<p>Records of Holstein cows from March 1992 to April 2008 from 194 large herds and comprising from 402,716 records for productive traits to 178,344 records of somatic cell count were used to study the effect of calf sex in different parities and calving season on the subsequent productive, reproductive and health traits in Holstein cows. T-test procedure of SAS software was used to investigate the effect of calf sex and season of calving on aforementioned traits. Cows with female calves had higher milk and fat yield, persistency of milk and fat yield and longer lactation length, while cows that gave birth to male calves had shorter calving interval and longer productive life. Also, cows with female calves had higher milk yield per day of lactation in the first two parities, but there was no difference in milk yield per day of lactation for parities ≥ 3. There was no relationship among mean somatic cell count and sex of born calf. Fall calves had the highest adjusted milk yield and milk yield per day of lactation, however, winter calves had the longest lactation lengthand productive life and the highest somatic cell count. Results from this study demonstrate that it seems necessary to consider the effect of calf sex on aforementioned traits when making decision to use sexed semen or conventional semen.</p>

Background: Fertility and health traits, other than production traits, have a major role in the profitability of dairy cattle. Therefore, it seems necessary to include the afore mentioned traits in breeding programs. Hence, genetic parameters are needed to establish breeding plans. Objective: To estimate heritabilities as well as genetic and environmental relationships among total milk yield (TMY), persistency of milk yield (PMY), mean somatic cell count (SCC), mean loge somatic cell count (LnSCC), standard deviation of somatic cell count (stdSCC), and calving interval (CI) using two-trait and multi-trait analyses in Iranian Holstein. Methods: The dataset consisted of 25,883 first lactation records collected from 2002 to 2007 in 97 Holstein dairy herds in Iran. Four criteria of persistency of milk yield (PMY) were calculated using the Wood's gamma function. The WOMBAT1.0 software was used to estimate the (co)variance components using the Average Information Restricted Maximum Likelihood algorithm. Results: Total milk yield (TMY) resulted in the highest heritability estimate (0.29). Heritability estimates for different criteria of persistency of milk yield (PMY) ranged from 0.05 to 0.10. The unfavorable genetic correlation between TMY and calving interval (CI) was 0.71, while that of PMY with CI was 0.46. The estimated environmental correlations were lower than the genetic correlations for all traits, but the trends were generally similar. Conclusion: The results indicate that including PMY in the breeding goals could increase TMY and CI, and decrease somatic cell count (SCC).Keywords: breeding goal, correlation, fertility, heritability, Wood's gamma function. ResumenAntecedentes: Las características de fertilidad y salud, además  de las de producción, tienen un papel importante en la rentabilidad de los hatos lecheros. Por lo tanto, parece necesario incluir los rasgos mencionados en los sistemas de mejoramiento. Por ende, los parámetros genéticos son necesarios para establecer planes de cría. Objetivo: Estimar la heredabilidad, así como las relaciones genéticas y ambientales entre el rendimiento total de leche (TMY), la persistencia del rendimiento lechero (PMY), el recuento medio de células somáticas (SCC), el recuento de células somáticas de loge promedio (LnSCC), la desviación estándar del recuento de células somáticas (stdSCC) y el intervalo de partos (CI) en vacas Holstein mediante análisis de dos rasgos y análisis múltiples. Métodos: Se analizaron registros de primera lactancia de 25.883 vacas Holstein, recolectados entre 2002 y 2007 en 97 rebaños lecheros de Irán. Se calcularon cuatro criterios de persistencia del rendimiento lacteo utilizando la función gamma de Wood. El software Wombat1.0 se utilizó para estimar los componentes de (co)varianza que emplean el algoritmo de máxima verosimilitud restringida de información promedio. Resultados: El rendimiento de leche (TMY) obtuvo la mayor heredabilidad estimada (0.29). Las estimaciones de heredabilidad para diferentes criterios de persistencia del rendimiento de la leche variaron de 0,05 a 0,10. La correlación genética desfavorable entre TMY e intervalo entre partos fue 0,71, mientras que la de PMY con el CI fue de 0,46. Las correlaciones ambientales estimadas fueron inferiores a las correlaciones genéticas para todos los rasgos, pero las tendencias fueron, en general, similares. Conclusión: Incluir el PMY en la meta de cría podría aumentar el TMY y CI, además de disminuir el recuento de células somáticas (SCC).Palabras clave: correlación, fertilidad, función gamma de Wood, heredabilidad, objetivo de cría. ResumoAntecedentes: As características de fertilidade e saúde, além das características de produção, têmum papel importante narentabilidade das vacas leiteiras. Por isso, parece necessário incluir as características já mencionadas nos sistemas de melhoramento genético. Assim, são necessários parâmetros genéticos para estabelecer planos de melhoramento genético. Objetivo: Estimar herdabilidade, bem como as relações genéticas e ambientais entre a produção total de leite (TMY), persistância da produção de leite (PMY), contagem médiade células somáticas (SCC), contagem média de células somáticas loge (LnSCC), desviopadrao da contagem média de células somáticas (stdSCC) e intervalo de pertosem (CI) vacas Holstein por duas análises de características e traços multiplos. Métodos: O conjunto de dados consistiuem registros de 25.883 vacas Holstein de primeira lactação coletadas de 2002 a 2007 em 97 rebanhos leiteiros em Iran. Foram calculados quatrocritérios de persistência da produção de leite utilizando a função gama de Wood. O software Wombat1.0 foi usado para estimar os componentes de (co)variância que empregam o algoritmo de máxima verossimilhança com informações restritas. Resultados: A maior herdabilidade (0.29) foi estimada para produção de leite. As estimativas de herdabilidade para diferentes critérios de persisténcia da produção de leite variaram 0,05 a 0,10. A correlação genética desfavorável entre o intervalo TMY eo intervalo de parto foi de 0,71 enquanto que a de PMY com CI foi de 0,46. As correlações ambientais estimadas foram inferiores às correlações genéticas para todos os traços, mas as tendencias foram geralmente semelhantes. Conclusão: Os resultados indicaram que a inclusão de PMY na meta de reprodução poderia aumentar TMY e CI, no entanto, diminuir a contagem de células somáticas.Palavras chave: correlação, fertilidade, função gama do Wood, herdabilidade, objetivo de criação.

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The objective of this study was to estimate genetic parameters including repeatability, heritability as well as genetic and environmental relationships between 305-day milk yield, milk fat and protein yield (Fat and Pro), milk fat and protein percentages (Fat% and Pro%), mastitis (Mast), number of mastitis occurrence and different measurements of somatic cell counts using linear and threshold animal as well as linear and threshold sire models in Holstein cows of Iran. Records of 33851 first lactation Holstein cows from five large dairy herds with calving dates from March 2002 to September 2014 were analysed, using Gibbs sampling methodology. Heritabilities of production traits estimated by linear animal model ranged from 0.14 (Fat%) to 0.29 (Pro%). Generally, udder health traits had low heritability (ranged from 0.005 to 0.10). Estimates of heritability for Mast using linear models were higher than those obtained with threshold models. However, in general estimates of heritabilities using threshold models were higher than those from linear models. There were unfavourable genetic correlations between production traits and Mast, which implies that breeding programs with emphasis on 305-day milk yield will experience deterioration in udder health. Despite low heritability of udder health traits, genetic variability exists for these traits that allow selecting superior animals and increasing resistance to Mast and animal welfare. Considering relatively high ratio of permanent environmental variance for Mast, culling decisions can be made with higher accuracy in order to reduce Mast incidence phenotypically over time.

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