Abstract :
[en] During the last decades, there is a declining trend in conception and calving rates in high yielding Holstein dairy cattle. At the same time, the gradual increase in stillbirth rates, especially in Holstein heifers, has until recently received relatively little attention. Birth weight and gender of the calf, parity, age and breed of the dam, and season of calving are all factors associated with calving difficulties and stillbirths. Other causes of stillbirths not related to calving difficulties are, for example, herd size, infections (e.g. BVD), insufficient placenta development and/or function, metabolic disorders of the cow, and congenital malformations of the calf.
The objective of the present study was to investigate the possible effect of hormonal disturbances on the incidence of stillbirth in dairy cows on a Holstein-Friesian dairy farm in Hungary.
Dairy cows (n=173) were sampled three times during the periparturient period (at drying-off, 3 weeks prior to expected calving, and within 1 h after calving) in 2006 and two times (3 weeks prior to expected calving, and within 1 h after calving) in 2007. Dairy cows were grouped according to the incidence of stillbirth: Group 1 (control): n=165 and Group 2 (stillbirth): n=8. Hormone and pregnancy protein parameters measured by RIA were as follows: progesterone (P4), estradiol (E2), cortisol, triiodine-thyronin (T3), thyroxin (T4), insulin, insulin-like growth factor (IGF-1) and pregnancy associated glycoprotein (PAG).
To determine, which of the hormones and PAG were the best predictors of the presence or absence of stillbirth at a given time (2 months and 3 weeks before calving and within 1 h after calving), a generalised linear model was used with binomial error distribution and logit link function (multivariate logistic regression). All analyses were carried out by R 2.7.2. Statistical Software. The significant level was set at P< 0.05 and an effect was considered a trend when P was between 0.05 and 0.10.
The overall prevalence of stillbirth was 4.6 % (4.0% in 2006 and 5.4% in 2007). Interestingly, most calves (7 out of 8) with stillbirth were bulls, but this difference was not significant. Weight of the calves, body score condition of the cows and number of people needed to assist at calving also did not affect the presence or absence of stillbirth significantly, and there was no significant difference among the groups regarding the gestation length or parity either (P>0.100 in all cases).
Regarding hormone and pregnancy protein parameters, no significant differences were found during the periparturient period (at 2 months and 3 weeks before expecting calving), however, there was a trend for lower IGF-1 values (P=0.079, OR=0.96) in stillbirth group compared to controls at dry off (2 months before expecting calving). Within one hour after calving significant differences were observed in case of P4 (P<0.001, OR= 3.06), and IGF-1 (P=0.021, OR= 0.94), resulting significantly higher values in P4 and lower values in IGF-1 in stillbirth cows compared to controls. The higher P4 values observed in stillbirth cows also resulted a higher P4/E2 ratio compared to controls (P=0.003, OR= 1.60).
Changes in the IGF-1, P4 and P4/E2 ratio may be one of the reasons for stillbirth in Holstein-Friesian dairy cows however more examinations are needed to be confirmed. Other hormones (P4, cortisol, T3, T4, insulin, PAG) did not mirror dependency due to the incidence of stillbirth in dairy cows.
