Sex or maternal care? Nursing oestrous ewes prefer to interact with rams over their lambs

Abstract

In some sheep production systems, the ewes are induced to come into oestrus whilst nursing their lambs. After that, mothers and offspring are usually moved into a paddock with sexually active rams leading to a conflict between sexual and maternal motivations. The aim of this study was to determine if a nursing oestrous ewe prefers its lamb or a sexually active ram in a two-choice test with full physical contact. During the breeding season, 23 multiparous Corriedale ewes nursing single lambs were induced to come into oestrus 72 days after parturition. Twenty ewes came into oestrus and were tested in a two-choice test with full physical contact between their single lamb and a sexually active ram. The latency to enter into a contact area surrounding each stimulus (ram or lamb) and the time spent in each area were recorded for 3 min. The number of vocalisations emitted by the lambs and the sexual behaviour displayed by the rams were also recorded. One nursing oestrous ewe did not enter any defined area and was excluded from the analysis, which included 19 tests. Nursing oestrous ewes entered earlier (X2 =8.05; P = 0.005; Survivance test) and stayed longer (Z = 􀀀 2.74; P = 0.006; Wilcoxon Signed-Rank test) in the ram’s contact area than in the lamb’s contact area. During the test, rams almost always displayed sexual behaviours when ewes entered their contact area (17/19 tests). The lambs vigorously vocalised during the test (19.7 ± 2.5 bleats/test), but the number of vocalisations was not related to the time the ewe spent near the lamb or the ram. In conclusion, nursing oestrous ewes strongly prefer sexually active rams over their lambs during the breeding season. This result gives rise to a greater understanding of sexual behaviour in the ewe, which may very well impact the reproductive management of sheep.