Defining breeding goal and designing breeding strategy for buffalo population of Khuzestan using computer simulation.

In this study, at first, the production and reproduction performance data of 526 buffalo herds from Khuzestan province, collected during 1993 to 2010, were studied. GLM procedure of SAS software was used to investigate the factors affecting studied traits. The average of milk yield in one lactation period, fat yield, fat percentage, protein yield, protein percentage, lactation length, milk yield per day of calving interval, milk yield per lactation day for buffaloes in Khuzestan were estimated as 1939.76 kg, 120.27 kg, 6.1%, 83.94 kg, 3.9 %, 200.34 days, 4.68 kg and 9.58 kg, respectively. Also, means of reproduction traits were estimated as 240.27 days for dry period, 156 days for open days, 465.21 days for calving interval and 3.68 years for age at first calving. The effects of herd, year of calving and lactation period were significant for all traits. In contrast, the season of calving was not significant for protein percentage, calving interval and days open. Variance components and heritability of each trait were estimated using restricted maximum likelihood method with the DFREML program. Heritability of production and reproduction traits for buffalo of Khuzestan were zero, except age at first calving with heritability of 0.21. Factors such as poor management and nutrition of buffalo herds and particularly the errors in buffalo milk recording, pedigree registration and their genetic relationships are the main reasons for this low estimation. In the study of economic weights of milk traits, the average of total profit per head was estimated as 536/215, 1/339/281, 591/685 and 2/872/164 Rials for Ahwaz, Dezful, Shoshtar and Dasht Azadegan (milk and cream sale situation) and -1/559/563 and -2/794/201 Rials for Sosh and Shadegan (milk sale situation), respectively. So the pricing system for milk (only based on the amount of milk) cannot be profitable for Khuzestan buffalo herds and milk and cream sale situation will provide greater profitability. Using maximum profit equation, the economic coefficients were obtained for milk production trait for the herds of Ahwaz, Dezful, Shoshtar, Dasht Azadegan, Shosh and Shadegan as 6/489, 7/550, 6/512, 7/179, 4/944 and 4/663 Rials, respectively. This coefficient for milk in both sale situations (only milk and milk and cream sale situations), using revenue to cost equation was estimated positive and in the range of 0.02 to 0.04% and in minimum cost equation, the results were contrary to the economic coefficients obtained for revenue to cost equation, in terms of orientation. Two of the cities with milk sale situation compared with cities of other sale situation, showed more fluctuation to the changes in the food costs, non-food costs and milk prices. Using maximum profit equation, the economic coefficients of the fat percentage for the cities of Ahwaz, Dezful, Shoshtar, Dasht Azadegan, Shosh and Shadegan were obtained as 40/401, 179/692, 81/326 and 112/043, -160/015 and -230/512 Rials, respectively. This coefficient for fat percentage in milk and cream sale situation with revenue to cost interest was obtained positive and in the range of 0.14 % for herds of Ahwaz to 0.69 % for herds of Dezful. In the milk and fat (cream) sale situation, the estimated economic value for fat was higher than milk. Thus, there is higher value for fat percentage compared of milk. Results of 30-year selection showed that in direct selection for milk (the first selection program), genetic and phenotypic trends for milk yield was positive and for fat and protein percentage, due to their negative genetic correlation with milk production, was negative. Genetic trends for studied traits (milk production and fat percentage) was calculated as 10.37kg and -0.002% per year and 63.46 kg and -0.02% per generation. The phenotypic improvement of studied traits also was estimated as 28.74 kg and -0.01% per year, and 150.4 kg and -0.05% per generation, respectively. In the second selection program, selection was considered based on fat percent. In the second program, selection based on fat percentage was considered. Estimation of genetic trends for direct selection on fat percent was also -13.81 kg and 0.085% per generation and -3.32 kg and 0.015% per year, respectively. Phenotypic trend per year for studied traits in this selection were calculated as -5.40kg and 0.04% per year and -28.51kg and 0.246% per generation, respectively. The genetic improvement of the third program (selection based on milk and fat percentage) for milk yield, fat and protein percentage were 12.95 kg and -0.004% per year and 72.97 kg and -0.02% per generation, respectively. Based on results of this program, the accuracy of selection (correlation between index and goal) increased (from 0.59 to 0.62) and the genetic progress for milk production was still positive, but decreasing trend was seen for two other traits (fat and protein percentage). Comparing results of genetic progress per year showed that genetic and economic progress achieved in each year from direct selection for milk production is less than the selection program based on milk and fat percent. In general, the comparison of the three indices used in selection showed that the second index (selection based on milk and fat percentage) was more suitable than selection based on milk, because of higher genetic and phenotypic development and also, the higher accuracy of selection. The genetic and phenotypic regression coefficients were significant in all three programs (p 0.01). Key words: buffalo, Khuzestan, production, heritability, reproduction, economic weight and simulation.