The effect of chloride ammonium, vitamin E and Se supplementation throughout the dry period on the prevention of retained fetal membranes, reproductive performance and milk yield of dairy cows

We assessed the effect of an anionic salt and supplementary administration of vitamin E and Se throughout the dry period, on the risk of retained fetal membranes (RFM), milk yield and reproductive performance of dairy cows. Data were collected from 456 dairy cows in three commercial farms. Each animal entering the dry period was assigned to one of two groups (treated and control group). All animals were then fed the same ration, which included 80 IU/kg vitamin E acetate and 0.2 ppm Se, but animals of the treated group also received an additional blend containing ammonium chloride (60 g), vitamin E [1000 IU (dl-α-tocopheryl acetate)] and Se (0.05 ppm). Calving ease was evaluated and no manual removal of placenta was attempted. Cows that retained their fetal membranes for more than 12 h after calving were considered to suffer from RFM. All animals experienced a 50-day voluntary waiting period before the first artificial insemination (AI). Treatment resulted in a decrease in the estimated average risk of RFM (10.6% vs 17.8%). Stratifying on farm the Mantel–Haenszel Relative Risk (MH-RR) estimate of RFM in treated animals relative to controls was 1.68 (95% confidence interval, CI, 1.05 to 2.68) and the Mantel–Haenszel test P-value was 0.028. Among cows that had not required assistance during delivery the average risk of RFM was greater for those without treatment (risk estimate: 10/208 or 9.7%) as compared to those with treatment (risk estimate: 20/207 or 4.8%). The MH-RR estimate of RFM in treated vs. control animals was 2.95 the respective 95% CI: (0.96 to 4.17) and the MH test of association P-value was 0.058). Conversely, among cows that did require assistance during calving, the average risk of RFM estimates were 77.8% (14/18) and 91.3% (21/23) in treated and non-treated animals, respectively (MH-relative risk estimate of RFM = 1.21, 95%CI: 0.91 to 1.60). Using analysis of variance with farm as a random effect, treatment did not appear to have an effect on milk production of cows without RFM either at 30 or 60 days postpartum (P > 0.10). Time intervals (in days) between parturition and first oestrus expression (POI), parturition and first AI (PFAI) and parturition and conception (PCI) were recorded for each animal. For each time-to-event variable, survivor functions were estimated for treated and control groups using the Kaplan–Meier methodology and survival curves of treated and control groups were compared using the log-rank test, separately for the animals that did or did not experience RFM in each farm. There were significant differences in the time-to-event survival curves in only one of the three farms. Median time between parturition and first oestrus expression among animals without RFM was 67 days in treated animals and 75 in control animals, and the survival curves were statistically significantly different (P = 0.021). Similarly, in the same farm, among animals that did not experience RFM the median time between parturition and conception was 114 in treated animals and 145 in controls, and the survival curves were statistically significantly different (P = 0.002). In conclusion, daily administration of a blend containing ammonium chloride, vitamin E and Se throughout the dry period seems to be safe and resulted in a decrease of RFM occurrence, without any effect on milk yield.