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Highlights • Crude protein (CP) value from red clover silage (RCS) and soybean meal were studied. • Undegraded and intestinal digestibility of CP reduced with increasing level of RCS. • Increasing level of RCS shifted the site of CP utilization from rumen to intestine. • The CP value of diets reduced with each increasing level of RCS. • RCS can be included up to 0.30 without impairment of protein value of diets. Abstract The objective of this study was to evaluate the effect of replacing crude protein (CP) of soybean meal (SBM) with red clover silage (RCS) in total mixed rations (TMR) on ruminally undegraded feed CP (RUP) and intestinal digestibility (ID) of RUP. Four TMR were formulated to replace CP from SBM with RCS. The TMR was comprised of forage and concentrates (0.75:0.25), with ratios of RCS in TMR of 0.15, 0.30, 0.45, and 0.60 on a dry matter (DM) basis. The ruminal degradation of CP was determined using the nylon bag technique. For this, samples of TMR were incubated for 2, 8, 16, 24, 32 and 72 h. The RUP content of TMR was estimated using passage rates of 2, 5 and 8%/h. Additionally, samples of TMR were incubated in the rumen for 16 h, and their feed residues were used for determination of ID of RUP using the mobile-bag technique. For in situ ruminal degradation, increasing RCS and reducing SBM proportions increased linearly the rapidly degradable CP (a) from 26.2 to 212 g/kg CP (P < 0.001). The potentially degradable CP (b) decreased linearly from 810 to 676 g/kg CP (P < 0.001). Assuming a passage rate of 8%/h, RUP reduced linearly from 315 to 253 g/kg CP (P < 0.001). The ID of RUP reduced linearly from 760 to 574 g/kg CP (P < 0.001) with increasing RCS levels. Although differences in ruminal CP degradation and ID of RUP were apparently caused by differences in the proportion of RCS and SBM, neither linear nor quadratic effects on total tract digestible CP were observed (P = 0.22 and 0.21, respectively), and averaged 943 g/kg CP among all TMR tested. This suggests that increasing RCS and decreasing SBM proportion shifted the site of CP utilization. The CP degraded in the rumen increased, and the amount of intestinally absorbable RUP reduced linearly from 184 to 79 g/kg CP (P < 0.001). In general, replacing CP from SBM with RCS in the TMR reduced its protein value. It is concluded, that an almost complete replacement of CP from SBM by RCS in rations of high-yielding dairy cows cannot be recommended. However a replacement rate up to 0.30 does not lead to a substantial reduction in RUP supply and digestibility, and therefore considerably reduces the use of SBM. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate fermentation characteristics and associative effects by replacing maize silage (MS) with red clover silage (RCS) using in vitro techniques. Treatments included total mixed rations (TMR) containing forage (MS and RCS) and concentrates (0.75:0.25) with targeted proportions of RCS in TMR of 0.15 (RCS 15 ), 0.30 (RCS 30 ), 0.45 (RCS 45 ), and 0.60 (RCS 60 ) on a dry matter (DM) basis. The Hohenheim gas test (HGT) was used to describe the kinetic of gas production. The modified HGT was used to estimate the utilizable crude protein at the duodenum (uCP). Effective uCP was calculated according to passage rates of 2, 5 and 8%/h (uCP 2 , uCP 5 and uCP 8 , respectively). Associative effects were defined as the differences (%) between the observed values of TMR and the sum of the observed values of the individual components of the TMR. The gas production from incubation time 8 to 72 h, the potential gas production (A), organic matter digestibility (OMD), and metabolizable energy (ME) decreased with increasing levels of RCS. The effective uCP 2 content was similar between TMR (average 93.7 g/kg DM). However, uCP 5 and uCP 8 were reduced with increasing level of RCS (from 145 to 136 g/kg DM, and from 172 to 157 g/kg DM). Positive associative effect was found for cumulative gas production. But this effect was reduced when increasing incubation time and when increasing levels of RCS. Associative effects of gas production at 24 h of incubation averaged 1.35%. Consequently, those of ME (−0.09 to 1.01%) and OMD (1.60 to 2.76%) were of minor relevance as well. Associative effects on uCP depended on rate of passage and on level of RCS. Within TMR, associative effects on uCP increased with increasing rate of passage (e.g. for RCS 15 ; 3.67 and 5.39% for 2 and 8%/h, respectively). Within rate of passage, associative effect was reduced with increasing level of RCS (e.g. for uCP 8 ; 5.39 and −0.95% for RCS 15 and RCS 60 , respectively). Based on associative effects of fermentation characteristics and estimated uCP content, this study suggests that incrementing levels of RCS may lead to a reduction on the feed value of diets, and that the optimal proportion of RCS:MS in TMR to achieve beneficial effects was 0.15:0.60 on DM basis. Therefore, caution should be taken before introducing high levels of RCS in rations of high-yielding dairy cows. However, these results should not be directly extrapolated to in vivo conditions. [ABSTRACT FROM AUTHOR]