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Cuban livestock faces the great problem of the low efficiency of dairy cattle, which is due to limitations in feeding and management, as well as to climatic conditions, mainly high temperatures and relative humidity (Álvarez 2006). If the environmental temperature reaches values above 35°C for animals of tropical origin, there is a failure in the thermoregulation systems, and the rectal temperature and respiratory rate increase, join to the decrease of food intake and milk production (Corrales 2014 and Salvador 2015). In this way, the animal faces the environmental conditions of the place, using its physiological capacities to adapt to the environment (West 2003 and Polsky and von Keyserlingk 2017).
The stress term is currently used in a much broader sense for its application to animal welfare (Sejian et al. 2015). That is why codes that regulate animal welfare have been published, such as the sanitary code for terrestrial animals (OIE, 2017). In its chapter 7.11.4, this code defines the measurable criteria of animal welfare, where it includes as indicators of negative behavior the decrease in dry matter intake, the increase in respiratory rate and other abnormal behaviors, related to the effect of management the animals are submitted. The objective of this study is to evaluate the effect of temperature and humidity index (THI) on the physiological and productive indicators of Siboney de Cuba crossbred cows in dairy 17 from Dos Ríos Enterprise (E).
Materials and Methods
The study was carried out in dairy 17, from Dos Ríos Enterprise, belonging to Managuaco agricultural enterprise, located at 210 56 ’N and 790 20’ W, in Sancti Spíritus municipality, Sancti Spíritus province. The predominant soil in this region is soft brown carbonate (Hernández et al. 2015).
A total of 25 cows from Siboney de Cuba breed were used, in milking, in different lactation phases, distributed in three groups according to lactation days: a) lactation initiation (high group, 38.4 ± 11.3 d of average lactation), b) middle lactation (average group, 105.7 ± 22.5 d of average lactation) and c) lactation end (low group, 182.3 ± 31.6 d of average lactation). The animals were between the second and third lactation.
The physiological states of gestation of cows were obtained from the reproductive control cards, once the pregnancy was confirmed three months after insemination and when they did not present heat.
Environmental measurements (relative humidity and environmental temperature) and physiological responses (respiratory rate and rectal temperature) were taken at three times of the day: in the grazing, between 7:00 and 9:00 h; in the shade buildings between 11:30 and 12:30 h, and in the milking parlor between 15:00 and 16:30 h.
The measurements of environmental temperature (ET) in degrees centigrade (0C) and relative humidity (RH) in percentage value (%) were taken at 1.20 m altitude. Likewise, the meteorological data (ET and RH) were recorded at the Sancti Spíritus Meteorological Station, coinciding with the measurements date in the dairy, so that the respective comparisons could be made.
To determine the temperature and relative humidity index of the environment (THI), the formula proposed by García et al. (2007) was used:
In the animals, rectal temperature was determined by introducing a maximum clinical thermometer into the rectal vial, free of fecal matter, to eight centimeters depth. The reading was carried out after four minutes. To avoid possible negative effects on dairy production with the management proposed for the measurement, the animals were adapted for a previous 15 d before starting the procedure. Respiratory rate was obtained by direct observation of the animal and by counting the movements of the flanks for one minute.
Milk production was individually measured in both milkings (morning and afternoon) and was taken as daily yield, with biweekly frequencies.
The statistical analysis was carried out according to a general linear model with nested effect, where the gestation or not and the milking groups are nested at each moment of the day in which measurements were made. In the necessary cases, Duncan's test (1955) was applied.
The main effect of the THI interactions and the milking groups and THI and pregnancy or not is shown when it is significant.
For milk production, analysis of variance was carried out, according to a multiplicative model for pregnancy or not and milking groups, respectively. In the necessary cases, Duncan's test (1955) was applied for P <0.05.
Where:
Yijklm = |
milk production kg/v/d |
Anb = |
effect of the lactation curve |
Ti = |
effect of i-th treatment |
Sj= |
effect of the j-th sample |
(THI)k= |
effect of the k-th temperature-humidity index |
GOl= |
effect of the l-th gestation or milking group. |
eijklm = |
normal random error distributed with mean 0 and variance σ2 |
The statistical package used was the InfoStat, version 2012 (Di Rienzo et al. 2012)
Results and Discussion
Due to the high heat stress ratio in dairy cows, with THI values outside their thermoneutrality range, which can significantly reduce the ability to lose latent heat by evaporation, it is possible to use this index as an estimate of heat stress parameters. (Cerqueira et al. 2013, Callejo 2015 and Ruiz et al. 2019).
In a general sense, it is considered that, with THI values lower than 72.0 units, the animals are in thermoneutral conditions, or it is estimated that there are no stressful conditions. Faced with figures between 72.0 and 79.0, the presence of light stress is considered; from 80.0 to 89.0 is understood to be moderate, and values from 90.0 to 99.0 show severe stress. Higher figures are considered serious, and can limit the animals lives (Anzures at al. 2015 and Veissier et al. 2018).
The environmental conditions (figure 1), mainly the temperature registered in the sampling times, are typical in the province. They are characterized by being relatively low in the morning (25.8 ± 0.030C), they are highest at midday (30.1 ± 0.030C) and high in the afternoon (34.6 ± 0.040C). These temperatures, combined with high humidity (average of 91 to 93 %) throughout the study period, lead to THI values of 69.59 ± 1.59 units (light stress), 79.61 ± 1.26 units (moderate stress) and 91.69 ± 1.24 units (severe stress), for the morning, midday and afternoon, respectively.
Figure 1 Climatic variables of environmental temperature (ET), relative humidity (RH) and temperature humidity index (THI), according to sampling hours
In general, the climatic information suggests that in the morning the cows were in a thermoneutral zone and under acceptable conditions to express their potential for milk production. At midday and in the afternoon, they were under moderate and severe heat stress respectively, since the dairy cow begins to experience the consequences of heat stress when the THI exceeds 72 units (Anzures et al. 2015, and Polsky and von Keyserlingk 2017).
Table 1 shows the interactions between the different stress levels and the physiological responses of rectal temperature (P = 0.0136) and respiratory rate (P = 0.0003) of pregnant and non-pregnant lactating cows. With these results it is shown that, regardless of the reproductive status of the animals, as the value of the THI increases, these two physiological variables increase.
When assessing the reproductive status (pregnant or not) of lactating dairy cows, in the values of light and moderate stress, it was found that there are no differences in the physiological response of rectal temperature. However, in pregnant animals with severe stress there was a higher (P = 0.0136) rectal temperature than in non-pregnant animals in 2.73 %.
The analysis of the effect of increasing the value of stress on both reproductive states showed (P = 0.0136) that rectal temperature increased by 1.62 and 2.73, 1.84 and 1.85%, when passing from light to moderate stress, and from the latter to severe , for pregnant and non-pregnant animals, respectively.
The interaction between stress and respiratory rate of lactating cows, being pregnant or not, does not differ under light stress conditions. In this case, the animals showed respiratory rate values in the normal range established for the species (Anzures et al. 2015 and Allen et al. 2015). However, from moderate stress, pregnant cows had higher (P = 0.0003) respiratory rates of 1.96 and 2.00 % than non-pregnant cows, for moderate and severe stress, respectively. Similarly, regardless of the physiological state of cows, when changing from light to moderate stress conditions, and from the latter to severe stress, the respiratory rate increased (P = 0.003) in 42.58, 20.74 and 39.21, 20.69 % for pregnant and non-pregnant, respectively.
Table 1 Interaction between heat stress and pregnancy or not, in rectal temperature and respiratory rate of dairy cows in production
| Indicator |
|
Light | Moderate | Severe | Sig. |
|---|---|---|---|---|---|
| Rectal temperature (0C) | Pregnant | 38.96 a ±0.04 | 39.59 b ±0.04 | 40.67 d ±0.04 | P=0.0136 |
| Non-pregnant | 38. 94 a ±0.04 | 39.66 b ±0,07 | 40.39 c ±0.04 | ||
| Respiratory rate (No min.-1) | Pregnant | 53. 27 a ±0,28 | 75.95 c ±0,45 | 91.70 e ±0,27 | P=0.0003 |
| Non- pregnant | 53.51 a ±0.27 | 74.49 b ±0.27 | 89.90 d ±0.28 |
a, b, c, d and e. Means with different letters differ at P<0.05 (Duncan 1955)
Table 2 shows the interactions of heat stress with rectal temperature (P = 0.0003) and respiratory rate (P = 0.0024) of dairy cows, according to the production group. These show that regardless of the production group of animals, as the stress value increases, these two physiological variables increase.
In the analysis of rectal temperature, face to light stress values, there were not effects on the physiological response of cows, regardless of the milking group. However, face to higher stress values, the cows from the high production group showed higher rectal temperature figures (P = 0.0003) in 0.16 and 0.21°C with respect to those of the medium group, for moderate and severe stress, respectively.
Regardless of stress, the cows in the low production group do not differ from those in the other two production groups, which may be due to the higher proportion of pregnant animals found in said group, since they end lactation. As could be observed in table 1, by itself the reproductive gestation state affects the animals equally, be under moderate or severe stress.
The rectal temperature variable of the animals according to the milking group increases (P = 0.0003) when going from light to moderate stress conditions, and from the latter to severe stress in 2.92, 1.73; 2.24, 1.61 and 2.55, 1.73 % for the high, medium and low milking groups, respectively.
Table 2 Interaction between stress and milking group on rectal temperature and respiratory rate of dairy cows in production
| Indicator |
|
Light | Moderate | Severe | Sig. |
|---|---|---|---|---|---|
| Rectal temperature (0C) | High | 38. 76 a ±0.05 | 39.89 c ±0.05 | 40.58 e ±0.05 | P=0.0003 |
| Medium | 38. 86 a ±0.06 | 39.73 b ±0.06 | 40.37 d ±0.06 | ||
| Low | 38. 83 a ±0.06 | 39.82 bc ±0.06 | 40.51 de ±0.06 | ||
| Respiratory rate (No min.-1) | High | 53.65 a ±1.25 | 77.78 c ±1.25 | 93.98 e ±1.25 | P=0.0024 |
| Medium | 53.07 a ±1.28 | 71.22 b ±1.27 | 87.11 d ±1.28 | ||
| Low | 52.64 a ±1.32 | 74.92 bc ±1.32 | 91.08 de ±1.33 |
a, b, c, d, e. Means with different letters differ at P<0.05 (Duncan 1955)
Likewise, the lactating cows, faced to light stress effects, did not show affectations in the respiratory rate, regardless of the milking group (table 2). However, this physiological response increased (P <0.0024) by 9.21 and 7.89 % for the high production group compared to the medium group, under moderate and severe stress, respectively. There was no difference between the low production group with respect to the other two.
These affectations in the physiological variables studied under moderate or severe stress in the animals from the high production group are in agreement with what is reported in the literature. Authors such as La Manna et al. (2014) and Leucen (2014) report that cows at the beginning of lactation are more affected by high THI values, since they showed higher metabolism due to high productive levels.
The variable of the respiratory rate of the animals increased (P = 0.0024) independently of the milking group, when going from the conditions of light to moderate stress, and from the latter to severe stress in 44.98, 20.83; 34.20, 22.31 and 42.32, 21.56 % for the high, medium and low milking groups, respectively.
The respiratory rate in thermoneutral conditions has been reported to fluctuate between 40 and 55 frequencies min. for dairy cattle (Anzures et al. 2015 and Allen et al. 2015). The increase in body temperature and respiratory rate are normal mechanisms, by which cows dissipate heat to maintain their homeothermic condition in hot environments, being about 38.5 °C the body temperature considered normal in cattle (Ganaie et al. 2013).
Thus, the respiration rate is one of the most important mechanisms to consider when evaluating the heat stress level in cattle (Beauregard et al. 2018), since it is one of the main observable responses in the animal when it is exposed at temperatures that exceed your comfort threshold. This increase in the respiration rate is intended to increase respiratory heat loss, which is one of the most important for maintaining thermal balance.
Brown-Brandl et al. (2005) showed that measuring the respiration rate of animals, determining that they are in the panting process, as well as quantifying it, is the easiest and most affordable way to assess heat stress in cattle under commercial production conditions, since this does not require sophisticated equipment.
Furthermore, unlike body temperature, the response is practically immediate in the animal, and it follows almost the same pattern as environmental temperature.
These heat stress conditions lead directly to the activation of thermoregulatory, physiological and metabolic mechanisms, which cause a decrease in milk production, higher dissipation of body heat and a reduction in the metabolic heat production (Ganaie et al. 2013, Barragán et al. 2015, Beauregard et al. 2018 and Kamal et al. 2018).
When analyzing the effect of milk production according to the production group (table 3), it was found that the animals with high production produced more (P = 0.0001) milk 1.47 and 2.18 times than those with medium and low, respectively. Likewise, the average cows produced more milk (P = 0.00001) in 48.01 % than the low animals.
These milk production values according to the production group are logical, since the animals are mainly grouped by their lactation days. Cows in early lactation are in the high production group, which is why they have higher potential for milk production and therefore, a higher metabolism to achieve these productions (NRC 2001, Corrales 2014). However, as table 2 shows, this group is more susceptible to stressful environments. The adoption of measures to try to reduce this negative effect, improving management and feeding, will make possible to increase milk production (Mendoza et al. 2016).
Table 3 Effect of the milking group on the milk production of lactating dairy cows
|
|
High | Medium | Low | Sig. |
|---|---|---|---|---|
| Milk prod kg cow-1 day-1 SE | 2.62 c (1) (14.24) ±0.05 | 2.25 b (1) (9.68) ±0.03 | 1.80 a (1) (6.54) ±0.04 | P=0.0001 |
Means transformed according to ln () Original means
a, b, c. Means with different letters differ at P<0.05
This research allowed assessing that under the described conditions, the midday and afternoon hours cause stress in the animals, regardless they were in the shade buildings. The effects on rectal temperature and respiratory rate under conditions of moderate or severe stress are more marked in lactating animals in gestation and in the group of high or highest production.
