In the last 25 years, increased interest in pheromone action and its effects has been observed in several species, such as cattle [
63,
64], pig [
58,
65,
66,
67], horse [
68], goat [
69], and sheep [
70]. In these species, several benefits associated with natural pheromones have been reported for social behavior and reproductive function. Therefore, the development and subsequent utilization of synthetic analogues of endogenously released compounds are expected to benefit livestock production.
Swine has been one of the main species focused on for the effects of pheromone utilization on behavior and performance of the flock. Indeed, maternal pheromones regulate nursing pig behavior in a manner that the lack of a specific odor from the skin of the sow leads to recognition and discrimination among maternal odors found in feces and other biological fluids, for example [
71,
72]. A decade later, Pageat (2001) was able to isolate secretions from the skin of mammals, leading to the development of a synthetic analogue similar to the endogenous secretion observed in the sow skin [
67]. In one of the first trials evaluating this technology, Pageat and Teissier (1998) demonstrated that pig aggressive biting behavior was reduced following weaning and commingling [
73]. Moreover, pigs treated with the synthetic substance at weaning presented altered behavior, including more time feeding and standing/walking, reduced amount of time drinking water, lying down, and engaging in agonistic behaviors [
74]. Over a 4-week period, treated pigs were heavier (+1 kg), had a greater ADG (23%), and feed efficiency (FE; 22%) vs. placebo-treated pigs [
74]. These data demonstrated that the synthetic pheromone analogue caused behavioral changes that positively affected post-weaning performance of the sounder.
In support of the aforementioned results in swine, a fair and valid rationale would be to evaluate the effects of an appeasing substance in ruminants, as these experience different stressful situations, such as weaning, transport, feedlot entry, and castration [
2]. Therefore, the application of a bovine appeasing substance (BAS; IRSEA Group, Quartier Salignan, France) has been evaluated by our and other research groups. For the current and upcoming sections, it is important to briefly state that BAS is based on a proprietary mixture of fatty acids including saturated (palmitic and oleic) and polyunsaturated (linoleic), which are added at 1% of the excipient, yielding a long-lasting effect of 15 days in the treated animal [
65,
66,
67]. Furthermore, BAS reproduces the components of the natural pheromone produced by beef and dairy females [
65,
66,
67].
5.1. BAS vs. Weaning
Among the several stressful events faced by the ruminants, weaning is highlighted [
1] and management alternatives to alleviate the stress-related losses following weaning have been addressed by other researchers [
75,
76,
77]. Nonetheless, technologies that could be employed at the moment that weaning occurs are still warranted, as most of the beneficial ones involve management plans and/or activities that production systems might not be able to apply in their daily operations. Therefore, our research group has evaluated the utilization of BAS in different weaning settings and how this technology might be able to impact the physiological responses, health, and productive function of the beef cattle herd.
Cooke and colleagues (2020) administered a single dose of BAS to
B. indicus ×
B. taurus beef calves at weaning (5 mL/head) and evaluated their performance for a 45-day period [
78]. These authors observed that BAS-treated calves had a greater ADG (+70 g/day) and final BW (+2.8 kg) when compared to non-treated cohorts (
p = 0.03;
Table 1). Following a similar experimental design,
Bos indicus beef calves receiving BAS at the moment of weaning gained more BW and were heavier at the end of the 45-day experimental period vs. control cohorts (
Table 1) [
79]. In a subsequent study, Schubach et al. (2020) also demonstrated that behavior of
B. taurus calves was greatly impacted following BAS administration at weaning, such as temperament, feeding, and allogrooming behaviors [
80].
One of the mechanisms by which BAS improves performance might be related to a less heightened neuroendocrine stress response. According to the aforementioned inflammatory cascade, BAS-administered beef steers had a reduced mean hair cortisol 14 days post-weaning compared with the non-treated group (
Figure 1) [
80] as well as reduced mean haptoglobin concentration during the post-weaning period (
Table 2) [
78,
80]. Stress also affects the efficacy by which a specific vaccine is able to induce an inflammatory response and the body to mount an effective and robust immunological memory [
1,
81]. Then, it would be feasible to speculate that an alleviated neuroendocrine stress response post-BAS administration could improve the efficacy of a specific vaccine. Indeed, calves that were vaccinated and received BAS at weaning had a greater concentration of antibodies against bovine respiratory disease (BRD) [
80].
5.2. BAS vs. Feedlot Entry
In particular, feedlot arrival and entry are simply the tip of the iceberg when we take into consideration all the stressors that an animal might be exposed to. For example, the animal might be managed in the working chute while still in the farm of origin, handled by humans, vaccinated, ear-tagged, castrated (if applied), loaded in a commercial truck, transported, restricted from feed and water, experienced environmental changes, unloaded in a novel environment, novel management, processing, commingled with a different group of animals from a different source/origin, and received novel sources of feed and water, among others. Under a production setting, these stressful situations might occur over a 24–48 h period, stimulating a neuroendocrine stress response at feedlot entry. Moreover, it is not surprising that BRD incidence is elevated in the beginning of the feedlot period (14–21 days), as the immune system is suppressed and BRD pathogens are able to establish the disease [
76,
81]. Therefore, BAS administration may be an alternative to alleviate these neuroendocrine responses.
Following this rationale, administering BAS at feedlot entry improved the performance of
B. indicus bulls in the first 15 days of the feedlot, whereas no benefits were observed in the whole 45 days of the experiment (
Table 3) [
78]. The lack of effects following BAS administration is unknown, but could be related to a compensatory gain in the non-treated group and/or the need for other BAS applications during the feedlot period. Nonetheless, in a subsequent study, Colombo and colleagues (2020) evaluated how BAS administration to cattle at feedlot arrival would affect their performance and health [
82]. Cattle used by Colombo et al. (2020) were purchased in an auction facility and originated from 16 different ranches, to mimic the stress load that commercial cattle are often exposed to [
82]. Administration of BAS reduced plasma cortisol and increased plasma glucose concentrations 7 days post-feedlot entry, indicating a reduced stress response and a greater nutritional status of the herd following feedlot entry, respectively. Over the initial 45 days of feedlot, ADG (0.857 vs. 1.013 kg/day) and FE (142 vs. 171 g/kg) were also improved due to BAS administration (
Table 3), supporting the rationale that a stress reduction in the beginning of a specific period (stocking and/or feedlot entry) positively impacts the performance and health of the beef cattle herd. This rationale has already been established and reported for dairy cattle in the transition/post-calving period [
83,
84], but few data are available in beef cattle.
An additional question that remained was whether the timing of BAS administration, pre- or post-transport, and if administering two doses, pre- and post-transport, would lead to different results in the entire feedlot period (108-day feeding period). Based on this rationale, Fonseca et al. (2021) designed a trial in which BAS was administered (1) pre-transport to a commercial feedlot (at loading); (2) post-transport, during the initial processing management at the commercial feedlot (at feedlot entry); (3) pre- and post-transport; and (4) no BAS administration [
85]. Administration of BAS at loading benefited animal performance during adaptation (19 days), tended to increase ADG during the finishing period, and improved overall ADG. As a result, bulls were heavier at the end of the experimental period (108 days) and also had a heavier carcass (
Table 4) [
85].
These results highlight, once more, how BAS might be able to improve the overall performance and carcass characteristics of beef cattle during finishing, a period where several stressors are observed and have been recognized to negatively impact the health and productivity of the herd [
1]. Based on the results above [
85], it can be argued that the main mechanism by which BAS improves herd performance is on nutrient utilization, denoted by the FE results, a trait greatly impacted in stressed animals [
1,
86]. In fact, a stressor, when perceived by the animal, might lead to the inflammatory cascade that acts as nutrient sink, removing the nutrients from an anabolic to a catabolic state [
16]. Moreover, blood mRNA expression of pro-inflammatory-related genes was reduced following weaning and feedlot entry in animals that received BAS [
87], demonstrating that the modulation of inflammation might be one of the mechanisms underlying the benefits observed by [
85].
On the other hand, BAS administration at feedlot entry yielded immediate benefits during the adaptation phase (19 days), but failed to promote long-term effects on performance over 108 days. One might argue that the lack of long-term effects is due to the fact that most of the stressful situations had occurred at feedlot entry, triggering an APR, and likely overriding the benefits of BAS in finishing animals [
88,
89]. Lastly, the same rationale might be used to explain the lack of positive effects when two applications of BAS had been performed, at loading and feedlot entry [
85].
5.3. BAS vs. Castration
Castration is a widely adopted management practice performed in feedlot cattle that eliminates aggressive behavior in male animals due to the removal of endogenous testosterone production, while also improving backfat thickness and meat characteristics [
90,
91]. On the other hand, castrated animals often present a reduced overall ADG, final BW, FE, HCW, and ribeye area (REA) following the feedlot phase and subsequent slaughter [
92]. In the U.S., it is estimated that 93% of the animals arriving at the feedlot are already castrated, being 50 and 43% surgically and band-castrated [
93], whereas an estimated age at which this procedure occurs is unknown. In developing countries such as Brazil, castration is mostly performed in operations that attend a prime niche beef market, such as restaurants and butcheries that sell a specific beef brand. Nonetheless, regardless of the region we focus our attention, due to public opinion, animal production, practices, care, and consequently welfare have been under scrutiny. Recent surveys indicated that public opinion is more positive when castration is performed with any kind of anesthesia and/or analgesia [
94].
The castration process itself also causes physical, physiological, and psychological stress in animals, resulting in inflammatory reactions and subsequent performance loss that might last until slaughter [
95]. One alternative to alleviate these immune responses and consequently maintain an adequate performance post-castration is the administration of meloxicam, a non-steroidal anti-inflammatory drug (NSAID) [
96]. Nonetheless, vaccination and/or intravenous or intramuscular pharmacological administration might also cause an immune response due to the resulting local tissue injury [
17,
97] and the industry itself has been avoiding the use of medicines in animals. Hence, technologies that do not cause a local tissue injury, immune response, and improve the performance of newly castrated feedlot animals are warranted.
Based on this rationale, our research group designed an experiment [
98] to evaluate the effects of administering BAS at castration on performance of Nellore × Angus calves (
n = 390; initial BW = 274 ± 21.0 kg). On day 0 of the study, individual calf BW was recorded and animals were assigned to receive BAS (
n = 195; 5 mL/animal) or placebo (CON;
n = 195; 5 mL/animal). Immediately after treatment administration, all calves were castrated using a burdizzo by trained feedlot personnel. During the feedlot entry period (days 0 to 30), all animals were offered a 60:40 roughage:concentrate diet based on grass hay, whereas, during the finishing period (days 31 to 258), a high-concentrate diet was offered. On day 30 of the study, BAS-administered animals were heavier and had a greater ADG than CON cohorts (
Table 5). Similarly, BW change and ADG were also greater for BAS vs. CON on day 258 (
Table 5). As a descriptive analysis, total DMI from days 0 to 30 of the study was 6.70 kg/d for CON and 6.75 kg/d for BAS, resulting in a greater numerical FE for BAS (146 vs. 172 g/kg, respectively). Overall, from days 0 to 258, DMI and FE were 7.58 vs. 7.59 kg/d and 141 vs. 146 g/kg for CON and BAS, respectively, whereas hot carcass weight tended to be greater for BAS (
Table 5). These data indicate that the heavier BW was translated into a heavier carcass, which is the main parameter that determines the economic profit of a feedlot operation. The increased ADG during the first 30 days following castration in BAS-administered beef animals might be related to reduced stress-induced physiological and inflammatory reactions known to impair cattle BW gain, such as the acute-phase protein response [
78]. In an ideal production setting, it would be interesting to investigate whether BAS administration at castration maintains similar performance when compared to non-castrated beef animals. Although positive results have been reported in beef cattle following different stressful procedures, more research is warranted to understand the underlying biological mechanisms, if more than reported by [
87], by which BAS promotes an improvement in the performance and health of the beef cattle herd, more specifically in different stressor types. The potential benefits of administering BAS under a pathogen challenge are also worth mentioning, as this might be tightly connected to stressful situations, such as transport/feedlot entry and the occurrence of the bovine respiratory disease complex in the first 30 days on feed.
In summary, BAS administration at castration improved ADG and BW change 30 days following castration, whereas these positive results persisted throughout the entire feedlot period. Additionally, hot carcass weight was also greater for BAS-administered vs. CON cohorts, demonstrating that BAS is a feasible technology to improve the performance and carcass traits of feedlot cattle.
5.4. BAS vs. Dark, Firm, and Dry Cuts
Prior to slaughter, animals face physical, psychological, and physiological stressors, increasing the chance of the occurrence of dark, firm, and dry (DFD) carcasses. These stressors and the resulting neuroendocrine stress response ultimately alter meat quality and customer acceptance of this edible product, particularly due to an increase in meat pH and changes in meat tenderness and color [
99]. The pH of the carcass is greatly affected by the total and rate of glycogen breakdown, which is impacted by acute and chronic stress [
100]. More specifically, pre-slaughter stressors might stimulate ATP reduction, muscle glycogen depletion, and alterations in important physical and chemical attributes of the meat [
101,
102,
103]. As a general definition, meat pH values greater than 5.80 from 12 to 48 h postmortem will yield DFD cuts, which, in turn, become more susceptible to microbial contamination and reduce shelf-life [
99,
103]. These changes are often associated with a reduction in product acceptance by customers, as DFD cuts are dark red to brown-black and have a dry, firm, and sticky consistency [
104]. Meat traits that have greater influence on consumer satisfaction are tenderness, juiciness, and flavor of the cooked meat, demonstrating the reason why DFD cuts are less accepted [
101].
It is important to mention that other factors also predispose carcasses to DFD, such as sex, breed, nutrition, animal category, temperament, and age. In different countries, DFD occurrence has been reported to be in the range of 2.0–13.5% [
105,
106]. Considering that
B. indicus breeds are more temperamental than
B. taurus [
107], it is reasonable to speculate that
B. indicus animals would have a heightened stress and APR response, resulting in a greater occurrence of DFD carcasses. Hence, technologies that alleviate neuroendocrine stress responses and improve carcass quality are warranted. In order to assess the efficacy of BAS in preventing a postmortem increase in meat pH, Cappellozza et al. [
79] applied BAS (5 mL per head) at the moment animals were being loaded into commercial trucks and transported to the slaughter plant. These authors reported that BAS administration at loading was effective for maintaining mean carcass pH below the 5.80 threshold and reduced the proportion of carcasses that were classified with a mean pH greater than 5.80 (
Table 6) and 6.00 (19.4 vs. 11.2% of the carcasses).
5.5. BAS vs. Dairy Cattle
The dairy production system is characterized by intensive management situations, including daily milking, weaning, changes in nutritional management, prepartum DMI reduction, late lactation dry-off, vaccination program, reproductive management, novel environment depending on the season and days on milk, as well as commingling with different animals on different days and stages of lactation that alter social hierarchy of the herd [
108,
109,
110]. These situations might predispose the animals to stress and consequently impact overall health, performance, and herd longevity.
In one of the first studies in dairy cattle, weekly BAS administration to lactating dairy cows at the moment of turn out to pasture resulted in greater milk production (+1.65 kg/day) and a reduction in somatic cell counts (13.0%), supporting the statement that BAS reduced the stress-related response of the animals due to an environmental change [
111]. In agreement with these data, an immediate increase in SCC was reported when lactating dairy cows were moved to a pasture setting [
112]. Recently, Angeli et al. [
113] addressed the effects of 14-day BAS administration on performance and health traits of pre-weaning Gir × Holstein dairy female calves. Bovine appeasing substance administration did not impact disease occurrence, but it tended to decrease the days of pharmacological intervention and reduced the cost of the pharmacological interventions (
Table 7). Additionally, BAS-administered calves were heavier at weaning (+3.8 kg) mainly due to greater ADG from days 42–56 and 56–weaning (
Table 7). Another interesting finding reported by Angeli and colleagues [
113] was the fact that BAS-administered animals diagnosed with a disease had greater ADG than control animals diagnosed with a disease and similar ADG vs. healthy control animals. This was the first study demonstrating that BAS administration might be able to recover the animals at a faster rate following a pathogen challenge and, consequently, improve pre-weaning performance. Additionally, the benefits on pathogen-challenged animals are novel and different from other technologies, such as NSAID, that have improved productivity in animals challenged with the neuroendocrine stress model [
86,
92], but the same effects were not observed upon an LPS or vaccine challenge [
14].