Retained placenta is a common reproductive condition in dairy cows, described as the inability to release foetal membranes within 24 hours following parturition, which increases the risk of uterine infections and infertility.
Due to increased culling risk, poorer reproductive performance, extended calving interval, higher veterinary expenditures, and decreased milk supply, retained placenta causes an estimated financial loss of US$ 150 to US$ 386 per cow every lactation. Previously, the emphasis was mostly on production and conformation qualities, which resulted in diminishing trends in health, reproduction, and lifespan features.
Although retained placenta has a modest heritability of 0.01 to 0.10, long-term selection on this reproductive abnormality may enhance resistance and boost herd profitability.
Risk hazards unique to cows
A lack of immunological function is one of the probable risk factors for retained placenta, since cows with retained foetal membranes have decreased neutrophil activity, which may affect their capacity to evacuate the placenta following parturition. Because of a shortage of dietary carotene, retained placenta is more common in the winter than in other seasons. Furthermore, shorter gestation durations and increasing parity are linked to a greater prevalence of retained placenta.
Retained placenta resistance
The anticipated resistance of dairy cow progeny to retained placenta in a herd with typical management circumstances is represented by resistance to retained placenta predicted transmission ability. The resistance rate is calculated by subtracting the incidence rate from 100. The average resistance rate in US Holsteins is 96%. Daughters of a Holstein bull with a predicted resistance to retained placenta of +2% are expected to have an average resistance rate to retained placenta of 98%, while daughters of a Holstein bull with a predicted resistance to retained placenta of -2% are expected to have an average resistance to retained placenta of 94%.
Furthermore, daughters from the bull with a projected transmitting capacity of -2% are likely to have three times the number of instances of retained placenta as daughters from the bull with a predicted transmitting ability of +2%.
Advantages of Choosing
Because retained placenta is a frequent risk factor for later metritis, improving resistance to retained placenta enhances resistance to metritis. Furthermore, retained placenta keeps the cervix open, which acts as a physical barrier to infection in unaffected animals. Retained placenta postpones uterine involution, lochia evacuation, and endometrial regeneration, and raises the risk of ovarian cystic degeneration, chronic endometritis, and pyometra.
However, the phenotypic occurrence of retained placenta reduces the afflicted dairy cow’s future milk output, and there is an antagonistic genetic association between retained placenta features and milk yield as well. Thus, improving resistance to retained placenta not only decreases the direct and indirect expenses associated with this condition, but it also improves dairy cow health, welfare, and reproductive performance.
Other reproductive problems
The discovery of a genetic link between retained placenta and other reproductive problems simplifies breeding for enhanced resistance to retained placenta. According to a research published in 2022 by Mahnani and colleagues, the estimated genetic connections with retained placenta were -0.04 for twinning, 0.32 for stillbirth, and 0.34 for dystocia. These findings suggest that twinning reduces the likelihood of retained placenta, and that selecting against retained placenta may indirectly select against dystocia and stillbirth.
Furthermore, modest genetic associations between retained placenta and dystocia and stillbirth show that cows that are vulnerable or resistant to retained placenta are genetically more susceptible or resistant to dystocia and stillbirth. The estimated genetic associations between retained placenta and production parameters such as milk, fat, and protein yields varied from -0.12 to -0.29 in this research, indicating that cows with greater output during early lactation are less likely to acquire retained placenta. The researchers also discovered a low negative genetic link (-0.09) between retained placenta and success of first insemination, but a significant positive genetic correlation (0.25) between retained placenta and days open, days from calving to first service, and number of inseminations per conception.
These findings indicate that dairy cows with retained placentas had longer days open, days from calving to first service, a higher number of inseminations per conception, and worse first insemination success. As a result, genetic selection against retained placenta enhances reproductive features.
Genetic regulation
When combined with appropriate management practises, improving disease resistant features via direct genetic selection gives a compelling potential for dairy farmers to better reduce disease incidence and enhance profitability. A helpful on-farm management tool is genomic prediction for health features such as resistance to retained placenta gained at a young age.
Genetically better heifers and cows may be bred with sexed sperm, whereas genetically inferior animals can be sold for meat early or bred with beef sperm. It is advised to assess the accuracy of genetic calculations in predicting the performance of each dairy cow. Furthermore, information gathered from commercial dairy herds may be utilised to correctly predict resistance features in dairy cows.
Conclusion
Retained placenta is a costly condition that impacts the health, welfare, and profitability of 7.8% of US dairy cows. To enhance dairy cow health, welfare, and performance, the genetic study of retained placenta and its relationship with other reproductive diseases, fertility, and production attributes must be prioritised.
More research is needed to examine health features and their relationship to retained placenta in order to properly classify dairy cows based on herd profitability.
