Hyperprolactinemia

Abstract

Consumption of toxic endophytic tall fescue grass is associated with reduced fertility rates in livestock. In this study, Angus bulls were fed a control diet (n = 3) or toxic fescue diet (n = 3) for 60 d. Semen was collected by electro-ejaculation twice weekly and evaluated for spermatozoal motility, morphology, and concentration. Scrotal temperatures, scrotal circumferences, and rectal temperatures were measured prior to each collection. Significant differences were observed for scrotal temperatures (P

(Key Words: Bovidae, Festuca, Spermatozoa.)

Introduction

Tall fescue (Festuca arundinacea Schreb.) is the major pasture for over 8.5 million cattle in this country (Paterson et al., 1995). The USDA (1999) estimated that over one-half of the tall fescue stands in this country are infected with an endophytic fungus (Neotyphodium coenophialum). The endophytic fungus is beneficial to the plant by imparting improved tolerance of environmental stresses, but produces ergot alkaloid compounds that can be detrimental to the health of animals ingesting it. Fescue toxicosis-induced losses have been estimated to have an annual $800 million impact on the beef industry in part because of a decline in cattle reproductive performance (Paterson et al., 1995). Although this loss is significant to cattle breeders, research pertaining to the toxic effects on bull reproductive performance is limited. In female cattle, endophytic toxins have been associated with alterations in reproductive hormone profiles (Browning et al., 1998; Burke et al., 2001), estrous cycle parameters (Jones et al., 2003), follicle diameter prior to ovulation (Burke and Rorie, 2002), and luteal dysfunction (Jet al., 2004). Eradication of vast hecterage of tall fescue is not a practical solution to the toxicosis problem both because of the extent of fescue establishment and because of its persistence. Substitution of endophyte-noninfected strains of fescue has not proven to be practical because of the diminished hardiness of the grass when lacking the fungus. The best chance of eliminating the deleterious reproductive effects of toxic fescue, therefore, appears to lie in understanding the action of the endophyte's active compounds on the bovine reproductive system so that a practical method can be devised to block those effects. To date, no information exists on bull reproductive performance after ingesting endophyte-infected (EI) fescue. Male rodents fed EI diets had decreased testicular weight, decreased numbers of spermatozoa produced per gram of testicular tissue, decreased pregnancy rates after breeding, and decreased litter weight when compared with controls fed an endophyte-noninfected diet (Zavos et al., 1986, 1987).

The purpose of this study was to determine the effect of toxic fescue consumption on reproductive parameters of Angus bulls.

Materials and Methods

Animals and Diets. Animal protocols were reviewed and accepted by the Southern Illinois University-Carbondale's Institutional Animal Care and Use Committee. This study took place from July 10 through September 11, 2003 at the Southern Illinois University-Carbondale Beef Center. Six Angus bulls between 21 and 29 mo of age were allocated by BW into two groups with three bulls in each group. All six bulls were fed a non-fescue diet for 1 mo prior to the beginning of the study. At the start of the study, three bulls were fed a pelleted EI treatment diet consisting of an endophytic fescue seed diet similar to a previous study (Jones et al., 2003). A composite sample of the treatment diet was sent to the University of Columbia, Missouri diagnostic laboratory and was determined to contain 1005 ppb ergovaline, a concentration-exceeding threshold to induce clinical disease (Aldrich-Markham and Pirelli, 1995). The remaining bulls were fed a corn and wheat middling control diet that was isonitrogenous and isocaloric to the treatment diet (Table 1). Each diet was formulated according to NRC (1996) recommendations to achieve 0.454 kg/d of BW gain. Diets for both groups were fed as growing diets calculated according to BW. Body weight was determined weekly. All animals were fed 7.72 kg/d of fescuefree alfalfa hay. All animals were maintained in individual pens to avoid diet cross-contamination, and orts were measured daily. Experimental diets were started on July 11, and observations were collected from July 14 to September 11.

Measures. Semen collections and analysis were performed using standard techniques (Herman et al., 1994) on Mondays and Thursdays throughout the experimental period. Heat indexes were recorded for each collection day after assessing a weather website (http://wunderground.com) for Carbondale, IL. Bull scrotal circumferences were measured using a scrotal circumference tape (Agtech Inc., Manhattan, KS). Rectal temperatures were taken with a digital thermometer prior to semen collection. Scrotal temperatures were measured using an infrared thermometer (Exergen Comfort Scanner, Watertown, MA) placed over the testicular artery. Bulls were collected by electroejaculation using a SF-I Standard Precision Portable Electro-ejaculator (Bovine Elite, Inc., College Station, TX). The ejaculate was evaluated for spermatozoa concentration using a densimeter (Animal Reproductive Systems, Chino, CA) calibrated to bovine parameters. One person determined spermatozoal motility using light microscopy for five microscopic fields for each collection. In addition, 100 sperm per ejaculate were stained with eosin/nigrosin and evaluated for aberrant sperm morphology using an inverted microscope (Olympus BX40, Nashua, NH) at 400× magnification.

Statistics. Data were analyzed using PROC MIXED with repeated measures (SAS®; SAS Inst., Inc., Cary NC). The independent variable was dietary treatment, day was the repeated measure, and heat index was a covariate. The dependent variables were rectal temperature, scrotal temperature, scrotal circumference, concentration, motility, and morphology. To determine the main effects of dietary treatment, day, and interaction of dietary treatment with day, data were also analyzed using the GLM procedure (SAS®) with the same dependent variables.

Results and Discussion

Regulation of scrotal temperature is necessary for production of viable spermatozoa. Testicular temperature in bulls must be 2° to 6°C cooler than core body temperature for the production of fertile spermatozoa (Waites, 1970). Elevated body temperatures, caused by the endophytic alkaloids affecting vasoconstriction, are a common symptom of fescue toxicity (Zhang et al., 1994). Symptoms of fescue toxicosis can be exacerbated by elevated ambient temperatures (Burke et al, 2001); however, rectal temperatures were not significantly (P>0.05) elevated in the endophytic diet treatment group in this study, even in the presence of summer heat indexes (Figure 1). This result might have been due to the time of day rectal temperatures were collected, between 0700 and 0900 h, or due to applying water to the bulls to reduce heat stress as required by the animal care protocol.

It is unknown whether the regulatory mechanisms controlling scrotal temperatures, including the testicular vascular cone acting as a counter-current heat exchanger, would be able to compensate for elevated body temperatures. Scrotal temperature varies according to the location measured. The top of the scrotum is warmest, having a surface temperature of 30.4°C and subcutaneous temperature of 34.3°C (Kastelic et al., 1996). Our infrared thermography data indicated that testicular artery temperatures are elevated in bulls fed toxic fescue (P

Scrotal circumference is used in breeding soundness exams as an indicator of bull reproductive potential. Scrotal circumference is correlated with daily sperm production, testicular weight, epididymal weight, and extragonadal sperm reserves (Johnson et al, 1995). In this study, the mean scrotal circumference was less (P

In heifers, heat stress in combination with toxic fescue consumption has been shown to have detrimental effects on total cholesterol, prolactin, progesterone, and estradiol concentrations (Burke et al., 2001). Specific ergot alkaloids associated with endophytic fescue have been shown to reduce leutinizing hormones (LH) in cows (Browning et al., 1989). A reduction in LH concentrations in the bull would lead to failure to stimulate the Leydig cells that are responsible for testosterone production and spermatogenesis.

Based on the observation of decreased scrotal circumference and likely reduced spermatogenesis, we expected sperm concentrations to be lessened for the treated bulls. Interestingly, spermatozoa concentrations in treated bulls increased (P

Dopaminergic mechanisms have been shown to regulate contractility of the accessory sex glands, seminal vesicle, and prostate. Dopamine has been reported to produce concentration-dependent contractions of the seminal vesicle (Sharif, 1994) and prostate (Rester et al., 1989). Dopamme also inhibits prolactin secretion in the pituitary. The dopaminergic effects of the ergot alkaloids imitate the native dopamine to create hypoprolactinaemia (Hurley et al, 1980). The dopamine agonist bromocryptine, when administered to stallions, decreased circulating prolactin and resulted in a reduction in gel-free seminal volume compared with controls (Thomson et al., 1996). Hyperprolactinemia also is associated with decreased seminal volume in men (Rocco et al., 1983) and rabbits (Yousef et al, 1989). Our studies, as well as others, indicate that a dopaminergic mechanism is present in the gonads (Kotwica et al., 1996; King et al., 2002; Dille et al., 2004). Therefore, these prolactin studies are confounded because, to modulate prolactin, dopamine agonists and antagonists were utilized. The responses observed may be induced by direct stimulation of the dopamine agonist or antagonist on the target tissue rather than by the presence or absence of prolactin.

Germ cells are more sensitive to heat than are Sertoli or Leydig cells. All stages of cells in the spermatogenic cycle are affected, but the magnitude of damage is dependent on the extent and duration of the heat (Waites and Setchel, 1990). Heating the testes decreases the percentage of progressively motile sperm and increases the percentage of abnormal sperm morphology (Earth and Oko, 1989). Unless stem cells are affected, the interval from heat damage to restoration of normal appearing spermatozoa corresponds to the beginning of differentiation to ejaculation. Decreased fertilization rates and increased embryonic death may continue after restoration of normal morphology and motility (Waites and Setchel, 1990); however, in our study, no differences (P>0.05) in the overall model were detected in either motility (Figure 3b) or morphology assessments (Figure 3c). Interestingly, motility appeared to be affected in the last 2 wk of the trial. These observations were made after a period of extended elevated heat indexes and may explain a trend (P=0.08) when the interaction of diet and day was analyzed. It is possible that this observation may be due to failure of the testicular temperature regulatory mechanisms to adequately adjust for environmental heat stress. However, we cannot rule out the possibility that the endophytic alkaloids may be altering hormone profiles necessary for normal spermatogenesis. In addition, no semen collections were recovered on d 10, 12, 14, 15, or 16 for one bull on the fescue diet. This bull was nonresponsive to the electro-ejaculation protocol, having no penis extension or ejaculation. No collection was retrieved on d 10 for one of the bulls fed the control diet. No significance difference in morphology was observed between the interaction of dietary treatment and day (P>0.05).

Implications

Ingestion of toxic fescue by bulls did not affect percent motile spermatozoa or abnormal spermatozoal morphology until after a sustained period of high environmental heat index. Throughout the study, the treated bulls had reduced scrotal size, an indicator of future reproductive performance. These results indicate that bulls fed endophytic fescue might have reduced fertility, especially after periods of heat stress. The timing of the interaction of this environmental factor could potentially coincide with the fall breeding season.

Acknowledgments

Funding was provided by Southern Illinois University Carbondale (SIUC) Undergraduate Research/Creative Activity Award and the SIUC College of Agricultural Sciences. Salary for C. R. McCleary was provided by the SIUC Undergraduate Assistantship Program. Thanks to D. Weakley (Purina Mills LLC, Gray Summit, MO) for ration preparation.

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K. L. JONES1, C. R. MCCLEARY, S. S. KING, PAS, G. A. APGAR, and K. E. GRISWOLD

Animal Science, Food and Nutrition, Southern Illinois University, Carbondale 62901

1 To whom correspondence should be addressed: kljones@siu.edu

Copyright American Registry of Professional Animal Scientists Oct 2004
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