337 s Research Note t Effects of Low-Selenium Diet on Levels of Plasma Luteinizing Hormone, Follicle-stimulating Hormone and Estradiol in Pullets and Laying Hens Takeshl OISHI, Katsuhisa YOSHIDA, Shin-ichi MORIGUCHI and Sumio INUZUKA Faculty of Agriculture, Kinki University, Higashiosaka-shi, 577, Japan. Two experiments were done to study the effects of a low-selenium diet on the plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and estradiol of pullets and laying hens. Thirteen pullets 169 days old and twelve laying hens 530 days old were used. They were fed a diet with selenium as DL-selenomethionine added to a low-selenium diet, with 0.24mg of selenium per kg of feed, or a diet without selenium during the experiment. The plasma levels of LH, FSH, estradiol and selenium, and the plasma GSHpx activity were assayed regularly. The plasma LH levels of the pullets decreased significantly with the lowselenium diet, and that of the laying hens also decreased, but not significantly. The level of plasma estradiol of both pullets and laying hens tended to decrease. The plasma FSH level was not affected. The plasma selenium level and GSHpx activity of both pullets and laying hens significantly decreased with the lowselenium diet. These results suggested that the decreased egg production rate caused by the low-selenium diet involved the factors, such as the effect of a low level of plasma LH on ovulation, the effect of a low level of plasma LH on the release of estradiol from the ovary, and the effect of a low plasma level on estradiol on the compounding of precursor of egg in the liver. (Jpn. Poult. Sci., 25: 337-342, 1988) Key words: selenium, egg production, plasma LH, plasma FSH, plasma estradiol Introduction The physiological role of selenium is now of interest in many fields1). There are many studies of the effect of selenium on poultry2,3). When laying hens are fed low-selenium diet, the feed intake and body weight are not affected, but the egg production rate decreases4,5). The lower egg production rate on the low-selenium diet could be a direct effect of the low level of selenium on the laying process6), but, details on the effect are not known. The purpose of this paper was to investigate the effects of a low-selenium diet on the plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and estradiol in pullets and laying hens. Received January 7, 1988
338 Jpn. Poult. Sci., 25 (5), 1988 Materials and Methods Experiment 1 The effects of a low-selenium diet on plasma LH, FSH and estradiol of pullets were studied. Thirteen pullets (White Leghorn) 169 days old were used. They were housed in individual cages in a room with controlled temperature (20 Ž) and light (14L:10D). Their egg production rate was about 85% at the start of the experiment. The total experimental period was nine weeks, and was divided into three three-week periods. In the first and third periods, the pullets were fed a control diet with selenium as DL-selenomethionine added to the low-selenium diet. The composition of low-selenium diet is shown in Table 1. The selenium level of the control diet was 0.24mg/kg. In the second period, the pullets were fed a low-selenium diet without added selenium. The selenium level of this diet was 0.06mg/kg. Each pullet was provided with 120g of the diets daily. Water was freely available. Its selenium content was below the limit of detection (0.001ƒÊg/ml) by the fluorescence analysis method used here7). On days 7, 14 and 21 of each period, blood was taken from each pullet, one hour after the production of an egg or else at 6p.m. for pullets that had no egg laid. The blood was centrifuged at 3000rpm for 10 minutes to separate the plasma. The plasma obtained was used in assays of plasma LH, FSH, estradiol, selenium content and plasma GSHpx activity of the pullets. The selenium content and GSHpx activity of the plasma were assayed by methods described elsewhere3). Plasma LH, FSH and estradiol were assayed by radioimmu- Table 1. Composition of low-selenium diet 1) Provided the following per kilogram of feed Vitamin B1 HC1, 100mg; Vitamin B2, 16mg; Vitamin B6, 10mg; Pantotheate, 25mg; Folic acid, 4mg; Niacin, 100mg; Vitamin K, 5mg; Vitamin B12, 0.015mg; Biotin, 0.6mg; Vitamin A, 18,000IU; Vitamin D, 1,600IU; Vitamin E, 55IU 2) Provided the following in grams per 100g of feed: CaCO3, 6.6; CaHPO4 2H2O, 3.75; KH2PO4, 1.0; NaCl, 0.3; MgCO3, 0.425; Fe-citrate 5H2O, 0.06; MnSO4 H2O, 0.03; ZnCO3, 0.0125; H3BO3, 0.01; KI, 0.0015; Cu(CH3COO)2 H2O, 0.004, CoSO4 7H2O, 0.0002; Na2MoO4 2H2O, 0.0006
noassay methods. OISHI et al.: Selenium levels and plasma hormone 339 Records were kept of the egg production rate and feed intake during the experimental period. The pullets were weighed weekly. Experiment 2 The effects of a low-selenium diet on plasma LH, FSH and estradiol of laying hens were studied. Twelve laying hens (White Leghorn) 530 days old were used. They fed the same control diet as for experiment 1 during a two-week period before the experiment. On basis of the egg production rate of during that period, they were divided into two groups that had equal egg production rates at the start of the experiment. Each group consisted of six laying hens. For four weeks, one group was fed a control diet, and the other group was fed a low-selenium diet. Weekly, by the method used in experiment 1, blood was taken from each laying hen. The plasma separated from the blood of each laying hen was used in assays of LH, FSH, estradiol, selenium and GSHpx activity by the same methods as used in experiment 1. Other materials and methods were the same as in experiment 1. Results and Discussion The effects of the low-selenium diet on the plasma LH, FSH and estradiol of pullets (experiment 1) and laying hens (experiment 2) are shown in Table 2. The results of the control diet in experiment 1 are shown as a mean of the first and third periods. The plasma LH level of the pullets decreased significantly (p<0.05) on the lowselenium diet compared to the control diet. The plasma LH level of the laying hens tended to decrease, but not significantly compared to the controls. The plasma FSH level of the pullets and laying hens were not affected by the low-selenium diet; it stayed at about 2ng/ml during all periods in both experiments. On the low-selenium diet, the plasma estradiol the controls, although level of both pullets and laying hens decreased compared to the difference was not significant statistically. The effects of the low-selenium diet on the egg production rate, feed intake and Table 2. Effects of low-selenium diet on plasma LH, FSH and estradiol in pullets and laying hens 1) Luteinizing Hormone 2) Follicle-stimulating Hormone 3) Mean }S. D. * Significant difference, p<0.05
340 Jpn. Poult. Sci., 25 (5), 1988 Table 3. Effects of low-selenium diet on egg production rate, feed intake and body weight in pullets and laying hens 1) Mean } S. D. * Significant difference, p<0.05 Table 4. Effects of low-selenium diet on plasma selenium content and GSHpx activity in pullets and laying hens 1) Mean }S. D. * Significant difference, p<0.05 body weight of the pullets and laying hens are shown in Table 3. The egg production rate of the pullets decreased by about 25% on the low-selenium diet, and that of the laying hens by about 30%. The decreases were significant statistically (p<0.05). The feed intake and body weight were not affected by the diet. Similar results have reported by CANTOR et al4). The effects of the low-selenium diet on the plasma selenium level and GSHpx activity in the pullets and laying hens are shown in Table 4. Both values were different statistically (p<0.05) with the selenium content of the diet. These results agree with those in a previous paper3) and in other studies4,8,9,10) The results suggested that the low-selenium diet used here decreased the plasma selenium content and plasma GSHpx activity; following these change, the egg production rate decreased. The low-selenium diet did not affect either feed intake or body weight, so it estimate that the low selenium content directly affecting the laying process. In a study of the plasma selenium level and the egg production rate, significant (p<0.05) correlation in the pullets (r=0.813) and in the laying hens (r= 0.756) were found. When the selenium level of the diet is varied largely, as in this study, the relationship between the plasma selenium level and egg production is close. The tendency for decreased plasma LH and estradiol levels in pullets and laying hens seen here suggested that the low-selenium diet affected the mechanism of these hormones, and especially that of LH. It was not clear whether the low selenium level affected the release of LH from the anterior pituitary or the secretion by the
OISHI et al.: Selenium levels and plasma hormone 341 hypothalamus of luteinizing hormone releasing factor (LRF), which promotes the release of LH from the anterior pituitary. These results showed that a low egg production rate caused by a low-selenium diet involved the factors such as the effects of a low level of plasma LH on ovulation, the effects of a low level of plasma LH on the release of estradiol from the ovary, and the effects of a low plasma estradiol level on compounding of precursor of egg in the liver. The reason for decreases in the plasma LH level being larger in the pullets seemed to be related to their more active hormone secretion. References 1) TAKAHASHI, K (1986) Selenium deficiency and glutathione peroxidase, Metabolism and Disease, 23: 57-64. 2) INUZUKA, S. and T. OISHI (1984) Selenium contents of blood and eggs before and after commencement of egg production in pullets, Jpn. J. Zootech. Sci., 55: 470-474. 3) OISHI, T., S. INUZUKA and S. AOKI (1986) Distribution of blood selenium in red blood cells and plasma of laying hens, Jpn. Poult. Sci., 23: 284-288. 4) CANTOR, A. H and M. L. SCOTT (1974) The effect of selenium in the hen's diet on egg production, hatchability, performance of progeny and selenium concentration in eggs, Poult. Sci., 53: 1870-1880. 5) LATSHAW, J. D. and M. OsMAN (1974) A selenium and vitamin E responsive condition in laying hen, Poult. Sci., 53: 1704-1708. 6) OISHI, T., S. INUZUKA and S. AOKI (1987) Effects of low-selenium feed with torula yeast on egg production rate and egg weight of laying hens, Mem. Fac. Agr. Kinki Univ., 20: 39-42. 7) OLSON, O. E. (1967) Fluorometric analysis of selenium in plants, J. Assoc. Off. Agric. Chem., 52: 627-637. 8) CHOW, C. K. and T. TAPPEL (1974) Response of glutathione peroxidase to dietary selenium in rat, J. Nutr., 104: 444-451. 9) YOSHIDA, M., H. IKUMO and H. HOsHII (1977) Selenium content in single cell proteins and selenium deficiency in chicks fed them as a sole protein source, Jpn. Poult. Sci., 14: 284-289. 10) IKUMO, H., H. HOSHII and M. YOSHIDA (1979) Availability of selenium in yeast by starting chicks, Jpn. Poult. Sci., 16: 80-84.
342 Jpn. Poult. Sci., 25 (5), 1988