ENVIRONMENTAL SOURCE OF STRESS IN LIVESTOCK PRODUCTIVITY – A STUDY OF MINNA CLIMATE DATA

: Stress emanating from environment is a factor limiting livestock productivity in the Tropics because of elevated temperature year round; hence this study took a look at Minna climate data for evaluation of Temperature-Humidity-Index (THI) as a way of identifying climate source of stress on livestock production. Climate Normals for Minna between years 1961 and 2018 were obtained, and the data were analyzed using general formulae for calculating Temperature-Humidity-Index for livestock production. Relationships between production parameters on commercial farms and the THI data indicated that heat stress is a potential cause of oxidative stress in the area. The THI showed that the environmental conditions in the study area has potential for heat stress on animals, and that it can aggravate oxidative stress in livestock under production in the study area, hence there is need for further studies to identify the pathophysiological mechanisms of heat stress so as to develop mitigation strategies for improved animal performance and productivity. The study suggested that instead of the penchant for importing exotic breeds of livestock with the aim of upgrading the indigenous breeds, the way forward could be the utilization of genetic expression of heat and oxidative stress genes in animals as candidate markers for improvement of their productive potentials.


Introduction
Temperature-Humidity-Index (THI) is an indicator for determining temperature comfort zone which integrate the relative effects of temperature and humidity for optimum livestock performance and productivity. It also has to do with environmental temperature and heat generation as factors controlling energy metabolism and exchange; hence avoidance of its extremes above and or below comfort zone, can influence animal health and production because it is also a measure of the relationship between environmental temperature and animal thermoregulatory status. The application of THI has been used for determination of comfort zones for humans and different livestock species including dairy cattle, swine, turkeys, laying hens, broilers and rabbits (Ogunjimi et al., 2008;Joseph et al., 2014;Behura et al., 2016). An evaluation of THI is a contribution for identification of the suitable environmental conditions under which animals will not be susceptible to oxidative stress damage which is a leading biochemical consequence of heat stress. Therefore, this study obtained climate data of Minna for evaluating THI and determine heat stress conditions under which animals can be produced in the area for prevention of oxidative stress damage and establishing basis for use of antioxidants in animal production operations in the study area.

Materials and Methods
Minna climate data for years between 1961 and 2018 were obtained from National Oceanic and Atmospheric Administration (NOAA, 2016). Data on parameters including mean monthly temperature, relative humidity and dew points temperature from these sources were compare with data of Nigeria Metrological Agency (NIMET) for Minna. From these data, Temperature-Humidity-Index (THI) was calculated on monthly basis for cattle and rabbits using the formulae i and ii, respectively: Holstein). The data obtained were used to determine average production and performance of the cattle. Descriptive relationships were further established between the production performance and the THI determined for the study area.

Results and Discussion
From the available dataset monthly Temperature-Humidity-Index (THI) values for Minna were determined using the equations above and are presented in the Table 1 and Figure 1. Average highest monthly environmental temperature occurs annually in the month of March (33.65 o C) while the lowest environmental temperature occur annually in the month of August (27.02 o C). Highest dew point temperature occurs during the month of July (19.70 o C) while the lowest dew point temperature occurs during month of February annually. The highest Temperature-Humidity-Index occurs annually in the month of April which followed the month having the highest environmental temperature while the lowest Temperature-Humidity-Index occurs annually in the month of January. The result showed that animals are always under stressful condition throughout the year in the study area going by the classification of Kulkarni et al. (2017) which stated that THI values in degree Fahrenheit below 70 is No stress, THI values between 70 and 75 is Mild Stress, THI values between 76 and 80 is Semi-Moderate Stress, THI values between 81 and 85 is Moderate Stress and THI values between 85 and 90 is Severe Stress. This also agrees with the THI classification reported by Ogunjimi et al. (2008), that THI values in degree celcius below 27.8 is no stress, 27.8 to 28.9 is moderate stress, 29 to 30 is severe stress and above 30 is very severe stress.

Figure 1. Monthly Temperature (TEMP), Dew Point temperature (DP) and THI (in o F)
Values of the THI as revealed in this study showed that throughout the year, heat stress is a potential threat to dairy cattle productivity because according to guidelines of heat stress management by Dairy Australia (2016), when the THI exceeds 72, cows are likely to begin experiencing heat stress and their in-calf rates will be affected. When the THI exceeds 78, milk production is seriously affected and when the THI rises above 82, very significant losses in milk production are likely, cows will show signs of severe stress and may ultimately die. The relationship between temperature and relative humidity using the trends between January and March ( Figure 2) annually confirmed that the period can be described as the safest time for animals in the study area. This is an indication that the THI analysis done in this study is correct and gives an understanding of heat stress condition of Minna as it affect animal performance and productivity. Although the temperature is still high, but because the relative humidity is lower than 40 % hence the THI indicated mild stress. This biologically can be confirm through performance and production capacities of animals under traditional management in the study area. Livestock in this area including cattle, sheep and goats mostly give birth to younger ones during this period which is a natural biological response of the animals to environmental challenge of heat stress.
Production and performance data obtained from the commercial dairy farm located in the study area gave an average monthly milk production for Holstein Friesian (HF) as 240.50 litres, Red Holstein (RH) as 454.80 litres and Crossbred (CB) as 123.50 litres. Gestation length was 9 months for all the breeds while conception rates upon artificial insemination were 50 % for HF, 70 % for RH and 50 % for CB; culling rates were 90 %, 35 % and 10 % for the HF, RF and CB respectively as well as other performance and production parameters as presented in Table 2. From the analysis of the THI for the study area, it showed that there exist a direct positive relationships between monthly mean temperatures and the monthly THI. The higher the monthly mean temperature, the higher the THI as presented in Figure 3 and Figure 4. A similar relationship also exist between dew point temperature and the THI; as the dew point temperature increases, so the THI increases. Biological confirmation of these relationships can be deduced from performance of the dairy cattle on a commercial dairy farm located in Minna as presented in Figure 3. The figure showed that the THI is high and constant throughout the year and this can be linked to the reasons why milk production of the cattle was low.
From 21 months lactation records obtained from the commercial dairy farm; it is possible to deduce that production and performance parameters of the exotic cattle were poor which can be linked to environmental stressors such as oxidative stress on the animals. Holsteins are high performing dairy animal worldwide but their reproductive and productive performance in Tropical countries are always different from their achievable performance in Europe. What was obtained as mean daily milk production for the cattle as presented in Table 2 is similar to daily milk production of 8.38 litres reported by Haftu (2015) for Holstein cattle in Ethiopia. It is also similar with what was reported for Holsteins in Sudan as reported by Abdel

Rahman and Alemam (2008).
However, these breeds are reported as excellent dairy cattle because of their superior genetic composition which is a reason why their choice for upgrading of indigenous cattle is a common livestock improvement practices (Ogundipe and Adeoye, 2013). Therefore, harsh environmental conditions such as high and unbearable THI and other different climatic conditions rather than poor management systems could be responsible for the poor production as revealed in this study. Confirmation of this observation is higher milk yield recorded (35 litres per day) in an experimental unit on the commercial farm where temperature control was carried out (18 o C -20 o C); it is however unsustainable for the farm to run such facilities for full scale production considering associated cost. The relationship between monthly THI and corresponding milk production by the cattle showed that the THI negatively affected milk production capacity of the cattle. From Figure 3 above, it can be deduced that crossbred cattle from the exotic breeds and the indigenous cattle breed have highest tolerance to the effect of THI because despite the THI constantly being high, the milk production of the crossbred remained relatively constant except by the 16 th month which correspond with April of the second year of production when the production level drops and remained unchanged till the 21 st month. Ability of the crossbred to display this tolerance is not far-fetched from the adaptation of the local breed used for the crossing (White Fulani) to the environmental conditions obtainable in Minna. This is further expressed in the high calving rate (70 %) and low culling rate (10 %) of the crossbred. This means that in spite of the consistently high THI, there is strong capability of the crossbred to survive which confers an added advantage for it over both imported breed.
This is a pointer that with careful selective breeding, the indigenous White Fulani cattle can be made to improve on its milking capacity. If farmers must import, then it should be semen for artificial insemination as keeping imported animals has implication on production cost. This is because, there will then be the need to engage in microclimate ameliorative practices. The high culling rate and lover calving rate when compare to the crossbred makes keeping the exotic breed in-situ on the farm uneconomical.
In rabbit production, elevated level of THI correspond with higher heat and moisture production especially in mature rabbits. Hence, to maintain optimum rabbit production in the study area maintenance of THI value below 27 o C will be optimum for rabbit as calculated using the Livestock Production Heat Stress Indices (LPHSI, 1990) formular which was reportedly modified for rabbit by Marai et al. (2001) is a must in order to provide comfortable environment for the animal. Following recommendations of Ogunjimi et al. (2008), physiological and productive conditions of rabbits are both susceptible to heat stress because under heat stress condition, there is reduced feed intake and continuous use of Metabolizable Energy (ME) for non-productive activities such as panting and faster respiration rates for the purpose of survival (El-Raffa, 2005;Ogunjimi, 2007) which shows that environmental conditions in the study area as presented in Table  3 is not too suitable for rabbit production without modifications. In Figure 6 below, it showed that only four months of the year is when the THI was below 27.00 (June -September) which is an indication that for excellent performance of rabbit in the study area, antioxidative management practices such as the use of antioxidant diets and drugs, modification of housing to encourage cross ventilation and care for animals to ameliorate stress conditions are highly important husbandry practices.

Figure 6: Monthly temperature-humidity-index for rabbits using climate data of Minna
Exposure to heat stress could lead to poor growth and reproduction because it decrease live weight gain, daily weight gain, feed intake, litter size at weaning, pre and post weaning weight gain in rabbits. In fact under heat stress, conception rates, overall nutrients digestibility as well as productivity loss is associated with incidence of heat loss in rabbit. Production loss involving conception rates, preweaning mortality of rabbit kits, litter weight at weaning are reported to be 70 % in a reproductive cycle of rabbit doe. This represent huge economic loss requiring multidimensional solution in housing, animal care and handling, nutrition and health management for a rabbit enterprise to be profitable (Marai et al., 2001).

Conclusion
Analysis of basic climate data between years 1961 and 2018 for Minna revealed that for most part of the year (nine months), animals in the study area live under heat stress and hence their potential for food production is under threats thereby contributing to food insecurity. Plans for improving animal productive performance should form basis for livestock production research in the area. Environmental modifications including cooling systems or modifications of housing facilities may not be the only feasible approaches to heat stress management in the study area considering associated costs. As a result, nutritional manipulations that promote animal health and production capacities is suggested as additional option worthy of exploration. Instead of the penchant for importing exotic breeds of livestock with the aim of upgrading the indigenous breeds, the way forward could be the utilization of the heat shock protein of the animals as candidate markers for improvement of their productive potentials. Further research is suggested to investigate pathophysiological mechanisms of heat stress for the purpose of determining appropriate mitigation measures for management of heat stress in the study area.