Date Published: April 30, 2019
Publisher: Public Library of Science
Author(s): Santiago T. Peña, Bruce Gummow, Anthony J. Parker, Damien B. B. P. Paris, Joël R. Drevet.
Heat stress-induced sperm DNA damage has recently been demonstrated in boars during tropical summer; which could negatively impact early embryo survival and litter size in sows. Given the boar’s inefficient capacity to sweat, non-pendulous scrotum and low antioxidant activity in seminal plasma, elevated endogenous levels of antioxidants are needed to combat reactive oxygen species induced during periods of heat stress. This should prevent the build-up of pathological levels of DNA damage in boar spermatozoa. Our aim was to investigate whether a combined antioxidant supplement could mitigate sperm DNA damage in boars exposed to tropical summer conditions. Terminal deoxynucleotidyl transferase dUTP nick end labelling and flow cytometry of 20,000 spermatozoa/boar/treatment revealed that boar diets supplemented with 100 g/day custom-mixed antioxidant during peak wet summer effectively reduced sperm DNA damage by as much as 55% after 42 and 84 days treatment respectively (16.1 ± 4.9 peak wet control vs. 9.9 ± 4.5 42 day vs. 7.2 ± 1.6% 84 day treatments; P ≤ 0.05). Supplementation did not improve sperm concentration beyond control levels for either season (P > 0.05); nor alter total motility, progressive motility or several other motion parameters measured by computer assisted sperm analysis of 20 x 106 sperm/mL at 38°C (P > 0.05). Antioxidant supplementation during tropical summer appears to mitigate the negative impact of heat stress on DNA integrity but not concentration nor motility of boar spermatozoa; which may provide one solution to the problem of summer infertility in the pig.
Tropical countries such as Brazil, Vietnam, The Philippines and Mexico are among the top 10 pork producers globally . Pig production during summer in the tropics can be impacted considerably by the phenomenon of seasonal or summer infertility. Summer temperature and humidity can predispose pigs to heat stress when ambient temperatures rise beyond the animal’s thermal comfort zone at about 18–20° C [2, 3]. This consequently affects food and water consumption, general comfort and reproductive performance, causing significant reduction in profitability. In pigs, poor reproductive performance due to summer infertility has been associated with reduced expression of oestrus and increased pregnancy failure in females [4, 5], and decreased breeding efficiency in males [6, 7].
Daily mean temperatures spanning the 42-day period immediately prior to semen collection were consistently hotter during peak wet than early dry season (P ≤ 0.05, Table 2). Moreover, daily mean temperatures were identical for the control and 42-day supplement groups during either the peak wet or early dry seasons. Daily mean relative humidity was generally similar for most treatments, ranging from 70–73%. However, the 84-day supplement group during the peak wet was more humid while the early dry control was dryer. Daily mean temperature-humidity index was consistently higher during the peak wet than early dry season (P ≤ 0.05), although values started to decline in the 84-day supplement groups during the peak wet, but was lowest for the early dry season (P ≤ 0.05).
The negative impact of heat stress on sperm DNA integrity coupled with its downstream effect on early embryo development , presents a new challenge to maintaining seasonal sperm quality in boars [39, 64]. Here, we demonstrate for the first time the beneficial effect of a multi-antioxidant supplement in reducing DNA damage in boar spermatozoa during periods of tropical heat stress. Supplementation of boars at 100 g/day using a custom-made antioxidant formula resulted in 38% to more than 55% reduction in sperm DNA damage after 42 and 84 days, respectively.