Trop Anim Health Prod (2014) 46:895–899 DOI 10.1007/s11250-014-0571-z

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Genetic correlations between growth and reproductive traits in Zandi sheep Kourosh Mohammadi & Mohammad Taghi Beigi Nassiri & Enayat Rahmatnejad & Rostam Abdollahi-Arpanahi & Seyed Mohammad Reza Hossaini & Saman Hagh Nadar

Accepted: 10 March 2014 / Published online: 6 April 2014 # Springer Science+Business Media Dordrecht 2014

Abstract For the first time, the current study reports the genetic and phenotypic correlations between growth and reproductive traits in Zandi sheep. The data were comprised of 4,309 records of lamb growth traits from 1,378 dams and 273 sires plus 2,588 records of reproductive traits from 577 ewes. These data were extracted from available performance records at Khojir Breeding Station of Zandi sheep in Tehran, Iran, from 1993 to 2008. Correlations were estimated from two animal models in a bivariate analysis using restricted maximum likelihood procedure between lamb growth traits [birth weight (BW), weaning weight at 3 months of age (WW), as well as six-month weight (6 MW)] and ewe reproductive traits [litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW)]. The genetic correlations between BW and reproductive traits varied from low to high ranges from 0.10 for BW–LSB to 0.86 for BW–TLWB. WW was moderately (0.37) to highly (0.96) correlated with all the reproductive traits. Moreover, the genetic correlations were observed between 6 MW and reproductive traits, varied from 0.19 to K. Mohammadi (*) : M. T. Beigi Nassiri : S. M. R. Hossaini Department of Animal Science, Faculty of Animal Science and Food Industries, Khuzestan Ramin Agricultural and Natural Resources University, Ahwaz, Iran e-mail: [email protected] E. Rahmatnejad Young Researchers & Elite Club, Hamedan Branch Islamic Azad University, Hamedan, Iran R. Abdollahi-Arpanahi Department of Animal Science, Faculty of Agricultural Science and Engineering, College of Agriculture and Natural Resources (UTCAN), University of Tehran, Tehran, Iran S. Hagh Nadar Department of Animal Science, Faculty of Agriculture, Islamic Azad University, Borujerd Branch, Khorramabad, Iran

0.95. Relationships between growth and reproductive traits ranged from 0.01 for BW–LSW to 0.28 for BW–TLWB in phenotypic effects. Results indicated that selection to improve WW would have high effect on genetic response in TLWW, and also, these results could be effective for all of the reproductive traits in Zandi sheep. Keywords Genetic correlation . Growth traits . Reproductive traits . Zandi sheep

Introduction Depending on the nutritional and management constrains within a production system, body weights at pre- or postweaning ages may be considered as selection objectives for improvement of carcass weight and characteristics. However, for arid conditions, selection for improvement of body weights will increase requirement for nutrients and animal sensitivities to environmental factors affecting nutrition such as drought. In these situations, net reproduction rate, defined as total weight of lambs weaned that accumulated over the lifetime of an ewe [total litter weight at weaning (TLWW)], has been suggested to be the most economically important trait for the improvement of carcass weight and characteristics (Snyman et al. 1997; Olivier et al. 2001). Nevertheless, before TLWW or other reproductive traits could be proposed as a selection trait, the phenotypic and genetic relationships with growth traits need to be obtained. The Zandi sheep is one of the major indigenous sheep breeds in Iran and adapted to the low land area in the central zone of the country. Historically, this breed has been originated in southern province of Iran, Fars. This breed is known for high grazing ability and resistance to unfavorable climatic conditions. These characteristics make this breed one of the best breeds under migratory system (Tavakkolian 1999). For

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Zandi sheep, no reports on correlations between growth and reproductive traits have been documented in the literature. Hence, the aim of this study was to estimate genetic, phenotypic, ewe permanent environmental, and environmental correlations between growth [birth weight (BW), weaning weight at 3 months of age (WW), and six-month weight (6 MW)] and reproductive [litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB), and TLWW] traits in Zandi sheep that are necessary to develop efficient selection strategies for planning optimal selection programs and improvement of mentioned important traits.

Materials and methods Geographical location and flock management The data used in the current study were collected from the Khojir Breeding Station of Zandi sheep, located between Tehran and Abali at 35° 45′ E longitude and 51° 40′ N latitude with an elevation of 1,547 m above sea level, from 1993 to 2008. Maiden ewes were exposed to rams at about 18 months of age and kept in the flock maximum up to six parities (8 years of age). The rams were used for one to two mating years (3–4 years of age). Rotationally, rams were allocated to each group of ewes in order to avoid inbreeding. The breeding period extended from early October to mid-November (15 ewes were randomly set aside to a ram), and consequently, the lambing season spanned between mid-February and late March. Newborn lambs were weighed at the birth time and/or 24 h afterwards. Coat color is black in newborns but changes into light brown and gray gradually. Weaning occurs at approximately 3 months of age. Flocks were mainly kept on pastures during the day and housed at night. Supplemental feeding comprising dried alfalfa and barely grain was offered during winter season and particularly prior to mating and late pregnancy.

Studied traits The genetic, phenotypic, ewe permanent environmental, and environmental correlations were analyzed between lamb growth traits (BW, WW, and 6 MW) and ewe reproductive traits (LSB, LSW, TLWB, and TLWW). LSB was the number of lambs born alive per ewe lambing within a specific year (1 or 2), and LSW was the number of lambs weaned per ewe lambing within a specific year (0, 1, or 2). TLWB and TLWW refer to sum of the weights of lambs born and weaned per ewe lambed, respectively. The structure of data set used in current study is presented in Table 1.

Trop Anim Health Prod (2014) 46:895–899

Statistical analysis The general linear model (GLM) procedure of SAS (SAS Institute 2002) was applied to identify important fixed effects to be considered in the final models. The statistical models included sex of lamb in 2 classes (male and female), year of birth in 16 classes (1993–2008), age of dam at lambing in 7 classes (2–8 years old), type of birth in 2 classes (single and twin), and age of lamb at 3 and 6 months of age (in days) as a covariate for WW and 6 MW (P

Genetic correlations between growth and reproductive traits in Zandi sheep.

For the first time, the current study reports the genetic and phenotypic correlations between growth and reproductive traits in Zandi sheep. The data ...
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