Effects of fescue toxicosis on bull growth, semen characteristics, and breeding soundness evaluation1

Abstract

Tall fescue possesses heat, drought, and pest resistance conferred to the plant by its mutualistic relationship with the ergot alkaloid producing fungal endophyte, Neotyphodium coenophialum. The objective of this study was to evaluate the impact of ergot alkaloid consumption on growth, scrotal circumference (SC), and semen quality. The SC measurement and percentage of motile and normal sperm were used to determine if a bull passed the breeding soundness exam (BSE) requirements. Bulls (n = 14) between 13 and 16 mo of age exhibiting ≥32 cm SC and having passed a BSE were assigned to 1 of 2 dietary treatments accounting for BCS and BW. Bulls were fed the treatment diet containing toxic tall fescue seed (E+; 0.8 μg of ergovaline and ergovalanine/g DM) or the control diet containing endophyte-free nontoxic tall fescue seed (E-) for 126 d. Blood samples were collected and BSE and BCS accessed at the start of the test (d 0) and every 21 d to the end of test (d 126). Weights were obtained on d 0 and d 126. Serum prolactin (PRL) concentrations were affected by treatment × day interactions (P = 0.04) verifying the effectiveness of the E+ diet. Bulls consuming the E+ diet exhibited declining PRL concentrations from 250 ± 52.1 ng/mL on d 0 to 30.6 ± 46.9 ng/mL by d 126 whereas bulls receiving the E- ration maintained serum PRL concentrations greater than or equal to 226.7 ± 50.4 ng/mL across the 126-d study. Body condition score (P = 0.4) and BW (P = 0.4) were not different between treatments. No difference due to treatment was observed for the percentage of bulls passing a standard BSE exam (P = 0.6) and no treatment effect was observed for any semen characteristic measured by computer-assisted semen analysis (CASA; P ≥ 0.2). The SC was negatively affected by treatment × day interaction (P = 0.04) with E- bulls exhibiting a larger SC at d 126 compared with E+ bulls of 36.7 ± 0.8 versus 34.3 ± 0.8 cm, respectively. Within treatment, E+ bulls exhibited a decrease in SC (P = 0.0001) with a d 0 SC of 37.3 ± 0.8 cm and dropping to 34.3 ± 0.8 by d 126. Theoretically, reduced SC would negatively impact semen quality, but this was not observed. However, CASA and BSE evaluation data are consistent with recent reports indicating that bulls grazing E+ tall fescue exhibited only subtle, if any, differences on semen characteristics.

Identification of bovine prolactin in seminal fluid, and expression and localization of the prolactin receptor and prolactin-inducible protein in the testis and epididymis of bulls exposed to ergot alkaloids

“…In addition, it was reported for breast cancer cells that maximum expression of PIP was because of synergistic effects of PRL and androgen [45]. In our model, PRL was still detectable and testosterone levels were unchanged [30,31], therefore PIP expression may not be altered in this model. As for PRLR mRNA expression in the epididymis, no treatment effect was observed within groups A or B because of Eþ or EÀ treatments for PIP, but PIP mRNA was decreased because of group (P < 0.05).…”

“…Interestingly, seminal fluid PRL concentrations did not differ in bulls during the pen-fed study but PRL was lowered because of the consumption of ergot alkaloids in the grazing study. Clearly, plane of nutrition could explain the differences between the two studies as the bulls in the pen-fed study [31] received a corn-based diet and all bulls were in positive energy balance and gaining weight regardless of treatment. However, in the grazing study [30] bulls consuming the Eþ forage did not gain weight during the 140-day study.…”

“…The toxins produced by many cultivars of tall fescue containing mutualistic endophytes are ergot alkaloids and are potent dopaminergic agonists. Consumption of ergot alkaloids clearly suppresses serum PRL concentrations in bulls [30,31,40,46]. Prolactin is known to be present in the human seminal fluid [13,14], so we evaluated its presence and determined if the levels of PRL in seminal fluid were impacted by the consumption of ergot alkaloids.…”

“…Means were compared using Fisher's least significant difference test for the pen-fed and grazing experiments. Furthermore, the correlation of seminal fluid PRL concentration with serum concentrations for the pen-fed experiment [31] and the grazing experiment [30] were determined. For qRT-PCR, expression differences were determined by subtracting Ct of target from Ct of GAPDH and the differences were subjected to analysis using LSMeans (JMP program; SAS Institute Inc.).…”

“…All reagents were purchased from Sigma Scientific (St. Louis, Missouri, USA) unless stated otherwise. Two separate studies were conducted for more than a 2-year period to assess effects of ergot alkaloid consumption on semen characteristics [30,31]. A pen experiment with either toxic or nontoxic seed fed as the treatment [31], and a grazing experiment conducted to make comparisons between bulls grazing either toxic or nontoxic endophyte-infected tall fescue pastures [30].…”