Inbreeding Effects on Reproductive Traits of Mehraban Sheep

Inbreeding effects on reproductive traits were measured in Mehraban sheep using 10275 lambing records (1994-2011) from the Breeding Station of Mehraban sheep (Hamedan Province, Iran). The reproductive traits were litter size at birth per ewe lambing (LSB), litter size at weaning per ewe lambing (LSW), total litter weight at birth per ewe lambing (TLWB), total litter weight at weaning per ewe lambing (TLWW), litter mean weight per lamb born (LMWLB) and litter mean weight of lambs at weaning (LMWLW). Inbreeding depression was estimated by the Reg procedure of SAS. Inbreeding of all animals was calculated by INBUPGF90 program. All animals were grouped into two classes according to their inbreeding coefficients: the first class included non-inbred animals (F=0); and the second class included inbred animals (F>0). In different inbreeding classes, the LSW and LMWLB showed significant differences (P<0.05), but there were no significant differences in LSB, LMWLW, TLWB and TLWW traits. The regression coefficients of LSB, LSW, LMWLB, LMWLW and TLWW on lamb inbreeding were estimated to be 0.13±0.01, 0.36±0.02, -7.79±0.54, 38.01±4.80 and 108.89±14.18 (P<0.01), respectively. The results showed that effect of inbreeding on reproductive traits in this breed was very pronounced in the flock. Both positive and negative inbreeding effects were found in the current study. However, planned matings would avoid accumulation of inbreeding and appearance of its deleterious effects

Effect of Somatic Cell Count on Milk Yield in Diff erent Parities and Stages of Lactation in Holstein Cows of Iran

The objective of this study was to investigate the relationship between somatic cell score (SCS) and milk yield in different stages of lactation for cows in different parities. Records between June 2003 and January 2014 from 209,781 cows in lactations one to nine in 845 herds, comprising 2,500,407 monthly test-day (TD) records extracted from the animal breeding center, were used. The MIXED procedure of SAS software was used to investigate the effect of SCS on milk yield in different stages of lactation. Defined model considered herd, year-season of calving, month of TD, weeks in lactation and previous dry period length as fixed effects and calving age and SCS as covariate. Lactations were divided into six stages and analyses were performed within each stage. Also, different lactations were analyzed separately. The amount of daily milk yield loss associated with increased SCS was higher with increased number of parity and also later in lactation (especially after peak in week nine). The regression coefficient for milk yield on SCS was -0.539 to -0.635 in different stages of lactation in first parity cows, while that was between -0.777 to -1.053 in third lactation cows

Modelling the biological aspects of broiler breeding: integrated and non-integrated systems

The objective of present study was to derive the economic values for important traits   in broiler breeding program and to specify their sensitivity to production circumstances, using a deterministic bio-economic model, reflecting an integrated or non-integrated broiler chicken’s production system. Model focuses on multiplier breeder, hatchery, commercial grower and processor stages. The estimated economic values ranged from -0.2035 to 0.2318 for both integrated and non-integrated systems. The estimated economic values based on non-integrated system were higher than those of integrated system except for hatching   egg number (0.0009 vs. 0.0014), mortality (-0.0078 vs. -0.0068) and wings yield (0.0206 vs. 0.0158). In integrated situation, the effect of changes in the mean of hatching egg number, finishing weight and mortality on the economic values of traits was examined. The results showed that hatching egg number did not affect the economic values of traits at the preceding stages. On the other hand, changes in traits at the commercial grower, namely finishing weight and mortality affected the economic values of traits at both commercial grower and processor stages. The results of sensitivity analysis (± 20%) showed that traits at the multiplier and hatchery stages were sensitive to changes in feed costs at rearing and laying periods and also changes in the price of parental stock chicks, but the traits relating to commercial stage did not show any sensitivity to these factors. Among different factors, feed cost in commercial stage had the most impact on economic values of finishing weight, feed consumption and mortality

Estimação de parâmetros genéticos para produção de leite no dia do controle em búfalas Khuzestan

The objective of this work was to estimate covariance functions for additive genetic and permanent environmental effects, as well as to obtain genetic parameters for buffalo test‑day milk yield using random regression models on Legendre polynomials (LPs). A total of 2,538 test‑day milk yield (TDMY) records from 516 first lactation records of Khuzestan buffalo, calving from 1993 to 2009 and belonging to 150 herds located in the state of Khuzestan, Iran, were analyzed. The residual variances were modeled through a step function with 1, 5, 6, 9, and 19 classes. The additive genetic and permanent environmental random effects were modeled by LPs of days in milk using quadratic to septic polynomial functions. The model with additive genetic and animal permanent environmental effects adjusted by cubic and third order LP, respectively, and with the residual variance modeled through a step function with nine classes was the most adequate one to describe the covariance structure. The model with the highest significant log‑likelihood ratio test (LRT) and with the lowest Akaike information criterion (AIC) and Bayesian information criterion (BIC) was considered to be the most appropriate one. Unexpected negative genetic correlation estimates were obtained between TDMY records of the twenty‑fifth and thirty-seventh week (‑0.03). Genetic correlation estimates were generally higher, close to unity, between adjacent weeks during the middle of lactation. Random regression models can be used for routine genetic evaluation of milk yield in Khuzestan buffalo.O objetivo deste trabalho foi estimar funções de covariância para efeitos aditivos genéticos e efeitos ambientais permanentes, bem como obter parâmetros genéticos para produção de leite de búfalas no dia do controle, por meio de modelos de regressão aleatória com polinômios de Legendre (LPs). Foram analisados um total de 2.538 registros da produção de leite no dia do controle (PLDC) obtidos de 516 registros de primeira lactação de búfalas Khuzestan, com parições entre 1993 e 2009, pertencentes a 150 rebanhos localizados no Estado do Kuzestão, Irã. As variâncias residuais foram modeladas por uma “step function” com 1, 5, 6, 9 e 19 classes. Os efeitos genéticos aditivos e os efeitos aleatórios ambientais permanentes foram ajustados por LPs, para os dias em lactação, por meio de funções polinomiais quadráticas até de sétimo grau. O modelo com efeitos aditivos genéticos e efeitos ambientais permanentes animais, ajustado por LP de grau cúbico e de terceira ordem, respectivamente, e com variância residual ajustada por uma função com nove classes foi o mais adequado para descrever a estrutura de covariância. O modelo com maior probabilidade significativa do teste da razão de verossimilhança (LRT) e com menor critério de informação de Akaike e critério de informação bayesiano foi considerado o mais apropriado. Estimativas de correlação genética negativas inesperadas foram obtidas entre os registros de PLDC da vigésima quinta e da trigésima sétima semana (‑0,03). As correlações genéticas geralmente foram mais elevadas, próximo da unidade, entre as semanas adjacentes durante o meio da lactação. Modelos de regressão aleatória podem ser usados para avaliação genética de rotina de produção de leite em búfalas Khuzestan

Genetic evaluation of dystocia and its relationship with productive and reproductive traits in Holstein cows

Background: dystocia is one of the most economically significant secondary traits in dairy cows and has adverse effects on the subsequent survival, health, and performance of mothers and offspring. Objective: the aim of this study was to estimate direct and maternal genetic parameters for calving ease (CE) and its relationship with productive and reproductive traits in Iranian Holstein cows. Methods: data from 1991 through 2011 were collected from the Animal Breeding Center of Iran, and contained 132,831 records of CE, 183,203 records of productive traits including 305-d adjusted milk yield (MY305), 305-d adjusted fat yield (FY305) and 305-d adjusted protein yield (PY305), and 129,199 records of reproductive traits including days open (DO), days to first service (DFS) and calving interval (CI). Univariate and bivariate linear animal models were used for the analysis of traits in two different models on which direct genetic effect (model 1) and direct + maternal genetic effects (model 2) using AI-REML algorithm were included. Results: estimated heritabilities for CE in model 1 were 0.02 in univariate and 0.02-0.03 in bivariate analyses. Direct and maternal heritabilities in model 2 were 0.02 and 0.002 for univariate, and 0.03 and 0.0004-0.006 in bivariate analyses, respectively. Genetic correlations between direct effects of CE with MY305, FY305, and PY305 were -0.99, 0.02 and -0.07 in model 1, and -0.2, -0.02 and -0.13 in model 2, respectively. Conclusion: this study suggested that a selection index that includes both direct and maternal effects should be included in CE breeding programs. , rendimiento productivo, aca lechera.   Resumo Palavras chave: correlação genética, desempenho produtivo, dificuldade de parto, parâmetros genéticos, vaca de leiteria

Comparison of Long-term Genomic Response under Restricted Inbreeding in Conventional and Modern Molecular Breeding Schemes: Review article

Reaction to selection in modern breeding programs has been expanded because of constant changes in the techniques for hereditary assessment. Without genomic data, hereditary assessment should center on amplifying the accuracy of evaluated breeding values (EBVs) and expanding the mean EBV of selected parents so there is no conspicuous chance to increase long-term response. The availability of single nucleotide polymorphism (SNP)-chips introduces new opportunities to optimize short versus long-term response under restricted inbreeding. Whenever frequencies and impacts of alleles underlying trait values can be assessed, an exchange between short and long-term optimum selection policies strategies will appear. Therefore, a technique to discover the optimum index to maximize long-term response is resulting from the weight given to a marker according to its frequency. It is probable that long-term genetic gain of genomic selection will be be improved by Jannink’s weighting (JW) method, in which rare favorable marker alleles are weighted in the selection criterion. The JW technique was spread by including an additional factor to decrease the stress on rare favorable alleles over the time horizon and has been called dynamic weighting (DW). In comparison to unweighted genomic estimate, both DW and JW can improve long- term genetic gain and decrease inbreeding rate

Comparison of the parameters of the lactation curve between normal and difficult calvings in Iranian Holstein cows

To evaluate effect of dystocia on the lactation curve characteristics for milk yield and composition in Holstein cows, six non-linear models (Brody, Wood, Sikka, Nelder, Dijkstra and Rook) were fitted on 5,917,677 test day records for milk yield (MY), fat (FP) and protein (PP) percentages, fat to protein ratio (FPR) and somatic cell score (SCS) of 643,625 first lactation Holstein cows with normal calving or dystocia from 3146 herds which were collected by the Animal Breeding Center of Iran. The models were tested for goodness of fit using adjusted coefficient of determination, root means square error, Akaike’s information criterion and Bayesian information criterion. Rook model provided the best fit of the lactation curve for MY and SCS in normal and difficult calvers and dairy cows with dystocia for FP. Dijkstra model provided the best fit of the lactation curve for PP and FPR in normal and difficult calvers and dairy cows with normal calving for FP. Dairy cows with dystocia had generally lower 100-d, 200-d and 305-d cumulative milk yield compared with normal calvers. Time to the peak milk yield was observed later for difficult calvers (89 days in milk vs. 79 days in milk) with lower peak milk yield (31.45 kg vs. 31.88 kg) compared with normal calvers. Evaluation of the different non-linear models indicated that dystocia had important negative effects on milk yield and lactation curve characteristics in dairy cows and it should be reduced as much as possible in dairy herds

Estimation of genetic parameters and genetic change for stillbirth in Iranian Holstein cows: a comparison between linear and threshold models

Data on stillbirth from the Animal Breeding Center of Iran collected from January 1990 to December 2007 and comprising 668810 Holstein calving events from 2506 herds were analyzed. Linear and threshold animal and sire models were used to estimate genetic parameters and genetic trends for stillbirth in the first, second, and third parities. Mean incidence of stillbirth decreased from first to third parities: 23.7%, 22.1%, and 21.8%, respectively. Phenotypic rates of stillbirth decreased from 1993 to 1998, for first, second and third calvings, and then increased from 1998 to 2007 for the first three parities. Direct heritability estimates of stillbirth for parities 1, 2 and 3 ranged from 2.2 to 8.7%, 0.6 to 5.1% and 0.1 to 3.8%, respectively, and maternal heritability estimates of stillbirth for parities 1, 2 and 3 ranged from 1.4 to 6.3%, 0.5 to 4.2% and 0.08 to 2.0%, respectively, using linear and threshold animal models. The threshold sire model estimates of heritabilities for stillbirth in this study were 0.021 to 0.071, while the linear sire model estimates of heritabilities for stillbirth in the current study were from 0.003 to 0.021 over the parities. There was a slightly increasing genetic trend for stillbirth rate in parities 1 and 2 over time with the analysis of linear animal and linear sire models. There was a significant decreasing genetic trend for stillbirth rate in parity 1 and 3 over time with the analysis of threshold animal and threshold sire models, but the genetic trend for stillbirth rate in parity 2 with these models of analysis was significantly positive. The low estimates of heritability obtained in this study implied that much of the improvement in stillbirth could be attained by improvement of production environment rather than genetic selection.vo

Comparison of the parameters of the lactation curve between normal and difficult calvings in Iranian Holstein cows

To evaluate effect of dystocia on the lactation curve characteristics for milk yield and composition in Holstein cows, six non-linear models (Brody, Wood, Sikka, Nelder, Dijkstra and Rook) were fitted on 5,917,677 test day records for milk yield (MY), fat (FP) and protein (PP) percentages, fat to protein ratio (FPR) and somatic cell score (SCS) of 643,625 first lactation Holstein cows with normal calving or dystocia from 3146 herds which were collected by the Animal Breeding Center of Iran. The models were tested for goodness of fit using adjusted coefficient of determination, root means square error, Akaike’s information criterion and Bayesian information criterion. Rook model provided the best fit of the lactation curve for MY and SCS in normal and difficult calvers and dairy cows with dystocia for FP. Dijkstra model provided the best fit of the lactation curve for PP and FPR in normal and difficult calvers and dairy cows with normal calving for FP. Dairy cows with dystocia had generally lower 100-d, 200-d and 305-d cumulative milk yield compared with normal calvers. Time to the peak milk yield was observed later for difficult calvers (89 days in milk vs. 79 days in milk) with lower peak milk yield (31.45 kg vs. 31.88 kg) compared with normal calvers. Evaluation of the different non-linear models indicated that dystocia had important negative effects on milk yield and lactation curve characteristics in dairy cows and it should be reduced as much as possible in dairy herds