Research Question: What is the scientific research scenario about technologies and innovations used in the production systems for the Santa Inês sheep breed in the last 5 years (2017 to 2021) in Brazil?

The conduction of a systematic review depends on the scope and quality of the included studies (15). Thus, to recover scientific articles of proven quality, we sought to use only electronic bases that retrieve journals that perform peer review of a manuscript, which were national and international. The bases used were Scopus, Scielo, Web of Science, and Portal de Periódicos Capes. According to Levy and Ellis (16), this step is called entry.

Next, the descriptors and Booleans used as search guidance in each database were determined. The Portuguese words were translated into English, and the search proceeded. The search method varied a few times among databases because they have some peculiarities.

Boolean operators were for establishing selection criteria and thus retrieving the maximum number of papers related to the theme. The AND operator was inserted between two words for searching articles that contain both (e.g., animal AND reproduction). Whereas, the Boolean operator OR was used to extend the search beyond one word (e.g., sheep OR ram searched for articles containing one or the other). Keywords between quotation marks were used for refining the search. Therefore, articles were retrieved only if the words appeared together.

After the search using the keywords and Booleans, it was proceeded to refine the results obtained through database restriction tools. In all databases, the time frame ranges from 2017 to 2021.

The articles retrieved from databases were selected according to the criteria described below. The criteria established were based on the objective proposed by the research. We selected only studies conducted in Brazil and excluded those that did not describe the place where the experiment was conducted.

The focus should be on meat sheep, using only the Santa Inês breed. Studies that involved crossbreeding, combined other breeds or species, or used no defined breeds were excluded. The only study selected that used a species other than sheep was the pasture system because other species such as cattle characterized a technology for endoparasite control.

They should obligatorily present a technique and/or innovation related to the different production systems for meat sheep. Clinical studies, case reports, or those that did not highlight a technology were also excluded.

After being selected according to the mentioned criteria, the articles were grouped into eight different knowledge fields (health, reproduction, animal breeding, behavior and welfare, nutrition and feeding, forage and pasture, carcass and meat quality, and economics and management of livestock systems), according to Table 1.

The articles chosen in the previous step were read in full to extract relevant aspects of the objectives, methodology, results, and conclusions. This analysis was also related to the quality of the studies, which should have a detailed description of the methodology (without experimental problems) and conclusive results with a thorough discussion.

The presentation of the results focused on describing the main characteristics of the studies, highlighting the places where they were conducted, the technologies, and the approaches used in the systems.

Some technologies employed to promote a positive impact or not cause damage to the health of Santa Inês sheep are described in Table 3. The highlight was for dietary strategies such as propolis extract, probiotics (Bacillus thuringiensis), biopolymer (chitosan), and by-products. Also, the use of drugs such as an antibiotic and hormones could be evidenced. Other techniques focused on endoparasites' control and combat (Table 3).

In the reproductive field, some studies addressed techniques used to increase reproductive efficiency in males and females, with a higher frequency of studies in females. Semen additives, dietary strategies, hormones, handling tools, ultrasound, and infrared thermography devices summarized the main techniques to support the increase in male or female sheep reproduction (Table 4).

For animal breeding, some papers identified genes linked to production characteristics. Others estimated genetic parameters or used computed tomography. The studies aimed primarily at supporting the selection of superior animals for breeding programs, and most of them involved the estimation of genetic parameters.

After applying the established criteria, there were no peer-reviewed scientific articles about Santa Inês sheep behavior. Only one study was selected about animal welfare, and it was related to stress at performing reproductive procedures (75).

There was a wide range of studies involving the use of by-products as an alternative in the formulation of diets, mainly aiming at reducing costs. Other technologies deal with the supply of non-protein nitrogen sources, handling, and lipid supplementation. All these technologies are listed in Table 5.

In this knowledge field, the studies addressed techniques of grazing systems and the use of different tropical or alternative forage plants as a technological increment for use in the production of Santa Inês sheep (Table 6).

The techniques and innovations aimed to improve, benefit, or not harm the quality of the carcass and meat of Santa Inês sheep. They were dietary strategies, supply of forage plants, and handling practices (Table 7).

The lack of studies on economic analysis and feasibility of production systems of the Santa Inês breed was evidenced in this article. Therefore, it was possible to select only one study that performed this analysis within the production system of meat sheep raised on cultivated pastures (126).

Additives to sheep diets are associated with their biological power to provide health benefits to these animals. For example, red propolis has powerful biological activities and a high content of isoflavonoids bringing benefits to the defense cells and the energy status of sheep at the beginning of lactation (21). The probiotic B. thuringiensis did not interfere with animal performance, did not cause intoxication, and can be safely used with the daily addition of 2.5 × 106 spores/kg body weight (22). Another additive to sheep diets is chitosan (an alternative biopolymer to ionophores), which was recommended to be used with cottonseed husk since it would not affect blood metabolites, liver histopathological profile, and rumen papillae morphometry (23).

The safety of using cottonseed due to the presence of gossypol (an anti-nutritional factor) has been evidenced since this by-product did not cause health impacts to sheep when replacing soybean meal (24). Similarly, agro-industrial guava (P.guajava L.) waste promotes beneficial effects on the health of sheep when included up to 30% in the diet with a decrease in cholesterol concentration (25).

In general, the food additives and by-products presented here as technological tools contribute to improving animals' health, or their use does not cause harm to them. However, more studies need to be carried out with the Santa Inês species to prove their effectiveness.

The use of pharmaceuticals applied to animal health as a technology has been highlighted in two studies. The recombinant bovine somatotropin hormone used in ewes reduced the risk of pregnancy toxemia (26). However, gentamycin (an antibiotic used for intramammary drying therapy) does not prevent new infections nor cure previous subclinical mastitis (27). Therefore, only the use of the first drug would be recommended since the antibiotic in the second situation would only increase production costs.

Endoparasites have been a significant problem for sheep producers, as they reduce or limit production (28). Good animal nutrition may be able to generate resistance to prevent helminth infections. Such as protein supplementation that promoted early activation of the ovarian follicle in peripubertal ewes infected with Haemonchus contortus (29). The use of forages rich in condensed tannins has been recorded as a tool for helminths control in sheep, such as those present in Acacia mearnsii that could be considered an alternative to commercial anthelmintics (30). Other technologies used for helminth control are the FAMACHA© system which has significantly reduced the need for treatments in animals of various categories (31, 32). Biological control (nematophagous fungi) brought beneficial results by reducing infective gastrointestinal nematode larvae in pastures (28). The Famacha method is not a recent technique and has been used also in other species to identify susceptible (anemic) animals in the herd (33). On the other hand, biological control is a strategy that needs more research to have its efficiency proven.

The addition of substances for semen cryopreservation to maintain its viability and quality has been evidenced, bringing benefits to the freezing (34, 35) or cooling of semen (36). And as a dietary strategy, the supplementation with palm kernel cake does not affect seminal parameters and thus could be used as an alternative ingredient in sheep diets (37). As for the frozen/thawed sperm selection methods, swim-up would be the most advantageous if the goal is in vitro fertilization (38).

Nutrition can be a handling tool for body condition score recovery of ewes in different reproductive phases. In pre and postpartum, the supplementation of 1.5% of body weight with concentrate is recommended to support the maintenance of minerals in homeostasis and reproductive performance (39). In prepartum, supplementation of ADE vitamins improved energy metabolism (40). In the postpartum period, protected fat was not recommended because it reduced the probability of gestation (41). As for energy by-products, crude glycerin could be recommended for up to 10%, not affecting reproductive performance before and during the breeding season (42). In addition, it has a positive effect on the energy balance in the critical phases of late gestation and early lactation (43).

The use of hormones in the estrous synchronization of ewes through hormonal protocols is a technological tool to increase reproductive performance. Progesterone is the most commonly used in protocols but is also expensive. Thus, a study reporting the reuse of devices with this hormone evidenced that this practice would not affect pregnancy rates in synchronization protocols (44). Also aiming to reduce costs, Prates et al. (45) evaluated human intravaginal tampons soaked with human progesterone for induction and synchronization of estrus in Santa Inês ewes, verifying that these can be used alternatively for this purpose. Comparing the effect of short and long protocols based on progesterone and equine chorionic gonadotropin (eCG), Silva et al. (46) found that under the Amazon environment, the second one showed better results.

As well as progesterone, other ovulation inducers have been used in protocols, such as human chorionic gonadotropin (eCG) (47), gonadotropin-releasing hormone (GnRH) (48), and pFSH in combination with eCG (49) or successive administration (50).

Hormones have also been studied to aid in non-surgical transcervical embryo transfer. For example, a cervical dilation protocol consisting of oxytocin alone (51) and a hormone combination (estradiol esters, d-cloprostenol, and oxytocin) to induce cervical dilatation before non-surgical retrieval (52).

The combination of hormone dose and interval of use allows various protocols to be created. Therefore, each protocol is a different technology and the choice of one depends on the analysis of the production system.

To verify the effectiveness of using the in vitro embryo production technique, Ferreira-Silva et al. (53) compared it with natural mating but observed no difference between the two methods studied.

Some management tools can also increment reproductive efficiency. For example, the exposure of the male to the female with temporary weaning for 24 h improved the reproductive performance in ewes under postpartum anestrous (54). Also, the male effect promotes pre-ovulatory LH peaks up to 80 h after physical contact (55).

Seeking to facilitate calf handling, dexamethasone in ewes at 145 days gestation (8 and 16 mg) is an effective alternative to induce labor and concentrate handling and attention to the neonates without altering labor (127).

Imaging and temperature measuring devices can assist reproductive handling as not invasive tools. They also can provide an immediate result, helping the agricultural science professional in decision-making. The study by Beltrame et al. (128) found that the manual evaluation allows more accurate identification of the onset and end of systole and diastole. Color Dopplers are also a reliable tool starting 17 days after mating to distinguish between pregnant and non-pregnant animals (129). Finally, infrared thermography has been employed in sheep reproduction and has proven efficient for detecting small temperature variations during different phases of the estrous cycle (130).

Research in animal behavior and welfare has been infrequently approached. Studies in this field are valuable because animals are adaptable to the environment and, in the presence of stressful agents, this may directly affect performance, impacting the entire production system (76). In this way, technologies capable of extinguishing or mitigating these variables that compromise well-being become of utmost importance.

This research needs to take into consideration the concept of the “five freedoms” to guarantee a minimum quality of life for animals: (1) Physiological freedom (freedom from hunger, thirst, and malnutrition); (2) Environmental freedom (physical environment suitable to the species); (3) Sanitary freedom (freedom from disease, wounds, and pain); (4) Behavioral freedom (the possibility to manifest behavioral characteristics proper to the species), and; (5) Psychological freedom (freedom from fear and discomfort) (77).

A single study for this review was selected, which used tools related to reproductive biotechniques. It showed that transcervical and laparotomy techniques affected the welfare of the ewes in embryo collection, but the first one was less stressful (75).

By-products with protein nutritional value have widely experimented on the studies. However, supplementation with cottonseed cake and coconut meal needs to be used with caution as it may decrease animal performance variables (78, 79). Castor meal and licuri cake are also by-products with the potential to be used as a protein source (80, 81). On the other hand, sunflower meals did not show satisfactory results regarding performance and other characteristics as a protein alternative (82).

Aiming to replace soybean meal with dehydrated distillers grains in the performance and carcass quality of confined lambs, Gomes et al. (83) recommend its use in up to 24% replacement in the dry matter of the diet. Another protein feed to provide to sheep is silage based on by-products from the industrialization of babassu palm (A. speciosa) with the inclusion of additives such as corn chips and cassava shavings, recommended by Codognoto et al. (131).

Regarding by-products with energy values, the replacement of corn with guava by-products was indicated to be included in the diet of sheep in confinement (84). Also, fats and oils have been used in ruminant feed to increase the energy density of the diet. Then, the supplementation with buriti oil improves consumption, digestibility, and animal performance (85). However, the use of other oils, such as canola, sunflower, or castor oil, did not provide milk yield or increase the final bodyweight of the lambs (86).

In this way, by-products become an alternative capable of reducing production costs with animal feed without compromising their performance in general. However, an inclusion limit must be respected as these foods may have antinutritional factors.

For maximizing microbial protein synthesis in the rumen, urea (source of nitrogen for the production of amino acids) needs to be associated with a rapidly degrading carbohydrate source to supply energy to the microorganisms. This association aims to replace all or part of a true protein source, such as soybean meal (87). However, the association of urea with cassava root, corn, or forage palm could not replace soybean meal in the diet of sheep in confinement (88). Also, encapsulated nitrate did not influence intake or nutrient digestibility replacing urea in lamb diets (132).

Feeding management is also able to influence animal performance. By evaluating the effects of feeding frequencies (once, twice, three times, and four times a day), Saldanha et al. (133) could recommend feeding once a day to avoid compromising the performance of confined male lambs.

The ratio of roughage and concentrate (V:C) can also be considered a handling strategy to improve performance and prevent metabolic problems. In hay-based diets, the ratio of 500:500 g/kg improved both performance and feed efficiency in lambs (134). For diets formulated with silage, it is recommended 600:400 g/kg for the highest weight gain (89).

Three different grazing systems (1-sheep grazing only, 2-sheep grazing after cattle, and 3-cattle and cattle grazing together) were studied by Santos et al. (90), who found that simultaneous-3 and isolated-1 resulted in the best forage production and animal performance.

Tropical forages are grass species that have the advantage of being adapted to the most adverse conditions. However, they are generally less productive. In a grazing system, Marandu and Piatã cultivars (Brachiaria brizantha) allowed better productive performance and body development of Santa Inês sheep (94). The spineless cactus occupies a prominent position in the diet composition of ruminants and is the most widely cultivated cactus in the Brazilian semi-arid region. However, the exclusive supply of this plant is not recommended, due to its low dry matter content and high degradability (134), but its use has been an alternative feed on sheep diet (91–93, 95, 135). Sisal (Agave sp) also is a cactus that can be present in sheep feed through its by-product, and its pulp provided lamb performance similar to those with Tifton hay-based diets, also reducing costs (96).

Still using plants adapted to semi-arid conditions, there have been reports of the M.tenuiflora (Willd.) hay (97). Also, the Leucaena (Leucaena leucocephala.), Gliricidia (Gliricidia sepium), and Macrotiloma (Macrotyloma axillare) leguminous plants were used as a source of protein (98, 99).

According to the works presented, it is evident that tropical forages and semi-arid cactus are viable alternatives for feeding Santa Inês sheep as they have good adaptation and are available in periods of greater scarcity. However, attention should be paid to the fact that these forages are less productive and, in the case of cactus, with high humidity. Therefore, it could compromise the consumption and performance of the animals. Another technology employed in the feed management of meat sheep can be demonstrated by Oliveira et al. (100) when they verified that bulking extrusion (heat treatments that modify physical and chemical properties) improved nutritional parameters when replacing corn silage in the diet of sheep.

Evaluations of carcass and meat quality from the supplementation with by-products were the majority of the selected studies in Santa Inês sheep. These studies aim to identify whether the use of these foods in the diet would cause any modification in carcass and meat characteristics.

As a protein feed, sunflower cake and cottonseed, combined with calcium lignosulfonate (a cellulose industry by-product) or with an antimicrobial (chitosan), can be included in sheep diets without overall harm to the carcass and meat quality (101–103). Another alternative protein feed would be mazoferm (a residue from the processing of corn) that can replace soybean meal without altering the carcass characteristics (104).

Some studies have addressed cassava wastewater (manipueira) as a source of energy in sheep diets. However, its use, among other effects, alters the physicochemical composition and fatty acid profile of the meat, not compromising the overall meat quality (105, 106). On the other hand, the supplementation with guava (P.guajava L.) agro-industrial by-products does not compromise the sensory characteristics of sheep meat if added in up to 30 to 40% (107, 108). And still considering energy by-products, despite being rich in unsaturated fatty acids, canola grain did not influence instrumental analysis, centesimal composition, and sensory attributes of meat (109).

The effect of protein-energy supplementation on carcass characteristics of sheep has also been verified. Nevertheless, despite favoring meat characteristics, this type of supplementation may increase lipid oxidation during the aging time and affect consumer acceptance (110). However, protein-mineral supplementation could improve the quantitative and qualitative carcass characteristics (120).

Some authors have studied feed restriction as a strategy that could benefit carcass quality and reduce system costs. Feed restriction of up to 60% does not affect carcass yield in sheep (121), improving meat quality and lipid profile (122). However, Campos et al. (111) recommend a lower dietary restriction (30%).

In an attempt to find an additional feed source, Luz et al. (137) found that babassu has the potential to replace elephant grass up to 50% without causing effects on carcass characteristics or meat quality. It was possible because of the by-product characteristics of bulky feed with 62.30% neutral detergent fiber, 19.06% crude protein, and 9.20% ethereal extract (112). Also, the supply of banana leftovers can cheapen the diet in places with availability, and its inclusion can replace up to 75% of corn bran (136).

The effects of supplementing sheep with spineless cactus, as well as in performance evaluation, were observed under meat quality. For instance, it improved lipid profile (113, 114) and meat sensory quality (117). In addition, this cactus could replace maniçoba (M. pseudogalziovii Pax and Hoffman) hay by up to 33% with increased carcass finishing fat without compromising meat quality (115). Another recommendation was to include <75.3% palm in sheep diets, replacing Tifton hay (116) or 44% palm, replacing sugarcane (138), with the proposal to obtain beneficial effects on most carcass traits.

Another plant adapted to semi-arid conditions is the legume M. tenuiflora. It can replace Brachiaria decumbens cv. Basilisk hay with the proposal of improving several meat characteristics (118). Also, when using diets based on plants from the Brazilian caatinga, Abdalla Filho et al. (119) observed that feeding babassu and mofumbo did not compromise the carcass characteristics and the meat fatty acid profile.

When verifying the effect of vitamin E supplementation and castration in Santa Inês lambs, Torres-Geraldo et al. (124) found no significant changes in meat quality characteristics. However, the technologies applied are not justified. On the other hand, Lima et al. (123) found that non-castrated animals produce better quality meat for human health, with a better lipid profile.

Regarding water management, when studying salinity levels, it was found that salinity levels up to 8,326 mg TDS/L do not affect the carcass and meat characteristics of Santa Inês lambs (125).

Therefore, most of the techniques presented to contribute or not alter carcass and meat quality involve animal feed or feed restriction. Nonetheless, the level of inclusion or restriction must be respected so that they do not bring negative results.

We highlight the need for economic approaches in studies involving the production systems of Santa Inês sheep. Economic analysis is essential because it identifies the items that should be part of the activity costs and the factors that compromise the system's profitability. It also describes the importance of productive indexes evaluation to identify precisely where the system is being harmed and contributes to generating solutions for greater efficiency and activity profitability (139).

The study identified in this review performed the economic analysis of sheep production systems in pastures of different cultivars of Panicum maximum (Aruana and Massai) and Brachiaria brizantha (Marandu and Piatã). The authors calculated mainly revenue, costs, annual operating profit, and internal rate of return, verifying greater feasibility and attractive remuneration rates in production systems of meat sheep on marandu and massai pastures (126).