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The effects of static magnetic field on tibia measurements, blood parameters and performance of day-old Hay-Line W-36 were investigated.A total of 180 fresh fertilized egg weighed and randomly assigned to 6 treatments namely, without and 5 static magnetic fields of 4, 5, 6, 7.5 and 10 μT (micro tesla) density. For implementation of treatments, magnets with dimensions of 0.36­3636 cm and 4000 μT density (40 G) were used. Treatments were implemented on 5, 7, 9, 11 and 15 days of incubation. Each egg was as a replicateunder complete randomized design. After hatching and weighting, 15 day-old birds were slathered from each treatment. Tibiae bone for characteristics and mechanical properties were separated. Tissue slices were prepared and width of epiphyseal plate in proximal and distal epiphysis were measured by motic software. In this study, in spite of similar weight of eggs (p>0.05), weight of day-old chicks in 10 μT treatment was significantly lower (p<0.05) than the control and 6 μT treatments. The percentage of hatchability and mortality were not affected by all treatments (p>0.05), but with the exception of 4 μT treatment, hatchability of the other treatments were marginally higher (p>0.05) than the control. The length of tibiae bone of 6 μT treatment was significantly increased (p<0.05), nonetheless, no significant difference was observed in bone density and mechanical strength parameters. The results of this study show that 6 μT treatment caused to improvement in hatching weight, increasing of epiphyseal plate and tibiae length.

In this research a random regression test day model was used to estimate genetic parameters and genetic trend for 305-day milk yield in Iranian Holsteins. A total of 171360 monthly test day milk records obtained from 34257 first lactation Iranian Holstein cattle (three times a day milking) distributed in 96 herds and calved from 1999 to 2008, were used. The fixed effects of province-herd- year-season of test day as contemporary group and age at calving and Holstein gene percentage as covariates were fitted in the model of analysis. Orthogonal Legendre polynomial up to order 3 was implemented to take account of genetic and environmental aspects of milk production over the course of lactation. The results showed that average of heritability estimates for the second half of lactation period was higher than that of the first half. The heritability estimate for the first month was lowest and for the eighth and ninth months of the lactation were the highest compared to the other months of lactation. The genetic correlations between monthly test day records decreased by increasing the distances between months of lactation. Linear regression of estimated breeding values on calving year was used to estimate genetic trend. Estimated genetic trends for sires and dams for milk yield were 25.13 and 15.45 kg per year, respectively. In this research, genetic trends were estimated by a random regression test day model; therefore using this method is the exact way to take account of genetic trend rather than the other ways.