Feeding yearling Angus bulls low-level ergot daily for 9 weeks decreased serum prolactin concentrations and had subtle effects on sperm end points

Highlights

• Ergot alkaloid feeding at 3.4 mg/kg of DMI/day for 9 weeks of yearling bulls transiently reduced plasma prolactin by 4-folds.

• Body weight, scrotal circumference, rectal temperature, or sperm concentrations were not remarkably affected.

• Subtle effects on progressive motility, mid-piece defects, and mitochondrial membrane potential were recorded.

• Current Canadian ergot standards (3 mg/kg of feed) are adequate for bull reproduction; prolactin decrease is concerning.

Abstract

Our objective was to determine whether feeding yearling bulls with the higher recommended Canadian limit of ergot alkaloids (∼3 mg/kg dry matter intake, DMI) would affect sperm characteristics and plasma prolactin concentrations. Aberdeen Angus bulls (12–13 mo old, n = 7/group) allocated by blocking for sperm concentration and body weight, were fed placebo or ergot alkaloids in gelatin capsules (60 μg/kg body weight daily, 3.4 mg/kg of DMI) for 9 wk. Semen samples were collected weekly by electroejaculation and examined with a computer assisted semen analyzer (CASA) and flow cytometry, for the intervals 5 wk before (Pre-exposure period), 9 wk during (Exposure period) and 9 wk after (Post-exposure period) treatment. Weekly plasma samples were analyzed for prolactin by radioimmunoassay. Plasma prolactin concentrations decreased markedly (mean ± SEM, 16.74 ± 3.70 in Exposure and 33.42 ± 3.08 ng/mL in Post-Exposure periods; P < 0.01) compared to Control (67.54 ± 21.47 and 42.59 ± 15.06 ng/mL). Treatment did not affect (P ≥ 0.17) body weight gain, sperm concentration, sperm count/ejaculate, motility or percent live sperm. Averaged over the exposure and post-exposure durations, the scrotal circumference was smaller (P = 0.02) by 2.7% in the Ergot group. Progressive motility remained unchanged from 59.92 ± 2.31% in Exposure to 59.61 ± 2.59% in Post-Exposure periods, compared to marked increase in Control (61.42 ± 1.60% to 67.52 ± 1.47%; P = 0.02). Straight-line sperm velocity decreased (−3.15 ± 1.53 μm/s) from exposure to post-exposure periods in Ergot group (P = 0.04) versus an increase (2.96 ± 2.17 μm/s) in Control. Midpiece defects decreased from Exposure to Post-exposure periods in Control group but remained unchanged in Ergot group (trt∗age, P < 0.01). Ergot feeding resulted in a smaller proportion of sperm with medium mitochondrial potential (Ergot: 22.65 ± 0.98%, Control: 24.35 ± 1.05%, P = 0.04). In conclusion, feeding ergot at Canadian permissible limit for 9-wk resulted in a 4-fold decrease in plasma prolactin concentrations. Semen end points were not significantly affected, although there were subtle effects on progressive motility, midpiece defects and mitochondrial membrane potential. Clinical relevance of observed changes requires further evaluation. Results supported our hypothesis that prolonged low-level ergot will adversely affect plasma prolactin. However, semen parameters were partially affected, supporting similar work on fescue toxicosis.

Introduction

The fungus Claviceps purpurea infects many cereal plants and produces ergot sclerotia containing alkaloids that are toxic to humans and livestock [1]. Although ergot poisoning is uncommon in humans, food animals are commonly exposed by grazing or consuming stored feeds. Claviceps infections are most prevalent in rye, triticale and wheat, although the fungus is able to infect all grasses and cultivated grains across Canada [2]. Increasing ergot contamination has become a major problem in western Canada in the past decade [3]. After being subjected to moisture in the spring, ergot sclerotia germinate, giving rise to ascospores that target the flowering stage and infect the plant ovary. A few days later, the ovary is replaced by stroma that releases a sugary substance called “honeydew”. Eventually, the entire seed-head is replaced with a dark, hard, kernel-like sclerotia [4]. Sclerotia are stable for 12 mo [5] and may survive for >3 y [6] and therefore remain infective for multiple crop cycles. Sclerotia contain six primary alkaloid toxins: ergometrine, ergotamine, ergosine, ergocristine, ergocryptine and ergocornine [7] and a group of agroclavines that are less bioactive. In a single sclerotium, the amount of ergot alkaloids can range from 0.15 to 0.5% by weight [8]; therefore, total alkaloid content cannot be accurately estimated from the weight of ergot bodies. Ergot alkaloids are divided into three structural groups (clavines, lysergic acid amides and peptides) that are separated into two major groups: water-soluble amino alcohol derivatives and water-insoluble peptide derivatives (∼20 and 80% of the total alkaloid mixture, respectively) [8]. Ergocristine and ergotamine are in the highest concentrations in most grains in Western Canada [9].

Ergot alkaloids act as receptor-binding agonists or partial agonists of dopaminergic, serotonergic and alpha-adrenergic receptors [1,10]. The most well-described changes due to the ergot exposure are peripheral vasoconstriction with subsequent gangrene formation, hallucinations, and decreased peripheral prolactin concentrations. There are four forms of toxicosis associated with ergot exposure in mammals: gangrenous, convulsive, hyperthermic and reproductive forms [11]. The convulsive form (nausea, convulsions, hallucinations and hyper-excitability) is common during human exposure, but rare in livestock. Gangrenous ergotism is associated with long-term feeding of ergot alkaloids that cause vasoconstriction of small blood vessels, leading to necrosis of extremities and sloughing of tails, ears, hooves, or lameness. Vasoconstrictive effects have been reported in the testicular artery [12] and extreme cold conditions in Canada may exacerbate these effects. Hyperthermic ergotism is associated with long-term exposure during hot weather. Due to the vasoconstrictive nature of ergot alkaloids, dissipation of body heat is reduced, and core body temperature rises, leading to hyperthermia. Reproductive toxicosis is caused by multiple mechanisms, with these effects of ergot better characterized in females than males [[13], [14], [15], [16], [17]]. Ergot alkaloids have primarily been linked with fertility effects in females, as reported in numerous studies. Some of these effects are delayed onset of lowered pregnancy rates [18,19], reproductive losses due to conception failure or early embryonic loss [20], decreased milk production [13], and abortion [21] in cattle. Few reports are available on the bull-specific reproductive toxicosis in literature [[22], [23], [24], [25], [26], [27], [28]].

Decreased blood prolactin concentrations are a major indicator of ergot alkaloid exposure in livestock. The ergoline ring of ergot alkaloids is structurally similar to dopamine and binds to D2 dopamine receptors in the anterior pituitary, mimicking the binding of dopamine [14] and thereby reducing release of prolactin; this hormone is necessary for maintenance of pregnancy, corpus luteum function [4], milk production [29] and it also supports testicular function [30,31]. Suppressed serum prolactin concentrations have also been used as an indicator of ergot alkaloid consumption in tall fescue grass toxicosis [[24], [25], [26], [27]].

Tall fescue grass is grown on an estimated 16 M ha of pasture in the mid-west and southern USA. Most of the grass is infected with a fungal endophyte Neotyphodium coenophialum that produces ergot alkaloids somewhat related to those from Claviceps, except ergovaline (main alkaloid produced by N. coenophilium but not produced by C. purpurea). The estimated economic loss due to tall fescue toxicosis during the summer months is ∼$1B annually [28]. These losses are primarily attributed to decreased body weight gain and milk production. There is growing concern that semen quality may be sufficiently affected by summer tall fescue toxicosis to result in suboptimal pregnancy rates [15,22,[24], [25], [26], [27],32,33]. In one study in bulls, there were no significant differences between the experimental (40 μg/kg body weight of ergotamine tartrate) and control groups for prolactin, scrotal circumference, testosterone, sperm motility, or sperm morphology [23]. The same investigators conducted a second study and reported no differences in percentage of normal sperm morphology or sperm motility [24]. In contrast, an in vitro study designed to investigate the signaling pathways involved in inhibitory effects of ergotamine and dihydroergotamine recorded a decrease in percent motile sperm [34], likely mediated via alpha adrenergic receptors. In another in vivo study, bulls were fed endophyte-infected Kentucky 31 tall fescue and evaluated for serum prolactin concentration and semen quality [27]; both sperm concentration and percent normal morphology were significantly decreased in treatment versus control groups. Further, percent motile and progressively motile sperm significantly decreased in bulls fed endophyte-infested tall fescue, whereas sperm velocities (smoothed sperm path and progressive velocity in a straight line) were lower in the group exposed to ergot alkaloids in pasture for 121 d [25]. Clearly, effects of ergot alkaloids on semen end points were not consistent. In a more recent study involving yearling and adult Angus bulls conducted over 2 y, ejaculate volume, sperm concentration, percent motile sperm, percent progressive motile sperm, percent normal sperm morphology, and velocities were not significantly different between treatment and control groups [35]. It is noteworthy that a major limitation of these studies was the lack of a reliable estimate of ergot alkaloids consumed per animal due to pasture grazing. The Canadian prairies have an extreme winter climate and a milder spring and summer; therefore, mechanisms associated with thermoregulation and temperature stresses for cattle may differ from those in the USA and Europe. Furthermore, there are regional differences in crops, crop management and presumably kinds of ergot alkaloids produced. Despite some studies on the effects of ergot alkaloids from tall fescue on reproduction in bulls, to the best of the authors’ knowledge, effects of cereal grain ergot on reproduction in bulls have not been reported.

The Canadian Food Inspection Agency (CFIA) permits up to 3 parts per million (PPMs) of ergot alkaloids in total mixed ration of cattle feed [36]. Our objective was to determine the effects of feeding the upper limit of ergot alkaloids for a 9-wk period on semen quality, sperm functions and plasma prolactin concentration of yearling bulls during and after the feeding period. We tested the null hypotheses that: 1) ergot alkaloids (∼3 ppm of dry matter intake) do not affect semen quality (sperm concentration, total number of sperm, motility, progressive motility, velocity and morphology) or sperm structural parameters (plasma membrane integrity, acrosome integrity, proportion of sperm with high and medium mitochondrial membrane potential) during the exposure or post-exposure periods; and 2) prolactin concentration will not decrease by eating ergot-contaminated feed compared to the Control group.