Effect of the donor´s age and type of extender (egg yolk versus clarified egg yolk) over the sperm quality of Majorera bucks preserved at 4 ºC: in vitro results and fertility trials

This study assessed the effect of donor´s age and two different extenders in the sperm quality of chilled semen in Majorera bucks. In experiment 1, semen was individually processed from 5 young (10–12 months old) and 4 mature (3–5 years old) bucks and then was diluted in two different extenders: EY (Tris‐glucose, 12% egg yolk) and CEY (Tris‐glucose, 12% clarified egg yolk) and cooled at 4°C; semen quality (sperm motility, percentages of alive spermatozoa, acrosome status and abnormal spermatozoa) was evaluated at 24, 48, 72 and 96 hr after cooling. In experiment II, 72 Majorera goats were assigned to four experimental groups: for groups 24‐EY (n = 18) and 24‐CEY (n = 18), goats were inseminated with EY and CEY cooled semen for 24 hr, respectively, while for groups 72‐EY (n = 18) and 72‐CEY (n = 18), goats were inseminated with EY and CEY cooled semen for 72 hr, respectively. In vitro results confirmed that only ejaculate volume and sperm concentration were significantly different between young and mature bucks. In addition, semen quality was similar between both diluents, presenting values for the first 48 hr similar to that recorded in fresh samples. The fertility rate was around 70% after 24 hr (4°C) in both groups, but the kidding rate was significantly lower (44.4%, p < .05) in goats inseminated with EY diluent preserved for 72 hr. Our results showed that the semen samples may be stored at 4°C in media with egg yolk or clarified egg yolk, and, therefore, the use of clarified egg yolk may represent a valid alternative to chill semen samples. Finally, young bucks (older than 10–12 months) of Majorera breed could be successfully used in breeding programmes with similar efficacy to older males.