8763

8124

كارشناسي ارشد

علوم دامي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده كشاورزي

1392

چهارده،109ص.: مصور،جدول،نمودار(رنگي)

ص.ع.به فارسي و انگليسي

غلامرضا قرباني

محمد خوروش، علي صادقي سفيدمزگي

2/2/93

مسعود عليخاني، جمشيد رزمجو

مهندسي كشاورزي

ID8124

Study the Temperature Humidity Index and Its Effect on Performance of Dairy Cows in Isfahan Hamed Ahangaran h ahangaran2011@gmail com December 2013 Department of Animal Science Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi G R Ghorbani Prof supervisor G R Ghorbani@cc iut ac irAbstractA temperature humidity index THI is a single value representing the combined effects of air temperatureand humidity associated with the level of heat stress The objective of this study was to evaluate the effects ofTHI on milk yield and milk composition of dairy cows in climatic conditions of 7 Isfahan dairy farms Theexperiment carried out during in July 2012 to October 2013 In this study eight THI with differentweightings of dry bulb temperature and humidity were compared Ambient temperature and relative humiditywere measured every 15 min with data loggers located throughout the farm According to THI values frommid October to early May the heat stress was lower than the threshold with lowest values in January then THI was higher than threshold until mid October which was the highest level in July Indices with higherweightings of humidity are more appropriate for humid climates and indices with the most emphasis onambient temperature are more suitable for semiarid climates Since that Isfahan is located in the dry climate THI 5 is the best indicator of its 8 temperature humidity indicators The threshold for heat stress was 65 byTHI 5 When THI increased one unit upper than treshold average milk production decreased 0 5 Kg Disintegration of estimated THI thresholds of heat stress into corresponding temperature and relativehumidity revealed that heat stress occurred in Isfahan at temperatures 21 C and relative humidity of 25 Results clearly showed a negative relationship between milk production and THI Indeed as THI increasesfrom 49 1 in the winter season to 70 8 in the summer season heat stress reduced total milk production by38 5 to 36 1 kg respectively This decrease can be largely explained by the effect of summer heat stress particularly in July August and September when THI values are well above the critical threshold of 65 Thereason for the drop in milk yield during the early fall could be explained by the carry over effect of theunfavorable conditions during the summer particularly in the absence of environmental control systems Key words temperature humidity index heat stress milk loss

غلامرضا قرباني

محمد خوروش، علي صادقي سفيدمزگي

مسعود عليخاني، جمشيد رزمجو