The results of the statistical analysis of Tables (2) and (3) indicated the same results in all measurements of milk components. At the end of the 1
st and 3
rd months of the experiment, the averages of (SCY + Sc + Zn) recorded the highest increase (P≤0.05) in milk production, solid-to-fat ratio, milk density and protein level among all transactions. In turn, (SCY) and (Se + Zn) groups, recorded their significant superiority (P≤0.05) over the control group in milk production, solid-to-fat ratio, milk density and protein level. While in milk fat ratio, also at the end of the 1
st and 3
rd months, (SCY + Sc + Zn) group gave its lowest rates (P≤0.05) compared to all the experiment transactions, as well as the yeast group (SCY) (P≤0.05) compared to the control, while the decrease was mathematically for the minerals group (Se + Zn) compared to the control.
(Gomes et al., 2012; Ferreira et al., 2010) who attributed the improvement in milk production levels, increasing its milk density, the percentage of protein and solid matter in animals that fed on
S.
Cerevisiae, to the containment of the outer membrane of yeast cells a high protein concentration and high level of solid matter, concurred with the results of the current study. According to
(Dobicki et al., 2006), S. Cerevisiae yeast increased milk production by enhancing microbiota metabolic activity, feed digestibility, energy metabolism and mammary gland health (
Milewski and Sobiec, 2009). There is some evidence that
S.
Cerevisiae influences the composition of milk in ruminants, in addition to some evidence that it has a favorable impact on milk production
(Coleman et al., 2023). S.
Cerevisiae supplementation dramatically reduced the amount of milk fat in ruminants
(Zaworski et al., 2014). Supplementing with
S.
Cerevisiae also markedly boosted the amount of total protein in ewe milk (
Mustafa, 2022). S. Cerevisiae altered the protein content of milk as well. After 70 days of supplementation with S. Cerevisiae at a daily dose of 30 g/animal during lactation, the concentrations of β-casein were significantly decreased, while
k-casein had a significant rise in ewe milk
(Milewski et al., 2012). Bioavailable chromium found in
S.
Cerevisiae may influence insulin-like growth factor 1 and boost milk output (IGF-1). Chromium was reported to upregulate IGF-1 mRNA and IGF-1 When insulin is present, chromium has been shown to increase the levels of IGF-1 mRNA and IGF-1 receptor in skeletal muscle cells
(Jia et al., 2018). At the end of the first and third months of the experiment, the goats treated with selenium and zinc produced more milk and milk protein and had less fat, which was consistent with the findings of (
Tufarelli and Laudadio, 2011), whose study showed that selenium-fed goats produced the most milk (P≤0.05) and had higher protein concentrations. Additionally, the findings of the group that combined selenium, zinc and
S.
Cerevisiae yeast were in line with
(Petrera et al., 2009) who observed that milk output was equivalent in Saanen dairy goats fed diets containing selenium-yeast. Selenium-supplemented yeast has been found to have a good impact on dairy goat milk production features and the health of the goat mammary gland
Reczyska et al. (2019). According to
(Salama et al., 2003), feeding dairy goats a diet high in zinc improved the levels of milk production and casein protein, increased the concentration of solid-fatty substances and improved the indicators of milk production recipes and their general specification.
The results of the statistical analysis indicated in Table (4) of the changes in the levels of hormones in the blood serum showed that there is a significant variation (P≤0.05) between the coefficients. The treatment of (SCY + Sc + Zn) recorded the highest concentration (P≤0.05) of the prolactin hormone compared to other groups. In contrast, the estrogen level was decreased (P≤0.05) in the (SCY + Sc + Zn) and (SCY) groups compared to the (Se + Zn) and control groups. While (SCY + Sc + Zn) had recorded the lowest level of T3 hormone, it recorded the highest level of the T4 hormone compared to the rest of the study groups. The (SCY + Sc + Zn) and (SCY) groups also showed higher levels of the hormone cortisol compared to the (Se + Zn) and Control groups. At the same time, one group (Se + Zn) had the lowest cortisol level compared to the other treated groups.
Saccharomyces cerevisiae, which could mobilize nutrients and ensure the supply of chemicals in the body, was given to goats in the current study and these goats had much greater cortisol levels. Strong evidence demonstrates that higher glucocorticoid levels are necessary for increased milk production in order to provide enough energy for galactose synthesis
(Mohammed et al., 2018). In addition to stimulating the expression of milk protein genes during lactation, cortisol, the main glucocorticoid in galactose production, also plays a critical role in fostering mammary epithelial cell differentiation
(Jia et al., 2021). These results imply that prolactin and cortisol may increase goat milk production. According to our findings,
Saccharomyces cerevisiae can make cortisol and prolactin work together in goats to boost production. Here, we discovered that the prolactin level increased together with the cortisol concentration in the treatment group, along with the fact that the combined milk output increased
(Du et al., 2022). S.
cerevisiae contained an endogenous ligand for the yeast estrogen-binding protein. Estrogen increases blood flow to the uterus and genital system. The endogenous ligand from S. cerevisiae has recently been demonstrated to have estrogenic action in mammalian systems, which is significant
(Feldman et al., 1984). Zinc’s involvement in enhancing ovarian function and increasing female fertility is thought to be the cause of a large rise in estrogen levels in the (Se + Zn) group compared to yeast-treated groups
(Ahmed et al., 2001). This could be the case because selenium stops mature follicles and ovarian tissue from oxidizing, which raises the amount of estrogen released by the follicle. The development of follicles, which are responsible for the release of estrogen, may be stimulated by zinc in the tonic immune system
(Shareef et al., 2021). All domesticated animals’ growth, development and metabolism are significantly influenced by thyroid hormones, either directly or indirectly. Thyroxine (T4) must be converted into tri-iodothyronine (T3) in order for the thyroid hormones to operate fully. This process is carried out by a special nuclear receptor protein that may influence the expression of particular regulatory areas of the target genes (
Schroede and Privalsky, 2014). After the thyroid hormone receptor was cloned, protein analysis revealed a region that included zinc and selenium ions, which are essential for the receptors’ ability to bind to their target genes
(Olivieri et al., 1996). As a result, it has been suggested that T3’s full biological functioning may depend on its zinc and selenium levels (
Shahid, 2022). Since the thyroid gland regulates this rate, increased T4 and T3 release increases body heat production and basal metabolic rate in nursing and lactating goats
(Aghwan et al., 2013). In both animals and humans, low selenium or zinc status decreased the T3/T4 ratio mostly through raising T4 levels rather than by lowering T3 levels
(Olivieri et al., 1996).