Genetics of Lifetime Reproductive Performance in Italian Heavy Draught Horse Mares.

Roberto Mantovani,Fabio Folla,Cristina Sartori,Giuseppe Pigozzi,Shogo Tsuruta

doi:10.3390/ani10061085

Abstract

Simple SummaryFertility is a very important fitness trait in animal production because of its significant economic importance, particularly in species with low reproductive efficiency. For this reason, it should be included as a breeding objective, particularly in horses, where the trait has received less interest than in other species. In this study, we attempted to identify a variable able to detect the lifetime reproductive performance of Italian Heavy Draught Horse (IHDH) mares and to analyze its possible implementation for breeding purposes, with the final aim to increase mares’ fertility efficiency. A phenotypic variable to be used early in life (at least after 3 breeding seasons) has been identified and validated in the study and its genetic component estimated. Results obtained indicated the proposed phenotypic measure of fertility as a good predictor of the lifetime reproductive success in IHDH mares and the variable showed high heritability (that is, the transmittable genetic component) for a fitness trait. Therefore, the use of the lifetime fertility rate proposed in this study for breeding purposes seems feasible, although some limitations could occur in the accuracy of individual breeding value estimates of mares and stallions.Our aims were to find a phenotypic variable to express mares’ lifetime reproductive performance after 6 breeding seasons (BS) in Italian Heavy Draught Horse breed (IHDH), and to estimate its heritability. At first, 1487 mares in a training dataset were used to implement and validate a set of predictive coefficients (LFR-C) or equations (LFR-E) to estimate a lifetime foaling rate (LFR) after 6 BS, i.e., the number of foals generated divided by the opportunities to do so. Then, 3033 mares in a dataset with at least 3 registered BS, was used to estimate LFR for mares with 3, 4, or 5 registered RS. This dataset contained actual (n = 1950) and estimated (n = 1443) LFR, obtained by LFR-C, and LFR-E; Arcsine transformation of LFR-C and LFR-E were also analyzed in single trait animal models to estimate heritability. Overall, the LFR showed a moderate but significant genetic variation, and the heritability of the trait was high (0.24) considering it is a fitness trait. The arcsine transformation of LFR did not show any improvement of heritability. The present study indicates the possible use of a linear LFR variable for breeding purposes in IHDH breed considering both complete and incomplete reproductive careers.

Highlights

Fertility has a well-recognized role in animal production for its implication on the economic efficiency of the whole productive system, independently from the species considered [1,2,3]
The present study indicates the possible use of a linear lifetime foaling rate (LFR) variable for breeding purposes in Italian Heavy Draught Horse (IHDH) breed considering both complete and incomplete reproductive careers
From a genetic point of view, Ponzoni et al [22] confirmed the better results obtainable through the use of a lifetime fertility trait as the calving rate, in comparison to a trait related to a breeding season like the calving date

Summary

Introduction

Fertility has a well-recognized role in animal production for its implication on the economic efficiency of the whole productive system, independently from the species considered [1,2,3]. Following the review of Cammack et al [21], focused on heritability of reproductive traits in beef cattle, there is no easy definition for fertility traits This fact depends on a large number of factors affecting the reproduction success in both sexes. Some deficiencies can be attributable to the use of lifetime fertility traits, the large amount of time necessary to estimate individual breeding values [4,22], delaying selection choices, and reducing genetic progress For this reason, and for the greater economic value of the calving date, this latter trait has been suggested as more suitable for breeding for fertility in beef cattle. The gestation length in mares can lead to unwanted absence of conception (i.e., open mares) [16], increasing the possible number of missing information on subsequent breeding seasons

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