روند ژنتیکی و فنوتیپی

 One of the most important environmental factors affecting the dairy industry is the temperature changes that showed a negative impact on the industry over the past few years. Increasing temperatures have declined the production and reproductive performance of herds in the tropics. Huge losses are caused annually due to heat stress. Heat stress in dairy cows is caused by a combination of environmental factors (temperature, relative humidity, solar radiation and air movement). Continual genetic selection for greater performance results to increased sensitivity to heat stress. It was one of the reasons why lactation curve during summer has decreasing trend compared to spring in which lactation curve maintained within high levels. Dairy cows at the beginning of lactation have small chances to fight off a thermal stress, and thus it has the strongest effect on the production of milk in the first 60 days of lactation. A negative balance of energy in dairy cows at the beginning of lactation is even more increased by creating and emitting of higher quantity of thermal energy in the period when animals consume less food. For this reason, a high-yielding dairy cows are more sensitive to heat stress than cows having a lower genetic potential for milk production. Impacts of heat stress on reproductive efficiency have been well documented and reviewed. Heat stress has been shown to alter the duration of estrus, colostrum quality, conception rate, uterine function, endocrine status, follicular growth and development, luteolytic mechanisms, early embryonic development and fetal growth. Therefore, the purpose of this study was to investigate the effect of heat stress on yield of dairy cattle in different months of production and also to estimate genetic parameters of production and reproductive traits under heat stress.

 In this study, 169655 records of 60322 dairy cows in different parity in Isfahan province of Iran were used. The studied traits included productive and reproductive traits. Milk test day and fat percent as productive traits and open days and days to first service were considered as reproductive traits. Climatic records of herds were collected from 7 stations less than 70 km away from herds and temperature-humidity index (THI) was calculated for each month in each herd. Dairy milk production records ranged from 5 kg to 60 kg for milk and milk fat percentage from 1 to 7%. Genetic and phenotypic trends were considered by regression of the estimated breeding values on year of the birth. The model used included the effect of herd-year of calving, calving month, parity and temperature-humidity index. An animal model was used to estimate genetic parameters of reproductive traits and random regression was used for production traits. SAS software was used to investigate the significance level of independent factors and DMU software was used to estimate genetic parameters.

 The results showed that the threshold of temperature-humidity index is 72 and more than it has adverse effects on performance. Average days open and difference to first service in different Parity 112 and 60 days respectively and was estimated the average heritability of days open and difference to first service 0.02 and 0.06, respectively. With increase in temperature- humidity index, mean of production traits decreased and this decrease for milk and fat yield traits occurred at temperature-humidity threshold of 72 and 65, respectively. The average of heritability was calculated as 0.32 for milk yield and 0.24 for milk fat percentage. The results indicated that with increasing temperature humidity index in 72 the genetic variance for both traits was increased. In on other words, the cows after heat stress (THI=72). Genetic differences were significantly increased. The results of this study indicate that the additive genetic variances were higher in early lactation (5 to 100 days of lactation), for both milk yield and fat percentage.

 Genetic variance increased with increasing temperature-humidity index (THI = 72) for the two traits of milk and fat production. Also breeding value of open day correction and difference to first calving under heat stress decreased. In other words, there is a significant genetic difference between animals exposed to heat stress after temperature-humidity index 72. Therefore, it may be possible to genetically identify animals more resistant to heat stress as parents of the next generation.

In this study, genetic parameters and (co) variance components were estimated for weights at birth, 3, 6, 9 month, daily weight gain and Keliber ratio from birth to 3 month and also form 3 month to 9 month. Records of 2544 kids, the progeny of 149 sires and 851 dams were used to analysis data by MTGSAM program. Six different animal models were fitted for all traits. The most appropriate model for weight at 6, 9 and daily weight gain and Keliber ratio form 3 to 9 month was model 2. Estimated direct heritability varied from 0.01 to 0.36, which was minimum (0.01) for daily weight gain and Keliber ratio from birth to 3 month and maximum (0.36) for birth weight. The genetic and phenotypic trends for all traits were estimated near to zero and non-significant. Generally, differences between estimated genetic trends for these traits and estimated values of other studies, is due to difference in animal breeding standard followed by different program selection, difference between models and calculation method, effects of environment, interaction between genetic and environmental, nutrition and climate conditions.

In this study، the number of 1802 longevity records of ewes collected during 1989 to 2010 in Breeding Station of Lori-Bakhtiari sheep flocks were used to estimate of genetic، environmental and phenotypic trends for economic lifetime. The breeding values of a ewe’s lifetime were estimated by restricted maximum likelihood procedure under an animal model of univariate analysis. The best linear unbiased prediction of breeding values estimated and genetic trends were estimated as a regression coefficient of average breeding values on the birth year of ewes. The environmental and phenotypic trends estimated as a regression coefficient of average environmental deviation and phenotypic deviation (deviations of phenotypic values from overall mean) on the birth year of ewes. The results showed that، genetic trend of longevity was positive (0. 033 days) but insignificant from zero. While the environmental and phenotypic trends were equal to -27. 81 and -27. 78 days، respectively، and significantly different from zero (P<0. 05). Thus، selection for growth traits did not affect longevity traits as genetically and to exhibit negative phenotypic trend for longevity the environmental factors should improve firstly

(Co) variance components and genetic parameters for growth traits including birth weight (BW), weaning weight (WW) and six-month weight (6MW) as well as parameters, genetic and phenotypic trends of reproductive traits including total weight of lambs weaned per the ewe (TWLW) and the number of lambs born at birth per ewe (NLBE) in Lori sheep were estimated using the Bayesian method. The data included 7363 records for BW, 7054 records for WW, 6765 records for 6MW, 1012 records for TWLW and 1048 records for NLBE. The data were collected by the Agricultural Organization of Lorestan Province between the 2001 to 2010 years (for growth traits) and 2003 to 2010 years (for reproductive traits). The estimates of direct heritability for lamb body weights were 0.36 at birth, 0.11 at weaning and 0.05 at six months of age. The genetic and phenotypic trends reproductive traits were calculated based on regression of the mean of breeding value on birth year and mean of phenotypic value on birth year, respectively. Heritability, genetic and phenotypic trends for TWLW trait were 0.05, 5.4±1.16 and 255±0.45 grams per year, respectively. Heritability, genetic and phenotypic trends of NLBE trait were 0.09, 0.002±0.02 and 0.125±0.07, respectively. Genetic improvement of TWLW and NLBE traits at considered period were 31.64 grams and 0.008 of Lamb. The estimate of heritability at birth was higher than other traits so selection based on this trait would increase the genetic advances. Genetic and phenotypic trends for reproductive traits were not significant and the genetic trend was low.

To estimate genetic and phenotypic trends of growth traits a data set collected from 1995 to 2008 by the Moghani breeding station were used. (Co) variance components for traits were estimated by derivative free restricted maximum likelihood (DFREML) and breeding values of animals were predicted with Best Linear Unbiased Prediction (BLUP) methodology under multi-trait animal models and then genetic trend estimated on based the most appropriate model. Genetic and phenotypic trends of studied traits were estimated regression mean of breeding value and phenotypic on birth year. Direct genetic and phenotypic trends for birth weight(BW), weaning weight(WW), 6- month weight(6MW), average daily gain birth to weaning(ADG0-3), average daily gain weaning to 6- month (ADG3-6), kleiber ratio from birth to weaning (KR0-3) and kleiber ratio from weaning to 6 month (KR3-6) were estimated 2 and 31; 36 and 528; 43 and; 0.617 and 4.258; 0.223 and 0.144; 0.016 and 0.165 and 0.007 and -0.235 gr per year, respectively. Total genetic progress of 14 years for BW, WW and 6MW were 38, 401 and 578 gr and 65.541, 2.697, 2.497 and 0.090 for ADGa, ADGb, KRa and KRb, respectively.

In the present research some reproductive traits in Holstein cows of Khoramdareh agro-industry were studied. The data set comprised of 10،891 records collected from 23 years (1988 to 2010) by animal breeding centre، Iran. The total number of animals in the pedigree file was 16/087. Genetic and phenotypic parameters using soft WOMBAT software and restricted maximum likelihood method under animal models and a multivariate trait was estimated. Genetic trend for each trait was estimated using SPSS programmer based upon regression of mean breeding value on year of calving. Phenotypic trend was also estimated based upon regression of phenotypic mean of the trait on year of calving. Levels of heritability from linear model for the traits age at first insemination (AFS)، age at first calving (AFC)، number of insemination resulted in conception (NSPC)، open days (OD)، pregnancy rate (PR)، calving interval (CI)، Non return rate to 90 days (NRR90) respectively 0. 037، 0. 016، 0. 01، 0. 032، 0. 021، 0. 051 and 0. 034، respectively. Maximum genetic correlation between traits and open days and pregnancy rates between insemination number of days open and pregnancy، respectively، leading to -0. 99 and 0/84 and the lowest genetic correlation between PR with NRR90 (0. 001) respectively. Open days and pregnancy rate with the open days and NRR9 respectively Olsen -0. 99 and 0. 00 the highest and lowest phenotypic correlation showed. Genetic trend for the reproduction traits was between -0/009 for NRR90 and -0/04 for CI respectively. Phenotype trend for the about traits has lower trend for (0/002) NRR90 and (-0/74) for AFS respectively. Lower among environmental trend (-0/007) for NSPC and upper among environmental trend for AFS (-6/52) respectively.