Impacts of zinc, manganese, and copper source on mature bull trace mineral status and spermatozoa characteristics

Abstract Text: Our objective was to measure impacts of trace mineral source on liver mineral status and spermatozoa characteristics in mature bulls.  Thirty-seven bulls (682 ± 147 kg) of mixed breeds, 2-4 years of age were used in a 71 d trial. Bulls were blocked by length of time without trace mineral supplementation and stratified by initial liver Cu status to one of three dietary treatments (4 pens/treatment): 1) Supplement without Cu, Zn, and Mn; 2) Supplement with Cu, Zn, and Mn sulfate (sulfate); and 3) Supplement with basic Cu chloride, Zn and Mn hydroxychloride (hydroxy). Liver biopsies were collected on d -73, -24, and 71 to determine trace mineral status. Supplements containing Cu, Zn, and Mn were fed at 75% of NRC requirements as top dressing to a feedlot (corn silage) diet. Semen collection and scrotal circumference measurements were collected on d 0, 36, and 70. Ejaculates were evaluated for spermatozoa concentration, motility, and morphology as part of a standard breeding soundness examination. Acrosome integrity, sperm viability, and mitochondrial membrane potential were evaluated via flow cytometry counting at least 5,000 sperm per ejaculate. The mixed procedure of SAS was used for statistical analysis. On d 71, liver Cu concentrations of bulls receiving hydroxy minerals were greater (P = 0.008) than bulls receiving no mineral supplement or sulfate minerals.  Liver Zn concentrations tended to be greater (P = 0.08) in bulls receiving hydroxy minerals compared to sulfate minerals.   All other trace minerals (Co, Mn, Mo, and Fe) were not different (P ≥ 0.16) due to dietary treatments. Liver concentration of Cu increased (P = 0.04) from the d -24 to 71 biopsy in bulls receiving hydroxy mineral. No differences (P ≥ 0.17) were observed in any other trace mineral concentrations between treatments from the d -24 to 71 liver biopsies. Bulls with greater liver Zn concentrations on d 71 were correlated (r = -0.39, P = 0.02) with less acrosome damaged spermatozoa and tended to be correlated with greater spermatozoa concentrations (r = 0.31, P = 0.06). We conclude that basic Cu chloride and Zn hydroxychloride is more bioavailable and more readily stored in the liver compared with Cu and Zn sulfate. Increased liver Zn concentrations may also improve acrosome integrity of bull spermatozoa. However, diets deficient in trace mineral for >170 d had no other detrimental effects on semen quality of mature bulls.

Keywords: trace mineral, bull, spermatozoa