A diet supplemented with l-carnitine improves the sperm quality of Piétrain but not of Duroc and Large White boars when photoperiod and temperature increase
Introduction
The use of artificial insemination (AI) in the swine industry has become widespread in recent years [1]. To find ways of improving the sperm quality of semen doses, different works have looked at the effects of a particular diet, for example l-carnitine supplementation, on boar studs’ sperm quality. l-Carnitine (β-hydroxy-γ-trimethyl ammonium butyrate) is a vitamin-like compound synthesized in the liver, kidney, and brain through the conversion of two essential amino acids, lysine and methionine [2], [3]. It plays an important role in cellular energy metabolism, because it functions as a carrier of fatty acids across the inner mitochondrial membrane, thereby facilitating β-oxidation and enhancing energy production for the cell [3], [4]. l-Carnitine is also known to fulfill important roles in mammalian sperm maturation and metabolism when spermatozoa pass through the epididymis [5] and seems to have an antiapoptotic effect on different cells, including neurons, myocytes, hepatocytes, and lymphocytes (see [6] for review).
Spermatozoa first come into contact with l-carnitine within the lumen of the epididymis. In boars, the levels of l-carnitine in epididymal plasma vary from 24.0 ± 5.7 nmol·mg-1 of protein in the proximal caput to 442.9 ± 39.1 nmol·mg-1of protein in the distal cauda [7]. With regard to its effects on sperm quality, Neuman et al. [8] have observed that when supplementing a rooster's diet with l-carnitine (500 mg·kg-1 of diet), sperm concentration increases and lipid peroxidation of spermatozoa decreases. This increasing effect on sperm concentration has also been observed in humans (asthenozoospermic patients) after administering l-carnitine (3 g·day−1) [9].
In boars, it has been reported that receiving l-carnitine 230 mg·day−1 [10] or 500 mg·day−1 [11] increases the volume of ejaculate and sperm concentration, thereby augmenting the number of AI doses produced per ejaculate. A commercial study has also reported that l-carnitine can increase the number of viable spermatozoa and the number of AI doses [12]. Conversely, Kozink et al. [13], who studied the effects of l-carnitine supplements on boar semen characteristics and the maintenance of sperm motility during 7-d liquid storage, observed beneficial effects of such supplements (500 mg·day−1) only when the boars were submitted to an intensive collection period in the first 3 d of the study, whereas no significant effects on semen characteristics either in young or in mature boars were reported at the normal collection rate.
Even though there are differences among porcine breeds in terms of sperm quality, to the authors’ knowledge there are no reports investigating the effects of an l-carnitine supplemented diet on the porcine breed. The current work takes into account the above-mentioned studies, considers differences among breeds [14], and aims to investigate the effects of feeding l-carnitine (250 mg·kg diet-1; 625 mg·day−1) on sperm quality by assessing not only ejaculate volume, sperm concentration, and sperm motility, but also sperm morphology, sperm viability, and the osmotic resistance of spermatozoa in three different porcine breeds (Sus domesticus) (Piétrain, Duroc, and Large White) over a 20-wk period with fluctuations of temperature and photoperiod (from February to July). As several authors have reported that less daylight in the autumn increases ejaculate volume and concentration in boars [15], [16], the experimental period was chosen because it is also well known that in spring, a reduction in sperm quality and production occurs in these animals [17].
Section snippets
Animals and sperm samples
In total, 120 boars (40 Piétrain, 40 Duroc, and 40 Large White) were used in the current study. These boars were all healthy and postpubertal (at the start of the experiment, between 10 and 15 mo old), with an average weight (mean ± SEM) of 161.0 ± 3.8 kg, and housed in 12 experimental rooms at a farm located in the temperate region of Girona (Spain). Every room, mechanically ventilated, measured 100 m2, 3.5 m high, and was divided into two rows of five boxes each. Boars were exposed to ambient
Ejaculate volume
No effect of diet was observed in ejaculate volume over the evaluation period (GEE diet, Wald χ2 = 0.02, df = 1, P > 0.05), and no breed by diet interaction was found (P > 0.05), that is why Fig. 2 shows the results for this sperm parameter in each breed without distinguishing between both diets. Significant differences were found among breeds (GEE breed, Wald χ2 = 134.06, df = 2, P < 0.001), the photoperiod (Wald χ2 = 1462.12, df = 1, P < 0.001), and mean temperature (Wald χ2 = 17.61, df = 1, P < 0.001) also affecting
Discussion
In the current study, it has been observed that an l-carnitine dietary supplement (625 mg·day−1) maintains sperm morphology in Piétrain boars after 13 wk of starting the experiment (coinciding with increases in photoperiod and temperature in our latitude), whereas no remarkable effects on Duroc and Large White breeds in terms of sperm quality were observed during the whole experimental period.
The sperm concentration of ejaculates and the semen doses obtained per ejaculate are important
Acknowledgments
The authors wish to thank Isabel Casas, Anna Fàbrega, and Estela Garcia for their technical support.
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