Scrotal circumference as a trait for reproductive selection in white merino breed

Abstract

Introduction Scrotal circumference (SC) is one of the parameters that can be measured in males. It is perfectly stablished the relationship between SC and many reproductive characters. In sheep there are recommendations of not using lamb or adult rams with SC less than 30 cm and 32 cm respectively and indicating satisfactory potential breeders, when rams between 6–13 months have SC of 30–35 cm and males >14 months have a SC of 33–39 cm. The use of primary traits, as general appearance, lamb growth rates and efficient gain as criteria for selection, disregarding reproductive traits as SC, can be responsible, in time, for decreasing the SC mean in the breed. It is important to understand the present status of Portuguese merino breed, advising farmers for the importance of this parameter as selection criteria. Material and methods SC was measured in white (n = 436, 352 animals) merino rams, included in the Portuguese flockbook, from 5–177 months (0–14 years). Animals were randomly measured along the year in 19 farms using a flexible measuring tape in the widest part of the scrotum, holding testis in a distal position. Five age categories were used for classification of the males and environmental traits such as season, body score and farm were analysed because of expected influence in SC. Statistical analysis was performed using SAS 9.4 software, through MEANS and GLM procedures. Results and discussion The means of the SC of animals of different age groups (6–12; 12–18; 18–24; 24–36 and >36 months) were estimated, respectively 25.7, 29.4, 31.1, 34.8 e 34.9 cm, and a greater variability was observed in the younger age groups (VC’s of 12.5 and 19.6%), partly because animals were in the growth phase and with individual differences in the onset of puberty, that is variable and usually occurs between 5–7 months of age, when 65% of body weight is achieved. Conclusion and implications Although the mean values of SC observed in animals >24 months are close to the values indicated by the American Sheep Industry Association (33 cm and 35 cm), of the 245 available records, only 175 (71%) are within these values. There were also significant differences (P < 0.05) in the SC of animals from different farms, maybe due to different environmental farm conditions, such as genetic differences, eventually because some breeders are more prone to the use this parameter in selection. This is the first study on the SC of this breed in Portugal and results can be an important standard indication, as well as a tool when selecting males. Acknowledgements and funding This presentation is funded by MED (Instituto Mediterrâneo para a Agricultura, Ambiente e Desenvolvimento). We thank the collaboration of the ACORME’s farmers in collecting this data on the farms.