Abstract
Simple SummaryDuring the first weeks of lactation, dairy cows typically experience negative energy balance, leading to the mobilization of energy reserves. This predisposes early lactating cows towards metabolic diseases, such as fatty liver syndrome and ketosis. The supplementation of rumen-protected choline (RPC) is a strategy to restrict negative effects associated with negative energy balance in early lactating cows, but reported effects are inconsistent. This meta-analysis revealed that the supplementation of RPC positively affected dry matter intake, but this effect was associated with increased milk yield, thus without improving energy balance and metabolic profile of the cows.After parturition, cows undergo negative energy balance leading to fat mobilization, predisposing them to fatty liver syndrome and ketosis with major consequences for health and reproduction. Supplementation of rumen-protected choline (RPC) has attracted major research efforts during the last decade, assuming that choline improves liver function by increasing very low-density lipoprotein exportation from the liver, thereby improving metabolic profiles, milk production, and reproduction. However, the effects of RPC on production, health, and reproduction have been inconsistent. Therefore, the aim of this meta-analysis was to evaluate the effects of RPC supplementation, starting from d 20 (± 12.2) ante partum to d 53 (± 31.0) postpartum, on feed intake, milk production performance and metabolic profiles of dairy cows early postpartum. Data analyses from 27 published studies showed an increase in postpartal dry matter intake (from on average 19.1 to 19.9 kg/d; p < 0.01) and milk yield (from on average 31.8 to 32.9 kg/d; p = 0.03) in cows receiving RPC. Milk fat yield and milk protein yield were also increased (p ≤ 0.05), without changing milk protein and fat contents. However, no interactive effects between cow’s milk yield level and RPC-supplementation as well as no dose-dependent effects of RPC supplementation were observed. Supplementing the diet with RPC showed no effects on blood metabolites (non-esterified fatty acids, beta-hydroxybutyrate, glucose, and cholesterol), independent of the milk yield level of the cows. An effect on liver triacylglycerol contents, incidence of ketosis, and mastitis could not be confirmed across all studies included in this meta-analysis. Also, the positive effects of RPC supplementation on reproductive performance were not consistent findings. In conclusion, supplementing RPC in lactating dairy cows showed positive effects on dry matter intake which likely caused the improved milk yield. However, RPC supplementation did not improve the metabolic health status of the cows. As several factors might be related to the responses to RPC, further research is needed to explore the precise mechanisms of RPC action in lactating cows, especially with regards to feed intake improvement and its related metabolic health-promoting potential in early lactating dairy cows.
Highlights
The transition period is critical for productivity, health, and fertility of dairy cows
As several factors might be related to the responses to rumen-protected choline (RPC), further research is needed to explore the precise mechanisms of RPC action in lactating cows, especially with regards to feed intake improvement and its related metabolic health-promoting potential in early lactating dairy cows
The analysis of available data showed that the RPC supplementation did not affect dry matter intake (DMI) pre-partum, but supplementing RPC increased postpartal DMI by an average of 0.79 kg/d (p < 0.01; Table 4)
Summary
The transition period is critical for productivity, health, and fertility of dairy cows. Due to the reduced dry matter intake (DMI) around parturition, the energy intake of high-producing dairy cows is usually insufficient to meet the high energy needs for milk production, resulting in a negative energy balance (NEB; [1]). This leads to the mobilization of fat from adipose tissue, mainly in the form of non-esterified fatty acids (NEFA), which are released into the blood as a source of energy [2]. The limited capacity of the bovine liver to oxidize NEFA or to secrete esterified fatty acids (triacylglycerol; TAG) as very low-density lipoproteins (VLDL) predisposes early lactating cows toward hepatic dysfunction [1]. The elevated levels of NEFA and BHBA further contribute to oxidative stress, inflammatory responses, and a compromised immune system, enhancing the susceptibility to infectious diseases and impairing fertility [3]
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