Studies on the relationship between the synchronization index and the microbial protein synthesis in the rumen of dairy cows

A total of eight Holstein cows equipped with ruminal and duodenal cannulae were used to evaluate the suitability of the synchronization index (SI) for optimizing microbial protein (MP) synthesis in the rumen in two experiments. In a preliminary study, degradation characteristics of the feedstuffs were estimated by the nylon bag technique and the quantities of organic matter (OM) and nitrogen (N) degraded per 4 h interval were calculated as difference between the cumulative amounts of OM and N degraded at successive intervals. The relationship between the sum of degraded N and the sum of degraded OM from the different feeds at each interval were used to calculate the SI. In the first in vivo experiment equal amounts of maize silage, grass hay, wheat grain and peas + urea and in the second experiment grass silage, maize grain and soyabean meal were fed to seven and five cows, respectively, four times daily in three different sequences (FS): in FS-A equal amounts of the protein and energy sources were offered at each feeding time; FS-B: first and third feeding time were offered only the energy sources, second and fourth feeding time only the protein sources; FS-C: separate feeding of energy and protein sources as in “FS-B”, but sequence was reversed. Mean feed intake was 14.2 and 17.0 kg DM in the first and second experiment, respectively.The ratio of N/OM release varied during the course of the day in dependence on the feeding sequences for both experiments. The variations of the ratios and the calculated SI were higher in the first compared to the second experiment. The SI was 0.76, 0.52, and 0.82 for FS-A, FS-B, and FS-C in the first experiment, respectively. In the second experiment, indices were 0.85, 0.90, and 0.72 for FS-A, FS-B, and FS-C, respectively.The means of rumen pH, ammonia-N, and total short chain fatty acids were not influenced by feeding sequences in both experiments.For both experiments, flow of non-ammonia-N at the duodenum and efficiency of microbial protein (MP) synthesis tended to be highest in FS-B where energy sources were fed at the first feeding time. This was significant only in the second experiment (187, 245, and 197 g microbial CP/kg fermented OM (FOM) for FS-A, FS-B, and FS-C, respectively). Microbial CP synthesis was not consistent with the SI parameters. Only in the second experiment, the highest SI corresponded with the highest microbial CP synthesis. The lowest SI in the first (0.52, FS-B) and second experiment (0.72, FS-C) was not associated with the lowest efficiencies of microbial CP synthesis (163 and 187 g microbial CP/kg FOM, FS-A in Experiments 1 and 2, respectively).