Nutritional Effects on Scrotal Circumference, Motility and Morphology of Spermatozoa and Cytokine Concentrations within Seminal Plasma of Beef Cattle

Sire fertility is impacted by a wide variety of environmental and management conditions, potentially causing critical losses within beef operations. Nutrition is a main influence on the ejaculate due to bulls undergoing multiple planes of nutrition yearly. By identifying the effects of nutritional planes on the ejaculate composition, reproductive efficiency could be maximized at pregnancy establishment. We hypothesized periods of differing nutritional planes and body condition score (BCS) would affect bull fertility and cytokine concentrations within the ejaculate of bulls. Mature Angus bulls (n = 11) were individually housed and randomly assigned to one of two treatments: 1) over-fed (OVER, n = 5) targeting a BCS of 8, or 2) restricted (RES, n = 6) targeting a BCS of 4. Bulls were fed the same ration at different intake volumes to achieve desired effects with different nutritional periods: gain, loss, ideal body condition steady-state (ISS) at a BCS of 6, and abnormal body condition steady-state (ABS), at a BCS of 8 or 4 as per treatment design. Body weight (BW) and BCS were taken every two weeks to monitor bull weight and adipose changes. Ejaculates were collected every 84 d to determine bull fertility and cytokine profiles within seminal plasma (SP). A completely randomized design was implemented and data analyzed with mixed model ANOVAs via PROC GLIMMIX (SAS 9.4, Cary, NC) to determine if nutrition period, treatment and the interaction influenced bull fertility. Progressive forward motility tended to be greater (P=0.10) during the ISS period regardless of treatment. Morphological head and total abnormalities of spermatozoa were influenced by an interaction (PP