Supplementation of dairy cows before calving with beta-carotene
The pre-calving supplementation of beta-carotene was evaluated. The data set contained 283 Holsteins that received a treatment for >14 d (29.1±6.9 d). Cows were paired blocked by parity and expected calving date and assigned to a treatment: Beta-carotene (1.2 g/cow/d. Rovimix, DSM) or Control. The same TMR batch was offered to all cows and beta-carotene was top dressed per cow once a day. Milk yield was recorded daily and sampled at 30.1±8.3 d post-calving. Frequency distributions were analyzed with GENMOD of SAS using logistic regression for binomial data. Continuous variables were analyzed with MIXED. Within parity, nonparametric estimates of the survivor function for reproductive variables were computed using the product-limit method of the Kaplan-Meier method with LIFETEST. Plasma beta-carotene content at the start of the experiment was similar (2.99 µg/mL, P=0.59) and peaked at 3.26 µg/mL on day -15 pre-calving for supplemented cows (2.62 µg/mL for Control, P<0.01). Colostrum density, milk yield, and milk solids content were similar (P>0.32). Milk yield from d 20 to 109 of lactation was 3105 kg for primiparous and 3595 kg for multiparous (P<0.01). Beta-carotene tended to increase milk protein content from 2.90 to 2.96% (P=0.09) and to decrease the proportion of primiparous with a milk fat to protein ratio >1.4 from 25.8 to 9.7% (P=0.10). The proportion of primiparous with difficult calving, SCC >200,000 cells/mL, metritis, progesterone >1 ng/mL at 21 and 42 d, % conception at first service, and % pregnant at 90 and 150 d were similar (P>0.46). There was a trend for decreased incidence of SCC >200,000 cells/mL in multiparous supplemented with beta-carotene (38.9% vs. 28.1%, P=0.12), other variables were similar (P>0.21). Beta-carotene reduced the proportion of multiparous with retained placenta 12 h post-calving from 29.9% to 21.7%, time of placenta release was 392 min (340 to 440) for beta-carotene and 490 min (395 to 540) for Control (Median and 95% confidence interval. LogRank P=0.05 and Wilcoxon P= 0.04). For primiparous, beta-carotene did not determine placenta release (incidence was 15.4%). Responses in the intervals from calving to first estrous, to first service, and to conception were not detected. The pre-calving supplementation of beta-carotene increased the plasma content around calving. There was no detectable response in milk yield or reproductive performance. Beta-carotene reduced the incidence of retained placenta in multiparous cows.
Beta-carotene, retained placenta, transition period