-Cervid populations are rapidly increasing in many part of Western Europe, where they cause damage to forest production. This necessitates a better understanding of what determines their dietary choices. In this experiment, we investigated the relationship between the relative availability of two tree species and diet selection of red deer Cervus elaphus. Three hypotheses were tested: (i) preference for rarity, frequently asserted by foresters, (ii) preference for the more abundant profitable species, as predicted by optimal foraging models, and (iii) frequency-independent selectivity, as already observed in moose and roe deer. Six red deer hinds were therefore observed in shortduration tests when offered two plant species, willow Salix caprea and ash Fraxinus excelsior, in varying proportions. The relation between the relative consumption and availability of the two plant species revealed that red deer prefer ash to willow, and that their short-term selectivity is not a frequency-dependent process. Individual animals differed in the intensity of their preference, but all reacted similarly to variations in the relative availability of the two plant species. Our results advance our understanding of the choices of red deer at the feeding site scale, but further research is needed to propose management practices, which would take advantage of their frequency-independent selectivity. Cervus elaphus / browsing / diet selection / food availability / Salix caprea / Fraxinus excelsiorRésumé -Choix alimentaires du cerf Cervus elaphus selon la disponibilité relative de deux espèces d'arbres. Les populations de Cervidés sont en rapide augmentation en Europe de l'ouest, où elles causent des dégâts à la forêt. Ceci nécessite de mieux comprendre les déterminants de leurs choix alimentaires. Nous avons étudié comment la disponibilité relative de deux espèces d'arbres influence les choix alimentaires du cerf Cervus elaphus en testant trois hypothèses : (i) une sélecti-vité accrue pour les espèces rares souvent évoquée par les forestiers, (ii) une sélectivité accrue pour l'espèce préférée lorsque son abondance augmente, prédite par les modèles d'optimisation, et (iii) une sélectivité indépendante de la disponibilité relative des espèces végétales comme cela a déjà été montré chez l'élan et le chevreuil. Nous avons pour cela observé les choix alimentaires de six biches dans des tests de courte durée, lorsqu'on faisait varier l'abondance relative du saule Salix caprea par N. Chevallier-Redor et al. 58
The aim of the present study was to assess the in vivo competence of in vitro-produced sika deer (Cervus nippon nippon) embryos after freezing–thawing and transfer into red deer (Cervus elaphus hippelaphus) recipients. During the breeding season, 11 adult sika deer hinds were synchronized as oocyte donors with an intravaginal sponge (45 mg of fluorogestone acetate, FGA) inserted for 12 days and removed immediately after laparoscopic ovum pick-up (LOPU), and renewed after 3 days. Ovarian stimulation was induced with an i.m. injection of 75 µg of cloprostenol (Estrumate) given on Day 8, followed by 3 i.m. injections of 0.1, 0.1, and 0.05 IU of ovine FSH (Ovagen) on Days 10 and 11 at 12-h intervals. On Day 12, hinds were anesthetized and oocytes were collected by LOPU from follicles >2 mm using an 18 G needle under moderate vacuum. COC were recovered and morphologically evaluated for quality (graded from 1 to 5). COC were then submitted to in vitro maturation, fertilization, and culture (IVM, IVF, and IVC) as described previously (Locatelli Y et al. 2005 Theriogenology 64, 1729–1739). For IVC, embryos were co-cultured with a monolayer of ovine oviduct epithelial cells in synthetic oviduct fluid medium supplemented with 10% FCS. On Day 8 post-insemination, all sika deer embryos at the blastocyst stage were cryopreserved via a standard bovine slow-freezing protocol. Of 44 LOPU sessions performed during the 1-month study, an average of 7.5 � 0.38 follicles were aspirated (mean � SEM), allowing the recovery of 3.65 � 0.38 COC per hind and per session, of which 80.0% were suitable for IVM (grades 1 and 2). Of 142 oocytes recovered, 57 cleaved after IVF (40.1%), and 14 embryos (24.6% of cleaved) reached the blastocyst stage after 8 days. At the end of the breeding season, 7 adult red deer hinds were synchronized as embryo recipients by inserting 2 intravaginal sponges per female (90 mg of FGA), for 13 days. Injections (i.m.) of 400 IU of eCG and 125 µg of cloprostenol (Estrumate) were administered 72 h before sponge removal. At Day 8 after sponge removal, straws containing frozen embryos were thawed and cryoprotectant was removed as described previously (see Locatelli Y et al. 2005 Theriogenology 64, 1729–1739). Two sika deer embryos were surgically transferred into uterine horn (unilaterally) of each red deer recipient. One of 7 red deer recipients was diagnosed pregnant by ultrasonography on Day 56. A healthy male sika deer fawn was born unassisted after 224 days of gestation. No complications were observed in initial recognition of the sika deer fawn by the red deer surrogate mother, nor in subsequent interactions. To our knowledge, this is the first report of an interspecific pregnancy obtained after in vitro embryo production and embryo transfer in deer species. In conclusion, interspecific embryo transfer after IVP may represent a useful tool for the preservation and amplification of captive residual populations of endangered deer species. Further studies are required to increase the rate of cleavage after LOPU-IVF as well as viability of frozen–thawed IVP embryos.
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