This study sought to: 1) identify herd-cow factors and their interactions on the risk of retained placenta (RP), 2) understanding the consequences and economic losses associated with RP, 3) infer heritability and genetic correlations between RP, reproduction disorders, production and reproduction traits and 4) establish different single or multiple trait selection indices to calculate genetic and economic gains by combining some production, reproduction and health traits in population of Iranian Holstein dairy cows. The data were collected from nine Holstein dairy herds in Isfahan province, Iran. The final dataset included 154,048 records for 59,610 cows which calved between March 2011 and December 2018. A logistic regression model was used to separately analyze the risk factors and their interactions for RP. A linear mixed model was developed to eva‎luate the effect of RP on individual performance of cows, and economic losses associated with the RP were finally estimated by a bio-economic model. Linear and logistic animal models were used to estimate genetic parameters. Finally, The SelAction software was used to perform the analyses based on selection index theory through a deterministic model. The average rate of RP was 12.3% (9.0e15.4%) at the herd level. In primiparous cows, occurrence of dystocia and stillbirth increased OR of RP 4.30 and 3.33 times, respectively. Multiparous cows with an extended dry period length (more than 75 d) and produced milk yield more than 13,000 kg/lactation were at higher risk of RP with an average of 13.5%. ). Each incidence of RP significantly reduced milk, fat and protein yields in primiparous and multiparous cows (P < 0.05). The adverse effect of RP on the milk production was much higher in the cows at the early phase of lactation (i.e. 100-d lactation group) than the cows in mid or late lactation. The estimated production losses (±standard deviation) due to the RP event were 282.1 ± 43.0 and 295.7 ± 40.8 kg per cow for a 305-d lactation period in primiparous and multiparous cows, respectively. . The average of days open increased by 8.3 ± 5.3 and 19.8 ± 7.1 d in primiparous and multiparous cows, respectively. The financial losses associated with RP were on average US$ 350.4 and US$ 481.2 per incidence in primiparous and multiparous cows, respectively, ranged from US$ 311.9 to 456.2 depending on the parity number (primi- or multiparous) and herd management. Estimated heritability (0.09) for RP in threshold model was higher than of heritability (0.031) obtained in linear model. Estimated genetic correlation between RP and milk, fat and protein yield ranged -0.12 to -0.29, which the highest correlation (- 0.29) was related to production in the first 100 days of lactation. Also, a moderate positive genetic correlation99 between days open (DO), days to first service (DFS), number of insemination per conception (NIC) and RP was estimated (about 0.25). Moreover, the economic value of each percent of the occurrence of RP was estimated at -172,500 Rials. The results showed that the use of selection index including production, reproduction, dystocia, stillbirth and RP traits led to a 30.3% improvement in economic response in the objective function compared to the index containing only production traits. Also, the accuracy of the estimate in this case increased from 0.13 to 0.63. Despite the low heritability of RP, the results of our research show that, RP is of high economic importance and also has a moderate genetic correlation with other disorders and reproductive traits. Therefore, using its information in genetic eva‎luation of bulls can play a significant role in improving genetic development and economic response.

علي صادقي سفيدمزگي

سعيد انصاري مهياري، غلامرضا قرباني

عباس پاكدل، محمود وطن خواه، محمدعلي ادريس