1. Introduction
Hu sheep are among the numerous white breeds worldwide and are indigenous to China [
1]. The Hu sheep are known for their high adaptability and reproductive ability in China. Prolific Hu sheep are considered a very good maternal resource in the current intensive and factory farming [
2]. Feed production costs in the livestock industry have increased by 70–80% over the last decade, largely because of the increase in the cost of raw materials [
3]. The development of new attractive low-price feed stuffs is warranted [
4].
The crude protein in the feed impacts the animal’s growth and profitability [
5,
6]. Animal scientists are paying more attention to plant protein alternatives to soybean meal (SBM). Cottonseed meal (CSM) and rapeseed meal (RSM) are of interest to farmers because they are less expensive and more readily available than soybean meal. CSM is a by-product of cottonseed oil extraction that contains around 34–40% crude proteins, 11% crude fiber, vitamin B, and organic phosphorus [
7]. RSM is produced by crushing rapeseed after the oil has been extracted. It contains a high proportion of protein (34–38%), a balanced amino acid profile, as well as 25–30% neutral detergent fiber (NDF) [
8]. The proteins of RSM are equivalent to SBM proteins and contain more sulfur-amino acids than most plant proteins [
9]. On the other hand, CSM and RSM diets contain anti-nutrients that may limit the availability of nutrients, eventually resulting in toxic effects and decreased livestock productivity [
10]. The use of CSM in animal diets is restricted due to the presence of free gossypol (FG), a toxic pigment that may have detrimental effects on animal growth, reproduction, and intestinal development, as well as result in internal organ abnormalities [
11,
12]. Nonetheless, due to anti-nutritional factors and high fiber levels, the inclusion of RSM in animal diets is also limited [
13]. Although RSM has a nutritional value comparable to SBM, it contains glucosinolate, sinapine, and tannin and phytic acid, which may have a negative impact on the growth, health, and general welfare of animals [
14].
Numerous detoxification strategies for cottonseed and rapeseed meal have been developed, including biological [
15], chemical [
16,
17], and physical [
18,
19] treatments. Nevertheless, chemical and physical treatments have shown several disadvantages, including high costs, environmental concerns, and significant nutrient loss. In comparison, microbial treatment is the optimum method for detoxification, as the rapid development of microorganisms may result in the release of compound enzymes that destroy the feed’s hazardous compounds. Microbial fermentation is another approach for eliminating anti-nutrient factors from feeds while improving their nutritional content [
20]. Microbial fermentation can boost crude protein and other nutrients in plants, decrease their toxin content, and aid in the maintenance of stomach microbial stability [
21,
22].
Fermented total mixed ration (FTMR) efficiently maximizes nutrient usage and feed shelf life. Fermentation of TMR with microorganisms has been widely recognized to improve feed quality and there is an energy cost and loss of dry matter [
23]. The intake, digestibility, rumen ecology, and milk production of mid-lactation Holstein cows were significantly changed by a TMR optimization method containing
L. casei TH14 and fermented sugarcane bagasse [
24]. After feeding a fermented diet to cattle, lamb, and other ruminants, the quality and quantity of milk and meat were greatly improved [
25,
26]. In a recent in vitro investigation, FTMRs containing CSM/RSM inoculated with mixed bacteria
B. clausii and
S. cariocanus at a 1:1 ratio increased crude protein (CP) and decreased neutral detergent fiber (NDF) and anti-nutritional factor content [
27]. According to previous research, diverse strains have additional practical importance in fermentation than using only one type of single strain [
28]. However, little is known about the effects of fermented TMR with CSM or RSM containing mixed
B. clausii and
S. cariocanus strains on Hu lamb growth performance and meat quality. The objective of this study was to assess the effect of microbial fermentation on TMR with CSM/RSM on the growth performance, rumen fermentation, carcass characteristics, and meat quality of Hu lambs.
4. Discussion
Our findings showed that FTMR with CSM/RSM had no negative effects on feed intake or growth performance of Hu lamb. Dietary intake is a critical factor in determining animal growth performance, and it is strongly related to meeting the necessities of the maintenance and production of animals. Nutrient levels in the feed, live weight and health conditions, and production levels were all factors that could influence the ruminant’s DMI [
40,
41]. Although there were differences in the body weight of the lambs at the middle and end of the trial, the average daily gain was never statistically affected by the diets. Similarly, our previous study showed that FTMRs containing CSM/RSM increased CP and decreased NDF and anti-nutritional factors [
27]. However, the results of our experiment showed that feeding the Hu lamb with FTMR with CSM/RSM did not improve the animals’ average intake of dry matter or their body weight. Energy plays an important role in maintaining normal life activities of the body. While protein is the main component of the body, NDF and ADF apparent digestibility can reflect the strength of the overall digestive function of the rumen [
42]. The study found that adding fermented feed to a ruminant diet can improve the utilization of feed by increasing the growth and reproduction of rumen microorganisms [
43]. In this study, we showed that replacing soybean meal for FTMR with cottonseed meal and rapeseed meal did not impact the apparent digestibility and nitrogen metabolism of Hu sheep.
Blood circulation transports nutrients from the digestive system to the body’s cells, tissues, and organs. Biochemical serum parameters are commonly used to assess animals’ nutritional status, physiological functions, and immunity. In this study, concentrations of TP, ALB, GLB, BUN, TC, TG, HDL, and LDL did not differ between the FTMR with CSM/RSM and the control group. BUN is a marker of nitrogen level in the animal body, and it is influenced via CP ingestion and breakdown [
44]. BUN levels are linked to rumen ammonia levels [
45]. On d 80, the lamb fed FTMR with CSM/RSM had BUN concentrations that were very similar to those of the control group; this was in line with the results of Li, Sun [
46] and it led to positive, normal BUN levels in the lamb that were given pelleted TMR. The levels of ALB, TP, and GLB inside the blood serum represent the body’s immunity [
47]. Despite this fact, this demonstrates that FTMR with CSM/RSM had no negative effect on animal health during the period of the study. Blood lipoproteins transport lipids that are linked to animal health. Previous research showed that HDL is superior to LDL in animals.
The volatile fatty acids are associated with influencing the composition and energy balance of ruminant end products [
48]. In ruminants, propionate is the primary source of glucose and even a substrate for gluconeogenesis, whereas acetate and butyrate serve as precursors for the long-chain fatty acids synthesis [
49]. Previous studies have confirmed that the kind of diet and the level of nutrients consumed may affect the propionate, acetate, and butyrate fractions in rumen; for instance, a concentrate-based or a high-energy meal can increase propionate production in the rumen [
50,
51,
52]. Our results demonstrated that the ruminal pH of lamb fed fermented total mixed ration with cottonseed or rapeseed meal decreased significantly when compared to unfermented feed. The higher molar proportions of acetate, propionate and concentrations of TVFA between d 40 and 80 might be attributed to the fermented diet, which decreased the pH level. Similarly, Overton, Cameron [
53] demonstrated that feed type, intake, and feeding system affect ruminal VFA production. The results of this study indicate that diets significantly affect the concentration of Total VFA, acetate, propionate and butyrate. However, previous research indicated that probiotics had a variable effect on ruminal VFAs. Sadiek and Bohm [
54] and Abd El-Ghani [
55] found that feeding pronifer or S. cerevisiae boosted lamb and goat VFA production, respectively. In this investigation, the rumen liquid pH levels of the mixed microbial strain (
B. clausii: and
S. cariocanus) decreased substantially; however, the TVFA levels of the rumen liquid increased when FTMR with CSM in a ratio of 1:5 was used.
The two groups of lambs fed FTMR with CSM/RSM had similar live weights, carcass weights and dressing percentages. The eye muscle area reveals the mass muscle’s strength, amount, and arrangement. The muscle tissue development rate was the rate of muscle meat progress in late-maturing muscle, particularly the longissimus muscle. The LT area of animals provides an excellent measure of the performance of the animals in terms of meat production [
56]. However, the physio-chemical composition of pH value, color measurements, cooking loss, drip loss, cooking percentage rate, and sheer force did not show significant differences among the three treatment groups, except for meat pH values, which decreased in lamb fed FTMR with CSM compared to the control. The pH of the meat is one of the primary indicators of meat quality [
57] because atypical pH values can affect the meat quality, particularly the color and tenderness of meat [
58,
59]. The type of feed does not influence the pH level of the meat [
60,
61]. The decrease in pH may be due to the post-mortem muscle glycogen conversion to lactic acid [
62]. The relationship between FTMR with CSM/RSM and the function of meat pH is poorly understood. Further studies are required to explore the pH of the meat in fermented TMR-CSM/RSM mechanisms of action. The color of meat is the most vital factor influencing consumer buying behavior for red meat, since customers relate red with freshness [
63]. Despite a relationship between feed consumption and meat color, our current investigation found no change in meat color between groups [
64]. However, our current findings are comparable with those of who found that the red and yellow color values of lamb meat from the same breed are extremely near to the average numerical values. Considering this, the color of the LT meat of Hu lambs fed TMR-CSM/RSM was identical to that of the control group. Drip loss quantifies the amount of water lost as a result of gravitometric forces when a muscle contracts; as the available space within the muscle decreases, water seeps out, resulting in weight loss [
65]. This metric can provide information about water holding capacity (WHC) and is thus useful in meat science. In this study, the effect of different FTMR with CSM/RSM and unfermented TMR on drip loss was not statistically significant. Cooking loss refers to the quantity of water that is lost during the process of cooking and preparing meat. Smaller muscles have a higher cooking loss; the meat maintains more moisture, and the meat quality is associated with larger muscles [
37]. However, there has been no significant variation in cooking loss in our current study. Shear force is commonly used to measure muscle tenderness, and meat tenderness is among the characteristics utilized to assess meat quality. Our results are in line with a previous study’s findings; earlier research has demonstrated that feed with high protein [
66] and energy [
67] contents can also decrease the shear force.
The amino acids perform an essential function in meat quality by delivering the nutrients and flavor attributes vital to human consumption [
68,
69]. Lamb meat contains eight important amino acids, including tryptophan, lysine, phenylalanine, threonine, methionine, valine, leucine, and isoleucine. Lamb meat is a source of lysine and methionine required for humans [
70]. Our current study evaluated essential, non-essential, and total amino acids; with the exception of methionine, there were no significant differences between the three treatment groups, demonstrating the significance and better performance of lamb fed FTMR with RSM compared to the control treatment. According to previous studies [
71], methionine is the most limiting amino acid for protein synthesis in growing lambs. Ruminants are particularly vulnerable to low levels of methionine in their diets because of the low concentrations found in feed proteins [
72]. In the current study, we discovered that FTMR with RSM improved methionine concentration levels compared to the control group. This increased concentration resulted in a change in the amino acid profile of methionine, which was the root cause of this event. However, our findings are consistent with those of Su, Chen [
73], who found that adding Broussonetia papyrifera (BP)-fermented feed to Hu lamb feed can enhance product performance and meat quality by improving the crude protein, crude fat, minerals, AA, and fatty acid composition of the muscle. According to the WHO [
74], a healthy diet should consist of about 40% EAA and 60% EAA to NEAA. In the present study, the essential amino acid content of lamb meat was around 40%, and the ratio of essential to non-essential amino acids was close to 60%. Consequently, it indicates that FTMR with RSM had no negative effect on the AA composition of the meat, which satisfies human demand for high-quality lamb.
Dietary composition influences the total fatty acid content of muscle [
75,
76]. Microorganisms in the rumen are essential for either bio-hydrogenation or conversion of fatty acids. High forage-content diets increase rumen activity [
77]. We discovered that the lamb fed FTMR with RSM had significantly greater levels of SFA than the control group. Our results indicate that the meat produced with the CSM diet has the lowest SFA content [
78], with antiprotozoal and antibacterial properties in the period of ruminal fermentation [
79,
80,
81], thus encouraging modifications in end products such as the fatty acid profile [
82]. SFA has been linked to various health concerns in humans [
83]. Nevertheless, lauric acid (C12:0) protects against heart disease by inhibiting LDL oxidation, increasing HDL concentrations in the blood, lowering blood pressure, and inducing apoptotic cell death [
84]. The LDL levels in the lamb fed FTMR with CSM/RSM and the control group are not significantly different, and the HDL levels in the blood of the lamb fed FTMR with CSM/RSM are also similar to those in the control group. Unsaturated fatty acids surpass saturated fatty acids in health benefits [
85]. In this study, compared to the control group, FTMR with CSM had higher unsaturated fatty acids (UFA), while FTMR with RSM had lower UFA. It is possible that fermented total mixed ration containing cottonseed or rapeseed meal increased the synthesis of unsaturated fatty acids with FTMR using CSM. Furthermore, the concentration of PUFA in FTMR with CSM/RSM muscle meat lamb was significantly lower than that in the control group. Since fatty acids are bio-hydrogenated during transit in the rumen, C18:0 and C18:1 cis9 acids are produced [
86]. Our findings coincided with those of Su, Chen [
73], which reported that the addition of Broussonetia papyrifera (BP)-fermented feed to a Hu lamb diet results in an increase in the amount of unsaturated fatty acids and the composition of the main fatty acids. Red meat contains n-3 polyunsaturates that are beneficial to human health [
87]. n-3 polyunsaturated fatty acids have received significant attention [
88], since they are believed to be capable of preventing a variety of diseases [
89]. The meat from the control group contains more n-3 fatty acids than the meat from lambs fed fermented TMR. On the other hand, n-6 fatty acids have been linked to several diseases [
90], including obesity [
91]. However, the n-6: n-3 ratio, on the other hand, is an important predictor of meat quality [
92]. Similarly, meat from the control lambs contained higher n-6 fatty acids than meat from the FTMR lambs. The n-6/n-3 ratio was lower in animals fed FTMR with RSM compared to the control and FTMR with CSM groups. According to the WHO [
93], an ordinary human healthy diet should have an n-6:n-3 PUFA ratio of 5 to 10, whereas the British Department of Health [
94] suggest a ratio of fewer than 4.0 [
85]. In our current investigation, the n-6: n-3 PUFA ratios of the control group, fermented TMR-CSM, and fermented TMR-RSM were 7.07, 7.71, and 6.43, respectively. However, the changes in meat FA profile observed in our study probably would not affect consumer acceptability, as Gravador, Brunton [
95] concluded that changing the fatty acid profile of lamb meat by dietary interventions may not adversely affect its general acceptance.