The objective of this study was to estimate genetic parameters coupled with genetic and phonotypic trends for age at first calving (AFC) and first and second calving interval (CI1 and CI2) in Iranian Holstein cows. Records of reproduction from 1983 to 2007 for AFC, CI1 and CI2 were 261116, 163234 and 92661, respectively. Single and two trait animal model was used to estimate genetic parameters by restricted maximum likelihood procedures using Average Information algorithm in ASREML software. Estimates of heritability were 0.19±0.005 for AFC, 0.04±0.003 for CI1, and 0.04±0.004 for CI2. Genetic trends for AFC, CI1 and CI2 were -0.75±0.11, 0.004±0.02, -0.02±0.01day per year and phonotypic trends were -2.35±0.38, -1.13±0.39, -0.28±0.23 day per year, for AFC, CI1 and CI2, respectively. The genetic, phonotypic and environmental correlations were -0.049, 0, 0.002 for AFC and CL1, 0.014, -0.004, -0.004 for AFC and CL2, and 0.877, 0.081, 0.043 for CL1 and CL2, respectively.

The objective of this study was to estimates the genetic and environmental components for the lactation curve parameters, milk yield, age at first calving (AFC), calving interval (CI) and somatic cell count (SCC) in Iranian Holstein cows. The dataset consisted of 210625 test day records from 25883 cows with milk yield in the first parity recorded from July 2002 to September 2007 in a total of 97 herds in Iran. The lactation curve and the selected lactation parameters were the scaling factor to represent yield at the beginning of lactation (a), the factor associated with the inclining (b) and declining (c) slopes of the lactation curves and the first 100-day milk yield, second 100-day milk yield, third 100-day milk yield, peak yield (Ymax), days in milk at peak yield (b/c), persistency (s), lactation length (LL) and the 305-day milk yield. The incomplete gamma function (Wood function) was used to estimate lactation curve and lactation parameters from daily milk records. Among the 100-day milk yield periods, the second 100-day milk yield had the highest herita-bility (0.29±0.024) and the highest genetic correlation with the 305-day milk yield (0.996±0.00). Lactation curve parameters had low h2 (0.017±0.007 to 0.051±0.011). The b / c had a relatively high genetic correla-tion with the 305-day milk yield (0.52±0.08), a moderate genetic correlation with CI (0.32±0.14) and nega-tive genetic correlations with measures of somatic cell count. This suggested that b / c could be used as a criterion to improve 305-day milk yield and resistance to subclinical mastitis.

For the current research the records of 62 farms in Isfahan province were available. To estimate genetic and phonotypic trends of reproductive traits such as age at first calving, calving interval, days open and number of insemination to conception rate the records of 63, 866 cows including 167793 reproductive records were employed. Farms were covered by Vahdat industrial Agriculturists and Dairymen Cooperative of Isfahan during 1986 to 2012. Genetic parameters estimated by linear animal model using Restricted Maximum Likelihood Method (REML). Genetic and phonotype trends were estimated by using regression of average breeding values and phonotype values on calving year. Heritability of age at first calving (0.19±0.007), calving interval (0.06±0.005), days open (0.041±0.004) and number of insemination to conception (0.071±0.004) were estimated. Phonotypic trends of age at first calving, calving interval, days open, number of insemination to conception in first parity and number of insemination to conception in second parity onward were estimated to be -3.48±1.08, -0.41±0.4, -0.42±0.2, 0.013±0.0025 and 0.031±0.01 respectively. Estimated genetic trends for age at first calving, calving interval, days open, for number of insemination to conception in first parity and number of insemination to conception in second parity onward were estimated to be 0.07±0.06, -0.56±0.5, -0.02±0.06, 0.0015±0.001 and 0.0005±0.005, respectively.

Retrospective data from Sebele Dairy Farm were analysed for reproductive performance of Friesian/Holstein cows. Three hundred records from 1989 to 1995 were used. The herd was zero grazed and the data was analysed for age at first calving (AFC), calf birth weights (BW), calving interval (CI), days open (DO), calving rate (CR), reproductive wastage (RW) and calving difficulty (CD); dystocia, after-birth retention and misrepresentation of foetus) and calving weights (CW). The effects of year of calving (YOC) and year of birth (YOB) were tested. The year of calving affected age at first calving (P<0.05) whereby in 1989/90 and 1990/91 cows were younger than the rest of the years. Calving weight at first calving was significantly affected (P<0.01) by year of calving. YOC had an effect (P<0.05) on both calving interval and days open. CW and CR were significantly affected (P<0.001 and more) by the year of calving. Reproductive wastage tended (P=0.065) to be affected by YOC while no effect (P>0.05) was observed for BW and CD. The year of birth of cows (YOB) had an effect (P<0.05) on age at first calving and it also significantly affected (P<0.01) CW of first calving heifers. Heifers born in the 1980’s had lower live weight at calving than those born in the 1990’s. Age categories (1=20–39 months; 2=40–69 months and 3=>70 months) tended (P=0.062) to influence the birth weights of calves. As cows’ age increased, birth weights of their calves decreased. However, age category did not affect (P>0.05) calving interval or days open. Male calves were heavier (P<0.05) at birth than females (38.7±1.3 kg vs.36.8±0.7 kg). CW was lower for heifers than for cows and represented 84% of the cows’ weights. Heifers had higher (P<0.01) CR than cows (100 vs.64.9%), however RW was higher (P<0.01) for heifers than cows (25.0 vs.11.0%). RW was significantly correlated with birth difficulty (r=0.50; P<0.001). It seems that a low temperature-humidity index in the month of conception resulted in higher CR nine months later. It is recommended that when cows are zero grazed, feed quality should be assured by nutrient balancing and should not affect performance between years.