Yearling bulls have reduced sperm concentration and increased seminal plasma interleukin‐8 after a 28‐day breeding season

Abstract

We hypothesized that yearling bulls selected for a 28‐d breeding season would have reduced sperm concentrations and morphology, and have increased seminal plasma concentrations of pro‐inflammatory cytokine interleukin‐8 (IL‐8). Yearling bulls were selected based on a breeding soundness examination (BSE) at approximately 415 d of age and contained at least 750 million sperm in the ejaculate, with 12 bulls randomly selected for breeding (BREEDERS) and 12 bulls not selected for breeding (NON‐BREEDERS). After a 28‐d breeding period, all bulls underwent a BSE. Plasma and seminal plasma were collected at each time point for analysis. Data were analysed utilizing either the MIXED or GLIMMIX procedures with repeated measures in SAS with breeding group, age and the interaction as fixed effects. Sperm concentration per ml of ejaculate was reduced (p < .05) in yearling bulls used for breeding compared with those not used for breeding at the end of the breeding season. Seminal plasma IL‐8 concentrations in yearling bulls used for breeding were increased (p < .05) after the breeding season compared with bulls not used for breeding. Taken together, yearling bulls selected for a 28‐d breeding season have reduced sperm production per ml of an ejaculate and increased inflammatory response in the seminal plasma that can lead to impaired breeding response if they are to be used for more than 30 d of breeding.

Kinematic and Morphometric Assessment of Fresh Semen, before, during and after Mating Period in Brahman Bulls

“…It has been reported that the potential fertility of a male is dependent on the interaction of multiple factors such as management, environment, and the individual’s own physical and reproductive conditions [ 47 ]. Moreover, when analyzing the data before and during the mating period, a similar effect to that described by Snider et al [ 57 ] can be observed, as sperm concentration decreases significantly during the mating period ( p < 0.05). These authors pointed out that the decline in sperm concentration is of great importance because males showing this effect may potentially be unable to fertilize with females in high male-to-female ratios during the mating season, affecting the pregnancy rate of the productive system.…”

“…Regarding sperm concentration, studies on B. taurus crossbreeds aged between one and two years suggest that animals used during a 28-day breeding season tend to experience a decrease in sperm concentration and an increase in seminal plasma interleukin-8 levels at the end of the mating period [ 57 ]. In our work, the bulls were in breeding pastures, in pairs, for a period of twenty-one days, and the mating season extended for approximately eighty days.…”

“…From these PCs, a total of four sperm subpopulations were identified and were consistent with other studies conducted in bulls [ 62 , 63 ]. There are no studies on kinetics subpopulations during a mating period, with prior analyses related to types of semen diluent used [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ], multivariate analysis, sperm velocity and linearity [ 62 ], membrane integrity [ 22 ], frames per second used [ 31 ], and the overall dataset [ 64 ]. Our results indicate, in general, that subpopulations with faster and straighter movement were SP3 in PMS, SP3 in DMS, and SP1 in AMS.…”

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“…At the age of 1 year, they have worse indicators of sperm production and sperm motility compared to older ones, although there is no difference in sperm motility after unfreezing cryopreserved sperm doses between younger and older bulls (Murphy et al, 2018). One-yearolds selected for breeding have not only reduced sperm production but also an increased inflammatory response, leading to poor reproduction if used intensively in breeding (Snider et al, 2022). Sexually mature bulls have betterquality sperm than young ones (Bhakat et al, 2011).…”