Abortion is an important trait with noticeable impacts on economic profit of dairy herds. This study was conducted to estimate variance components and genetic, environmental and phenotypic trends for abortions in Iranian Holstein Friesian cows. The data used were 247230 calving and abortion records of 84421 Hol-stein cows, collected during years 1991-2016, from 51 herds in Iran. Variance components and genetic pa-rameters were estimated using a logit link function, fitting an animal mixed model by ASReml software. In this model, parity and milk yield were fixed, while direct additive genetic, herd-year-season and permanent environment effects were considered as random factors. Genetic, phenotypic and environmental trends were estimated as weighted regression coefficients of breeding values, phenotypic values and environmental deviations averages on birth year, respectively and the number of observations was considered as the weighting factor. Generally, abortion risk in the first parity was lower than the later parities and in autumn was lower than the other seasons. Abortion risk also increased by increase in milk yield level. Heritability and repeatability estimates for abortion were both 0. 165 ± 0. 010. A significant positive genetic trend (0. 038 rate/year) and a significant negative environmental trend (-0. 033 rate/year) were estimated for abortion, which indicated significant increase of genetic predisposition to abortions and improvement of environ-mental conditions to prevent abortion incidence. A significant positive phenotypic trend (0. 002 rate/year) was also estimated, which showed overall increase of abortion rate during the studied years. Overall, it could be concluded that genetic predisposition to abortion is increasing in Iranian Holstein cows, but inclusion of abortion risk in bull proofs and selection indices may help to reduce abortion incidence and increase economic profit of dairy cattle industry.

The present study aimed to estimate the effects of parity, calving season and year of calving on the prevalence of subclinical mastitis in Holstein cows. A total of 2682 records from 869 Holstein cows in a large dairy farm (Azarbaijan province, Iran), respecting the period from 2006 to 2009, were collected. Data was analyzed using Proc Mixed of SAS software by MIVQUE method. Subclinical mastitis was also studied based on three different models including: 1) considering each udder quarter as a separate unit (Udder quarter model), 2) considering all the four udder quarters of a cow as one overall unit (Subclinm model) and 3) considering the sum of positive subclinical mastitis scores in all udder quarters of an animal (Episode model). Diagnosis of subclinical mastitis was based on California Mastitis Test. Results showed that the prevalence of subclinical mastitis was 20.83%. The prevalence of cows with only one udder quarter affected by subclinical mastitis was 23.71%. Parity and year of calving significantly affected the prevalence of subclinical mastitis (P<0.001). Older cows with higher parity number had increased prevalence of subclinical mastitis. Therefore, the highest prevalence of subclinical mastitis was observed in cows having number of parities between 5 and 11. The lowest subclinical mastitis prevalence (using three mastitis models) was recorded in 2010, whilst its highest prevalence was observed in 2008. Season of calving also significantly influenced subclinical mastitis prevalence (P<0.05): cows calving in autumn had higher prevalence of subclinical mastitis than those calving in the other seasons. Concluding, data from the present study demonstrated that parity, calving season and year of calving influenced the prevalence of subclinical mastitis on the three mentioned models.

A total of 72124 fertility records was used to estimate the genetic and phenotypic trend of fertility traits in Iranian Holstein cow from 1981 to 2007. Fertility traits in this study were: days from calving to first service (DFS), number of insemination per conception (INS), days open (DO), interval between first and last in semination (IFL), calving interval (CI) and success to first insemination (SF). The overall genetic trend in fertility traits was as desired and statistically significant. Mean breeding value of SF increase by 0.00067 percent per year. The annual genetic trends for INS, DFS, IFL, CI and DO were -0.0029 number/year, -0.062 days/year, -0.041 days/year, -0.23 days/year and -0.24 days/year, respectively. Phenotypes trends for fertility traits were unfavorable except for DFS and DO. Phenotypic trends in IFL, INS and SF were as un-desirable positive. Phenotypically DO and CI did not change over the time period. Phenotypically IFL has increased 1.6 days/year and DFS has decreased 1.6 days/year. The annual phenotypic trends for INS and SF were 0.04 and -0.018, respectively.

The objective of this study was to analyze the association of somatic cell score (SCS) with milk, fat and protein yields across parities. Records of production traits and somatic cell counts (SCC) from first, second and third parity that were collected by the Animal Breeding Center of Iran from 1993 to 2010 were used. All animals were grouped into six classes according to SCC and production traits were evaluated in these SCC classes. To obtain an approximate normal distribution, SCC records were transformed on the base of Loge to somatic cell score (LSCS, the lactation mean of the natural log of test-day somatic cell count). A single trait animal model that LSCS was fitted as covariate was used to assess relations of SCS with production traits in fist, second and third parities. Effect of SCS on production traits in all of parities was negative and significant (P<0.05). Ranges of depressing effects on milk, fat and protein production were 107.78-220.41, 2.32-7.08 and 2.1-5.2 kg per 1 unit increase in SCS.

Objective: The cows that don’t have access to sufficient energy in their ration can get sickness. Milk production has a high priority in metabolism of dairy cows so lactating cows are more prone to get sick This can ruin all the benefits of higher milk yield because of the higher prevalence of the disorders.Methods: Data for this research had gathered from a herd with 1600 Holstein cattle in East Azarbayjan province of Iran. Data were from 5052 lactation period of 1796 Holstein-Frisian cows which had parturition among 2005-2009. Seven groups of disorders have been analyzed. They are as follow: Cecal dilatation and rotation, diarrhea, abomasal distention and displacement to the right or left, locomotion problems and metritis. Each model consists of milk yield, parity, season and the year of calving. To determine the correlation between 305-day milk yield and occurring of disorders data have been analyzed with logistic regression model.Results: In this research current lactation was used as the lactation with occurrence of particular disorder. According to performed analysis on all cattle (heifers and the cows) higher milk yield was not a risk factor for the disorders occurrence except for diarrhea. Our outcomes showed a negative correlation between milk production with abomasal distention and left abomasal displacement. Analysis of correlation between prevalence of the disorders and 305- day yield showed a negative correlation with abomasal dilatation and displacement to the left and a positive correlation with diarrhea. Parity had a negative correlation with cecal rotation and dilatation, and a positive correlation with diarrhea. The year of calving had a significant correlation with abomasal dilatation and displacement of that to the right, cecal dilatation and rotation, diarrhea and locomotion problems. Calving season had only a significant relationship with cecal dilation and rotation. This research showed a complete correlation between some diseases and disorders in dairy cows and parameters that refer to milk production.