Data on 361 lambs of Mehraban (n=90), Ghezel (n=92), Ghezel × Mehraban (n=87), and Mehraban × Ghezel (n=92, sire breed listed first) were used to estimate individual Heterosisfor lamb growth. The obtained results demonstrated that lambs of purebreds of Ghezel and Mehraban showed the highest and the lowest birth weight, respectively (P<0.05). Crossbred lambs of Mehraban × Ghezel showed significantly higher (P<0.05) average birth weight per ewe than Ghezel × Mehraban. Purebred Mehraban lambs showed the lowest total and average six month old weight per ewe (P<0.05) but the average and total six month old weight per ewe of Ghezel was not different than crossbreds groups of Ghezel × Mehraban and Mehraban × Ghezel lambs (P≥0.05). Individual heterosis for the average birth weight, total birth weight, average six month old weight and total six month old weight was estimated to be -0.37, -0.30, 0.22 and -1.03%, respectively (P≥0.05). تفاصيل المقالة

The association of birth type (single vs. double) and pregnancy type (single vs. double) with lactation performance and lactation curve was investigated in Holstein cows in Iran. Data of 243298 lactations on 138021 cows in 261 herds collected during January 2000 to December 2012 were used. The average twinning rate was 3.64% and ranged from 1.44% (primiparous) to 5.41% (multiparous). Factors associated with twining were calving season, calving year, herd, and parity. The rate of twinning increased from 2.49% in 2000 to 3.42% in 2012. The probability of twinning was higher in multiparous cows than that in primiparous [Odds ratio (OR) (95% confidence interval (CI))= 3.64 (3.44-3.84) for multiparous vs. primiparous cows]. The probability of twin pregnancy was higher in cows previously delivering twins than that in those delivering singles [OR (95% CI)= 3.17 (3.02-3.34) for cows delivering twins vs. cows delivering singles]. The lactation curve for cows delivering singles in previous gestation and pregnant with twins in subsequent gestation tended to be lower and flatter. The incidence of twin pregnancy was increased as the cow reached its peak yield earlier, and produced more milk at peak lactation. Primiparous cows delivering singletons in their previous gestation and having twins in their subsequent gestation produced more 100-d, 200-d and 305-d milk than those pregnant with singletons. Multiparous cows that delivered singleton in previous gestation and were pregnant with twin in the subsequent gestation, produced more milk during the first 100-d and 200-d of lactation than those pregnant with singles. تفاصيل المقالة

The objective of this study was to investigate the effect of inbreeding on lactation performance in Holstein cows of Iran.The pedigree file contained information of 1,025,281 animals born between 1965 and 2007.Lactation performance records from March 2000 to April 2009 comprising 193,501calving events on 123,751 cows in 85 dairy herds were included in the data set. The potential consequent effects of inbreeding on lactation traits were analyzed through mixed linear model using the MIXED procedure of the SAS. The mean level of inbreeding was shown to be 0.7%. Less than 37% of all animals were inbred, and a small proportion, 3.45%, of inbreed animals had inbreeding coefficients greater than 5%, with a maximum inbreeding coefficient of 38%. Overall mean (±SD) of 305-d milk, fat and protein yields were estimated to be 7812 (±1780), 252.5 (±64.5), and 247.8 (±50.6) kg, respectively. The 305-d milk, fat and protein yields decreased by -19 (±3.7), -0.7 (±0.13), and -0.43 (±0.13) kg per lactation for each 1% increase in inbreeding, respectively. Inbreeding showed no significant impact on fat and protein percentages. تفاصيل المقالة

The aim of this study was to investigate the effect of milking frequency (three times daily vs. two times daily) on the lactation curve shape, partial and 305-d lactation performance in Holstein dairy cows in Iran. Data from February 2000 to December 2012 comprising 217345 lactations on 141364 cows distributed in 324 herds collected by the Animal Breeding Center of Iran were used. The mean milking frequency was 2.88 (0.32) times and increased from 2.72 (0.004) times in 2000 to 2.97 (0.002) times in 2012. The shape of the lactation curve for cows milked thrice daily tended to be higher and flatter than that for those milked twice. The first parity cows milked twice daily had a significant lower days in milk (DIM) until peak (79.52 (0.49) days) than those milked thrice (88.66 (0.28) days). In all parities except for parity ≥ 4, lactation persistency was higher in the cows milked thrice daily than in those milked twice. The percentages of increase in 305-d milk yield due to increasing milking frequency from two times to three times daily, were 12.34, 14.02, 12.79 and 14.76% for cows in parity 1 to parity ≥ 4, respectively. The 305-d milk yield was higher by 959 (28.89), 1175 (32.7), 1099 (38.6) and 1271 (45.0) kg for cows milked thrice daily than those milked twice in parity 1 to parity ≥ 4, respectively. The corresponding values for the 305-d fat yield were 4.35 (0.98), 16.68 (1.11), 17.19 (1.28) and 18.76 (1.51) kg. Based on the results of this study, it can be concluded that increasing milking frequency not only increased milk yield but also improved the initial yield, peak yield and lactation persistency. تفاصيل المقالة

The objectives were to estimate (co)variance components and genetic parameters for lactation curve traits in Holstein dairy cows in Iran. The used data were records on Holstein cows collected during January 2003 to December 2012 by the Animal Breeding Center of Iran (Karaj, Iran). In order to describe the lactation curve, an incomplete gamma function was fitted to 691200 test-day records on 96263 lactations, 377696 test-day records on 52168 lactations, and 182143 test-day records on 24951 lactations for the first three parities, respectively. Lactation curve traits that were analyzed included a scaling factor associated with initial yield, the inclining and declining slopes of the curve, peak time, peak yield, 305-d milk yield and a lactation persistency measure derived from the incomplete gamma function. The estimated heritability of lactation curve traits for the first, second and third lactation ranged from 0.012 to 0.29, 0.017 to 0.15, and 0.02 to 0.13, respectively. Genetic correlations among lactation curve traits for the first, second and third lactation ranged from -0.68 to 0.99, -0.84 to 0.98 and -0.90 to 0.94, respectively. The estimated repeatability of lactation curve traits ranged from 0.07 to 0.40. The moderate to large positive genetic correlations of 305-d milk yield with initial yield, peak yield and lactation persistency suggest that one of these traits could be used as a selection criterion to improve all four traits. However, the peak yield and 305-d milk yield were more heritable than lactation were persistency and initial yield. تفاصيل المقالة

78 Ghezel and 76 Mehraban sheep were used to evaluate the effect of fat-tail docking on reproductive performance. Within two days after birth the tails of 32 Ghezel female lambs and 28 Mehraban female lambs were docked using a tight rubber ring. The lambs were allowed to reproduce for three lambing opportunities and their reproductive performances were evaluated. The effect of docking on the fertility (ewe lambing per ewe exposed), litter size (lambs born per ewe lambing) were evaluated employing a multivariate logistic regression procedure, through the inclusion of tail docking in a 2-way interaction with breed, the fixed effect of parity and the random effect of the ewe. The results showed that the interaction of docking and breed significantly impacted fertility rate (P<0.05). In Ghezel ewes, docking reduced fertility [odds ratio (OR) (95%confidence interval (CI))= 0.29 (0.11-0.79) for docked vs. undocked Ghezel ewes]. Docking had no effect on fertility in Mehraban ewes [odds ratio (OR) (95% confidence interval (CI))= 1.19 (0.38-3.71) for docked vs. undocked Mehraban ewes]. The interaction effect of docking and breed had no impact on litter size, lamb birth weight and lamb weaning weight. تفاصيل المقالة