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.

Sixty castrated male Haimen white growing goats with an initial age of 100 days old and similar body weight (16 ± 1.5 kg) were selected and randomly allocated into five groups with three replicates in each group with four goats in each pen (5 m × 3.2 m). Goats in the control group (CG) were fed a basal pelleted total mixed ration supplemented with 30% alfalfa hay pellet, while experimental treatments (G6, G12, G18, or G24) were supplemented with four levels (6%, 12%, 18%, or 24%) of GBLR replacing alfalfa hay pellet in the diet, separately. Results showed that (1) the final body weight, average daily gain, and average feed intake of G18 was significantly higher (p < 0.05) than CG; in contrast, the feed conversion ratio of G18 was significantly lower than CG and G12 (p < 0.05); the feed cost per head per day of CG was significantly higher (p < 0.05) than that of G18 and G24, and exhibited obvious linearly decrease (p = 0.04) with increasing GBLR supplementation; and apparent total-tract digestibility of DM and NDF in GBLR treatments were significantly higher (p < 0.05) than CG; (2) alanine transaminase (ALT) concentration in the G18 group was significantly lower (p < 0.05) than those in the control group; aspartate transaminase (AST) concentration in the G24 was significantly lower (p < 0.05) than those in the control group, and an increase in dietary level of GBLR tended to result in a linear decrease (p = 0.09) in the concentration of serum AST; (3) the concentration of malondialdehyde (MDA) demonstrated a tendency to decrease (p = 0.06) linearly with increasing GBLR supplementation; however, glutathione peroxidase (GSH-PX) activity in G12 was significantly higher (p < 0.05) than CG, G6, and G24; in addition, superoxide dismutase (SOD) activity in G18 was significantly higher (p < 0.05) than CG and G6; concentration of immunoglobulin M (IgM), immunoglobulin G (IgG), and immunoglobulin A (IgA) were not affected by GBLR, but increasing dietary GBLR showed a tendency (p = 0.08) to linearly increase the IgG concentration; the content of interleukin 4 (IL4) was significantly higher (p < 0.05) in G12, G18, and G24 than that in CG and G6; (4) There were similar NH₃-N, pH, TVFA, and butyrate for goats fed different levels of GBLR supplementation; the C2 (p = 0.07) and acetate: propionate (p = 0.06) demonstrated a tendency to increase linearly with increasing level of GBLR supplementation, separately; however, it was observed that concentration of propionate showed a tendency to decrease (p = 0.08) linearly in response to GBLR supplementation; and (5) Increasing dietary GBLR tended to linearly enhance the lightness (L*) (p = 0.07) and yellowness (b*) (p = 0.09) values of longissimus dorsi muscles; the redness (a*) value in G18 was significantly higher than that in CG (p < 0.05).

The rac-GR24, an artificial analog of strigolactone, is known for its roles in inhibiting branches, and previous studies have reported that it has a certain mechanism to relieve abiotic stress, but the underlying metabolic mechanisms of mitigation for drought-induced remain unclear. Therefore, the objectives of this study were to identify associated metabolic pathways that are regulated by rac-GR24 in alfalfa (Medicago sativa L.) and to determine the metabolic mechanisms of rac-GR24 that are involved in drought-induced root exudate. The alfalfa seedling WL-712 was treated with 5% PEG to simulate drought, and rac-GR24 at a concentration of 0.1 µM was sprayed. After three days of treatment, root secretions within 24 h were collected. Osmotic adjustment substances and antioxidant enzyme activities were measured as physiological indicators, while LS/MS was performed to identify metabolites regulated by rac-GR24 of root exudate under drought. The results demonstrated that rac-GR24 treatment could alleviate the negative effects from drought-induced on alfalfa root, as manifested by increased osmotic adjustment substance content, cell membrane stability, and antioxidant enzyme activities. Among the 14 differential metabolites, five metabolites were uniquely downregulated in plants in rac-GR24 treatment. In addition, rac-GR24 could relieve drought-induced adverse effects on alfalfa through metabolic reprogramming in the pathways of the TCA cycle, pentose phosphate, tyrosine metabolism, and the purine pathway. This study indicated that rac-GR24 could improve the drought resistance of alfalfa by influencing the components of root exudates.