Responses to rumen-protected choline in transition cows do not depend on prepartum body condition.

Choline is a known essential nutrient as it is required for synthesis of essential membrane phospholipids, acts as a precursor for synthesis of acetylcholine, and in particular, has a role in lipid intermediary metabolism. Improving choline status pre-calving has the potential to reduce the risk of fatty liver and improve health and lactation. It is, however, often suggested that the benefits of supplemental choline, which needs to be supplemented in the rumen-protected format (RPC), might be greater in cows predisposed to fatty liver, such as those that are over-conditioned; however, limited data support this suggestion. Therefore, the hypothesis of the study by Dr J.M. Bollatti and co-workers was that responses to supplementing RPC to transition dairy cows is not dependent on the degree of fatness before calving. Their objectives were therefore to evaluate the effects of supplementing RPC to transition dairy cows according to body condition score (BCS) pre-calving on production and metabolic responses. Their results were published in the Journal of Dairy Science, Volume 103 of 2020, page 2272 to 2286, the title being: Responses to rumen-protected choline in transition cows do not depend on prepartum body condition.

The data from two randomized block experiments that evaluated the effects of RPC supplementation during the transition period were combined. Within each experiment, cows were assigned randomly to receive 0 (Control) or 12.9 g/d choline ion in a rumen-protected form (Choline) daily top-dressed onto the diet from 21 days pre-calving to 21 days post-calving. Body condition was evaluated twice pre-calving before enrolment and the mean value was used in statistical analyses. The data were collected for the last 21 days of gestation and the first 105 days post-calving. The BCS’s (mean ± standard deviation) pre-calving were 3.51 ± 0.29 and 3.51 ± 0.32 for Control and Choline, respectively, and ranged from 2.69 to 4.25. A total of 215 cows were enrolled in the respective experiments and they contributed data for the incidence of diseases, whereas 192 cows contributed data for analyses of production responses, plasma metabolites, and liver composition.

The results showed that, irrespective of BCS, supplementing transition diets with choline increased yields of milk by 1.8 kg per day, fat by 0.08 kg per day, lactose by 0.08 kg per day, true protein by 0.04 kg per day, energy-corrected milk by 1.9 kg per day, and fat-corrected milk by 2.1 kg per day. The improvements in productive performance were not followed by increased dry matter intake or measures of fat mobilization. Therefore, Choline cows were more efficient in converting dry matter intake into energy-corrected milk. Feeding choline increased the concentration of hepatic triacylglycerol (Control = 3.23 versus Choline = 3.87% wet basis) in the first 21 days post-calving. Over-conditioned cows were more prone to having exacerbated fat mobilization and increased prevalence and incidence of fatty liver, but no interactions between treatment and BCS were observed for body weight, BCS, or concentrations of metabolites in plasma or hepatic triacylglycerol. Treatment did not affect the incidence of clinical diseases. Opposite to common suggestions, cows with increased hepatic triacylglycerol content also had increased yields of milk and energy-corrected milk in the first 105 days post-calving. 

In conclusion, these findings indicate that the effects of RPC supplementation during the transition period are independent of the degree of fatness of dairy cows pre-calving. The findings also suggest that the effects on productive performance are not necessarily mediated by improvements in parameters of metabolic health or reductions in hepatic triacylglycerol.