N. TODOROV1, M. SIMEONOV2 and E. YILDIZ1
1 Trakia University, Faculty of Agriculture, Department of Animal Physiology, Morphology and Nutrition, BG-6000 Stara Zagora, Bulgaria
2 Research Institute for Forage Crops, BG-5800 Pleven, Bulgaria
TODOROV, N., M. SIMEONOV and E. YILDIZ, 2016. Rumen degradability of dry matter and protein in four protein sources and their relationships with milk protein yield in dairy cows. Bulg. J. Agric. Sci.,22: 278–285
This study evaluated the in situ ruminal degradability of sunflower meal (SFM), soybean meal (SBM), rapeseed meal, canola type (RSM) and dry distillers grain with solubles from maize (DDGS). The same feeds are used as a sole supplementary protein sources in rations of dairy cows to estimate their effect on true milk protein yield. In situ dry matter (DM) and crude protein (CP) degradability was estimated following Orskov and McDonald (1979) method using three rumen-fistulated cows at 0, 2, 4, 8, 16, 24 and 48 h rumen incubation time for totally 6 samples of each feed and incubation interval. Ruminal disappearance of DM of SFM and DDGS was much slower, and after 8 h of rumen incubation differences were significant (P < 0.05) compared to DM disappearance of SBM and RSM. Disappearance of DM of SBM and RSM was very similar and didn’t differ significantly at any time of rumen incubation. Disappearance of CP of DDGS was slower and after 8 h of incubation differences were significant (P < 0.05) compared to other three protein feeds. SFM had faster (P < 0.05) protein degradability during the first 8 hours of rumen incubation compared to the other three feeds. On the opposite, SBM and RSM protein degradability was slower than that of SFM for the first 8 h of rumen incubation, but later SBM degradability was slightly better than that for SFM and RSM. There was no correlation between DM and CP values of the rapidly disappearing fraction a in different feeds. The rapidly degradable DM fraction a had higher value than protein fraction a in all tested feeds. SFM and DDGS had significantly (P < 0.05) higher easily degradable CP fraction a, compared to SBM and RSM. Rate of degradation of DM and CP of DDGS was much lower (P < 0.05) than in other feeds. Effective degradability values independently of passage rate of rumen content of DM in SFM and DDGS were significantly lower, than for SBM and RSM. Effective degradability of CP was significantly lower (P < 0.05) for DDGS than for the other three feeds. Effective degradability of SFM was the highest, followed by SBM and RSM but the differences were not significant (P > 0.05). There was a relatively high correlation between protein digestible into intestine (PDI) (equal to metabolizable protein) calculated from average data for degradability published in literature (r = 0.72) or from real degradability determined in this experiment (r = 0.75). Differences between two correlation coefficients were not significant. Correlation coefficient between milk true protein yields and lysine digestible in small intestine, calculated from literature data for CP degradability into rumen was 0.57, whereas the value calculated from real rumen degradability of supplementary protein was 0.48. There was a big discrepancy between lysine supply to cows and milk protein yield especially for the diet with DDGS. Presumably microbial protein synthesis into rumen was increased when DDGS was used as source of protein in the ration. A second possibility is the better mammary extraction of amino acids which are in small shortage compared to requirements.