Meta-Analysis of Various Environmental and Genetic Parameters of Fertility-Related Traits in Dairy Cows

Fertility is one of the most important economic traits in dairy cattle breeding which, in addition to negative effects on functional traits such as milk production, reduces the profitability of the dairy cattle breeding industry. Therefore, the aim of this study was to Meta-analyze traits related to fertility in dairy cows and determine an appropriate strategy to control and improve fertility in dairy cows.

For this purpose, by searching in databases, 38 articles related to fertility in different herds of dairy cows were collected and different parameters including additive genetic and residual variance components, heritability, reproducibility, descriptive characteristics of traits including mean, minimum, maximum, coefficient variation, standard deviation as well as genetic correlations between traits that were present in at least three reports were extracted as a new variable and statistically analyzed. The studied traits included age at first service, age at first calving, calving interval, open days, number of services, conception length, the first service leading to conception and non-return rate at 56 days. Data analysis was performed with SAS software version 9.2 and Comprehensive Meta-analysis. Finally, the articles were grouped into four regions of Asia, Africa, America and Europe and different parameters including mean, heritability and reproducibility of different fertility traits were analyzed by SAS software GLM procedure and comparison of mean groups by Turkey’s test at the level 5% probability was done.

Mean of open days, age at first calving, age at first service, calving interval, conception length, first service leading to conception rate, no-conception rate in 56 days and numbers of services for each conception traits were 139.2, 888.3, ​​501.6, 411.8, 278.8 days, 62.8, 21% and 2.1, respectively. Also, the heritability of the mentioned traits was estimated to be 0.06, 0.2, 0.3, 0.06, 0.1, 0.1, 0.07 and 0.08, respectively. The reproducibility of traits were open days, calving interval, first service leading to conception, conception length and number of services per conception were 0.1, 0.1, 0.07, 0.1 and 0.06, respectively. There was a moderate and sometimes high positive and negative genetic correlation between most of the fertility-related traits. The results of comparison of estimates in the four continents of Asia, Africa, Europe and the Americas were not significant in all fertility-related traits.

Therefore, all the mentioned estimates, which in most cases are reliable and close to each other, indicate a low degree of heritability and repeatability of the mentioned traits, and the use of conventional breeding methods cannot determine high genetic value with good accuracy and it is recommended to improve the management of dairy cows and control environmental factors and the use of breeding programs as well as genomic evaluation of dairy cow.