Rate of Stillbirths and the Effect on Dam Survival and Reproductive Performance
Posted: November 22, 2007
Stillbirth is a major issue within the dairy industry. In 2000 results of a comprehensive study from Iowa State documented that 7 percent of the Holstein calves born in the United States die within 48 h of birth. Data were accumulated from 666,341 births from the MidStates Dairy Records Processing Center and the National Association of Animal Breeders. This research examined parity, season of birth, dystocia and gestation length as factors contributing to stillbirth rates. The rate of stillbirths for primiparous and multiparous cows was 11.0 and 5.7 percent, respectively. Dystocia followed parity as the next most important factor within both primiparous and multiparous cows.
This year a study from the College of Veterinary Medicine at Cornell published in the Journal of Dairy Science evaluated the effects of stillbirth on the survival and reproductive performance of lactating cows from seven large dairy herds (13,608 calvings) in two regions of the US. In this study stillbirths were defined as death of the calf just before, during and within 48 hours of calving. Calving ease scores (CES) ranked 1 to 5 was recorded on the farms and then the data was categorized into calving ease groups (CEG). CEG 0 were unassisted calvings (CES 1 and 2) and CEG 1 included all calvings that required assistance. The overall incidence of stillbirths was 6.6 percent but ranged from 4.1 percent to 10 percent across the seven farms. Figure 1 illustrates the incidence of stillbirth across parity (JDS 2007. 90:2799). Numbers above the bars represent the total number of animals in that parity grouping. The incidence was significantly higher for first parity cows - 10.7 percent compared to 3.6 percent, 5 percent and 4.2 percent for 2nd, 3rd and 4th parities, respectively:
Figure 2 illustrates the significant trend in rate of stillbirths by CES, ranging from 3.6 percent to 60.1 percent. The odds of stillbirth were 88 percent lower for unassisted calvings compared to assisted calvings. Furthermore, cows that gave birth to female calves were at a 23 percent decreased odds of having a stillborn calf compared to cows that gave birth to male calves.
Cows that had stillbirths were 41 percent more likely to be culled. The rate of becoming pregnant was 24 percent lower for cows with stillbirths compared to cows that gave birth to live calves. Figure 3 (JDS 2007.90:2801) shows the survival analysis plot for dam's calving to conception interval (cows with live calves dotted line, cows with stillbirths solid line). The difference in mean days open for cows with stillbirths compared to cows that gave birth to live calves was 26 days.
These data document the severe impact stillbirths have on dairy profitability. Not only is there a loss of the calf but the effects on dam survival and reproductive performance are significant. Others have shown that cows with stillbirths have an increased incidence of postpartum disorders including prolapsed uterus, uterine infection and displaced abomasum. Obviously these events result in prolonged days to conception and increased cull rate.
Several attempts have been made to identify risk factors, other than parity and calving score, which increase risk of stillbirths. Since there was large variation in the incidence of stillbirth among the farms in this study the research team suggested a management component to this problem. Those specific management factors were not identified. Since calving ease score is significantly related to stillbirth, any management intervention to reduce the incidence of difficult births should reduce incidence of stillbirth. Utilize sire and daughter calving ease information when selecting sires to breed heifers. This is considered a best management practice.
Use of such sires will not eliminate dystocia but it will certainly reduce the risk. Fortunately the 2006 revision of net merit dollars index (NM$) for genetic evaluations of service sires includes an improved definition of productive life (PL) and new genetic evaluations for service sire and daughter stillbirth. Because calving ease and stillbirth are correlated, economic values for these traits are combined and included in NM$ via a calving ability index (CA$) that is not published separately (VanRaden 7/06 USDA AIPL). Herd managers should review calving procedures with their veterinarian to assure that proper timing and calving assistance techniques are used when providing assistance during parturition. If there are several employees who are responsible for monitoring cows prior to and during calving, review procedures with them and post SOPs. Evaluate dry cow feeding management so heifers and cows are in the appropriate condition at calving. Provide a good environment for dry and prefresh cows that minimizes stress.
Until the physiological mechanisms and other significant risk factors for stillbirths are identified, best management practices must be used consistently to reduce the risk of stillbirths.Michael O'Connor, Dairy and Animal Science Extension