Short-lived corpora lutea syndrome in anoestrous ewes following 17ß-oestradiol or MAP treatments applied before an allogenic sexual stimulation with rams and oestrous ewes.

When induced to ovulate during anoestrus, ewes, does and cows frequently develop a short-lived corpora lutea (SLCL) syndrome associated to lack of previous progesterone. Exogenous progesterone precludes SLCL by blocking oxytocin endometrial receptors, thus inducing normal life-span CL (NLCL). Paradoxically, circa 50% of unprimed ewes do not develop SLCL. We report results from 3 trials assessing follicular, oestrous, ovulatory, and luteal end-points after 17ß-oestradiol or MAP treatments. Oestradiol benzoate (50µg) induced follicular turnover, provoked ovulation in 40% (24/60) of ewes treated (93% of which developed SLCL), but did not affect the incidence of SLCL (26/53) after an allogenic sexual stimulation (ASS) by rams and oestrous ewes. By the onset of the ASS, most NLCL ewes (26/27) had already experienced turnover of their largest follicle, had smaller largest and second largest follicles, and ovulated their largest follicle more frequently than SLCL ewes did. Most SLCL ewes (19/25) did not ovulate their largest follicles, ovulating instead smaller follicles of identical size to those of NLCL ewes. Priming (40mg of MAP for 12 days) was partially effective at preventing SLCL even when terminated 14 days in advance of an ASS, but failed at completely preventing SLCL when terminated 6 or more days in advance. The coupling of a timed acquisition of full steroidogenic capability before ovulation with a system of endometrial oestradiol-progesterone-oxytocin receptors linked in an unstable equilibrium controlling the amplification of the luteolytic feed-forward loop of oxytocin and prostaglandin F(2)α explains occurrence and relative incidences of both NLCL and SLCL, and links proximate and ultimate causes of the SLCL syndrome.

Ram-induced oestrus and ovulation in lactating and weaned Corriedale ewes.

Two experiments were conducted in consecutive years in which recently (Experiment 1) or temporarily (Experiment 2) weaned ewes and matched post-partum non-lactating flockmates (DRY) were exposed to a stimulus group of rams and oestrous ewes (10 and 20 in Experiment 1, 20 and 20 in Experiment 2) for 28 days in spring. Lactating ewes (n = 130) in Experiment 1 were isolated from their lambs 4 (W-4), 2 (W-2), 1 (W-1) or 0 (W-0) days in advance and exposed along with a group of 32 DRY flockmates. Lactating ewes in Experiment 2 (n = 230) were allocated to an unreplicated factorial of two levels of temporary weaning before stimulation (B0: control; B24: lambs removed 24 h before stimulation) by four levels of ewe-lamb contact imposed at the start of the stimulation (A0: control; A12, A24 and A36: lamb-ewe separation during the initial 12, 24 or 36 h of exposure); DRY ewes (n = 54) acted as an augmented factorial control. Oestrus (rump marks) and ovulation (laparoscopy on day 5 and on day 28 (Experiment 1) or day 32 (Experiment 2)) were recorded. Ovulation and oestrous responses in Experiment 1 were similar for DRY (90.6% and 55.2%, respectively) and recently weaned ewes (83.8% and 53.7%, respectively). Amongst recently weaned ewes, the immediate ovulation response to the rams and the proportion of ewes still cycling by day 28 tended to be lower (P = 0.065 and P = 0.011) in ewes weaned on the day of ram exposure (71.9% and 54.8% v. 87.8% and 80.0%, respectively). Ovulation rate was lower (P < 0.003) in W-2 ewes (1.3 ± 0.10) than in the other recently weaned groups. In Experiment 2, ovulation (83.3%) and oestrous (68.9%) responses in DRY ewes were higher (P = 0.022 and P = 0.053, respectively) than in lactating ewes (66.2% and 51.0%, respectively). More ewes ovulated (P = 0.036) in B24 (70.5%) than in B0 (61.8%). Ewes having their lambs returned 12 h after the onset of stimulation (A12) had poorer ovulation responses (54.9%) than control ewes (A0, 72.9%, P < 0.05); this was probably associated to lamb restitution after the sunset. Main conclusions were that (i) the presence of the lambs is a depressing factor of both ovulation and oestrous responses to the ram effect in lactating ewes, (ii) the ovulation response of lactating ewes will probably benefit from removing lambs for a period of 24 h before the onset of stimulation, (iii) until additional information becomes available, temporary weaning protocols should be designed avoiding lamb restitution during the night.

Role of early experience in the development of preference for low-quality food in sheep.

Domestic ruminant selectivity induces floristic changes in pasturelands, risking sustainability and limiting the subsequent availability of susceptible plant species. Development of preferences for species of lower nutritional quality may help to overcome those problems. In this study, we tested the hypothesis that early experience of sheep with a low-quality food (LQF) in a nutritional enriched context increases preference for LQF in adulthood. We predicted a higher proportional consumption of LQF in experienced lambs (EL) than in inexperienced lambs (IL) in choice situations involving LQF and alternative foods. Additionally, we determined intake of LQF by EL and IL at different levels of high-quality food (HQF) availability. From 60 to 210 days of age, EL were fed in separated feed bunks mature oat hay (LQF) simultaneously with sunflower meal (SM) and corn grain (CG), whereas IL were fed alfalfa hay (HQF) simultaneously with SM and CG. After exposure, EL and IL were offered LQF in free choice situations involving alternative foods, and also at five levels of HQF availability (100%, 75%, 50%, 25% and 0% of ad libitum intake). Proportional consumption of LQF was lower or similar in EL than IL. Intake of LQF was also lower or similar in EL than IL at all levels of HQF availability, except when the LQF was the only food available. Our results did not support the hypothesis that early experience with a LQF in a nutritional enriched context increases preference for LQF in adulthood. On the contrary, experience with LQF diminished subsequent preference for LQF in adulthood. It is proposed that, in the conditions of our study, continuous comparison between the LQF and the high-quality supplements (CG and SM) during the early exposure period lead to devaluation of LQF by EL through a simultaneous negative contrast effect.

Introduction of meat sheep breeds in extensive systems of Patagonia: lamb growth and survival.

Genotype effects on lamb growth, survival, and commercial finishing were estimated in a 5-yr study aimed at assessing potential benefits from introducing meat breeds into extensive sheep systems of northeastern Patagonia. Five ram [Corriedale: CO; Border Leicester: BL; Ile de France: IF; Texel: TX; and synthetic CRIII (25% Merino, 37.5% IF, 37.5% TX)] and 5 dam (CO; synthetic CRIII; BLCO: BL x CO; IFCO: IF x CO; and TXCO: TX x CO) genotypes were represented in the study. Data were collected from 1,426 born and 1,258 weaned lambs of 9 resulting genotypes (CO x CO, BL x CO, IF x CO, TX x CO, CRIII x CO, CRIII x BLCO, CRIII x IFCO, CRIII x TXCO, and CRIII x CRIII). Birth weight was recorded on all lambs; subsequently, BW and BCS (scale 1 to 5) were recorded at regular intervals until weaning. Body weights were adjusted to 60 and 90 (weaning) d of age, and ADG were calculated from the adjusted BW for the periods 0 to 60 d and 60 to 90 d; BCS was adjusted to 90 d. Survival to weaning and percentage of lambs reaching commercial finishing (BW >or= 23 kg and BCS >or= 2.5 points) were also recorded. Significant (P < 0.05) genotype x litter size interactions were detected for birth weight and ADG 60 to 90 d. With the exception of CRIII x CO, crossbred and synthetic genotypes presented greater (P < 0.05) ADG 0 to 60 d and BW at 60 and 90 d than CO x CO lambs. Second cross lambs reared as singles presented greater ADG 60 to 90 d (P < 0.05) than BL x CO, TX x CO, and CRIII x CO, but less (P < 0.05) ADG 60 to 90 d, and no differences were observed for twins. The IF x CO, CRIII x BLCO, CRIII x IFCO, and CRIII x CRIII genotypes showed greater BCS at 90 d (P < 0.05) than CO x CO. The probability of greater commercial finishing for crossbred and synthetic genotypes relative to CO x CO was at least 79%. Probabilities of greater survival to weaning in CO x CO and CRIII x BLCO lambs relative to IF x CO, TX x CO, CRIII x CO, and CRIII x CRIII lambs were greater than 81%. Results indicate significant improvements in lamb BW and saleable lambs from the introduction of meat genotypes. Among the terminal sire breeds evaluated, BL and IF would produce the greatest impact. Differential nutritional management of pregnant ewes carrying twins and of twin lambs beyond 60 d should be implemented to mitigate litter size x genotype interactions constraining growth potential benefits, which may be critical for northeastern Patagonia conditions.

LH response of seasonally anovular Corriedale ewes acutely exposed to rams and estrous ewes.

Serial blood sampling before and after exposing four anovular Corriedale ewes to a group of rams and estrous ewes during the non-breeding season revealed a pattern of LH secretion similar to that previously observed in Merinos. Mean LH values doubled (P<0.001) from 0.24+/-0.06 microgL(-1) (mean+/-s.e.m.) before to 0.55+/-0.05 microgL(-1) after 2h of visual, auditory, and odor exposure to rams and estrous ewes in an indoor facility. A non-significant (P<0.17) increase of LH pulses per hour was also observed (0.7+/-0.3 pulses per hour before compared with 1.3+/-0.3 during stimulation). All four ewes had recently formed corpora lutea by five days after stimulation. Results are consistent with the pattern of sudden increase and sustained release of LH observed in other sheep breeds, particularly the Merino.