The results of the present study contribute to understanding the capacity of reaction and adaptation of animals to the environment.
Body temperature rhythmicity of farm animals is important from a comparative point of view (human beings and laboratory animals), but in particular from an economic aspect to guarantee the improvement in livestock production practices.
It is known that environmental temperature can affect skin surface temperature and influences the thermal exchange between the organism and the environment, especially in mild stress conditions (Martello et al. 2016).
The ideal ambient temperature (“thermoneutral” zone) for a cow is between 5°C and 25°C (Roenfeldt 1998). As ambient temperature increases, it becomes more difficult for a cow to cool herself adequately and she enters heat stress (Mazzullo et al. 2014). The climatic conditions in this region, show an extreme ambient temperature of more than 26.1°C. It’s a sub-tropical climate that can physiologically influence cows according to species and breeds.
Circadian patterns of some physiological parameters such as body temperature or locomotor activity have been identified in a variety of mammals, with the highest level monitored during the morning hours and the lowest level in the early evening for diurnal species. On the contrary for nocturnal animals the peak coincides with the onset of darkness. Our results confirmed previous studies showing a diurnal daily rhythm of locomotor activity (Giannetto et al. 2010; Bazzano et al. 2015; Rizzo et al. 2017) in cattle and Bos taurus species (Holstein and Herford). Cattle is known to have a marked diurnal behavior pattern; therefore, grazing is set to sunlight (Rizzo et al. 2017).
In diurnal species, locomotor activity increase during the morning and decreases during the evening and there is a preference for warmer ambient temperature in the morning and cooler ones in the evening (Piccione et al. 2011).
Our findings showed a circadian rhythm of total locomotor activity during scotofase in Bos indicus specie (Bradford). The Bradford breed was developed from crosses between Bos taurus and Bos indicus cattle (Utsunomiya et al. 2019).
Bos indicus was domesticated 2000 years later than was Bos taurus cattle. From the domestication site in the Indus Valley, Bos indicus spread across the globe, leaving a legacy of tropical adaptation to their descendants.
The adaptation of this specie to tropical and sub-tropical environments makes them more efficient in coping with heat, humidity, nutritionally poor food and disease challenges. Under warm conditions, these animals have better balance between heat production and heat loss than Bos Taurus cattles. This improved balance is achieved via intrinsic metabolic differences and efficient heat dissipation through conduction, radiation and evaporation by sweating and panting (Hansen 2004). Very little is known about the genetic and epigenetic control of heat tolerance in Bos indicus cattle but much promise comes from modern monitoring of body temperature, rumination, locomotor activity and other physiological parameters.
The absence of diurnal rhythm of total locomotor activity in group B of our study can be explained by the dependence of physiological pattern on the sleep-wake schedule. Generally, ruminants do not enter the deep state of sleep as do men or other domestic animals. Sleep periods in ruminants are linked directly to the digestive need of the animal since rumination requires both time and consciousness (Abebe and Scott 1990).
The presence of total locomotor activity nocturnal rhythm in Bos indicus is probably physiological related to the lack of deep sleep (Abebe and Scott 1992).
The destruction of the species-typical time organization of the individual animals forces them to shift the time of their main activity to the night (Mitloehner and Laube 2003).
A multi-step neuronal pathway from SNC to sleep/wake switch may allow the SNC output signal to be modulated and integrated with other physiological signals. Our results support this hypothesis by noticing that external stimuli may modulate a single oscillator (SNC) output switching phenotypes from diurnal to nocturnal (Phillips et al. 2013).
In this case the activity rhythms of our cows are primarily diurnal but group B of our study switches from diurnal to nocturnal behavior by changing how the SNC respond to light (Oster et al. 2002). It should be considered that the daily distribution of activity differs not only from species to species but also from individual to individual in the same species (Refinetti, 2006).
We can affirm that goats exhibit a daily rhythm of total locomotor activity, with the highest daily amount of activity during the photophase following the onset of light. The zeitgeber of the total locomotor activity is identified as the photic stimuli and the rhythm was diurnal (Giannetto et al. 2010). For other species of cows (Bos indicus) the total locomotor activity was expressed during the scotophase, probably because the zeitgeber is a non-photic stimulus (ambient temperature, environmental patterns or food availability), during food stress the animals were active at a time they previously associated with food availability (Giannetto et al. 2010).
Subcutaneous temperature showed a daily circadian rhythm for all groups reflecting temperature difference between day and night, it depends on skin and epidermis vascularization at the body surface. Ambient temperatures and all environmental parameters affect thermogenesis by basal metabolic processes. Heat loss is enhanced by increasing peripheral blood flow, which would be expected to reduce surface temperature (Rey et al. 2015).
Physical activity leads to peripheral vasodilatation, typically to balance heat production, and affects both core and peripheral temperatures (Webb 1995) in a non-predictable manner. measuring subcutaneous temperature was previously discussed to estimates of the resting metabolic rates of endotherms (Rey et al. 2015).
Environmental conditions such as ambient temperature, solar radiation relative humidity and atmospheric pressure significantly affect locomotor activity and body temperature together with species and breeds.
The three cows’ breeds behaved differently during the experimental period. Holstein and Herford showed a diurnal peak of the rhythm of TLA as opposite to the nocturnal in Bradford.
As an indigenous species, Bradford group showed a remarkable variability among the analyzed data and although the homogeneous group a statistical difference was observed among the subjects, unlike ST which showed its acrophase always during the light hours.
Herford group showed a significant variability in the amplitude of the rhythm, in particular for TLA, compared to the other species, while Holstein, being the breed that has been subjected to farm management for the longest time, is therefore more adapted to such conditions, in fact the circadian rhythm remained stable within the group and it did not show high oscillations of amplitude. It can be assumed that it had a better generational adaptation to the breeding conditions.
Some cows’ species are better able to cope and adapt themselves to environmental stress. Considering the subtropical conditions suitable measures should be adopted in order to minimize environmental stress and to improve animal welfare.
Therefore, further studies are expected to establish how management conditions may affect the physiological parameters of animals living in subtropical regions.