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ANIMAL PRODUCTION |
* Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Lennoxville, Quebec, J1M 1Z3 Canada;
and
Department of Animal Science, Laval University, Ste-Foy, Quebec, G1K 7P4 Canada; and
and
École Nationale Vétérinaire de Toulouse, Toulouse Cedex, France 31076
Abstract
The aim of the present study was to determine the effects of dietary supplements of vitamins on vitamin status, libido, and semen characteristics in young boars under normal and intensive semen collection. Sixty Landrace, Yorkshire, and Duroc boars were allocated randomly from 6 to 10 mo of age to one of the following diets: 1) basal diet (industry level) for minerals and vitamins (Control, n = 15); 2) basal diet supplemented with vitamin C (ASC, n = 15); 3) basal diet supplemented with fat-soluble vitamins (FSV, n = 15); and 4) basal diet supplemented with water-soluble vitamins (WSV, n = 15). After puberty (approximately 12 mo of age), semen was collected at a regular frequency (three times every 2 wk) for 5 wk. Thereafter, all boars were intensively collected (daily during 2 wk). A recovery period (semen collection three times every 2 wk) followed and lasted for 10 wk. Sperm quality (percentage of motile cells and percentage of morphologically normal cells) and quantity (sperm concentration, semen volume, and total sperm number) were recorded as well as direct and hormone related measurements of boar libido. Blood and seminal plasma samples were taken to monitor vitamin status. High concentrations of B6 (P < 0.05) and folic acid (P < 0.05) were observed in the blood plasma of WSV boars, whereas greater concentrations of vitamin E (P < 0.01) were obtained in FSV boars. In the seminal plasma, folic acid concentrations tended to be greater in WSV boars (P < 0.08). During the intensive collection period, there was a tendency (P < 0.06) for semen production to be greater in WSV boars, the effect being less pronounced (P < 0.10) in FSV boars. During the recovery period, the percentage of motile sperm cells was greater in WSV boars (P < 0.03) and, to a lesser extent, in FSV boars (P < 0.10) compared with Control boars. Sperm morphology and libido were not affected by treatments. These results indicate that the transfer of vitamins from blood to seminal plasma is limited and the dietary supplements of water-soluble and fat-soluble vitamins may increase semen production during intensive semen collection.
Key Words: Boar • Semen • Vitamin
Introduction
It is generally assumed that the feed used for gestating sows is sufficient to cover the requirements in energy, protein, lysine, and methionine for boars (Close and Roberts, 1993
). However, the feed restriction imposed on boars is usually more severe than that for gestating sows (Close and Roberts, 1993) and could limit the daily provision of micronutrients, such as vitamins, required for optimal reproductive performance.
In boars, the effect of micronutrients on reproductive performance is not well documented. It was demonstrated that a diet supplemented with selenium and vitamin E improved sperm quality (Marin-Guzman et al., 1997). Brzezinska-Slebodzinska et al. (1995) observed that supplementation with vitamin E increased the concentration of spermatozoa in semen, an effect possibly linked to the antioxidant properties of this vitamin. In chicken, vitamin E tended to improve semen quality traits by increasing concentrations of spermatozoa and cell viability (Franchini et al., 2001). In rams, it was suggested that vitamins B1, B6, and B12 play a key role in thermoregulation of rectal and scrotal skin temperature during heat stress and maintain libido, semen quality, and fertility (El-Darawany, 1999). Results on the effect of vitamin C on the reproduction of boars are inconsistent. Ivos et al. (1971) observed that addition of ascorbic acid to the boar’s diet improved fertility during a period of heat stress. However, Lin et al. (1985) observed inconsistent responses and Wilson et al. (2001) failed to find any significant response to a supplement of vitamin C on reproductive performance of boars.
The present study was therefore carried out to determine the effects of increasing the daily provision of vitamin C and dietary fat- or water-soluble vitamins on vitamin status, libido, and semen characteristics in boars.
Materials and Methods
Animals and Treatments
Sixty boars (20 Duroc, 20 Landrace and 20 Yorkshire) were selected at (mean ± SEM) 34.2 ± 0.6 wk for this study and they were housed individually in pens on semi-slatted floors. Average BW were (mean ± SEM) 144.6 ± 2.53 kg and 235.4 ± 3.01 kg at the initiation of treatment and the end of the experiment, respectively. The boars were distributed, according to their BW, age, and breed, to five blocks (repetitions) of 12 animals each. Within each block, the animals were assigned randomly to one of the four experimental groups: 1) basal diet (Table 1) with a vitamin premix providing concentrations corresponding to the industry average according to a survey carried out by BASF (1993), which exceeded the recommended NRC (1998) levels (Table 2; Control, n = 15); 2) basal diet supplemented with the control premix and vitamin C (Table 2; ASC, n = 15); 3) basal diet supplemented with the control premix and extra fat-soluble vitamins (Table 2; FSV, n = 15); and 4) basal diet supplemented with the control premix and extra water-soluble vitamins (Table 2) (WSV, n = 15). The daily food allowance for the whole experimental period was 3 kg per boar and the premixes were given as a top dressing of 50 g.
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Libido was evaluated as described by Louis et al. (1994) throughout the experiment. Briefly, two measurements were recorded: T1, the time between entrance in the collection area and onset of ejaculation, and T2, the duration of ejaculation. The collected semen was strained through sterile gauze in a prewarmed insulated container kept at 37°C, to remove the gelatinous phase. Sperm volume was weighed (±0.1 g) and the sperm concentration was estimated using a spectrophotometer (Novaspec II, Pharmacia Biotech; Cambridge, U.K.) calibrated with a hemacytometer (Young et al., 1960). Each semen sample was immediately diluted to a final concentration of 3 x 109 spermatozoa per dose of 85 mL in a commercial extender (BTS extender; Bio’dil, Genes Diffusion, Douai, France) at a final concentration of 3.5 x 107 cells/mL. Sperm quality was estimated from the percentage of motile cells and of morphologically normal cells. Sperm production was measured as sperm concentration, semen volume and total sperm number.
Those measurements were taken for each ejaculate during the regular collection and the recovery period. During the intensive collection period, only the sperm quantity was evaluated. Sperm motility was determined on a warmed sample (37°C) at a magnification of 400x with an optical microscope. Total motility was determined as the percentage of spermatozoa that had any sign of motility (Rodriguez-Gil and Rigau, 1995) in two areas with a count of 100 cells per area. The morphology of spermatozoa was determined on slides stained with eosin-nigrosin also containing glucose and TES-Tris (Bamba, 1988). Observations on sperm morphology were made under a light microscope (400x) for 100 cells in two areas of the slides. The number of normal sperm, abnormal tails, abnormal heads, loose heads, proximal cytoplasmic droplets, and distal cytoplasmic droplets was counted.
The semen response to preservation was also evaluated during a period of 7 d in the regular collection period and at the end of the recovery period. One dose of semen per boar was kept at 16°C and agitated manually twice a day. Sperm cell motility and the percentage of cells with normal morphology were evaluated daily.
Sampling
Blood samples were taken from the jugular vein by venipuncture during the experiment to measure concentrations of estradiol-17ß and vitamin C as well as some of the fat- (vitamin E) and water-soluble vitamins (B2, B6, and folates) included in the dietary supplements. These samples were collected at the beginning of the experiment (before the treatment allocation), before and after the intensive collection period, and at the end of the recovery period. Seminal plasma samples were taken at the same time as blood samples except for the first one, the boars being not trained yet for semen collection.
At the end of the recovery period, a jugular catheter was inserted using a nonsurgical technique described by Matte (1999). Two days after catheterization, serial blood samples were collected to determine the profile of plasma estradiol-17ß at 0, 120, 240, 480 min and during an ejaculation. Such measurements were done because the metabolism of estradiol-17ß has been related to libido (Joshi and Raeside, 1973; Levis and Ford, 1989). In fact, Louis et al. (1994) observed a negative relation between estradiol-17ß concentrations and boar libido (time required to start ejaculating).
Vitamin and Estradiol Measurements
The concentrations of vitamins C, E, and B2 were determined in blood plasma, and B6 and folates were determined in blood serum. All those vitamins were also measured in seminal plasma.
Serum folates were measured in duplicate by radioassay using commercial kits containing 125I-pteroylglutamic acid (Quantaphase Folate, Bio-Rad Laboratories Ltd., Mississauga, Canada). The validated procedure for pigs described by Tremblay et al. (1986) was used for the serum folates and validation tests were done for the measurement of folates in seminal plasma. The intra- and interassay CV were 3.0 and 4.2%, respectively, and the recovery rate was 97.3%. Serum concentrations of pyridoxal-5-phosphate (P-5-P) were determined in duplicate using a fluorimetric method adapted by Matte et al. (1997) from the technique of Srivastava and Beutler (1973). Intra- and interassay CV for the P-5-P in seminal plasma were 3.2 and 5.2%, respectively, and the recovery rate was 102.8%.
Measurements of riboflavin (B2) were done by HPLC using a method adapted by Giguère et al. (2002) from that of Zempleni (1995) and Schüep et al. (1988). Intra- and interassay CV for the riboflavin in seminal plasma were 5.2 and 8.5%, and the recovery rate was 94.3%.
Measurements of vitamin E (
-tocopherol) were done by HPLC according to a modification of the method described by Bieri et al. (1979) and Driskell et al. (1982) and validated for blood plasma and seminal plasma. Intra- and interassay CV were 3.82 and 9.03%, and the recovery rate was 100%. A 250-µL aliquot of sample or standard solutions was mixed with 500 µL of 100% ethanol. Hexane (1 mL for blood plasma and 2 mL for seminal plasma) was added and the mixture was centrifuged 1.5 min at 1,800 x g. The supernatant was removed and transferred to another tube. The procedure was repeated, the supernatant was again transferred in the tube and the hexane was evaporated with a stream of nitrogen. The residue was redissolved in 500 µL of ethanol 100%. A 20-µL aliquot of this solution was injected into the HPLC. The HPLC system and column were the same as those used for riboflavin (Giguère et al., 2002); the elution (96% ethanol, 4% water) was done at a flow rate of 1 mL/min, and the fluorimetric detection was adjusted for an emission of 320 nm and an excitation of 285 nm.
Ascorbic acid was determined in duplicate in plasma samples by the fluorimetric method described by Brudacher and Vuilleumier (1974). Intra- and interassay CV for the measurements in seminal plasma were 3.1 and 5.3%, respectively, and the recovery rate was 98.1%.
Serum estradiol-17ß were measured in duplicate by RIA using commercial kits containing 125I 17ß-estradiol, (ICN Biomedicals Inc, Costa Mesa, CA) and validated for pigs. Intra- and interassay CV were 3 and 5.3%, respectively, and the recovery rate was 103.5%.
Statistical Analyses
Data were analyzed using the SAS procedure for mixed models (SAS Inst., Inc., Cary, NC; Littell et al., 1996) according to a randomized arrangement of treatments with the dietary supplement of vitamins as the main independent variable. Due to the lack of significant difference among breeds, this variable was not considered in the model. The boar was considered as the experimental unit. The following model was used:
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where Yij = dependent variable, Fj = vitamins supplements, and eij = residual error.
For the analysis of vitamins assayed in blood and seminal plasma, periods of sampling were added to the model as a second factor and were analyzed using the repeated option of the MIXED procedure of SAS with the auto regressive option. For blood vitamins, data were corrected as a percentage of initial value. A logarithm transformation was done to normalize for experimental error for all blood and seminal plasma vitamins.
For the sperm production and the sperm quality, separate analyses were performed for the three collection periods: regular (eight ejaculates in 5 wk), intensive (14 ejaculates in 2 wk), and recovery period (15 ejaculates in 10 wk). The time of ejaculate collection within each period was added to the model as a second factor and those were analyzed using the repeat option of the MIXED procedure with the auto regressive option. During the intensive semen collection, the first ejaculate was used as a covariate and a logarithm transformation was done to normalize for experimental error. Pearson coefficients of correlation were performed between estradiol values and the corresponding libido measurements T1 and T2 for each collection periods.
A Dunnett test was used for all measurements to compare the data from the different treatments versus those from the Control. Differences were considered significant at P < 0.05.
Results
Blood Vitamin Status
Serum concentrations of folates were greater (P < 0.05) in WSV than in Control boars, and this effect was amplified after the intensive semen collection period (treatment x time, P < 0.05) (Figure 1). Serum concentrations of vitamin B6 were also greater (P < 0.05) in WSV than in Control boars (Figure 2). The FSV boars had greater blood plasma concentrations of vitamin E than Control boars (P < 0.01) (Figure 3). Finally, no treatment effect was observed for plasma concentrations of vitamin C; the overall mean ± SEM was 16.34 ± 0.34 µg/mL.
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. No treatment effect was observed on the seminal concentrations of vitamins except for total folates (folates concentration (semen volume), which tended to be greater in WSV than in Control boars, particularly at the end of the recovery period (P < 0.08). Mean total folate concentrations ± SEM were 382.5 ± 47.9, 302.9 ± 32.3, 304.3 ± 30.4, and 490.1 ± 41.6 ng/ejaculate, respectively, for Control, ASC, FSV, and WSV treatments.
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No treatment effect was observed for the average total sperm number per ejaculate or the cumulative sperm production per boar during the regular collection period (8 ejaculates per boar); the overall means were 5.28 x 1010 ± 0.12 x 1010 and 41.97 x 1010 ± 2.13 x 1010 total sperm number, respectively. During the intensive collection period (daily for 14 d), sperm production decreased drastically from d 1 to 7 and remained stable thereafter (Figure 4). In response to this intensive collection, sperm production in WSV and FSV boars tended to remain greater (P < 0.06 and P < 0.1, respectively) than in Control animals. The average total sperm number (means ± SEM) from the 14 ejaculates collected during the intensive period were 2.412 x 1010 ± 0.135 x 1010, 2.592 x 1010 ± 0.147 x 1010, and 2.667 x 1010 ± 0.123 x 1010 sperm cells for the Control, FSV, and WSV treatments, respectively. The cumulated values for the 15 ejaculates collected during the recovery period were not influenced by the treatments; the overall mean was 83.22 x 1010 ± 4.44 x 1010 of total sperm number, and the total sperm number per ejaculate per boar at the end of the recovery period was 5.598 x 1010 ± 0.197 x 1010 sperm.
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Discussion
Vitamins Status
According to the analytical values, the dietary provisions of vitamins were, in some cases, different to those expected. Such differences have been reported previously and could be related in part to the analytical techniques (Matte et al., 1994). Nevertheless, the ratio between analytical values of supplemented and control diets were still high (4.4 for vitamin E and 5.5 in average for WSV).
In spite of an increase in serum folates and vitamin B6 in WSV boars and an increase in blood plasma vitamin E in FSV boars, vitamins did not seem to be readily transferred to the seminal plasma, except for folates. In humans, it was also observed that folate concentrations in blood plasma are highly correlated with seminal folates (Wallock et al., 2001). Folates are essential for basic metabolism, such as methylation and DNA synthesis (McDowell, 1989; Le Grusse and Watier, 1993). Therefore, adequate amounts of folates are critical for cell division and differentiation (McDowell, 1989; Le Grusse and Watier, 1993), two physiological processes essential for spermatogenesis. The biological significance of this folate transfer from blood to seminal plasma remains to be elucidated. For vitamin E, the absence of -tocopherol in the seminal plasma is consistent with the observations of Marin-Guzman et al. (1997), who showed that -tocopherol was accumulated in spermatozoa and testis but not in seminal plasma of boars receiving a dietary supplement of vitamin E. No measurements of vitamin E were done on sperm or testis in the present experiment.
Sperm Production
The higher sperm production in WSV boars during the intensive collection period suggests that those boars were more resistant to such challenge than were Control boars. The fat-soluble vitamins also tended to be beneficial for sperm production during the intensive collection period, but it was less pronounced than with the water-soluble vitamins. This intensive collection was performed in order to estimate the basal level of spermatogenesis. Because WSV and FSV treatment effects were observed during the intensive collection period, it appears that these dietary supplements of vitamins may have influenced directly or indirectly the spermatogenesis of the boars. Folic acid may be one of the important vitamins involved in the present effect of water-soluble vitamins. In humans, nonmethyltetrahydrofolate concentrations in seminal plasma were positively correlated with total sperm count and sperm density (Wallock et al., 2001) suggesting that these forms of folates may play an important role in reproductive function. The same phenomenon might have occurred in the present experiment, since WSV diet induced an increased transfer of folates to the seminal pool. Vitamin E is believed to play an important role in spermatogenesis (Mason, 1954; Marin-Guzman et al., 1997). In rats, using a deficiency model, Cooper et al. (1987) suggested that the effect of vitamin E occurs through intratesticular factors that regulate steps in development of the germ cell of the rats. The mechanism might be different in boars since dietary supplement of vitamin E do not influence testicular sperm reserves or sertoli or germ cell populations (Marin-Guzman, 2000).
No treatment effect was noted on the sperm concentration in ASC boars. As mentioned earlier, inconsistent results were reported in the literature. In the chicken, vitamin C supplementation led to a reduction in concentrations of spermatozoa (Franchini et al., 2001). In rabbit, it was demonstrated that the combination of supranutritional levels of vitamin C and E improved the viability, the kinetics of spermatozoa and increased the fertility rate (Castellini et al., 2000). However, high levels of vitamin C associated with low levels of vitamin E can be detrimental, the antioxidant role of the vitamin C being completely reversed as prooxydant under such conditions (Castellini et al., 2000). Present results are in agreement with the absence of vitamin supplements effects on semen concentration in the pigs (Wilson et al., 2001).
Sperm Quality
The percentage of motile sperm cells in boars was greater (WSV) or tended to be greater (FSV) than in Control boars during the recovery period. Those results suggest that the beneficial effect of vitamins on sperm production during the intensive collection period had a carry-over effect on sperm quality during the recovery period. This could be possible since the present length of the recovery period (10 wk) covered the delay (5 to 7 wk) of response required for the transformation of a stem cell to a spermatozoa and the passage through the epididymis (Flowers, 1996). Nevertheless, a direct effect of WSV or FSV treatments during the recovery period cannot be ruled out. The present experiment does not allow us to clearly confirm this hypothesis since the sperm-quality measurements were done before and after, but not during, the intensive collection period. For fat-soluble vitamins, vitamin E could be involved in the tendency observed since vitamin E may provide a direct protection of the sperm cells from morphological damage (Brzezinska-Slebodzinska et al., 1995). In fact, the morphology and the motility of sperm cells would be preserved by binding of this vitamin to endoperoxides (Marin-Guzman et al., 1997).
In the present experiment, the observed effects of WSV on sperm motility were not associated with other aspects of sperm quality, such as the percentage of morphologically normal sperm or the semen preservation during a 7-d period. The biological mechanism involved in the response of different aspects of sperm quality to dietary vitamins remains to be investigated.
In conclusion, dietary supplements of water- and fat-soluble vitamins appeared efficient to attenuate the depressed sperm production during a period of intensive collection. Semen quality was maintained and even slightly increased following such a challenge with fat- and water-soluble vitamins, respectively. Some of those vitamins could be involved in the process of spermatogenesis.
Implications
It seems that circulating vitamins can be altered by vitamin supplementation in boars, although such treatment did not seem to affect semen quality or output to an appreciable extent in normal conditions. Vitamin supplementation might be needed if frequency of semen collection is increased. Those vitamin effects on both semen production and quality need to be confirmed with large numbers of animals taking into account the individual variation associated with the measured criteria.
Footnotes
1 The authors are grateful to M. Guillette and A. Giguère for technical assistance, D. Morissette, C. Mayrand, F. Champagne, F. Phaneuf, J. Boudreau, M. Turcotte, E. Bérubé, and A. Marsh for animal care, and S. Méthot for advice in statistical analyses. This work was subsidized by la Fédération des Producteurs de Porc du Québec (FPPQ), la Société des Éleveurs de Porcs du Québec (SEPQ), le Centre d’insémination artificielle du Québec (CIPQ inc.), Roche Vitamins Canada and the Matching Investment Initiative of Agriculture and Agri-Food Canada. 
3 Correspondence: 2000 Rte. 108, CP 90 (phone: 819-565-9171; fax: 819-564-5507; e-mail: mattej{at}agr.gc.ca).
Received for publication July 29, 2003. Accepted for publication November 10, 2003.
Literature Cited
Bamba, K. 1988. Evaluation of acrosomal integrity of boar spermatozoa by bright field microscopy using an eosin-nigrosin stain. Theriogenology 29:1245–1251.
BASF Corp. 1993. Vitamin Supplementation Rates for U.S. Commercial Poultry, Swine and Dairy Cattle. BASF Corp., Mount Olive, NJ.
Bieri, J. G., T. J. Tolliver, and G. L. Catignani. 1979. Simultaneous determination of alpha-tocopherol and retinol in plasma or red cells by high pressure liquid chromatography. Am. J. Clin. Nutr. 32:2143–2149.
Brudacher, G., and J. P. Vuilleumier. 1974. Pages 989–997 in Vitamin C in Clinical Biochemistry Principles and Methods. Vol. II. H. Ch. Curtius and M. Roth, ed. Walter de Gruyter, New York.
Brzezinska-Slebodzinska, E., A. B. Slebodzinski, B. Pietras, and G. Wieczorek. 1995. Antioxidant effect of vitamin E and glutathione on lipid peroxidation in boar semen plasma. Biol. Trace Elem. Res. 47:69–74.[Medline]
Castellini, C., P. Lattaioli, M. Bernardini and A. Dal Bosco. 2000. Effect of dietary -tocopheryl acetate and ascorbic acid on rabbit semen stored at 5°C. Theriogenology 54:523–533.[Medline]
Close, W. H., and F. G. Roberts. 1993. Pages 347–368 in Recent Developments in Pig Nutrition 2. D. J. A. Cole, W. Haresinh, and P. C. Garnsworthy, ed. Nottingham University Press, Nottingham, U.K.
Cooper, D. R., O. R. Kling, and M. P. Carpenter. 1987. Effect of vitamin E deficiency on serum concentrations of follicle-stimulating hormone and testosterone during testicular maturation and degeneration. Endocrinology 120:83–90.[Abstract]
Driskell, W. J., J. W. Neese, C. C. Bryant, and M. M. Bashor. 1982. Measurement of vitamin A and vitamin E in human serum by high-performance liquid chromatography. J Chromatogr. 231:439–444.[Medline]
El-Darawany, A. A. 1999. Improving semen quality of heat stressed rams in Egypt. Indian J. of Anim. Sc. 69:1020–1023.
Flowers, B. 1996. Reproductive physiology of the boar. Pages 1–6 in Proc. of the Swine Reprod. Symp. Am. Assoc. of Swine Practitioners and Soc. for Theriogenology. Kansas City, MO.
Franchini, A., M. L. Bergonzoni, C. Melotti, and G. Minelli. 2001. The effects of dietary supplementation with high doses of vitamin E and C on the quality traits of chicken semen. Arch. Geflügelk. 65:76–81.
Giguère, A., C. L. Girard and J. J. Matte. 2002. Erythrocyte glutathione reductase activity and riboflavin nutritional status in early-weaned piglets. Int. J. Vitam. Nutr. Res. 72:383–387.[Medline]
Ivos, J., C. Dophinar, and G. Muhaxhiri. 1971. Thermic stress as a factor of disturbances in the reproduction of pigs and possibility of prevention of these disturbances by the addition of ascorbic acid. Vet. Arh. 41:202–216.
Joshi, H. S., and J. I. Raeside. 1973. Synergestic effects of testosterone and oestrogens on accessory sex glands and sexual behavior of the boar. J. Reprod. Fertil. 33:411–423.[Medline]
Le Grusse, J., and B. Watier. 1993. Les vitamines, données biochimiques, nutritionnelles et cliniques. Centre d’Étude et d’Informations sur les Vitamines, Produits Roche, Neuilly-sur-Seine, France.
Levis, D. G., and J. J. Ford. 1989. The influence of androgenic and estrogenic hormones on sexual behavior in castrated adult male pigs. Horm. Behav. 23:393–411.[Medline]
Lin, H. K., S. Y. Chen, C. Y. Huang, Y. H. Kuo, and L. C. Wung. 1985. Studies on improving semen quality of working boars fed diet with addition of vitamin C in summer season. Annual Res. Rep. of the Anim. Res. Inst., Taiwan Sugar Corp. 73/74:59–73.
Littell, R. C., G. A. Milliken, W. W. Stroup, and R. D. Wolfinger. 1996. SAS System for Mixed Models. SAS Inst. Inc, Cary, NC.
Louis, G. F., A. J. Lewis, W. C. Weldon, P. S. Miller, R. J. Kittok, and W. W. Stroup. 1994. The effect of protein intake on boar libido, semen characteristics, and plasma hormone concentrations. J. Anim. Sci. 72:2038–2050.[Abstract]
Marin-Guzman, J., D. C. Mahan, Y. K. Chung, J. L. Pate, and W. F. Pope. 1997. Effects of dietary selenium and vitamin E on boar performance and tissue responses, semen quality and subsequent fertilization rates in mature gilts. J. Anim. Sci. 75:2994–3003.
Marin-Guzman, J., D. C. Mahan, and J. L. Pate. 2000. Effect of dietary selenium and vitamin E on spermatogenic development in boars. J. Anim. Sci. 78:1537–1543.
Mason, K. E. 1954. The tocopherols: Effects of deficiency. Pages 514–572 in The Vitamins. Vol. 3. W. H. Sebrell and R. S. Harris, ed. Academic Press, New York, NY.
Matte, J. J. 1999. A rapid and non-surgical procedure for jugular catheterization of pigs. Lab. Anim. 33:258–264.
Matte, J. J., and C. L. Girard. 1994. Pteroylglutamic (folic) acid in different feedstuffs: The pteroylglutamic content and an attempt to measure the bioavailability in pigs. Brit. J. Nutr. 72:911–922.[Medline]
Matte, J. J, A. A. Ponter, and B. Sève. 1997. Effects of chronic parental pyridoxine and acute enteric tryptophan on pyridoxine status, glycemia and insulinemia stimulated by enteric glucose in weanling piglets. Can. J. Anim. Sci. 77:663–668.
McDowell, L. R. 1989. Vitamins in Animal Nutrition. Academic Press, San Diego, CA.
NRC. 1998. Nutrient Requirements of Swine. 10th ed. Natl. Acad. Press, Washington, DC.
Rodriguez-Gil, J. E., and T. Rigau. 1995. Effects of slight agitation on the quality of refrigerated boar semen. Anim. Reprod. Sci. 39:141–146.
Schüep, W., and K. Steiner. 1988. Determination of vitamin B2 in complete feeds and premixes with HPLC. In Analytical Methods for Vitamins and Carotenoids in feed. H. Keller, ed. Basel, Switzerland.
Srivastava, S. K., and E. Beutler. 1973. A new fluorimetric method for the determination of pyridoxal 5-phosphate. Biochim. Biophys. Acta. 304:765–773.[Medline]
Tremblay, G. F., J. J. Matte, L. Lemieux, and G. J. Brisson. 1986. Serum folates in gestating swine after folic acid addition to diet. J. Anim. Sci. 63:1173–1178.
Wallock, L. M., T. Tamura, C. A. Mayr, K. E. Johnston, B. N. Ames, and R. A. Jacob. 2001. Low seminal plasma folate concentrations are associated with low sperm density and count in male smokers and nonsmokers. Fertil. Steril. 75:252–259.[Medline]
Wilson, M. E., T. J. Gall, L. L. Peterson, and K. J. Rozeboom. 2001. Feeding the boar for optimum performance. Pages 312–322 in Proc. of the 22nd Western Nutr. Conf. on Responsible Anim. Agric., Saskatoon, Canada.
Young, D. C., R. H. Foote, A. R. Turkheimer, and H. D. Hafs. 1960. A photoelectric method for estimating the concentration of sperm in boar semen. J. Anim. Sci. 19:20–25.
Zempleni, J. 1995. Determination of riboflavin and flavocoenzymes in human blood plasma by high-performance liquid chromatography. Ann. Nutr. Metab. 39:224–226.[Medline]
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