Non-genetic effects affecting fertility traits in local Reggiana cattle

Abstract

Submitted 2020-07-24 | Accepted 2020-09-22 | Available 2020-12-01 https://doi.org/10.15414/afz.2020.23.mi-fpap.338-346 The objectives of this study were to investigate non-genetic sources of variation of fertility in Reggiana cattle and identify the best model for future genetic analysis. Moreover, the variation of target fertility traits in the different parities and months of first service was evaluated. The investigated fertility traits were interval between calving and first insemination, interval between calving and conception, number of inseminations per conception, and calving interval. The dataset included 22,731 records of 10,502 cows, collected between 1986 and 2019. Four different models were tested: Model 1 included the fixed effects of herd-year-month of first service and parity; Model 2 separately accounted for herd-year and month of first service, in addition to parity; Model 1a and Model 2a were Model 1 and Model 2 with the addition of the effect of age at first insemination. Model 1 had an average coefficient of determination of 0.40 for the traits, and this value increased to 0.48 in Model 1a. Moving to Models 2 and 2a, the coefficient of determination dropped to average values of 0.21 and 0.27, respectively. Regarding the effect of month of first service, the best fertility performances were observed in March and April, whereas for parity effect the best performance was in third lactation. Model 1a presented the best R2 for all studied traits but data editing for age at first insemination was too strict. On the other hand, in Models 2 and 2a variance absorbed by fixed effects was low, and this resulted in potentially biased estimates. Model 1 was therefore the best trade off between data loss and predictivity. Keywords: fertility, local cattle, Reggiana, source of variation, modelling References Cavestany, D. et al. (1985). Effect of season and high environmental temperature on fertility of Holstein cattle. Journal of Dairy Science, 68(6), 1471–1478. https://doi.org/10.3168/jds.S0022-0302(85)80985-1 Forabosco, F., Mantovani, R. and Meneghini, B. (2011). European and Indigenous Cattle Breeds in Italy. Schiel & Denver Publishing Limited. Retrieved from https://books.google.it/books?id=BiA0YAAACAAJ Gandini, G. et al. (2007). Comparing local and commercial breeds on functional traits and profitability: The case of Reggiana dairy cattle. Journal of Dairy Science, 90(4), 2004–2011. https://doi.org/10.3168/jds.2006-204 Gonzalez-Recio, O. and Alenda, R. (2005). Genetic parameters for female fertility traits and a fertility index in Spanish dairy cattle. Journal of Dairy Science, 88(9), 3282–3289. https://doi.org/10.3168/jds.S0022-0302(05)73011-3 Groen, A. F. et al. (1997). Economic values in dairy cattle breeding, with special reference to functional traits. Report of an EAAP-working group. Livestock Production Science, 49(1), 1–21. https://doi.org/10.1016/S0301-6226(97)00041-9 R Core Team. (2017). R: A Language and Environment for Statistical Computing. Vienna, Austria. Schaeffer, L. R. (2018). Necessary changes to improve animal models. Journal of Animal Breeding and Genetics, 135(2), 124–131. https://doi.org/10.1111/jbg.12321 Tiezzi, F. et al. (2012). Genetic parameters for fertility of dairy heifers and cows at different parities and relationships with production traits in first lactation. Journal of Dairy Science, 95(12), 7355–7362. https://doi.org/10.3168/jds.2012-5775 Tiezzi, F. et al. (2011). Genetic analysis of fertility in the Italian Brown Swiss population using different models and trait definitions. Journal of Dairy Science, 94(12), 6162–6172. https://doi.org/10.3168/jds.2011-4661 Van Bebber, J. et al. (1997). Accounting for herd, year and season effects in genetic evaluations of dairy cattle: A review. Livestock Production Science, 51(1–3), 191–203. https://doi.org/10.1016/S0301-6226(97)00058-4