydroxide could enhance the nutritive value of rice straw. In addition, dry matter intake (DMI) and nutrient digestibility (DM, CP, OM, NDF and ADF) were significantly increased by straw treatments (P<0.01), however, no difference between urea and urea-calcium hydroxide treatments was found. In contrast, ruminal pH and temperature were similar among treatments (P>0.05). Ruminal NH3-N concentration was increased in both treated straw groups while BUN was similar. While TVFA and C3 were improved in cows receiving urea and urea-calcium hydroxide treated rice straw, C2 and C4 remained stable. Furthermore, total bacterial and fungal zoospores were higher in the treated groups, while protozoa were not different. Ruminal viable bacterial groups were higher in the urea and urea-calcium hydroxide treated, except for proteolytic bacteria. Cows received treated rice straw consumed more N intake as well as N absorption (P < 0.05). Remarkably, the PD, microbial protein and EMPS were enhanced by treated straw. Urea-calcium hydroxide treated rice straw significantly (P < 0.05) increased milk yield and milk compositions. Based on this study, either 2 + 2% urea-calcium hydroxide or 3% urea treated rice straw could be fed to lactating dairy cows as for improvement of feed intake, nutrient digestibility, rumen fermentation and milk production, thus be recommended for use by dairy farmers.
Key words: Rice straw, urea, Calcium hydroxide, rumen fermentation, milk production, dairy cow.
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