The Application of Recursive Mixed Models for Estimating Genetic and Phenotypic Relationships between Calving Difficulty and Lactation Curve Traits in Iranian Holsteins: A Comparison with Standard Mixed Models

محورهای موضوعی : Camel

م.س. مختاری ¹ , م. مرادی شهربابک ² , ا. نجاتی جوارمی ³ , گ.جی.ام روزا ⁴

1 - Department of Animal Science, Faculty of Agriculture, University of Jiroft, Jiroft, Iran
2 - Department of Animal Science, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
3 - Department of Animal Science, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
4 - Department of Animal Science, University of Wisconsin-Madison, Madison, WI 53706, USA

تاریخ دریافت : 1396/12/11 تاریخ پذیرش : 1397/02/10 تاریخ انتشار : 1397/09/10

کلید واژه: lactation curve, calving difficulty, recursive model, standard model,

چکیده مقاله :

In the present study, records on 22872 first-parity Holsteins collected from 131 herds by the Animal Breeding and Improvement Center of Iran from 1995 to 2014 were considered to estimate genetic and phenotypic relationships between calving difficulty (CD) and the lactation curve traits, including initial milk yield (Ap), ascending (Bp) and descending (Cp) slope of the lactation curves, peak milk yield (Ym), days to attain peak yield (Tm) and milk persistency (Pers) under recursive mixed models (RMMs) and standard mixed models (SMMs). Recursive mixed models (RMMs) were applied by fitting CD as a covariate for any of the studied lactation curve traits while considering genetic relationships between CD and these traits. The obtained results denoted a statistically significant non-zero magnitude of the causal relationships of CD with Ap and Bp, while the former influencing the latter. The causal effects of CD on Ap and were -0.351 kg and 0.005, respectively. Direct genetic correlations between CD and the studied traits under RMMs and standard mixed models (SMMs) were not statistically different from zero, except for the correlations of CD with Tm; indicating that genes associated with difficult births also increase peak days in milk. Comparison of both models by the deviance information criterion (DIC) demonstrated the plausibility of RMMs over SMMs for studying the relationships of CD with Ap and Bp while SMMs performed better for estimating the relationships of CD with Cp, Ym, Tm and Pers.

چکیده انگلیسی:

در پژوهش کنونی رکوردهای 22872 رأس گاو هلشتاین شکم نخست که طی سال‌های 1384 تا 1393 توسط مرکز اصلاح نژاد و بهبود تولیدات دامی کشور در 131 گله جمع­ آوری شده بودند برای تخمین همبستگی ­های ژنتیکی و فنوتیپی بین سخت ­زایی و صفات منحنی شیردهی شامل تولید شیر اولیه، شیب­ های افزایشی و کاهشی منحنی شیردهی، تولید در اوج شیردهی، تعداد روز لازم برای رسیدن به اوج شیردهی و تداوم شیردهی تحت مدل‌های مختلط یک طرفه و استاندارد استفاده شدند. مدل­ های مختلط یک طرفه با در نظر گرفتن سخت ­زایی به عنوان کواریت هر یک از صفات منحنی شیردهی و نیز در نظر گرفتن وجود همبستگی ژنتیکی بین سخت ­زایی و این صفات برازش گردیدند. نتایج به دست آمده بر وجود روابط علّی معنی‌دار‌ از طرف سخت­زایی بر تولید شیر اولیه و شیب افزایشی منحنی شیردهی دلالت داشتند. اثرات علّی سخت ­زایی بر تولید شیر اولیه و شیب افزایشی منحنی به ترتیب 0.351- کیلوگرم و 0.005 بودند. همبستگی ژنتیکی مستقیم بین سخت ­زایی و صفات منحنی شیردهی به جز تعداد روز لازم برای رسیدن به اوج شیردهی تحت هر دو مدل مختلط یک طرفه و استاندارد از لحاظ آماری تفاوت معنی‌داری با صفر نداشتند که نشان می‌دهد ژن‌های مرتبط با سخت­زایی تعداد روز لازم برای رسیدن به اوج شیردهی را نیز افزایش می‌دهند. مقایسه هر دو مدل با معیار انحراف از اطلاعات (DIC) برتری مدل‌های مختلط یک طرفه بر مدل‌های مختلط استاندارد را در مطالعه روابط بین سخت­زایی با تولید شیر اولیه و شیب افزایشی منحنی شیردهی نشان داد در حالیکه مدل‌های مختلط استاندارد در بررسی روابط سخت ­زایی با شیب کاهشی منحنی شیردهی، تولید در اوج شیردهی، تعداد روز لازم برای رسیدن به اوج شیردهی و تداوم شیردهی عملکرد بهتری داشتند.

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