Breeding objectives for sheep in Ireland: A bio-economic approach

Nowadays, the fibre diameter (FD) is considered the main selection objective in alpaca populations all over the world. International Committee for Animal Recording recommendations define the FD and its CV as the first two traits to be considered in breeding programmes for this specie. In addition to these main criteria, other selection criteria of economic value used are comfort factor (CF) or standard deviation (s.d.); also other less important traits being used as selection objectives are these morphological traits: density (DE), crimp (CR) or lock structure (LS) for, respectively, Huacaya (HU) and Suri (SU) ecotypes, head (HE), coverage (CO) and balance (BA). The goal of this study was to establish how to implement a combined selection index starting from genetic parameters and to study the expected correlation between genetic trends by considering different alternative procedures of weighting all the involved traits, and the consequences of a wrongly proceeding way. Heritabilities and genetic and phenotypic correlations were estimated from the data set belonging to the PACOMARCA experimental farm for SU and HU. Two approaches were used to check the consequences of a set of subjective weights essayed. The coefficients of selection indexes were obtained for two sets of reference weights. In addition, equivalent weights were drawn if applied those reference values as coefficients of hypothetical selection indexes directly on phenotypes; relative expected genetic responses were computed in different cases. Results showed that almost in all cases for both ecotypes, the weight applied to CF should be surprisingly negative. Concerning genetic responses, only CO was compromised in some cases for the HU ecotype. The essayed methodology allowed explaining the differences between ecotypes in the genetic trends. The proposed methodology was shown to be effective to study the relative importance of the traits granted by the manager of a breeding scheme.

Section: Introductionmentioning

confidence: 99%

Weighting fibre and morphological traits in a genetic index for an alpaca breeding programme

Gutiérrez

Cervantes

Pérez-Cabal

et al. 2014

“…De Vries (1989) divided the growth period of pigs into three stages, assumed linear growth within each segment (growth of piglets till weaning, in rearing and during fattening) and considered mature weight of sows to be a separate trait. These same growth periods were utilised by Houška et al (2004), but they defined weight gain from birth to slaughter as the only growth trait in the breeding objective for pigs.The EVs of growth rate in a specific time period can easily be converted to EVs for alternative traits to characterise growth ability, for example, animal weight at a certain age or animal age at a fixed weight (Coopman et al, 1999;Bett et al, 2007;Byrne et al, 2010;Houška et al, 2010).As shown in this section, growth ability of animals can be described by many different traits. The approaches and assumptions used for the calculation of the EV for a specific growth trait (in particular for mature weight) by different authors are highly variable, having a material impact on the EV of this trait.…”

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confidence: 99%

“…Hirooka et al (1998b) changed the genetic levels of growth and carcass traits in beef cattle proportionally in different sexes and divided the change in biological and economical efficiency by the total change (weighted sum across all categories) of the evaluated trait in the defined system. Wolfová et al (2009) andByrne et al (2010) used average survival rates of female and male lambs at birth or till weaning, taking into account the proportions of singles, twins and so on.In this section, many different approaches for treating repeated performances when calculating the EV of a trait were discussed. The availability of performance records for a trait expressed in different sexes, oestrus cycles or parities and the effects in the model for breeding value estimation for this trait should be decisive when searching for the Economic values of traits in livestock 1407 appropriate definition of repeatedly expressed trait and for a correct approach when calculating its EV.…”

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confidence: 99%

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Strategies for defining traits when calculating economic values for livestock breeding: a review

Wolfová

Wolf

2013

The objective of the present review was (i) to survey different approaches for choosing the complex of traits for which economic values (EVs) are calculated, (ii) to call attention to the proper definition of traits and (iii) to discuss the manner and extent to which relationships among traits have been considered in the calculation of EVs. For this purpose, papers dealing with the estimation of EVs of traits in livestock were reviewed. The most important reasons for incompatibility of EVs for similar traits estimated in different countries and by different authors were found to be inconsistencies in trait definitions and in assumptions being made about relationships among traits. An important problem identified was how to choose the most appropriate criterion to characterise production or functional ability for a particular class of animals. Accordingly, the review covered the following three topics: (i) which trait(s) would best characterise the growth ability of an animal; (ii) how to define traits expressed repeatedly in subsequent reproductive cycles of breeding females and (iii) how to deal with traits that differ in average value between sexes or among animal groups. Various approaches that have been used to solve these problems were discussed. Furthermore, the manner in which diverse authors chose one or more traits from a group of alternatives for describing a specific biological potential were reviewed and commented on. The consequences of including or excluding relationships among economically important traits when estimating the EV for a specific trait were also examined. An important conclusion of the review is that, for a better comparability and interpretability of estimated EVs in the literature, it is desirable that clear and unique definitions of the traits, complete information on assumptions used in analytical models and details on interrelationships between traits are documented. Furthermore, the method and the model used for the genetic evaluation of specific traits in a certain breeding organisation are important for the exact definition of traits, for which the economic values will be calculated, and for the inclusion or exclusion of relationships among traits in the calculation of the EVs in livestock breeding. Keywords: livestock, economic values, definition of traits, relationships among traits ImplicationsA literature review was conducted on different ways of defining traits and considering relationships among them in the calculation of economic values (EVs) in livestock breeding. Diversity among trait definitions makes it difficult to compare EVs from different investigations and individual authors. It was shown that, for the EV of a trait to be correctly interpreted, it is necessary to know exactly how the trait was defined, how its relationships with other traits were accounted for and what assumptions were made in the model for the calculation of EVs. IntroductionHazel (1943) proposed the breeding objective or aggregate genotype of an animal to be defined as 'the sum of its sever...

“…These analyses focus mainly on the impact of changes in economic input parameters (product prices and costs) and on the impact of output or input restrictions (milk or meat quotas, restricted feed resources). See, for example, Kosgey et al (2003), Haghdoost et al (2008) and Byrne et al (2010) in meat sheep and Wolfová et al (2001) and Vargas et al (2002) in dairy cattle. Fewer sensitivity analyses have investigated the influence of performance levels of traits or of management practices on MEVs or on REVs.…”

Section: Impact Of Production Circumstances On Revsmentioning

confidence: 99%

Impact of production strategies and animal performance on economic values of dairy sheep traits

Krupová

Wolfová

Krupa

et al. 2012

The objective of this study was to carry out a sensitivity analysis on the impact of various production strategies and performance levels on the relative economic values (REVs) of traits in dairy sheep. A bio-economic model implemented in the program package ECOWEIGHT was used to simulate the profit function for a semi-extensive production system with the Slovak multi-purpose breed Improved Valachian and to calculate the REV of 14 production and functional traits. The following production strategies were analysed: differing proportions of milk processed to cheese, customary weaning and early weaning of lambs with immediate sale or sale after artificial rearing, seasonal lambing in winter and aseasonal lambing in autumn. Results of the sensitivity analysis are presented in detail for the four economically most important traits: 150 days milk yield, conception rate of ewes, litter size and ewe productive lifetime. Impacts of the differences in the mean value of each of these four traits on REVs of all other traits were also examined. Simulated changes in the production circumstances had a higher impact on the REV for milk yield than on REVs of the other traits investigated. The proportion of milk processed to cheese, weaning management strategy for lambs and level of milk yield were the main factors influencing the REV of milk yield. The REVs for conception rate of ewes were highly sensitive to the current mean level of the trait. The REV of ewe productive lifetime was most sensitive to variation in ewe conception rate, and the REV of litter size was most affected by weaning strategy for lambs. On the basis of the results of sensitivity analyses, it is recommended that economic values of traits for the overall breeding objective for dairy sheep be calculated as the weighted average of the economic values obtained for the most common production strategies of Slovak dairy sheep farms and that economic values be adjusted after substantial changes in performance levels of the traits.