Date received: 05/12/2017
Date accepted: 27/2/2019
Introduction
Dairy cows mobilize body reserves to meet energy demands on the days before parturition
and the first three weeks post-calving. As a result, plasma concentration of non-esterified
fatty acids (NEFA) increase and are oxidized in the liver. Increased fatty acid (FA)
oxidation depends, among others, on augmented carnitine palmitoyl transferase-I (CPT-1)
activity, which increases by 49% on day one prepartum (Dann et al., 1999). This implies a proportional increase in the substrates (FA and carnitine) used
by the enzyme CPT-1. Mobilization of protein reserves provides the necessary precursors
for L-carnitine synthesis (Bell et al., 2000). Under the prevailing nutritional conditions of dairy farms in the Colombian high
tropics, it is likely that the negative energy balance (NEB) during the transition
period forces cows to increase the use of amino acids for energy, diminishing the
lysine and methionine pools, which are substrates for carnitine synthesis. Under these
conditions, significant associations have been reported between NEB and hepatic ammonium
concentration, and between liver ammonium and pyruvate, suggesting increased usage
of amino acids from body reserves as an energy source (Galvis et al., 2010). This situation can decrease carnitine precursors, possibly limiting CPT-1 activity.
Under in vitro conditions, palmitate oxidation increases when bovine hepatocytes are supplemented
with carnitine. Adding a CPT-1 inhibitor stops this increase, demonstrating how sensitive
CPT-1 is to carnitine availability and suggesting that carnitine supplementation could
modulate the enzyme activity (Drackley et al., 1991a). It is also known that carnitine supplementation in dairy cows produces variable
results depending on dose and delivery route (Lacount et al., 1995; Lacount et al., 1996a; 1996b; Carlson et al., 2006; Carlson et al., 2007a).
Therefore, the objective of this study was to evaluate the lipotropic potential of
L-carnitine in Holstein dairy cows during the transition period to lactation.
Materials and methods
Ethical considerations
The ethics committee for research of Universidad Nacional de Colombia (Medellín campus)
approved this study (CEMED 200 communication, minute # 13, October 5th, 2010).
Location
The experiment was conducted at Paysandú Center, property of Universidad Nacional
de Colombia, located in a tropical lower montane wet forest region according to the Holdridge classification of life zones (Espinal, 1977).
Animals and diet
A total of 21 Holstein cows between 2nd and 6th parity were used. Cows were between
d 260 of gestation to d 20 postpartum. The cows grazed on kikuyu (Cenchrus clandestinum) grasslands and during pre-partum received 2 kg/d of feed supplement containing 0,
100, or 200 g L-carnitine fumarate according to treatment (T0, T100, and T200, respectively).
After calving, the cows received 6 kg/d of feed supplement containing 0, 100, or 200
g of L-carnitine fumarate according to treatment. After the third postpartum day,
milk production was recorded daily. When milk production was greater than 24 L, one
additional kg of base supplement without L-carnitine fumarate was supplied for every
4 L of milk produced. The nutritional composition of grass and feed supplements are
described in Table 1.
Concentrations of crude protein (PC, Kjeldahl method, Icontec, 1999, standard NTC-4657),
fiber in neutral detergent (FDN, AOAC standard 2002.04), fiber in acid detergent (FDA,
AOAC 973.18 standard), ash (Cen, AOAC standard 942.05), ether extract [EE, Icontec
(2002), NTC-668 standard] and lignin (Lig, potassium permanganate) in kikuyu grass
(C. clandestinum), and feed supplements are presented in Table 2.
Ruminal degradability of L-carnitine fumarate was estimated through the in vitro incubation test described by Galvis (2016), who reported 89.7% degradability. L-carnitine fumarate (99.59% L-carnitine fumarate,
58% of L-carnitine, Suzhou Vitajoy Biotech, China) was added to the basal feed formula.
The inclusion levels of carnitine fumarate were 100 and 200 g. According to Galvis
(2016), these levels were used to achieve approximately 6 and 12 g L-carnitine available
for intestinal absorption, respectively. The experiment included seven cows per treatment.
The experimental treatments were as follows: Control (T0), 100 g/d L-carnitine fumarate
(T100), and 200 g/d L-carnitine fumarate (T200).
Table 1
Ingredients used in the formulation of the feed supplement
Table 2
Chemical composition of kikuyu grass (Cenchrus clandestinum) and feed supplement.
Sampling and laboratory analysis
Cows were weighed, blood-sampled (approximately 5 mL per cow), and body condition
evaluated on d 270 of pregnancy, on the day of calving, and on d 10 and 20 postpartum.
Liver biopsies were taken from each cow on d 270 of pregnancy and d 10 and 20 postpartum
using previously described procedures (Galvis et al., 2016). Blood samples were taken from the base of the tail, thereby reducing pain or stress
compared with other puncture sites such as the jugular vein. Local anesthesia was
used and mild sedation was induced to collect liver biopsy samples through standard
protocols (Waver et al., 2005). Serum was analyzed with spectrophotometric kits for NEFA, NEFA Fa-115 (Randox,
London, UK), β-hydroxybutyrate (β-HB) by Ranbut RB 1008 (Randox, London, UK), and
urea by UREA/BUN Color (Biosystems, Barcelona, Spain) concentrations. Liver samples
were analyzed for total carnitine, free carnitine and acylcarnitine following the
methods described by Prieto et al. (2006). Liver triglycerides were analyzed with a previously described method by Galvis et al. (2016). A Genesys 10S UV-VIS spectrophotometer (Thermo Scientific, NY, USA) was used.
Estimation of dry matter intake was previously described by Madrid et al. (2015).
Net energy for lactation (NEL), live weight change (WeightC), balances of metabolizable
protein (MP) and rumen-degradable protein (RDP) were calculated using NRC Software
(NRC, 2001).
Statistical analysis
Data from repeated measures over time were analyzed using PROC MIXED of the SAS statistical
package, version 8 (SAS, 1999). Composite symmetric and first-order auto-regressive covariance structures were
modeled following Littell et al. (1998). First-order autoregressive was the most suitable covariance structure for all variables.
Calving number, corrected milk yield (305d-2X-ME) in the previous lactation, and body
condition at the beginning of the experiment were used as covariates. Mean comparison
was performed using the LSD test. Statistical differences were considered at p<0.05.
The statistical model included the fixed effects of treatment, sampling period and
the interaction between treatment and sampling period.
Results
No interactions were observed between treatments and sampling periods for any of the
variables (blood concentrations of NEFA, β-HB and urea, balances of NEL, MP and RDP,
WeightC and hepatic concentrations of triglycerides, total carnitine, free carnitine
and acyl-carnitine; p>0.05). None of the covariates [calving number, corrected milk
yield (305d-2X-ME) in the previous lactation, and body condition at the beginning
of the experiment] had a significant effect (p>0.05). Table 3 shows the nutritional balance and plasma indicators for each treatment. There were
no significant differences (p>0.05) between treatments for NEFA, β-HB, NEL, MP, RDP,
and WeightC. In contrast, blood urea concentrations were significantly lower in the
control treatment (T0; p>0.05). Table 4 shows plasma indicators and nutritional balance per sampling period. All variables
presented significant differences (p<0.05) between sampling periods. The ENL, MP,
and RDP balances were significantly lower during postpartum. Blood concentrations
of glucose and NEFA increased significantly at calving. Blood urea and β-HB were related
to the variations of RDP and ENL in the different periods.
Table 3
Treatment means for nutritional balance and plasma indicators in Holstein cows fed
increasing levels of L-carnitine fumarate.
Table 4
Sampling-period means for nutritional balance and plasma indicators in Holstein cows.
There were no significant differences (p>0.05) between treatments with respect to
liver concentration of acylcarnitine, free carnitine, and total carnitine. In contrast,
hepatic triglyceride concentration was significantly lower (p<0.05) in T200 (Table 5).
Table 5
Treatment means for hepatic concentration of triglycerides, acylcarnitine, and total
carnitine in Holstein cows fed increasing levels of L-carnitine fumarate.
No significant differences were found between sampling periods for hepatic triglycerideconcentrations,
acylcarnitine, free carnitine, and total carnitine (p>0.05; Table 6).
Table 6
Sampling period means for hepatic triglycerides and carnitine concentrations in Holstein
cows.
Discussion
Significant differences (p<0.05) were found in NEFA and β-HB concentrations within
the different periods. The NEFA values around calving were significantly higher. This
is due to the decrease in dry matter intake that occurs together with the increase
of cortisol (Weber et al., 2013), which induces NEFA mobilization from the adipose tissue. The β-HB values at 10
days postpartum were significantly lower than the values found at d 10 and 20 postpartum;
increased milk production leads to energy deficit and NEFA oxidation, which combines
with increasing glucose deficit leading to greater β-HB concentration. The relationship
between NEFA and β-HB at calving was not evident, because the increase in gluconeogenesis
induced by cortisol during this period (Hammon et al., 2005) increased glucose levels, preventing the elevation of β-HB values (Erfle et al., 1971). Plasma urea values were higher at d 10 prepartum and at calving day. High values
during prepartum can be explained by a higher rumen degradable protein balance during
this period (Putnam and Varga, 1998). The high plasma urea values around calving result from the intense catabolism of
amino acids destined for cortisol-induced gluconeogenesis (Hammon et al., 2005). This increases oxidative deamination of amino acids, generating ammonium, which
is mostly transformed into urea (Madsen, 1983).
L-carnitine fumarate supplementation significantly increased plasma urea concentration
(Table 3). According to other reports, administration of L-carnitine in sheep (Chapa et al., 1998; 2001) and growing bovines (White et al., 2001) increases plasma ammonium removal, possibly due to its conversion to urea. Most
reports about carnitine effects on urea synthesis have been conducted in species other
than bovines. Studies on monkeys with induced hyperammonemia (Ratnakumar et al., 1993; O’Connor et al., 1987a, O’Connor et al., 1987b), and on rat hepatocytes (Takeuchi et al., 1988; Tomomura et al., 1996) reported decreased hyperammonemia and increased urea synthesis in response to carnitine,
which was attributed to several mechanisms (i.e. changes in enzyme expression, in
enzymatic activity, and in the concentration of allosteric effectors). Indeed, a decrease
in the carnitine-dependent fatty acid transport system causes an accumulation of acyl-CoA
molecules in the cytosol, and these metabolites inhibit the urea cycle (Malaguarnera, 2013). Therefore, we suggest that the rise in plasma urea observed in animals supplemented
with L-carnitine fumarate could be due to a significant increase in the urea cycle
activity induced by L-carnitine. The first study with L-carnitine in cows indicated
that carnitine infusion in the blood significantly increases blood concentrations
of total ketones (Erfle et al., 1971), accounting for an increase in fatty acid oxidation. Researchers found that β-HB
concentrations tended to be higher (p =0.07) in cows receiving 10 and 20 g carnitine
available for intestinal absorption (Carlson et al., 2007a). However, the amount of ketone production in response to carnitine depends
on the availability of carbohydrates (Erfle et al., 1971). In the present study, elevation in β-HB concentrations was not observed, possibly
due to the amount of available glucose (Table 4), so that the increase of fatty acid oxidation could be significant, but without
apparent changes in β-HB concentration.
Liver concentration of triglycerides (Tables 5 and 6) was low, according with levels reported by other authors (Kalaitzakis et al., 2007; Starke et al., 2010; Gross et al., 2013). Supplementation with 200 g/d L-carnitine fumarate significantly decreased hepatic
triglyceride concentrations (Table 5), possibly due to a higher rate of fatty acid oxidation by the liver, decreasing
their availability for esterification. Liver slices from cows during early lactation
showed that carnitine increases total palmitate oxidation and decreases its esterification
(Drackley et al., 1991b). In rat liver cells, distribution of fatty acids between esterification and oxidation
is regulated by cytoplasmic concentrations of glycerol-phosphate or carnitine, respectively
(Bremer et al., 1978). Carlson et al. (2007a) found that carnitine supply during early lactation decreases hepatic triglycerides
and increases plasma concentrations of β-HB, even when liver triglycerides are low
in the control treatment. Hepatic concentrations of the different forms of L-carnitine
were lower (Tables 5 and 6) than those reported in other studies (Erfle et al., 1971; LaCount et al., 1995; Carlson et al., 2007a; 2007b) and were not affected by supplementation with L-carnitine fumarate. Other
studies were able to increase hepatic carnitine concentrations only when they gave
doses higher than 10g/d carnitine available for intestinal absorption, or 20 g/d in
abomasal infusion (Carlson et al., 2007a; 2007b). The carnitine transport system in the liver has been characterized in human,
rat and mouse (Ramsay et al., 2001). Carnitine uptake by the liver depends on relatively high carnitine concentration
in the blood, since carnitine enters the liver through OCTN2 (organic cation transporter
2), a carrier with high Km (Michaelis-Menten constant) for carnitine (Km = 5.6 mM:
Christiansen and Bremer, 1976), thus the liver takes carnitine from the blood when its concentration is significantly
rised. It is possible that the low amounts of carnitine available for intestinal absorption
in our study did not increase enough plasma carnitine concentration to achieve a significant
increase in its entrance to the liver, thus its concentration was not increased. In
conclusion, supplementation with 200 g/d L-carnitine fumarate significantly reduces
hepatic triglyceride concentration, even when NEFA and hepatic triglycerides are low.
Hepatic triglycerides decreased in response to carnitine supplementation possibly
due to increased fatty acid oxidation. Supplementation with L-carnitine increases
blood urea levels possibly due to an increase in the conversion of ammonia into urea.
Both effects of the supplementation with L-carnitine can be beneficial for the metabolic
health of dairy cows under energy deficit and dietary excess of rumen degradable protein.
Acknowledgements
This study was funded by Colciencias (call 521, Project number: 1118-521-28602) and
co-financed by the Universidad Nacional de Colombia, Medellin campus
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