Alpaca semen quality in relation to different diets

Abstract

The aim of the present study was to evaluate the biochemical composition of seminal plasma, along with semen quality, of alpacas maintained on different diets (hay; hay + pasture grazing; pasture grazing + sheep concentrate; pasture grazing + horse concentrate; Periods 1–4, respectively). Alpacas (n = 5) were fed the four different diets for a period of 6 weeks each. During the period of feeding of each diet, semen was collected using an artificial vagina to determine its volume, viscosity, sperm concentration and sperm motility. Moreover, testicular volume and body condition score were evaluated. Seminal plasma was analysed biochemically to measure total protein, triglyceride, cholesterol, γ-glutamyl transferase, alanine aminotransferase (ALT) and alkaline phosphatase levels. Protein profiles were investigated using one-dimensional sodium dodecyl sulfate–polyacrylamide gel electrophoresis. There was high variability in semen parameters between different males maintained on the same diet. Semen volume increased significantly (P < 0.05) when alpacas were fed diets containing commercial sheep and horse concentrates. In contrast, sperm concentration and motility decreased significantly (P < 0.05) from Period 1 to Period 4. Dietary changes had no effect on viscosity. Significant reductions were seen in triglyceride and cholesterol content, as well as γ-glutamyl transferase, ALT and alkaline phosphatase concentrations, from Period 1 to Period 4. Regardless of experimental period, a wide variation was seen in seminal plasma enzyme concentrations between alpacas, whereas diet had no effect on glucose and total protein concentrations in the seminal plasma. Eight protein bands, with molecular weights ranging from 200 to 14 kDa, were considered in electrophoresis gel after image analysis. Proteins fractions of the 14-kDa (total protein express in md dL–1 with a molecular weight of 14-kDa, TP8) and 21-kDa (total protein express in md dL–1 with a molecular weight of 21-kDa, TP7) bands were not present in all samples of alpaca seminal plasma. There were no significant changes in the concentration of any protein fractions during the four periods. Moreover, the protein fraction of the 60-kDa (total protein express in md dL–1 with a molecular weight of 60-kDa, TP3) band was the most prevalent in all periods. These results demonstrate that there are marked changes in semen quality, as well as some parameters related to the composition of alpaca seminal plasma, that are dependent on diet, which may indicate the need for specific diet formulation to improve reproductive performance. We hypothesise that, in alpacas, the mechanisms underlying the changes in some reproductive traits in response to feeding regimens could be related to changes in the endocrine–gonadal system.