Effects of Breeding for Short-Tailedness in Sheep on Parameters of Reproduction and Lamb Development.

Background: Sheep's tail docking is a widespread practice, which is banned or critically discussed in some countries to improve animal welfare.

Objective: The aim was to determine the influence of breeding for short-tailedness (ST) or long-tailedness (LT) in sheep on the development of reproduction parameters and lamb performance.

Method: One hundred forty-nine ewes were mated with four rams according to tail length. Pregnancy and pregnancy loss rates were calculated. During pregnancy, the progesterone levels (P4) of the ewes were measured. The weight and length of the 254 lambs were recorded up to 14 weeks of life. Litter size, placenta weight, sex, stillbirths, vitality, morbidity and mortality of the lambs were also documented.

Results: No significant differences were found for P4 and placental weight for the two mating groups (ST and LT). Although the pregnancy rate for ST was slightly lower (75.71%) than for LT (87.34%), there was only a low significant difference (p = 0.07). The sex distribution was 61 (48.80%) male and 64 (51.20%) female lambs in the ST group and 67 (51.94%) male and 62 (48.06%) female lambs in the LT group. The twinning rate was not significantly different (ST 75.20%; LT 75.97%), and no significant difference was found in the average body length and vitality of the lambs. However, LT lambs showed better weight gains that were marginally significant (p = 0.09).

Conclusion: This study found no evidence that reproductive parameters or lamb performance were affected by selective breeding based on tail length.