Effect of length of productive life on genetic trend of milk production and profitability: A simulation study

Longevity is an important economic trait in dairy cattle. Including this trait in a breeding scheme, increases profit. The aim of this study was to evaluate the relationship between length of productive life (LPL), genetic trend of milk production and profitability of herds. LPL has been defined as time from first calving to culling.A Dynamic stochastic model was used to simulate dairy herd system. This model consisted of biological characteristics such as reproduction, genetic and economic components. Both discrete (time-oriented) events such as freshening and breeding as well as continuous processes such as milk production and feed consumption were simulated individually for each animal. The basiccharacteristics of the animal component included pedigree, genetics, age at calving, number of service per conception, number of lactations and LPL. Other characteristics included time-oriented characteristics such as weight, age, physiological status, lactation stage, open days, pregnancy days,estrus cycle, service date and feed requirements. The herd was described as several animal groups: young stock (<1 year old), heifers (>1 year old) and several groups of lactating and dry cows. Increasing mean LPL of herd from 35 to 65 months over 20 years resulted in decreased herd genetic merit of milk from 2025 to 1751 kg and mean of herd genetic trend per year was decreased from 101.24 to 87.56 kg, because of increased generation interval. Increasing LPL resulted in increased profit. Increasing LPL was associated with decreased costs for raising replacement heifers and sale of surplus heifers increased. The ratio of cumulative discounted profit (CDP) for herds with 40, 45, 50, 55, 60 and 65 months of LPL to the lowest level of LPL (35 month), were 1.22, 1.43, 1.55, 1.68, 1.79 and 1.90respectively across time

The impact of information quantity and strength of relationship between training set and validation set on accuracy of genomic estimated breeding values

Recent advances in genomic selection are a revolution in animal breeding. A genome consisting 10 chromosomes each with 100 cM in length with 100 equally spaced markers (1 cM) were simulated. After 50 generations of random mating in a finite population (Ne = 100) in order to create sufficient linkage disequilibrium, population was expanded to two different population sizes of 500 and 1000. This structure was conserved until generation 59. Only females of generations 51 to 58 had phenotypicrecords and were included in the training set. The generation 59 was assumed as juveniles without any phenotypic records (validation set). Two measures of heritability (h2 = 0.1 and h2 = 0.5) were considered.Each simulation was replicated 10 times and results were averaged across replications. The results showed that using individuals of more recent generations in training set led to higher accuracy of genomic estimated breeding values (GEBVs) than individuals from more distant generations. However, increase in the amount of phenotypic records in training set even from individuals of older generations will increase accuracy of GEBVs. Number of phenotypic records in training set was shown to haveimportant role in accuracy of GEBVs especially for low heritability traits

Effect of transient postpubertal hypo- and hyperthyroidism on reproductive parameters of Iranian broiler breeder hens

One hundred and thirty two 26-week-old broiler breeder hens were randomly assigned into one of three treatments as control, hypothyroid (HYPO; propylthiouracil (PTU)-treated) or hyperthyroid (HYPER;thyroxine (T4)-treated) group. PTU and T4 were administered between weeks 30 and 33 of age. Blood sampling was started at week 29, and repeated every week until week 35, coinciding with weekly bodyweighing. Using ELISA, plasma levels of T3, T4 and estradiol were assayed. Egg number, fertility, hatchability, grading of day-old chicks and embryonic developmental stage of unhatched eggs weredetermined for individual artificially inseminated hen. Effects of PTU and T4 treatment on plasma T4 levels were significant (P 0.05). In conclusion, among the different reproductive parameters in this study, hatchability and weekly egg production werethe most responsive parameters to decreased or increased plasma thyroid hormone levels, respectively