Sexual performance and semen quality of pubertal lambs treated with different weaning methods

Abstract

The objective of this study was to determine the effect of the weaning method on lamb stress, body weight, sexual behavior, and semen quality of Saint Croix male lambs. The present study was carried out during the late spring and summer of 2018 in the northeast of Mexico. Sixty male lambs born as twins or triplets (3.2 $\pm$ 0.6 kg birth weight) and weaned at 60 d of age (19.21 $\pm$ 1.8 kg weaning weight) were divided into two weaning methods: complete separation from the dams (CS; the lambs were moved to a pen that was at 500 m of distance from the dams) and separation with contact from the dams (SCD); the lambs were physically separated by a steel mesh that prevented the lambs from having the possibility of sucking milk from their mothers, but they maintained permanent visual and auditory contact. Cortisol levels were determined 3 d before and 7 d after weaning. Lambs were evaluated as 3-month-old lambs for sexual behavior and semen quality for 9 weeks. The effects of the weaning method (M), week (W), and the interaction M $\times$ W were significant on body weight and cortisol levels ( $P<0.001$ ). The SCD lambs had higher cortisol levels at 3, 5, and 7 d after weaning than CS lambs ( $P<0.001$ ). The CS lambs had higher body weight during the first 4 weeks after weaning than SCD lambs ( $P<0.001$ ). The weaning method had no effect on scrotal circumference, sexual behavior, and semen quality traits, except for progressive sperm motility, being better for the lambs that were completely separated ( $P<0.05$ ). The results from this study show that complete separation of lambs and ewes at weaning is an effective method to reduce lamb stress and improve lamb growth after weaning, but it did not have long-term effects on sexual behavior and semen quality of Saint Croix male lambs.

Figure 1

Study plan.

Figure 2

Cortisol levels (a) and body weight (b) in Saint Croix lambs after weaning on average at 60 d of age following two methods: complete separation (dotted line) where the lambs were placed in a pen located 500 m of distance from the dams and separation with contact from the dams (black line) where the lambs were placed in a pen separated with a steel mesh from the pen of dams ( $P\mathit{<}\mathrm{0.05}$ ).