فصلنامه تحقیقات تولیدات دامی
سال یکم شماره 1 (بهار 1391)

In dairy cattle breeding, in addition to milk yield, consideration of other productive and reproductive traits is necessary. In order to determine optimum Holstein inheritance in Iranian crossbred dairy cattle, first lactation records of 4917 crossbred dairy cattle collected by Animal Breeding Center between 1991 to 2007 were utilized. Crossbred cows were consisted of different Holstein inheritance including 12.5, 25, 37.5, 50, 62.5, 75 and 87.5 percent. Phenotypic and genetic (co) variance components for milk yield, fat yield, lactation length and age at first calving were estimated by restricted maximum likelihood using single and multiple traits animal models. Then, a selection index was constructed to combine these traits. Optimum Holstein inheritance based on this index was determined by least squares mean comparisons of the index for different Holstein inheritance and simple linear regression. Results indicated that 87.5 percent Holstein inheritance was the optimum level.

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.

A data set consists of 6,030 weight records of Iran Black sheep (3,051 males and 2,979 females) progeny of 141 rams and 1525 ewes of Iran Black collected during 1973-2010 from Abbas Abad breeding centre, Mashhad were utilized for investigating inbreeding trend and its effect on body weight traits. The traits under consideration were birth weight (BW), weaning weight (WW), weight at 6-month (W6), weight at 9-month (W9), yearling weight (YW) and pre-weaning daily gain (PWDG). Inbreeding coefficient of all animals was computed using CFC software. A mixed linear model was applied for analyzing the data using SAS software. Among the animals, 5,333 (88.44%) were inbred indicating that the effective number of base population might be low. Average (standard deviation) of inbreeding coefficient were found to be 8.78 (6.34) and 9.33 (5.83) % for whole and inbred populations, respectively. Minimum and maximum inbreeding coefficients were 0 and 38.48 %, respectively. In whole population, average (standard deviation) of inbreeding coefficients were 8.75 (6.31) and 8.82 (6.37) % for male and female lambs, respectively. The corresponding figures were 8.69 (6.25) and 8.90 (6.37) % for single and twin lambs, respectively. Inbreeding depression was detected for WW, W3, W6, W9 and YW in twin males, for BW in twin females, and for W9 in twin females. Annual trends of inbreeding coefficient were 0.2022 and 0.1632 % for whole and inbred animals which were found to be statistically significant (P<0.0001).

The present study was attempted to produce MAS software. This software uses a combination of quantitative and molecular information for the prediction of breeding values. Some genes that control a trait have major effects comparing with others. These genes are called major genes which are located on QTLs (quantitative trait loci). Our understanding on inheritance pattern of QTL can be helpful in selection programs via marker assisted selection (MAS). This provides an opportunity to increase the genetic progress of domestic animals by MAS. The marker assisted selection performance are based on an index, consists of phenotypic and molecular markers data. The MAS software based on mixed model methods (MMM) was established with the C# programming language. This software designed based on animal models with matrix form for predicting breeding values. To identify polymorphism in promoter region of DGAT1 gene, DNA was extracted from blood samples, the PCR process performed on DNA samples. Allelic and genotypic frequencies of animals were characterized. MASS software was used for the prediction of breeding values for 80 male lambs of Afshari sheep in research-education farm of Zanjan University. To compare the results, analyses were also performed using SAS software. Comparing the predicted breeding values obtained from MAS software and SAS indicated the effect of molecular marker in selection based on the combination of molecular and phenotypic information.

Days dry affects especially on milk production and reproduction. Persistency of high milk production cows increases income over feed cost per cow per day of calving interval. Also a shorter dry period reduces the frequency of diet change and facilitates nutrition management. Effect of length of days dry on productive performance of Holstein cows in Yazd province was studied by 1780 records of dairy herds of Yazd province. Strategy of shortening days dry from 60-d to 40-d increases 8% in income over feed cost per cow per day of calving interval in Yazd province. This result suggests increases in the efficiency of milk production especially in hot and dry areas.

Metritis as one of the substantial disorder is one of the major diseases in dairy farm. The purpose of this study was to evaluate the detrimental effects of metritis on a dairy farm complex in Guilan province. Data from years 2000 to 2004 was analyzed using logistic regression procedure. In this research, rate of metritis during the study period was 19.99 %. Results indicated that year and herd significantly affected the incidence of metritis (P<0.01). This rate was highest in year 2002 and for the herd of number 1. The sex and season had not significant effects on the incidence of metritis (P>0.05). Also metritis had a significant effect on mean milk yield by five months after parturition (P<0.01). The average milk yield in dairy cows that affected by metritis and cows without metritis were 20.73 and 21.76 kg, respectively. Furthermore, metritis had a significant effect on some of the reproductive parameters (P<0.01) and the average of days open in the cows with metritis was 17.82 day greater than the cows without metritis. Also, the average of interval from calving to first insemination was 6.33 days greater than cows without metritis. Metritis had not significant effect on services per conception (P >0.05). It is concluded that effects of herd and year on metritis and effects of metritis on mean milk yield and days open were effective.

This research was aimed to determine the lactaction performance and to study the animal behavior during milking in Raienian Cashmere goat using machine milking. The test-day milk records started at first week of lactation and then test-day milk records was recorded every two week and continued up to two months of lactation. The procedure used for the analysis of the test-day milk yield, milking rate and milking time was MIXED model and for animal behavior during milking was categorical data and generalized linear models (CATMOD) in the SAS software. Average milk yeild was 787.16 gr per day two months lactation. The peak of milk yield was in the fifth week in lactation and mean (±SE) of test-day milk yield in the peak yeild was 909±24 gr per day. The parity, latter size, stage of lactation, animal and animal weight had significant effects on test-day milk yield (P<0. 05). The stage of lactation and animal have significant effects on milking rate and milking time (P<0. 05). The stage of lactation and parity had significant effects on animal behavior during milking (P<0. 05). mean (±SE) of test-day milk yield in the peak yeild was 909±24 gram per day. Mean (±SE) of test-day milk yield for goats with two kids and goats with single kids were 856±38 and 738±26 gr per day, respectively. mean (±SE) of test-day milk yield for goats of first lactation and goats of second lactation were 727±37 and 871±30 gram per day, respectively. Average of milking rate and milking time of goats were 9.69 gr/sec and 87.35 sec, respectively.