Introduction

Selenium is an important trace mineral and selenium deficiency has a negative effect on the health of humans and animals (Alfthan et al., 2015; Hatfield, Tsuji, Carlson, & Gladyshev, 2014). One of the important functions of selenium can be its antioxidant role against free radicals containing particles to prevent cancer and its role in the functions of glutathione peroxidase and other reductase (Albanes et al., 2014; Shaheen, Rinklebe, Frohne, White, & DeLaune, 2014; Speckmann & Grune, 2015). Due to the increasing age of the population and the increase in the number of people involved with cancer and other immune-related diseases, there is a demand for selenium-rich milk. Therefore, increasing selenium intake by selenium-rich foods, such as rice, garlic, onions and broccoli, meat, milk and eggs have been considered as one of the interesting topics (Calamari, Petrera, & Bertin, 2010; Lin, 2014; Pophaly, Singh, Kumar, Tomar, & Singh, 2014; Yasin, El-Mehdawi, Anwar, Pilon-Smits, & Faisal, 2015). Foods can be supplemented with selenium in two forms, an inorganic form such as sodium selenite and sodium selenate or an organic form such as selenium yeast and selenium methionine. The metabolism of these two forms is different in animals. Organic selenium is absorbed through active transmission in the small intestine and in the synthesis of proteins; it is stored instead of methionine in tissues. It provides a source of selenium in the organs and tissues (Schrauzer, 2003). However, inorganic selenium is absorbed through passive transmission and is retained in small amounts in the body's stores, and a large amount is excreted through feces and urine. Thus, in recent years, the shift in supplements from the form of inorganic selenium (sodium selenite) to organic forms (selenium yeast and selenium methionine) is further emphasized.

Selenium deficiency presents a factor favoring the appearance of perinatal metritis and retention of placenta in dairy cattle. In addition, selenium deficiency can cause a malfunction of the testosterone and spermatozoon synthesis, which causes infertility in males. Selenium is known to influence the gross and histological morphology of the testis. Selenium deficiency is often characterized by reduced spermatozoon motility due to the fragility of its intermediate piece. Some selenoproteins were localized in the testes as selenophosphate synthase-2 (SPS-2) and the mitochondrial capsule selenoprotein (MCSeP). An increase of the selenium content in the testes of cattle was reported during the supplementation with selenium enriched cereals, mineral selenium (selenite) and organic selenium (yeast). The increase in fertility when adding selenium can be attributed to the reduction in embryonic death in the first month of gestation (Mehdi & Dufrasne, 2016).

According to Hall et al. (2014) feeding selenium-replete cows during late gestation a supranutritional selenium yeast supplement improves antioxidant status and immune responses after calving. There is a relationship between selenium content in the diet and mastitis frequency in cows, knowing that the phagocytic activity of neutrophils is the primary defense mechanism against mastitis. Selenium affects the innate and the adaptive immune responses of the mammary gland through humoral and cellular activities (Mehdi & Dufrasne, 2016). According to Finch and Turner (1996) several researchers have demonstrated a significant reduction in the incidence of mastitis in dairy cows after they were supplemented with selenium and/or vitamin E. The aim of this study is to investigate the effects of selenomethionine, selenium yeast and sodium selenium supplements on hematological blood parameters, reproduction and health of dairy cows in the transition period.

Material and methods

Animal and dietary treatment

The present study was conducted in the FKA animal husbandry and Agriculture Company in the province of Isfahan Iran. The study began in the early May and lasted to late July, 2016. Twenty-four multiparous dairy Holstein cows (parity 3) with an average weight of 791 ± 50 kg were selected 21 days before the expected parturition. The previous production of their milk did not differ significantly (p = 0.88) and they were randomly assigned to four groups and placed in separate 3 × 3 m booths with separate drinkers and feeders. The diets were formulated based on NRC (2001) recommendation for a dry cow (close up period) and fresh lactating dairy cow (Table 1). The diets included: 1) basal diet without selenium supplementation (C); 2) basal diet plus 0.5 ppm Se in the form of sodium selenite (Se-S) 3) basal diet plus 0.5 ppm Se in the form of selenium yeast (Se-Y); 4) basal diet plus 0.5 ppm Se in the form of selenomethionine (Se-M). The Na2SeO3 (MerkCo., Germany) was used as the inorganic source of Se. The organic sources of Se were in the form of Se-enriched yeast (Biorigin., Brazil - Selemax 2000 ppm) and the form of Se-methionine (Arkop., Poland - Amino Selstar 2000 ppm). Selenium methionine, selenium yeast and sodium selenite supplements were used in addition to the control diet. The mineral supplement of the control diet was without selenium and all three forms of selenium were added to the total mixed ration as topdress. Before the morning feeding, daily feed residuals were collected, weighed and 300 g of them were frozen in nylon bags for the analysis. The amounts of Se concentrations in diets were measured by an Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) device (using a Varian Model SpectrAA 220 atomic absorption spectrometer, Mulgrave, Victoria, Australia) (Table 1).

Sampling and data collection

Samples of total mixed ration (TMR) and orts were weekly taken for dry matter (DM) measurement, and were dried at 60° C for 48 h, and then composited by treatment. Dried pooled samples of TMR diets and refusal were ground through a 1-mm screen in a Wiley Mill and analyzed for analytical DM Association Official Analytical Chemist [AOAC], 2005), method 930.15), crude protein (CP) by the Kjeldahl method (AOAC, 2005), method 984.13), ether extract by the Soxhlet extraction method with diethyl ether (AOAC, 2005), method 920.39), ash (ignition at 600° C for 2 h; (AOAC, 2005), method 942.05), and ADF by the cetyl-trimethyl-ammonium bromide H₂SO₄ (CTAB) and 1N method (AOAC, 2005), method 973.18). The NDF content was determined by heat-stable α-amylase and sodium sulfite (Van Soest, Robertson, & Lewis, 1991). The amounts of Se concentrations in diets were measured by an Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) device (using a Varian Model SpectrAA 220 atomic absorption spectrometer, Mulgrave, Victoria, Australia).

Blood samples were also collected from all the cows, -21, -10, 0, +10 and +21 days relative to calving. Blood samples were obtained by 20 ml vein puncture of the jugular vein during 4 h after morning feeding. After blood was collected, each sample was poured into tubes containing ethylene diamine tetraacetic acid (EDTA) for determining blood hematology parameters.

Blood hematology parameters such as: including lymphocyte, red blood cells, hemoglobin and hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC) and red blood cell distribution width (RDWc) were evaluated by sysmex system (Sysmex K1000, TOA Ltd., Tokyo, Japan).

Measuring rectum temperature and vaginal discharge scores

The rectum temperature recorded for 10 days and measured by a thermometer during the morning feeding, and the recorded data were statistically analyzed.

Vaginal discharge scores measured at 10 and 21 days postpartum, the vaginal contents of the cows were extracted and graded from zero to 3 scores (Williams et al., 2005), as follows, and data were analyzed statistically.

Score 1: C (Clean mucous, lochia or no discharge)

Score 2: M (Mucopurulent)

Score 3: P (Purulent)

Reproduction data

Reproduction data the assessment of the reproductive status was carried out by rectal palpation, vaginal and ultrasonography examinations that were carried out from week two after parturition in weekly intervals to the confirmation of pregnancy. The following parameters were monitored: occurrence of clinical metabolic disorders (acidosis, ketosis, milk fever, retained placenta and displaced abomasum), clinical puerperal complications (mastitis and ovarian cyst) and distance to first estrus, insemination indexes and number of open days.

Statistical analysis

The data were analyzed by PROC MIXED of Statistical Analysis Software (SAS, 2004). Hematological blood parameters data (pre and postpartum) and average rectal temperature were analyzed as repeated measures and Time (DIM and week) was included in the model as a repeated variable. Based on the lowest Akaike information criterion, corrected Akaike information criterion, and Bayesian information criterion values for each variable analyzed the most suitable covariance structure were used (Littell, Henry, & Ammerman, 1998), 1998). The following model was used: Y_ijk = μ + T_i + Time_j + (T × Time)_ij + Cow(i)_k + e_ijk,

where Y_ijkis the dependent variable, μ is the overall mean, T_i is the fixed effect of treatment, Time_j is the fixed effect of sampling time (T × Time)_ij is fixed interaction between treatment and sampling time, Cow(i)_k is random effect of cow nested within treatment, and e_ijk is the error term. Previous lactation yield and the concentrations of hematological blood parameters obtained at −21 d relative to expected calving date were used as covariates and covariates were excluded from the model if they were not significant (p > 0.1). Data are reported as LSM and statistical significances were indicated at p ≤ 0.05 and 0.05 < p ( 0.10 as trends toward significance using the Tukey’s multiple comparison test.

Results and discussion

Hematological blood parameters

The results of blood tests showed that selenium supplementation had no significant effect on any hematological parameters of the blood during the transition period (Table 2 and 3). In the prepartum period, MCH tended to increase significantly in selenium methionine treatment (p = 0.07).

Hematological analysis is a good way to detect metabolic disorders. It is also a useful way to diagnose diseases of some systems and organs. Although diagnosis of a disease can only be done based on the total number of complete red blood cells (CBCs), measurement of blood cells in the patient may provide valuable information for diagnosis (Roland, Drillich, & Iwersen, 2014). As with other species, a certain amount of physiological variability is observed in the hematological profile of the cattle, which depends on the age, sex, stress, ration, body condition score, production conditions, and animal activity (Wood, Mandell, & Swanson, 2010). White blood cells or leukocytes have an essential role in the immune system, and include subgroups of different neutrophils, eosinophils, granulocytes, monocytes and lymphocytes.

Research done to investigate the effect of selenium on hematological parameters has led to different results, which can be attributed to the length of the study period, the type of supplementation used, the type of livestock and the amount of selenium in the base diet.

Shinde, Dass, and Garg (2009) consuming 0.3 ppm dry selenium in the form of sodium selenite in young buffalo rations, the researchers did not observe a change in the number of red blood cells, white blood cells, hematocrit, and hemoglobin concentration, which is consistent with the results of our study. Juniper, Phipps, Jones, and Bertin (2006) reported no significant difference in the number of red blood cells, white blood cells, hematocrit, and hemoglobin concentration in dairy cattle, broiler and sheep. There was no difference in hematological parameters in selenium fed lambs in the study of Mohri, Ehsani, Norouzian, Bami, and Seifi (2011). Faixova et al. (2007) observed that the number and resistance of red blood cells increased in lambs fed with diet containing 0.3 ppm selenium in dry matter in the form of selenium yeast.

Lymphocytes are produced in the lymphoid tissue and are dominated by white blood cells, but their ratio varies with age (Roland et al., 2014). In our study although lymphocyte percentage was not statistically significant, there was a significant difference between the treatments but the addition of selenium supplements was significantly higher in selenium methionine. White blood cells or leukocytes play a fundamental role in the defense system. Lymphocytosis can occur in the recovery phase of infectious diseases, and its reactive type is seen in acute infectious diseases, such as hepatitis, peritonitis, pericarditis, and mastitis (Gunter, Beck, & Phillips, 2003). The causes of lymphocytopenia include acute stress, bacterial infection, and reduced immunity. It also occurs in the event of destruction of lymph nodes (in tuberculosis, inflammation, and tumor incidence). The role of provoking selenium in immunity has already been proven (Mckenzie et al., 2003). Unfortunately, most studies have focused on the effects of selenium supplementation on selenium-deficient rations, and only limited reports of the effects of selenium sources on the safety performance of cows have been investigated. Selenium deficiency is an effective factor in reducing the fertility of lymphocytes and the transferrin receptor, which determines the proliferation of lymphocytes, reduces the number of lymphocytes in animals with selenium deficiency (Pighetti, Eskew, Reddy, & Sordillo, 1998). Researchers believe that selenium deficiency causes immunosuppression by preventing proliferation of lymphocytes (Sadeghian, Kojouri, & Mohebbi, 2012). In our study, with regard to the lack of difference between selenium-fed and control groups, it seems that the amount of selenium in the diet was sufficient to prevent the possible adverse effects of deficiency on white blood cells.

Rectal temperature and vaginal contents

The average rectal temperature in the experimental treatments is shown in Fig 1. The rectal temperature in the treatment containing selenium methionine was significantly (p < 0.05) lower than that of the control group. On the other hand, vaginal secretions were less in this group than in other groups (Tables 4 and 5).

In our study, cows fed selenium supplementation showed less rectal temperature and purulent discharge. Selenium increases the immune function of dairy cattle and cows that have normal rectal temperature after delivery usually do not have inflammatory challenges after delivery and it may be associated with more feed intake, better milk production and enhanced immune system. In agreement with our results, Seboussi et al., (2016) significantly showed less purulent discharge in dairy cows supplemented with selenium yeast.

Reproductive parameters

The present study showed that addition of selenium supplement during transition period reduced distance to the first estrus, first insemination and distance from delivery to pregnancy and increase conception percent in the first insemination (Table 6).

In addition, organic selenium supplements during the transition period have a positive influence on reproductive indices. In agreement with our research, other studies have shown the beneficial effects of selenium supplementation on pregnancy parameters in cattle and sheep (Gabryszuk & Klewiec, 2002; Sattar, Mirza, & Hussain, 2007). Contrary to the current research, Gunter et al. (2003) in cattle and Boland, Keane, Nowakowski, Brophy, and Crosby (2005) in sheep did not report any effect of selenium supplement on reproductive parameters.

In our study, selenium supplements (especially organic supplements) improve health status of dairy cows that prevent the increase of the rectal temperature, uterine disorders and retained placenta; so, improvements in reproductive parameters may be due to these reasons. Also uncontrolled or impaired immune and inflammatory responses in periparturient dairy cows are associated with increased incidence and severity of infectious diseases. The progressive development of oxidative stress during the transition from late gestation to peak lactation is thought to be a significant underlying factor leading to dysfunctional immune cell responses. Certain trace minerals, such as selenium, can ameliorate oxidative stress and reduce the severity of several economically important diseases in dairy cattle including mastitis and metritis. Many of the health benefits of Se can be attributed to the antioxidant functions of selenoproteins. Changes in selenoprotein activity as a consequence of Se nutritional status can directly alter a number of critical cellular functions involved in the inflammatory response. A better understanding of how selenium can optimize immune cell responses may facilitate the design of nutritional regimes that will reduce health disorders during the periparturient period (Sordillo, 2013).

Selenium and vitamin E as natural antioxidants have an important role in preventing the occurrence of retained placenta. These nutrients increase the activity of neutrophils, enhance their chemotactic effect and phagocytosis of opsonized pathogenic microorganisms. Oxidative stress may also contribute to placenta retaining. A great number of studies show that adequate supplement of selenium, zinc, cooper, iron and vitamins A, C and E playing a role of antioxidant; can reduce the percent of individuals with retained placenta. Adequately balanced rations with sufficient content of selenium, vitamin E and other antioxidants in food, appropriate housing of animals and good management lead to reducing the incidence of one of the most often ailments in dairy cows in postparturition period (Joksimović-Todorović & Davidović, 2013).

As shown in Table 7, the use of selenium supplementation during the transition period did not affect the incidence of milk fever, ketosis, acidosis, displaced abomasum and ovarian cyst. While there was a lower incidence of retained placenta and mastitis in selenium-fed cows compared to the control group, there was no observation of retained placenta and mastitis in selenium methionine group. Similar to our study results, other studies have shown that selenium supplementation has reduced retained placenta (Joksimović-Todorović & Davidović, 2013; Yosathai, 2014) and mastitis (Mehdi & Dufrasne, 2016; Sordillo, 2013) in dairy cows.

Conclusion

There was no significant difference in hematological parameters before and after delivery in experimental and control groups. However, in the prepartum period, MCH tended to increase significantly in selenium methionine treatment (p < 0.05). The mean of rectum temperature in the treatment of selenium methionine was significantly lower than that of the control group (p < 0.05). On the other hand, the purulent vaginal content, retained placenta, and mastitis were lower in this group. The results of this experiment showed that feeding organic selenium supplementation in multiparous dairy cow’s diet may improve their health and reproduction.

Acknowledgements

This project was supported by Roshd Toyor Zavareh Company (managed by Mr. Amir Hossein Akhtari Zavareh) on behalf Arkop Corporation and FKA Animal Husbandry and Agriculture Company (managed by Mr. Jamshid JalilNejad), Isfahan, Iran.

Reference

Albanes, D., Till, C., Klein, E. A., Goodman, P. J., Mondul, A. M., Weinstein, S. J., ... Song, X. (2014). Plasma tocopherols and risk of prostate cancer in the selenium and vitamin E cancer prevention trial (SELECT). Cancer Prevention Research, 7(9), 886-895.doi: 10.1158/19406207.CAPR-14-0058

Alfthan, G., Eurola, M., Ekholm, P., Venäläinen, E.-R., Root, T., Korkalainen, K., ... Aspila, P. (2015). Effects of nationwide addition of selenium to fertilizers on foods, and animal and human health in Finland: From deficiency to optimal selenium status of the population. Journal of Trace Elements in Medicine and Biology, 31, 142-147. doi: 10.1016/j.jtemb.2014.04.009

Association Official Analytical Chemist [AOAC]. (2005). Official Methods of Analysis (18th ed.). Gaitherburg, MD: AOAC International.

Boland, T. M., Keane, N., Nowakowski, P., Brophy, P. O. & Crosby, T. F. (2005). High mineral and vitamin E intake by pregnant ewes lowers colostral immunoglobulin G absorption by the lamb. Journal of Animal Science, 83(4), 871-878. doi: 10.2527/2005.834871x

Calamari, L., Petrera, F. & Bertin, G. (2010). Effects of either sodium selenite or Se yeast (Sc CNCM I-3060) supplementation on selenium status and milk characteristics in dairy cows. Livestock Science, 128(1-3), 154-165. doi: 10.1016/j.livsci.2009.12.005

Faixova, Z., Faix, Š., Leng, Ľ., Vaczi, P., Makova, Z. & Szaboova, R. (2007). Haematological, blood and rumen chemistry changes in lambs following supplementation with Se-yeast. Acta Veterinaria Brno, 76(1), 3-8. doi: 10.2754/avb200776010003

Finch, J. M. & Turner, R. J. (1996). Effects of selenium and vitamin E on the immune responses of domestic animals. Research in Veterinary Science, 60(2), 97-106. doi: 10.1016/S0034-5288(96)90001-6

Gabryszuk, M. & Klewiec, J. (2002). Effect of injecting 2-and 3-year-old ewes with selenium and selenium-vitamin E on reproduction and rearing of lambs. Small Ruminant Research, 43(2), 127-132. doi: 10.1016/S0921-4488(02)00005-6

Gunter, S. A., Beck, P. A. & Phillips, J. M. (2003). Effects of supplementary selenium source on the performance and blood measurements in beef cows and their calves. Journal of Animal Science, 81(4), 856-864. doi: 10.2527/2003.814856x

Hall, J. A., Bobe, G., Vorachek, W. R., Kasper, K., Traber, M. G., Mosher, W. D., ... Gamroth, M. (2014). Effect of supranutritional organic selenium supplementation on postpartum blood micronutrients, antioxidants, metabolites, and inflammation biomarkers in selenium-replete dairy cows. Biological Trace Element Research, 161(3), 272-287. doi: 10.1007/s12011-014-0107-4

Hatfield, D. L., Tsuji, P. A., Carlson, B. A. & Gladyshev, V. N. (2014). Selenium and selenocysteine: roles in cancer, health, and development. Trends in Biochemical Sciences, 39(3), 112-120. doi: 39:112-120,10.1016/j.tibs.2013.12.007

Joksimović-Todorović, M. & Davidović, V. (2013). The effect of antioxidants on preventing the retained placenta in dairy cows. Biotechnology in Animal Husbandry, 29(4), 581-589. doi: 10.2298/BAH1304581J

Juniper, D. T., Phipps, R. H., Jones, A. K. & Bertin, G. (2006). Selenium supplementation of lactating dairy cows: effect on selenium concentration in blood, milk, urine, and feces. Journal of Dairy Science, 89(9), 3544-3551. doi: 10.3168/jds.S0022-0302(06)72394-3

Lin, Y.-H. (2014). Effects of dietary organic and inorganic selenium on the growth, selenium concentration and meat quality of juvenile grouper Epinephelus malabaricus. Aquaculture, 430, 114-119. doi: 10.1016/j.aquaculture.2014.03.048

Littell, R. C., Henry, P. R. & Ammerman, C. B. (1998). Statistical analysis of repeated measures data using SAS procedures. Journal of Animal Science, 76(4), 1216-1231. doi: 10.2527/1998.7641216x

Mckenzie, R. C., Lewin, M. H., Rafferty, T., Howie, A. F., Arthur, J. R. & Beckett, G. J. (2003). Selenium protects keratinocytes from ultraviolet radiation-induced lipid peroxidation and cell death by oxidative stress. British Journal of Dermatology, 148(4), 864.

Mehdi, Y. & Dufrasne, I. (2016). Selenium in cattle: a review. Molecules, 21(4), 1-14. doi: 10.1186/1751-0147-46-229.10.3390/molecules21040545

Mohri, M., Ehsani, A., Norouzian, M. A., Bami, M. H. & Seifi, H. A. (2011). Parenteral selenium and vitamin E supplementation to lambs: hematology, serum biochemistry, performance, and relationship with other trace elements. Biological Trace Element Research, 139(3), 308-316. doi: 10.1007/s12011-010-8659-4

National Research Counci [NRC]. (2001). Nutrient Requirements of Dairy Cattle (7th ed.). Washington, DC: National Academy Press.

Pighetti, G. M., Eskew, M. L., Reddy, C. C. & Sordillo, L. M. (1998). Selenium and vitamin E deficiency impair transferrin receptor internalization but not IL-2, IL-2 receptor, or transferrin receptor expression. Journal of Leukocyte Biology, 63(1), 131-137.

Pophaly, S. D., Singh, P., Kumar, H., Tomar, S. K. & Singh, R. (2014). Selenium enrichment of lactic acid bacteria and bifidobacteria: A functional food perspective. Trends in Food Science & Technology, 39(2), 135-145. doi: 10.1016/j.tifs.2014.07.006

Roland, L., Drillich, M. & Iwersen, M. (2014). Hematology as a diagnostic tool in bovine medicine. Journal of Veterinary Diagnostic Investigation, 26(5), 592-598. doi: 10.1177/1040638714546490

Sadeghian, S., Kojouri, G. A. & Mohebbi, A. (2012). Nanoparticles of selenium as species with stronger physiological effects in sheep in comparison with sodium selenite. Biological Trace Element Research, 146(3), 302-308. doi: 10.1007/s12011-011-9266-8

Sattar, A., Mirza, R. H. & Hussain, S. M. I. (2007). Effect of prepartum treatment of vitamin e-selenium on postpartum reproductive and productive performance of exotic cows and their calves under subtropical conditions. Pakistan Veterinary Journal, 27(3), 105.

Schrauzer, G. N. (2003). The nutritional significance, metabolism and toxicology of selenomethionine. Advances in Food and Nutrition Research, 47, 73-112. doi: 10.1016/S1043-4526(03)47002-2

Seboussi, R., Tremblay, G. F., Ouellet, V., Chouinard, P. Y., Chorfi, Y., Belanger, G. & Charbonneau, E. (2016). Selenium-fertilized forage as a way to supplement lactating dairy cows. Journal of Dairy Science, 99, 5358-5369. doi: 10.3168/jds.2015-10758

Shaheen, S. M., Rinklebe, J., Frohne, T., White, J. R. & DeLaune, R. D. (2014). Biogeochemical factors governing cobalt, nickel, selenium, and vanadium dynamics in periodically flooded Egyptian North Nile Delta rice soils. Soil Science Society of America Journal, 78(3), 1065-1078. doi: 10.2136/sssaj2013.10.0441

Shinde, P. L., Dass, R. S. & Garg, A. K. (2009). Effect of vitamin E and selenium supplementation on haematology, blood chemistry and thyroid hormones in male buffalo (Bubalus bubalis) calves. Journal of Animal and Feed Sciences, 18(2), 241-256. doi: 10.22358/jafs/66388/2009

Sordillo, L. M. (2013). Selenium-dependent regulation o f oxidative stress and immunity in periparturient dairy cattle. Veterinary Medicine International, 2013, 1-8. doi: 10.1155/2013/154045.

Speckmann, B. & Grune, T. (2015). Epigenetic effects of selenium and their implications for health. Epigenetics, 10(3), 179-190. doi: 10.1080/15592294.2015.1013792

Statistical Analysis Software [SAS]. (2004). SAS/STAT User guide, Version 9.3. Cary, NC: SAS Institute Inc.

Van Soest, P. J., Robertson, J. B. & Lewis, B. A. (1991). Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of Dairy Science, 74(10), 3583-3597. doi: 10.3168/jds.S0022-0302(91)78551-2

Williams, E. J., Fischer, D. P., Pfeiffer, D. U., England, G. C. W., Noakes, D. E., Dobson, H. & Sheldon, I. M. (2005). Clinical evaluation of postpartum vaginal mucus reflects uterine bacterial infection and the immune response in cattle. Theriogenology, 63(1), 102-117. doi: 10.1016/j.theriogenology.2004.03.017

Wood, K. M., Mandell, I. B. & Swanson, K. C. (2010). The influence of supplementation with haylage, haylage plus soybean meal or haylage plus corn dried distillers’ grains with solubles on the performance of wintering pregnant beef cows fed wheat straw. Canadian Journal of Animal Science, 90(4), 547-553. doi: 10.4141/cjas09107

Yasin, M., El-Mehdawi, A. F., Anwar, A., Pilon-Smits, E. A. H. & Faisal, M. (2015). Microbial-enhanced selenium and iron biofortification of wheat (Triticum aestivum L.)-applications in phytoremediation and biofortification. International journal of phytoremediation, 17(4), 341-347. doi: 10.1080/15226514.2014.922920

Yosathai, R. (2014). Importance of minerals on reproduction in dairy cattle. International Journal of Science, Environment and Technology, 3(6), 2051-2057.

Author notes

* Author for correspondence. E-mail: m.chamani@srbiau.ac.ir