Effect of variety, stages of maturity and botanical fractions on phosphorous concentration and in situ degradability characteristics of phosphorous of whole crop rice silage

The effect of seven varieties of whole crop rice harvested and ensiled each at four stages of maturity was investigated for P content, in situ degradability and ruminal availability of P in a 7×4 factorial experiment. Rice (Akichikara, Fukuhibiki, Habataki, Hamasari, Kusanami, Tamakei 96 and Yumetoiro) were grown at Saitama, Japan and harvested in 1998 on 10, 22, 34 and 45 days after flowering. Variety and maturity affected (P<0.001; except c for variety, P<0.01) the P content, in situ degradability parameters and effective degradability of P of whole crop rice silage (WCRS). Significant (P<0.001; except a+b, P<0.01 and c, P<0.05) interactions between variety and maturity also existed in all above parameters. The P content, immediately soluble and effective degradability of P decreased, but b and c increased (P<0.001) with maturity. In another study, botanical fractions of wilted WCRS (Hamasari) incubated in situ to investigate the P content and in situ degradability characteristics of P. Head contained higher (P<0.001) P content, but lower (P<0.001) soluble P than that of leaf or stem. Effective degradability of P was the highest (P<0.001) from stem. Stages of maturity significantly (P<0.001) related to P content, in situ degradability and effective degradability of P (except a+b, P<0.05). Immediately soluble P measured by loss due to washing was significantly (P<0.001) related (except a+b and c, P>0.05) to in situ parameters and effective degradability of P, which suggests that the data on washing loss of P may be used to estimate P degradability of forages in the rumen. In conclusion, variety, stages of maturity and botanical fraction of WCRS affected significantly on P content and availability of P of WCRS in the rumen. Most of the phosphorous in WCRS solubilized immediately in the rumen. The results also indicate that the excretion of P of WCRS from different categories of ruminants is likely to be minimal.