Location: Forage-animal Production ResearchTitle: Effects of toxicosis on bull growth, semen characteristics and breeding soundness evaluation) Author
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2013
Publication Date: 11/25/2014
Citation: Stowe, H.M., Millar, M., Burns, M.G., Calcatera, S.M., Andrae, J.G., Aiken, G.E., Schrick, F.N., Cushing, T., Bridges, W.C., Pratt, S.L. 2014. Effects of toxicosis on bull growth, semen characteristics and breeding soundness evaluation. Journal of Animal Science. 91:3686-3692. Interpretive Summary: Tall fescue (Lolium arundinaceum) is present on approximately 16 million ha in the mid-Atlantic and southern regions of the USA and serves as a forage for approximately 8.5 million cattle, making this species the dominant cool-season perennial grass in the region. The majority of tall fescue plants are infected with a fungal endophyte, Neotyphodium coenophialum, that produces ergot alkaloids that confers drought, grazing tolerance, and insect resistance to tall fescue. Unfortunately, ergot alkaloids are causal agents of fescue toxicosis, a malady of cattle that is characterized by their maintaining rough hair coats in the summer, increased core body temperature, and poor growth and reproductive performance. There has been limited research on determining the effects of ergot alkaloids on reproductive function and most of this research has focused on cow and not bull fertility. An experiment was conducted to evaluate semen characteristics of yearling beef bulls being fed a constant amount of ergot alkaloid in a high-concentrate ration for 126 days to observe toxic effects of the ergot alkaloids from possible reduced body condition and plane of nutrition of animals grazing tall fescue pastures. Although there were no differences in semen characteristics between bulls consuming diets with or without ergot alkaloids, those consuming ergot alkaloids had less scrotal circumference than those on alkaloid-free diets. This research indicates that adverse effects of ergot alkaloids on bull fertility are minimal over the short-term, but a concurrent reduction in scrotal circumference could negatively impact semen quality over long-term consumption of toxic endophyte-infected tall fescue. Therefore, because of the substantial cow-calf production in the “fescue belt’, more research is needed to address the impacts of fescue toxicosis on bull fertility.
Technical Abstract: Tall fescue (Lolium arundinaceum) 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). Bulls (n = 14) between 13 to 16 months of age exhibiting > 32 cm SC and having passed a BSE were assigned to one of two dietary treatments accounting for body condition score (BCS), and bodyweight. Bulls were fed the treatment diet containing toxic tall fescue seed (E+; 0.8 'g of ergovaline & ergovalanine/g DM) or the control diet containing endophyte-free non-toxic tall fescue seed (E-) for 126 d. Blood samples were collected and BSE, and BCS accessed at the start of the test (d0); and every 21 days to the end of test (d126). Weights were obtained on d0 and d126. Serum prolactin (PRL) levels were affected by treatment x d 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 d0 to 30.6 + 46.9 ng/mL by d126; whereas bulls receiving the E- ration maintained serum PRL concentrations > 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 treatment 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 x d interaction (P = 0.04) with E- bulls exhibiting a larger SC (36.7 + 0.8 cm) at d126 compared to E+ bulls (34.3 + 0.8 cm). Within treatment, E+ bulls exhibited a decrease in SC (P = 0.0001) with a d0 SC of 37.3 + 0.8 cm and dropping to 34.3 + 0.8 by d126. 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.