Genetic analysis of retained placenta and its association with reproductive disorder, production, and fertility traits of Iranian Holstein dairy cows.

To facilitate breeding for improved resistance to the reproductive disorder of retained placenta (RP), genetic parameters were estimated for RP and its genetic correlation with other reproductive disorders as well as with production and fertility traits of Iranian Holstein dairy cows. Data were 154,048 lactation records collected between 2011 and 2018 from 59,610 Holstein dairy cows in 9 Iranian herds. Other reproductive disorders included dystocia, stillbirth, and twinning. Fertility records were available for days from calving to first service (DFS), days open (DO), number of inseminations per conception (NIC), and success of first insemination (SFI). Genetic parameters for RP were estimated using univariate linear and logistic animal models with ASREML software. The univariate linear animal model was used to implement bivariate analysis to investigate potential genetic correlations of RP with other reproductive disorders and with production and fertility traits. Heritability estimates for RP were low from both linear (0.031) and logistic (0.092) animal models. Estimated genetic correlations with RP were -0.04 for twinning, 0.32 for stillbirth, and 0.34 for dystocia, which indicates that selection against RP could indirectly select against dystocia and stillbirth. Estimated genetic correlations between RP and production traits (milk, fat, and protein yields) at 100, 200, and 305 d in milk ranged from -0.12 to -0.29; the greatest correlation (-0.29) was for the first 100 d in milk. A moderate positive genetic correlation (0.25) was found for RP and DO, DFS, and NIC, whereas a low negative genetic correlation (-0.09) was found between RP and SFI. The pedigree-based genetic analysis of RP showed that this trait has a low heritability, is linked to other reproductive disorders, and generally has an unfavorable relationship with production and fertility traits. Selection against RP can reduce the incidence of reproductive disorders and improve fertility and production traits.

Assessing the consequences and economic impact of retained placenta in Holstein dairy cattle.

Retained placenta (RP) is as an important reproductive disorder which adversely affects the economic performance of dairy cows. Understanding the consequences and economic losses associated with RP can persuade dairy farmers to consider it more effectively in their management decisions. Hence, the aims of this research were to assess the effect of RP on production and reproduction attributes as well as economic losses in Iranian Holstein cows. The data was collected from nine Holstein dairy herds in Isfahan province of Iran. The final dataset comprised of 139,508 records of 58,086 cows which calved between March 2011 and December 2018. A linear mixed model was developed to evaluate the effect of RP on individual performance of primiparous and multiparous cows. The economic losses associated with the RP were finally estimated. The average incidence of RP per cow over a year was 12.3% (ranged between 9.0 and 15.4%). 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. However, the fertility performance was less affected by the RP in primiparous compared to multiparous cows. 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. The highest financial losses due to RP were associated with reduction in milk production (38.5% of total loss) and low fertility (28.5% of total loss) had the highest contribution in in primiparous and multiparous cows, respectively. The results of our research highlight the economic importance of improved calving management to reduce RP occurrence in dairy cows.

Farm and cow factors and their interactions on the incidence of retained placenta in holstein dairy cows.

Risk factors for retained placenta (RP), as a common and economically important disorder, have been widely investigated. However, comprehensive studies are rare. Therefore, this study sought to identify herd-cow factors and their interactions on the risk of RP in Iranian dairy herds. 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 in primiparous and multiparous cows. The average rate of RP was 12.3% (9.0-15.4%) at the herd level. The highest rate of RP was recorded in spring compared with other seasons. Regardless of calving season, occurrence of dystocia, stillbirth and twinning increased the odds ratio (OR) of RP. In primiparous cows, occurrence of dystocia and stillbirth increased OR of RP 4.30 and 3.33 times, respectively. In multiparous cows, dystocia, twinning and stillbirth increased OR of RP 4.36, 3.94 and 1.29 times, respectively. Cows with an age at first calving of >28 months had the highest rate of RP compared with other cows. Multiparous and primiparous cows with a short (less than 271 d) and long (more than 281 d) pregnancy, respectively, had the highest risk of RP compared to cows in other groups. Furthermore, 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%. With an interaction analysis, although the potential effect of each factors depends on the effect of other factors, but in general dystocia, stillbirth, an extended age at first calving (>28 months), and calving during the spring increased risk of RP for both groups. In conclusion, identification of risk factors for RP with an interaction analysis can help farm managers to employ the best strategies to reduce the occurrence of this reproductive disorder.