In this study, we isolated a novel bacterium, Bacillus megaterium 1259 (BM1259), from chicken manure. Whole-genome sequencing analysis showed that the BM1259 complete genome is composed of a 5,043,095 bp circular chromosome and three circular plasmids, and it encodes 5379 coding genes and 182 RNA genes. Among these genes, a series of nitrate assimilation-related genes and pathways were identified, implying a potential role of BM1259 in nitrate metabolism. In addition, 24 lactating Holstein dairy cows were randomly assigned to four groups that were fed a total mixed ration (TMR) diet only (C), a TMR diet supplemented with 5 g/day of BM1259 (T1), a TMR diet supplemented with 10 g/day of BM1259 (T2), or a TMR diet supplemented with 15 g/day of BM1259 (T3). The results showed that supplementing dairy cows with 15 g/day of BM1259 increased 4% fat-corrected milk production. The molar proportion of propionate (C3) was significantly higher in T2 than in C. The C2:C3 ratio of T3 was higher than those of C and T2. No negative effect of BM1259 on blood indicators was detected. This study demonstrates BM1259 can be applied as a potential probiotic to improve nitrogen utilization and milk production in lactating dairy cows.

Bacillus megaterium is an ideal microecologics in the feed industry. BM1259 was already isolated from chicken manure and the whole-genome sequencing was also analyzed in our previous study. However, few studies concentrated on dietary supplementation with BM1259 in young ruminants and especially its effect on Holstein bull calves have not been reported. Hence, this experiment was conducted with the aim to evaluate the effects of BM1259 on growth performance, nutrient digestibility, rumen fermentation, and blood biochemical parameters in Holstein bull calves. Twenty-four healthy Holstein bull calves with the initial age of 90 days old and a similar body weight (115 ± 6.5 kg) were selected and randomly allocated into two groups with one Holstein bull calf in each pen (2.5 m × 2.2 m). Holstein bull calves in the control group (COG) were fed a basal total mixed ration (TMR), while experimental treatments (BMG) were fed with the TMR diet supplemented with 12 g/head/day of BM1259 powder (1 × 10¹⁰ cfu/g) separately. Results showed that (1) the average daily gain and dry matter intake of the BMG were significantly higher than those of the COG (p < 0.01), increased by 12.5% and 8.79%, respectively, during the 4–8 weeks after the addition of 12 g/head/day of BM1259; from 0 to 8 weeks, ADG (p < 0.05) and DMI (p < 0.05) in the BMG were significantly higher than those in the COG, increased by 14.9% and 6.04%, respectively. (2) At the end of the fourth week, the apparent digestibility of crude protein and neutral detergent fiber in the BMG was significantly higher than that in the COG (p < 0.05), increased by 5.97% and 6.70%, respectively; at the end of the eighth week, the apparent digestibility of crude protein and neutral detergent fiber was significantly higher than that of the COG (p < 0.01), increased by 5.88% and 10.26%, respectively. (3) At the end of the eighth week, the rumen fluid pH (p < 0.05), MCP (p < 0.05), and acetate (p < 0.05) in the BMG were significantly higher than those in the COG, increased by 9.03%, 19.68%, and 12.74%, respectively; at the end of the fourth and eighth week, NH₃-N concentration in the BMG was significantly lower than that in the COG, with a decrease of 21.81% and 16.40%, respectively. (4) At the end of the fourth (p < 0.05) and eighth week (p < 0.05), the glutamate content of the rumen fluid of the Holstein bull calves in the BMG was significantly higher than that in the COG, increased by 13.21% and 14.32%, respectively; at the end of the fourth week, the contents of glutamate in the serum (p < 0.05), urine (p < 0.05), and feces (p < 0.05) of the Holstein bull calves in the BMG were significantly lower than those in the COG, decreased by 25.76%, 33.87%, and 9.23%, respectively; at the end of the eighth week, the contents of glutamate in the serum, urine, and feces of the Holstein bull calves in the BMG were significantly lower than those in the COG (p < 0.01), decreased by 26.69%, 27.94%, and 11.11%, respectively. (5) After adding 12 g/head/day of BM1259, the urine ammonia–nitrogen content of the BMG was extremely significantly lower than that of the COG at the end of the fourth and eighth week (p < 0.01), decreased by 54.60% and 40.31%, respectively. (6) After adding 12 g/head/day of BM1259, there was no significant effect on the level of blood biochemical parameters of the Holstein bull calves. This study demonstrates that BM1259 can be applied as a potential microecologics to improve growth performance, nutrient digestibility, rumen fermentation, and nitrogen utilization in Holstein bull calves.

This study investigated the effects of a low-protein diet without soybean meal on the growth performance, nutrient digestibility, plasma-free amino acids, and meat quality of finishing pigs. A total of 81 barrows and 81 gilts ([Yorkshire × Landrace] × Duroc) of 150 days old with similar body weights (103.64 ± 3.65 kg) were selected and randomly allocated into three groups with three replicates in each group and 18 finishing pigs in each pen (4.5 m × 8.5 m). Three dietary formulations were established in this experiment: (1) 14% crude protein, and 14% soybean meal for the control group diet (CON); (2) 13% crude protein, and 7% soybean meal for half soybean meal group diet (HSB); (3) 12% crude protein, and 0% soybean meal for soybean meal free group diet (SBF). Three groups of diets were equal to standard ileal digestible amino acids and swine net energy. Results showed that (1) there was no significant difference in final body weight, average daily feed intake, and average daily gain in CON, HSB, and SBF groups (p > 0.05). However, the feed conversion rate was higher in the SBF but the differences were not significant (p = 0.08). (2) Compared with the CON group, the apparent digestibility of dry matter, crude protein, and calcium in the SBF group was significantly increased by 6.42%, 4.78%, and 9.82%, respectively (p < 0.05). However, ether extract and phosphorus did not differ significantly between the three groups (p > 0.05). All groups had no significant differences in serum biochemical indexes (p > 0.05). (3) Compared with the CON group, the plasma-free contents of glycine and glutamate in the HSB and SBF groups were significantly decreased by 42.90% and 37.06%, respectively (p < 0.05). Compared with the CON group, the contents of plasma-free histidine and valine in the SBF group were significantly decreased by 16.72% and 16.21%, respectively (p < 0.05), but there was no significant difference compared with the HSB group (p > 0.05). Compared with the CON group, plasma-free isoleucine content in the HSB group was significantly decreased by 50.39% (p < 0.05), but there was no significant difference compared with the SBF group (p > 0.05). (4) Backfat thickness in the SBF group was significantly increased by 3.53% compared with that in the CON group (p < 0.05), but there was no significant difference compared with the HSB group (p > 0.05). Compared with the CON group, lean meat percentage in the HSB and SBF groups showed a tendency to increase and decrease, respectively (p = 0.09). (5) The urine ammonia-nitrogen content of finishing pigs in the SBF group was significantly lower than that of the CON (p < 0.05), at a rate of 28.80%. H₂S content in the urine of the SBF group tended to decrease (p = 0.06). This study demonstrates that a low-protein diet without soybean meal can be applied as a dietary strategy for finishing pigs with no adverse influence on growth performance.