Growth and Productive performance of beef bulls
The highest body weight gain was found in bulls received a mixture of
B. subtilis and green microalgae when compared to control and
B. subtilis groups, while there was no significant difference to green microalgae group (Table 3).
Digestibility coefficient and nutritive value were improved in groups supplemented with green microalgae and a mixture of green microalgae and
B. subtilis (Table 4).
Bacillus subtilis and/or green microalgae supplementation increased values of total digestible nutrients, starch value, digestible crude protein and digestible energy. The significant effects of
Chlorella vulgaris algae or green microalgae on body health and productive performances were confirmed in several studies
(Kholif et al., 2020). It has been proved higher body weight gain and nutrient digestibility due to green microalgae or
B. subtilis supplementation in several studies
(Kholif et al., 2020; Jia et al., 2022). This may be due to the increasing digestibility of nutrients, which may be attributed to the accumulation of large amounts of readily fermentable carbohydrates liberated by the action of the bacteria and probiotics in the bulls’ rations
(Mousa et al., 2022). The improvement in most nutrient digestibility parameters could be attributed to
B. subtilis and high protein content and b
-carotene in green microalgae. This may improve the ruminal microbial activity and communities, thus increasing the gut health through rumen maturity by favoring microbial establishment, increasing the fiber digestion of feedstuff, reducing the fluid viscosity and ruminal ammonia and improving the concentration of volatile fatty acids in the rumen
(Jiang et al., 2020). B. subtilis have been used as beneficial supplements in farm animals to lower morbidity and mortality
(Rai et al., 2013), improve feeding performance
(Jia et al., 2018). Moreover, green microalgae provides organic acids and vitamins to stimulate the growth of lactic acid bacteria, which improve rumen metabolism by stabilizing the rumen pH, increasing the production of cellulolytic bacteria and improving anaerobiosis by scavenging the oxygen available in the rumen, as well as improving microbial protein synthesis and fiber digestibility
(Bomba et al., 2002).
Blood parameters
B. subtilis and green microalgae supplementation to bulls improved the hematological and immunological parameters (Fig 1).
Other studies concluded that hematological profile showed an insignificant change between different groups
(Justine and Oluwatosin, 2008;
Al-Mufarji et al., 2022). This indicated the improved health status of the supplemented beef bulls. Such effects may be due to the improved synthesis of vitamin B12 by
B. subtilis and higher content of green microalgae with vitamins B1, B2, B3, B6, B12, E, K and D
(Becker, 2007) and improved iron salt absorption by the small intestine, resulting in better hematopoiesis
(LaFleur-Brooks and LaFleur-Brooks, 2008). White blood cells are a major component of the body’s immune system and are extremely important in defending the body against infections. The results of WBC count were consistent with those obtained by earlier reports
(Milewski and Sobiech, 2009) who found that
B. subtilis and green microalgae in bulls had a greater WBC count that participated in increasing lymphocyte percentages in the leukogram
(Talha et al., 2009).
Biochemical parameters
B. subtilis and green microalgae supplementation to bulls improved the serum biochemical parameters (Fig 2).
The
B. subtilis and green microalgae supplementation in our study increased blood total protein. This effect is expected, as protein digestibility was improved in the treated groups. The increased activity of hepatic function is suggested when green microalgae were fed
(Tousson et al., 2011), which resulted in higher concentration of total proteins as recorded in the present study. In fact, probiotics can synthesize protease enzymes and, thus, provide some specific amino acids that can boost microbial protein synthesis
(Talha et al., 2009). Furthermore, microalgae biomass microalgae contain 40-70% proteins
(Becker, 2007) and is rich in proteins that compete favorably, in terms of quantity and quality, with conventional food proteins such as soybeans, eggs and fish, making the unicellular organisms a promising source of food protein
(Batista et al., 2013).
B. subtilis and microalgae supplementation improved energy status of beef bulls as indicated by glucose concentration. This enhancement can be associated with improved gluconeogenesis. Earlier studies have demonstrated that probiotic supplementation can improve gluconeogenesis by increasing propionate concentrations with a significant effect on glucose concentration in ruminants
(Sayed, 2003). Furthermore, propionate is considered as the primary gluconeogenic volatile fatty acids used for glucose biosynthesis
(Vanhatalo et al., 2003). In addition, earlier reports found that the concentrations of total cholesterol and triglycerides were high in the green microalgae groups
(Senosy et al., 2017; Kholif et al., 2020; Al-Mufarji et al., 2022).
Blood urea nitrogen concentration can be used as an indicator of protein status as well as nitrogen utilization
(Whang et al., 2003; Mohammed et al., 2019; 2020). The concentration of BUN increased as nitrogen intake increased up to a certain level and then reached a plateau. This can explain why increased nutrient density led to higher BUN concentration in the current study. Urea nitrogen is a major waste product of protein catabolism. Our results were contrary to those of earlier researchers regarding lower blood urea nitrogen and creatinine
(Senosy et al., 2017; Odhaib et al., 2018).
The increased AST and ALT activities may also be associated with disorders in the energy metabolism of the body as well as stress
(Odhaib et al., 2018). Thus, the similarity in the levels of serum AST and ALT among the treatments is an indication that the supplementation of
B. subtilis or green microalgae had no detrimental effects on tissues and organs in beef bulls. Higher levels of AST can be a clue of liver damage, especially when paralleled with increased ALT
(Pagana and Pagana, 2006). Moreover, the AST levels reported in the present study fall well within the normal bovine range
(Aiello and Moses, 2019;
Al-Mufarji et al., 2022).
