Propylene glycol energy supplementation during peripartal period in dairy cows and reproducion [i.e. reproduction] efficiency parameters

The aim of this work was to investigate the impact of two energy supplements based on propylene glycol in dairy cows diet on ovarian and follicular morphology, conception, insemination index and length of service period. A total number of 60 Holstein Friesian dairy cows, parity between 2-8, with an average milk production of 7000 kg/305 days of lactation were divided into three experimental groups (20 dairy cows per group). The first group of dairy cows was supplemented daily with Energy-plus (O1 group; 200 mL propylene-glycol supplement) and the second group was supplemented with Ketal (O2 group; 160 mL propylene-glycol supplement), two weeks before partus until 30 days post partum. The third experimental group were non supplemented dairy cows (O3, control group). Ultrasound examination of the reproductive system using real time echo camera Falco VET 100 (ESAOTE PieMedical, Holland, B-shaped scan with linear-array endorectal 5–8 MHz probe) was conducted on every animal starting from day 40 postpartum. The diameters of the ovaries (left and right) and of the dominant follicle(s) were recorded. Ultrasound testing was repeated on day 50 and 60 postpartum only in cows which in the meantime were not inseminated. Reproduction efficiency parameters (conception rate, number of inseminations and length of service period) were recorded individually. The statistical significance of the differences between groups was tested using ANOVA with LSD test at the level of significance p is less than 0.05, chi-square test and Kaplan-Meier survival analysis (the length of service period). There was no significant impact of the propylene glycol supplementation on the ovarian and follicular morphology at the first ultrasound examination. At the second ultrasound examination there was a significant difference between left ovarian dominant follicle diameter in the control and supplemented dairy cows (1.67 +/- 0.53 vs 1.12 +/- 0.29 and 1.11 +/- 0.35 cm, p is less than 0.05, O3 vs O1 and O2, respectively). The cumulative percentage of conception after the first and second insemination was 60%, 81% and 25% in groups O1, O2 and O3, respectively (p is less than 0.05, chi-square test). The insemination index was lowest in group O2 and statistically significant differences were found between groups O2 and O3 (1.69 +/- 0.79 : 3.38 +/- 1.36, respectively, p is less than 0,05). The length of the service period was significantly (p is less than 0.05, LSD test) shorter in the O2 group (100 +/- 35 days) compared to groups O1 and O3 (168 +/- 59 and 157 +/- 52 days, respectively), that was confirmed by the Kaplan-Meier survival analysis of days open periods. The use of propylene glycol supplement in dairy cows diet during peripartal period induced higher percentage of pregnancy rates after the first and second insemination, significantly shortened the length of the service period and reduced the insemination index.