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

Abstract

It has been reported that a diet supplemented with l-carnitine can improve sperm quality in some mammalian species. Against this background, the current study seeks to determine the effects of feeding l-carnitine (625 mg·day⁻¹) on boar semen characteristics (ejaculate volume, sperm concentration, sperm viability, acrosome and mitochondrial sheath integrity, sperm motility, sperm morphology, and osmotic resistance of spermatozoa) in three different porcine breeds (Sus domesticus) (Piétrain, Duroc, and Large White) exposed to natural environmental changes in temperature and photoperiod over a 20-wk period (February to July 2007). One hundred twenty boars (40 per breed) were randomly separated into two groups (60 boars each): the first (20 boars per breed) was fed a control diet and the second (also 20 males per breed) the same diet supplemented with l-carnitine (625 mg·day⁻¹). Whereas the l-carnitine supplement did not affect ejaculate volume, concentration, motility, viability, or the osmotic resistance of spermatozoa, it did improve sperm morphology in Piétrain boars by reducing the percentage of immature spermatozoa when the temperature and the photoperiod increased. Conversely, no effect on sperm morphology from supplementing feed with l-carnitine was observed in both Duroc and Large White breeds. We can therefore conclude that the addition of l-carnitine to the diet of males may maintain the level of normal sperm morphology in Piétrain boars when a drop in sperm quality occurs (due to increases in photoperiod and temperature), without affecting the other sperm quality parameters.

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].