Physiological parameters of semen of Italian Simmental young bulls in relation to feed efficiency and environmental parameters.

The study's goals were to assess how the environmental condition, depicted by temperature-humidity indexes (THI), and the feed efficiency parameters depicted by residual feed intake (RFI), average daily gain (ADG), dry matter intake (DMI), muscularity and estimated body weight at 12 months affected the characteristics of semen quality of young Italian Simmental bulls (n = 81). The young bulls were all raised in the same genetic center and sampled using the artificial vagina (AV) method. In this study, semen motility parameters such as total motility (TM), progressive motility (PM), average path velocity (VAP), curvilinear velocity (VCL), VSL, straightness (STR), linearity (LIN), average and maximum of amplitude lateral head displacement (ALH and mALH, respectively), beat cross frequency (BCF), wobble (WOB) and the percentage of slow, medium and rapid spermatozoa were assessed. In addition, morphological parameters such as major and minor abnormalities, percentage of normal and normal-alive spermatozoa, ejaculate concentration and volume were recorded. Oxidative status parameters of seminal plasma (SP) such as advanced oxidation protein products (AOPP), carbonyl groups (CT) and thiols are evaluated. Correlation test was performed to identify significant correlation (r ≥ 0,30; p < 0.05) between all those features. Carbonyl groups (nmol/mgTP) have been observed to negatively correlate with the percentage of normal alive spermatozoa (r = -0,37; p < 0,05) and positive correlate with the major abnormalities (r = 0,35; p < 0,05). Thiols were positively correlated with both RFI (r = 0,49) and DMI (r = 0,32), whereas they were negatively correlated with ADG (r = - 0,31). In addition, mixed linear models were performed to study the effect of THI (both THI 60 days before collection day and THI 24 hours before collection day) on all semen quality and feed efficiency parameters (dependent variables). According to our results, THI at 60 days and 24 hours significantly affect (p<0,05) TM and AOPP concentration on SP. Moreover, minor abnormalities are dependent on THI in the previous 24 hours. In our study both environmental and feeding factors were able to influence reproductive parameters. THI has been demonstrated to directly impact spermatozoa morphology and oxidative status of SP. ADG may also change the ratio of ROS to antioxidant species and negatively impact the thiol content of SP. To reduce the negative effect of oxidative stress, a supplementary diet could maintain optimal thiol levels. In addition, the continuously monitoring of environmental THI and further investigations on the effect of THI variation during spermatogenesis could better elucidate how environmental conditions influence animal reproductive physiology in order to improve the physiological parameters of semen.