1. Introduction
The water buffalo (
Bubalus bubalis) is a species that has been recently introduced in Cuba [
1,
2,
3] and other tropical countries in the Americas such as Brazil and Colombia [
4], where they are managed in grazing systems with the provision of shade [
4,
5,
6].
With the increase in solar radiation, and the increase in temperature because of climate change [
7], animals are forced to change their habits during the daylight period, when the stressors of climate have a higher influence on their behavior [
8]. Heat stress affects animal behavior, causes production losses, and can impair animal welfare.
Alternatives such as the use of trees, changes in management and grazing schedules, and the genetic improvement of species more in line with the new climatic conditions are some of the strategies considered to address this issue [
9].
Housing systems and pastoral systems with different forest arrangements for buffaloes are known in Latin American countries [
10,
11,
12]. For example, buffaloes housed with artificial shade and water sprinklers for cooling in a monocropping natural grass system are observed in the wallowing area to release excess heat [
5,
6]. In this regard, Simon and Galloso [
6] found a better milk production per hectare and a better daily weight gain of buffalos reared in silvopastoral systems (SPSs) in comparison with conventional systems (CVSs). Recently, a higher daily weight gain was reported for buffalos compared to bovine males during the growing phase in a silvopastoral system [
2].
However, the effect of trees on the grazing behavior of buffaloes in hot-humid conditions has not been studied in depth, and it is not known whether the presence of trees can help their thermoregulatory behavior and increase grazing activity while simultaneously reducing wallowing time.
Hence, the objective of this research was to characterize foraging activity and thermoregulatory behavior of heifer buffaloes in the tropics in SPSs and CVSs, comparing both in the intense heat stress and moderate heat stress conditions in Cuba.
4. Discussion
The dry season in Cuba coincides with moderate temperatures, which is favorable for animal welfare; however, a harsher season, with higher temperatures, would have a negative effect on animal welfare [
9,
11,
18,
19]. The HR season is the period of the year when animals developed intense heat stress and spent more time in the wallowing area, which is attributed to the higher temperature regime in that period, above 35 °C. Regardless of the expected comfort in the SPS, the animals were motivated to enter the water for immersion, although it is important to consider that the animals also had shade available in the wallowing area, where there were trees around the pond [
20]. Frisch and Vercoe [
21] indicated that this species has only one-sixth of the number of sweat glands of cattle (
Bos indicus) and is sparsely covered with hairs. In addition, its dark skin, thick epidermis, and less dense sweat glands make it difficult for these animals to resist high temperatures and a dry environment [
22]; hence, buffaloes tend to suffer heat stress when they are exposed to solar radiation [
21] and seek water for immersion to avoid this stressful environmental condition [
23]. It is important to consider that this species is well adapted to swamps and areas subject to flooding [
24].
One of the limitations of this study was the reduced number of animals used, which in turn helped improve the effectiveness of behavioral records by reducing agonistic behaviors [
12]. The longitudinal design additionally contributed to the robustness of the subsequent analyses in this study. This contributed to the understanding of the evolution of the behavior of these animals subjected to different conditions of thermal stress under shade and in the CVS, in accordance with what was previously described by Galloso [
11].
The differences in time spent in the shade of trees in the moderate heat stress season between the SPS and the CVS are because, during this season, the paddocks had lower grass availability and were dryer, especially in the CVS system; hence, the animals of the SPS tried to satisfy their need for fodder grazing under the trees.
The relation established (animals, wallowing, and tree shade) is more complex than is simply observed when only wallowing is considered. While wallowing allows for cooling with water or mud, this cannot be considered as enough for animal welfare, because radiation in the head and spine is not avoided [
11,
20]. It would be interesting to have data on how radiation influences the temperature in different areas of the body, as was done under infrared thermography, through which microvascular changes in the head were previously studied, particularly in the area of the eye orbits and in the muscles of the spine, scrotum, or mammary gland [
24,
25], both while in and out the water, and with or without tree shade [
26].
When buffaloes are more affected by stress factors (solar radiation, heat stress, and excess temperatures) [
27,
28], they prefer to eat in the shade [
11,
20,
27]. This has been described in other species; i.e., in cattle breeds of the tropics where time spent in the shade has been positively correlated with mean radiant temperature and solar radiation [
29].
The statistical differences found (thermoregulatory behavior, wallowing, and browsing), particularly in the SPS during the intense heat stress season, have also been reported for grazing cattle in SPSs [
2,
10].
The differences in sheltering behavior during the intense heat stress season are probably influenced by the low nutritional values of the pastures in the CVS [
26,
30], which forces the animals to return earlier to the grazing paddock in order to satisfy their nutritional requirements.
Similar results for the thermoregulatory behavior in favor of silvopastoralism were reported by Yadav et al. [
31] when comparing the influence of different methods of cooling down on productivity, and metabolic and blood profiles; they found that nebulization or wallowing favors blood indicators. In periods of greater heat stress, the silvopastoral environment reduces the temperature by 1.5 °C in comparison to direct sunlight [
28]. Other cooling systems (showers and artificial shade) have been reported by Barros et al. [
26] and Sevegnani et al. [
29], and, with the use of infrared thermography, it was proven that the buffalo body temperature is reduced by around 2 °C.
An element to be considered on buffalo farms is that trees provide a better environment and assure more welfare in the tropics. Trees have advantages for hygrothermal stability in the farm [
28] and food stability [
1] and must be considered as important handling alternatives for the welfare of the species [
6].
The results found of longer feeding behavior in the SPS could be attributed to the filter shade values, as was found by Penton and Blanco [
17], who observed that trees such as
L. leucocephala and other legume species offer filterable radiation in SPSs in the tropics and reported between 10% and 30% more production of dry matter of grass in SPSs compared with monoculture pastures [
30,
32].
It is known that SPSs (pastures, trees, and animals) contribute to improving the condition of the grass (more nutritional values) and animal welfare [
18,
30,
33]; this is also the case in other latitudes, species, and agroforestry systems [
34].
The time spent ingesting tree leaves was always higher in the SPS, which is quite obvious, although the consumption of tree branches was also possible when the animals were in the wallowing area in both systems. This means an additional effort is required to browse this resource in the CVS, because this fodder was only available there while they wallowed under the D. cinerea canopy.
These observations confirm the importance of feeding ruminants with branches or tree fodders as a nutritional complement of the ration. It is known that the ingestion of leaves from trees favors the uptake of nitrogen, and this could be the cause of the increase in its consumption, helping the ruminal microflora, as reported by Wanapat and Phesatcha [
35]. Hence, it is important to consider the role of trees in increasing the supply of nitrogen in a diet at times when pastures are not meeting the requirements of animals [
36]. Different authors [
18,
32,
33] reported that, when SPSs have high edible biomass availability (higher than 30 Ton DM/ha and year), of which pasture represents 75–90% of the fresh diet intake and tree foliage represents 10–25% of the fresh fodder, animals improve their performance.
Leucaena produces between 14.2 and 18.0 Ton DM/ha a year with irrigation (whole plant) and between 7 and 14 Ton DM/ha a year under rain-fed conditions [
32,
33]. Its contents of DM (24–27%), protein (20–24.26%), DAF (30%), Ca (0.83–2.0%), and P (0.29–0.38%) fluctuate.
D. cinerea is an invasive species in Cuba and its nutritional composition is 44.2% DM, 14.7% protein, and 30.3% DNF [
37].
The sum of activities included in grazing behavior (grazing and ingestion of tree leaves) showed a significant correlation with the sum of activities included in feeding behavior (grazing, rumination, the ingestion of tree leaves, and water intake). Furthermore, the thermoregulation behavior (wallowing and sheltering in the tree shade) showed an interesting correlation and corroborates how important the thermoregulation activities are in these conditions of intense heat stress.
Hence, tree shade is necessary because wallowing areas alone are not enough. Therefore, these animals need tree shade to complement their cooling needs.
In the CVS, the longer time spent wallowing under intense heat stress conditions, with 2.35 h, and the time positioned under the shade of the D. cinerea trees in the wallowing area, with 1.71 h, reflects the greater need for cooling in this season.
In the SPS during the intense heat stress season, the elevated combination of wallowing and shading, 1.18 h and 2.62 h, equivalent at 3.81 h in thermoregulatory behavior, suggests that the animals spend more time in the shade of trees to forage comfortably. However, wallowing does not seem to be as important under moderate heat stress conditions under SPS.
Obviously, there was sheltering under the shade of trees for a longer time in the SPS. Part of this time was spent positioned under the trees in order to browse tree leaves.
The less time spent in the shade of D. cinerea in the CVS and the wallowing behavior suggest that the animals replaced the activities of cooling for collecting food in the CVS paddock.
During the diurnal period, grazing is reduced by the influence of stressors, such as high temperature, and modifies some metabolic indicators related to animal welfare, such as thyroid hormones, respiratory rate, and rectal temperature [
8,
26]. In this regard, the highest index of consumption in the SPS in both stress conditions can be considered proof that grazing time increases when animals are less stressed [
8].
The rumination reduction in intense heat stress conditions can be attributed to the better quality in the diet [
30], despite a greater availability of fodder (
Table 4). Furthermore, in the intense heat stress period, the rumination time increased in the SPS, in contrast to the CVS.
In the SPS, it is possible that an increase in bathing time during the intense heat stress season contributes to a reduction of foraging activities in the afternoon.
In short, these results (regarding time spent wallowing, grazing, and engaging in thermoregulatory behavior in the SPS) can explain the role played by trees distributed in the paddocks and can explain the most productive results found by some researchers in bovine [
18,
19,
32] and in male buffaloes [
2] in the tropics, with 0.775 kg/d of daily weight gain and 4.32 Ton DM/ha per rotation during 180 days of growth period for this species in the last studies to which we referred.
These elements can be particularly important to understanding why heifer buffaloes maintain their wallowing habits independently of the provision of natural shade, particularly because, as some authors suggest [
6,
38,
39,
40], more attention should be paid to shade to improve animal welfare and performance.