Dietary n-6:n-3 ratio and Vitamin E improve motility characteristics in association with membrane properties of boar spermatozoa

Abstract

This study was aimed to evaluate the effects of dietary n-6:n-3 ratio and Vitamin E on the membrane properties and motility characteristics of spermatozoa in boars. Forty Duroc boars were randomly distributed in a 2 × 2 factorial design with two n-6:n-3 ratios (14.4 and 6.6) and two Vitamin E levels (200 and 400 mg kg−1). During 16 weeks of treatment, fresh semen was collected at weeks 0, 8, 12, and 16 for measurements of motility characteristics, contents of fatty acids, membrane properties (membrane fluidity and membrane integrity), and lipid peroxidation of the spermatozoa. The semen was diluted in Beltsville Thawing Solution (BTS) extender and stored at 17°C, and the sperm motility was assessed at 12, 36, 72, and 120 h of storage. The 6.6 n-6:n-3 dietary ratio increased the contents of n-3 polyunsaturated fatty acids (PUFAs) and docosahexaenoic acid (DHA) and improved the membrane integrity and membrane fluidity of the spermatozoa, resulting in notably increased total motility, sperm progressive motility, and velocity parameters of fresh semen. Feeding diet with Vitamin E (400 mg kg−1) prevented sperm lipid peroxidation, and resulted in higher total motility and sperm progressive motility in fresh and liquid stored semen. In conclusion, the adjustment of n-6:n-3 ratio (6.6) and supply of Vitamin E (400 mg kg−1) successfully improved sperm motility characteristics and thus may be beneficial to the fertility of boars, which might be due to the modification of the physical and functional properties of spermatozoa membrane in response to dietary supplementation.

The Effect of Dietary Supplementation of Vitamin E, Selenium, Zinc, Folic Acid, and N-3 Polyunsaturated Fatty Acids on Sperm Motility and Membrane Properties in Dogs

“…Changes in the fatty acid profile of the sperm membrane and its lipidic peroxidation are closely associated with variations in the physical and functional properties of the sperm cell membrane [85,86]. The supplementation with n-3 PUFA, decreasing the n-6:n-3 ratio, as already demonstrated in pigs, improves the characteristics of the cytoplasmic membrane, influencing the composition of fatty acids in spermatozoa [10]. On the other hand, the enrichment of the diet with n-3- PUFA, only, could result in spermatozoa that are more likely subject to lipidic peroxidation, which negatively affects structural and functional properties of membrane and sperm motility [13,81].…”

“…It should also be pointed out that the present study was performed on healthy normospermic dogs, to evaluate the possible effects of a dietary supplementation on seminal parameters, and to exclude any potential side effect of this complex at the given dosages on semen quality, in order to later transpose present results to non-normospermic dogs. Several studies from the literature describe similar protocols, even if with different procedures and alimentary additions, not only in the canine species [8,48], but also in rams [10] and in men [56].…”

“…To increase fertility, as suggested by the literature, in both human and veterinary medicine, the cumulative effect of specific trace elements and vitamins has to be considered [7,8,10,18,48,56]. In previous studies, many authors, who focused attention on the comparison between mono- and complex-integrations, finally vividly recommended the use of combined formulations to improve sperm concentration and motility [7,8,10,18,48,56]. Moreover, some authors already demonstrated that, when micronutrients can act synergistically with each other, their effect has to be considered as the enhanced sum of the partly augmentative effects of each other [18].…”

“…As previously reported by other authors in similar clinical studies [7,10,48], the structural membrane integrity was evaluated by Eosin/Nigrosin staining method. The proportion of spermatozoa with intact cytoplasmic membrane was estimated using Eosine/Nigrosine staining, with the observation of at least 100 spermatozoa at ×400 magnification.…”

“…Moreover, some authors suggested that n-3 PUFA-enriched diets manage to change the n-6:n-3 ratio of spermatozoa, improving sperm motility [9]. These results would imply that dietary n-3 PUFA might help improve sperm functions, especially motility, by modifying membrane properties, as well as decreasing spermatozoa lipidic peroxidation [10]. On the other hand, it was recently demonstrated that dietary n-3 PUFA modify the spermatozoa fatty acid (FA) profile [9,11] and promote the susceptibility of membrane PUFA to lipidic peroxidation [12,13], thus change membrane integrity and function, and subsequently modify sperm motility and fertility [13,14].…”