بررسی معادلات مختلف تعیین تنش گرمایی و تاثیر آن بر تولید شیر روزانه در یک گاوداری بزرگ صنعتی مشهد

Abstract

It has been known that, weather condition has a great effect on living being. Now a days the study of the effect of weather conditions on plant, animals and all living being is considered as an interdisciplinary science, which has a great effect on the quality and quantity of living being productions. In order to survive and maintain their physiological activities, warm-blooded animals’ body temperature should be in a specific rang. Therefor in warm days, in order to restrain their body temperature in an optimized rage, their transpiration, breathing and heart beat will raise, while the feeding rate decrease. In these situation if the relative humidity was high too, these cooling reaction cannot response well and therefore animals’ body temperature will raise, and it has been said that animals are under the heat stress. As a consequence of that feeding rate and animal production reduce, reproductive problems accrues, and the rate of getting sick raise. In this regard, researches show that air temperature and environmental humidity are two parameters which has a great effect on cows’ heat stress. In order to evaluate and assess the heat stress, most of the researchers use Temperature Humidity Index (THI). There are numbers of equation to obtain THI, and also their coefficient must be calibrated for every different regions, therefore using them, are sometimes, confusing. Therefore the aim of this study is determining the best THI equation for dairy industry in Mashhad, and also finding the reduction in milk production during the heat stress period. The meteorological data (daily wet and dry bulb and relative humidity records) were obtained from Iran meteorological organization. Then by using 8 common equations, temperature humidity index (THI) were calculated for 7 year period (2007-2013). The daily milk production data was also obtained from improvement center of milk production in Karaj. Then the relationship between daily milk production and 8 obtained THI were calculated for annual and seasonal time scale. At that point by using the correlation coefficients and P-value the best equation to determine THI was chosen. Finding the best THI equation for the study area, led to find a warning heat stress point. As a final point, daily milk production during the heat stress calculated and reduced milk production was estimated during the heat stress time. The results show that there are no significant correlation between annually milk production and obtained THI. Also the relationship between THI and milk production in seasonal scale (spring, fall and winter) were not significant to. Nevertheless, only daily milk production in summer has a significant relationship with temperature-humidity index, which was negative. Which means that daily milk production decreases with increasing THI. Among from 8 investigative equation, the forth equation (which calculate THI by using dry bulb and dew point temperature) has the best correlation coefficient and P-value with daily milk production. By definition the break point in summer daily THI and milk production, the heat stress warning point for Mashhad dairy industry was found. The results show that when temperature-humidity index raise above 75, the milk production significantly decrease. In order to calculate the amount of milk reduction as a result of THI increasing, the relationship between milk production and THIs’ more than 75 was estimated. Then by subtracting the calculated THI from average milk production in a non-stress day, the loss of milk production were calculated for each cow. Then by multiplying one cow milk lost, by the number of cows, the final milk production loss were calculated for each year. The results show in 2013, the temperature humidity stress had a greatest effect on milk production, so that during a summer time, each cow averagely produce 138.8 lit milk less than usual. This amount is also equal to 1.5 lit milk per a day. During 7 years period investigation, the total milk loss was calculated 401 ton. In conclusion, raising air temperature can cause a heat stress and a reduced milk reduction. When the heat comes with high relative humidity, these effects highlighted and cows were under enormous stress therefore their body temperature transpiration, breathing and heart beat raise, while the feeding rate decrease, and as a result of that milk production reduced which can cause a great damage in diary industry