Long interval prostaglandin-based treatment regimens do not affect ovulatory or prolificacy rates of multiparous ewes after cervical fixed timed AI.

To evaluate effects of a longer, than conventional, interval between time of prostaglandin F2α (PG)-based administrations in a PG-based treatment regimen for fixed timed AI (FTAI) on ovulation rate (OR), non-estrous return rate on Day 21 subsequent to the time of AI (NRR21), as well as conception, prolificacy and fecundity rates, ewes were assigned to two groups. Ewes of treatment group (PG15) were estrous-synchronized using two PG doses 15 days apart and FTAI was conducted at 56 h after the second PG administration (Day 0). Ewes of the Control group (SE) had imposed a pre-estrous synchrony treatment regimen with two PG doses 7 days apart and AI was conducted after detection of spontaneous estrus from 17 to 19 days after the second PG administration (Day 0). Ovulation rate on Day 8, NRR21, conception, prolificacy and fecundity rates on Day 60 were evaluated. There were no differences (P > 0.05) between ewes of the PG15 and SE groups in OR (1.47 ± 0.50 and 1.54 ± 0.50, respectively) or prolificacy (1.42 ± 0.80 and 1.33 ± 0.62, respectively), however, there were lesser values (P< 0.05) in the PG15 than SE group for NRR21 (65.2% and 91.3%, respectively), conception (59.8% and 91.3%, respectively) and fecundity (84.8% and 120%, respectively). The longer interval with the PG-based treatment regimen does not affect OR and prolificacy, but there is a lesser NRR21, conception and fecundity rate in comparison to ewes of the Control group.

Short-term dietary protein supplementation improves reproductive performance of estrous-synchronized ewes when there are long intervals of prostaglandin or progesterone-based treatments for timed AI.

To evaluate the reproductive effects of a short-term dietary protein supplementation (Days -10 to -3) before timed AI (TAI = Day 0), 471 Merino ewes grazing native pastures were estrous-synchronized when there were either long intervals between prostaglandin administrations (two prostaglandin injections 15 or 16 d apart; PG15 and PG16, respectively) or with a progesterone-eCG (P4-eCG) protocol, resulting in a 3 × 2 experimental design. Ovulation rate on Day 8 (OR), non-estrous-return to Day 21 (NRR21), and fertility, prolificacy and fecundity on Day 70 were evaluated. The interaction between estrous synchronization protocol and supplementation was not significant for any of these variables (P > 0.05). Supplementation increased OR, prolificacy and fecundity (+0.14, +0.15 and +0.14, respectively, P < 0.01), but did not affect NRR21 or fertility of ewes (+6.2% and +6.7% respectively, P > 0.05). Ewes treated using the PG15 and PG16 protocols had a lesser OR (-0.27), prolificacy (-0.22) and fecundity (-0.20) than ewes treated using P4-eCG protocol (P < 0.01 for each), and similar NRR21 and fertility (-5.4% and -7.9% respectively, P > 0.05 for both variables), without significant differences between the PG15 and PG16 groups. In conclusion, a short-term dietary protein supplementation before TAI improved OR, prolificacy and fecundity of ewes which were estrous-synchronized by imposing long interval PG (15 or 16 d apart) or P4-eCG-based protocols. There was a greater OR, prolificacy and fecundity when there was use of the P4-eCG compared to long interval PG-based protocols. Estrous-non-return rate after AI and fertility as a result TAI were not affected by either the supplementation or the estrous synchronization protocols used.

Short term protein supplementation during a long interval prostaglandin-based protocol for timed AI in sheep.

The aim of this study was to evaluate the reproductive impact of a short-term protein supplementation on a long interval prostaglandin-based protocol (two PG injections 15 d apart; PG15) for timed artificial insemination in sheep. During the breeding season, 437 multiparous Merino ewes grazing native pastures (forage allowance of 6 kg of dry matter/100 kg of live weight; crude protein: 10.8%, metabolic energy: 2.1 Mcal/kg of dry matter) were selected. Ewes were allocated, according to body condition score (3.2 ± 0.2) and body weight (40.6 ± 4.9 kg, mean ± SD), to a 2 × 2 factorial design: type of estrus -spontaneous estrus (SE) or induced with PG15 (PG15)-, and supplementation (yes or no) before insemination (+FF; soybean meal at Days -10 to -3; crude protein: 51.9%, metabolic energy: 2.8 Mcal/kg of dry matter; average consumption 0.9% live weight/ewe/day of dry matter). All ewes were cervically artificial inseminated (Day -2 to -3 in SE ewes at estrus detection; Day 0 = timed artificial insemination in PG15 ewes). Ovulation rate on Day 7, non-return to service on Day 23, conception, fertility, prolificacy and fecundity on Day 60 were evaluated. Ovulation rate (1.17 ± 0.40 vs. 1.06 ± 0.25), non-return to service at Day 23 (81.7 vs. 64.2%), conception (78.8 vs. 61.5%), fertility (75.2 vs. 61.5%) and fecundity (0.77 vs. 0.62) were higher in ewes from SE than PG15 group (P < 0.05). However, no differences were observed in prolificacy (1.02 ± 0.16 vs. 1.01 ± 0,12) between groups (P > 0.05). Protein supplementation increased ovulation rate (1.30 ± 0.45 vs. 1.17 ± 0.40), prolificacy (1.18 ± 0.39 vs. 1.02 ± 0.16) and fecundity (0.94 vs. 0.77%; P < 0.05), but not non-return to service on Day 23 (83.8 vs. 81.7%), conception (82.9 vs. 78.8%) or fertility (79.1 vs. 75.2%; P > 0.05) in SE group. The supplement feed to PG15 ewes increased ovulation rate (1.35 ± 0.45 vs. 1.06 ± 0.25), prolificacy (1.25 ± 0.43 vs. 1.01 ± 0.12) and fecundity (0.79 vs. 0.62%; P < 0.05) to levels comparable to SE + FF ewes (P > 0.05). The magnitude of the increase in ovulation rate in PG15 was greater than in the SE group (27 vs. 11%; P < 0.05). However, non-return to service on Day 23 (65.1 vs. 64.2%), conception (63.3 vs 61.5%), and fertility rate (63.3 vs. 61.5%; P < 0.05) remained similar in PG15 supplemented or not supplemented ewes. In conclusion, a short-term protein supplementation before cervical time artificial insemination improved the reproductive performance of ewes synchronized with the PG15 protocol to levels comparable to the SE group.

Long interval prostaglandin as an alternative to progesterone-eCG based protocols for timed AI in sheep.

To compare the reproductive performance after TAI in ewes synchronized with mid (12 or 13) or long (14-16 d) interval prostaglandin (PG) or progesterone plus eCG (P4-eCG) based protocols, 440 multiparous Corriedale ewes were synchronized with two PG injections administered 12-16 d apart (PG12, PG13, PG14, PG15 and PG16 respectively), or P4-eCG (MAP sponges 14 d and eCG). Cervical TAI (Day 0) was performed with fresh semen. It was evaluated the ovulated ewes (OE, %) and the ovulation rate (OR) on Day 8 by trans-rectal ultrasonography, the rate of non-return to service between Days 13 and 21 by painted rams, and the pregnancy rate, prolificacy and fecundity on Day 60 by trans-abdominal ultrasonography. No significant differences were found in OE among groups (P>0.05), but P4-eCG achieved higher OR (P<0.05) compared to PG protocols, without differences among them (P>0.05). Similar NRR-21, pregnancy and fecundity were observed among PG15 (64.3, 62.9 and 84.3), PG16 (59.7, 59.7 and 77.8) and P4-eCG (70.3, 66.2 and 95.9), but higher compared to PG12 (42.5, 39.7 and 52.1) and PG13 group (44.0, 40.0 and 48.0, respectively; P<0.05). PG14 achieved intermediate results compared to other groups. No differences were found in prolificacy among groups (P>0.05), except PG13 that was lower compared to P4-eCG (P<0.05). In conclusion, long interval between PG injections (15 or 16 d) determined better reproductive outcome that mid interval (12 or 13 d), equating the P4-eCG based protocol after cervical TAI with fresh semen during the breeding season in sheep.

Long term prostaglandin based-protocols improve the reproductive performance after timed artificial insemination in sheep.

The aim of the experiment was to evaluate the reproductive performance of ewes synchronized with two doses of prostaglandin F2α (PG) at different intervals and inseminated at a fixed time. During the breeding season (April to June), 370 multiparous Corriedale ewes were assigned to five groups according to body condition score and body weight, and synchronized with two doses of PG administered 7, 10, 12, 14 or 16 days apart (groups PG7, PG10, PG12, PG14 or PG16; n = 73, 76, 74, 72, 75; respectively). Cervical timed artificial insemination (Day 0) was performed at 48 ± 1.0 h (group PG7) or 56 ± 1.0 h (groups PG10, PG12, PG14 and PG16) after the second PG injection, with diluted fresh semen pooled from six adult rams. The percentage of ovulating ewes after the second PG injection and the ovulation rate (number of corpus luteum/ovulating ewes) were assessed on Day 10 by trans-rectal ultrasonography. The rate of non return to service (ewes not returning to service/inseminated ewes × 100; NRR-21) was evaluated using painted vasectomized rams. Pregnancy rate (pregnant ewes/inseminated ewes × 100) and prolificacy (foetuses/pregnant ewes) were determined on Day 60 by trans-abdominal ultrasonography. Higher NRR-21 and pregnancy rates was observed in groups PG12 (46.0%, 46.0%), PG14 (59.7%, 56.9%) and PG16 (58.7%, 56.0%) compared to PG7 (30.1%, 28.8%) and PG10 (30.3%, 30.3%; respectively P < 0.05). No significant differences were observed in the percentage of ovulating ewes, ovulation rate and prolificacy among groups (P > 0.05). Under the condition of this trial, 12, 14 or 16 days interval between PG injections enhances the pregnancy rate of ewes at cervical timed artificial insemination with fresh semen.

Concentrations of steroid hormones, estrous, ovarian and reproductive responses in sheep estrous synchronized with different prostaglandin-based protocols.

To determine estrous, ovarian and reproductive responses after different prostaglandin (PG)-based protocols, ewes were assigned to groups PG10, PG12, PG14 or PG16 (twoPG injections administered 10, 12, 14 or 16 days apart; respectively). Experiment I (n=132) was conducted to evaluate the estrous response, ovulation rate (OR), conception and fertility. Experiment II (n=24) was conducted to evaluate ovarian follicle growth, steroid concentrations and the interval from the second PG injection to estrus (PG-estrus) and ovulation (PG-ovulation). Estrous response was less with the PG16 (P<0.05) treatment, and the extent of estrous synchrony was greater with the PG10 and PG12 treatments. Ovarian follicle growth and the intervals for the variables PG-estrus, PG-ovulation and OR were similar among groups (P>0.05). From 8 to 4 days before estrus, progesterone (P4) concentrations were greater for the PG14 and PG16 than for the PG10 and PG12 (P<0.05) groups. There were more days where concentrations of P4 were above 3.18 nmol/L with the PG14 and PG16 than PG10 and PG12 (P<0.05) treatments. Use of the PG14 and PG16 treatments resulted in greater estradiol (E2) at estrus and 12h later than use of the PG10 and PG12 treatments. A positive correlation was observed between the duration of the luteal phase and maximum E2 concentrations, and between duration of the luteal phase and days with E2 concentrations above 10 pmol/L. Conception and fertility were greater with use of the PG14 compared with PG10 and PG12 (P<0.05) treatments. The administration of two PG injections 10, 12, 14 or 16 days apart resulted in different durations of the luteal phase that were positively associated with E2 concentrations and the reproductive outcome. The shorter luteal phases were associated with greater synchrony in time of estrus. The intervals for the variables PG-estrus, PG-ovulation and OR were similar among groups.

Protein supplementation during a short-interval prostaglandin-based protocol for timed AI in sheep.

The aim of this experiment was to improve the reproductive performance of a short-interval prostaglandin (PG)-based protocol for timed artificial insemination in sheep, using a short-term nutritional treatment. During the breeding season (March-April), 132 multiparous and 61 nulliparous Corriedale ewes grazing natural pastures (600 kg DM/ha, 8.5% CP), were allocated to two groups: 1, Control group (n=100) two injections of D-Cloprostenol (75 µg per dose, 7d apart: Synchrovine(®) protocol); and 2, Supplemented group (n=93) ewes in which stage of the oestrous cycle was synchronised with Synchrovine(®) protocol plus focus feeding of a protein supplement (33.8% CP) between PG doses (Day -7 to -2). Cervical AI was performed at fixed time (Day 0), 46 ± 1.0 h after the second PG injection using 150 million sperm per ewe. Ovulation rate (Day 10), pregnancy rate, prolificacy and fecundity at Day 69 were evaluated by ultrasonography. Ovulation rate at Day 10 (1.20 ± 0.05 vs. 1.22 ± 0.05), pregnancy (46 ± 0.05 vs. 56 ± 0.05), prolificacy (1.09 ± 0.04 vs. 1.06 ± 0.05), and fecundity (0.49 ± 0.06 vs. 0.59 ± 0.06) at Day 69, were similar between groups (P>0.05; Control and Supplemented group respectively). It is concluded that focus feeding for 6d with protein supplementation during a short-interval PG-based protocol (Synchrovine(®)) did not improve the reproductive outcome associated with this protocol.

Reproductive outcome with GnRH inclusion at 24 or 36h following a prostaglandin F2α-based protocol for timed AI in ewes.

The objective of this experiment was to study the reproductive performance obtained after a short-interval prostaglandin (PG) F2α-based protocol for timed artificial insemination (TAI) in sheep (Synchrovine®: two injections of PG 7 d apart), including a GnRH analogue at 24 or 36h after the second PG injection. The experiment involved 296 Corriedale ewes (206 multiparous and 90 nulliparous) grazing natural pastures during the breeding season (March-April; UTU "La Carolina", Flores Uruguay, 33° S-57° W). Ewes were assigned to three treatment groups: a) Synchrovine® (Control, n=101): two injections of D-Cloprostenol 75µg, 7 d apart, b) Synchrovine®+GnRH24 (n=98): Synchrovine® plus GnRH (busereline acetate 8.4µg) 24h after the second PG injection, and c) Synchrovine®+GnRH36 (n=97): Synchrovine® plus GnRH 36h after the second PG injection. All ewes were subjected to cervical TAI (Day 0), 44 to 47h after second PG injection, with fresh extended semen pool from six rams. Reproductive performance of ewes having ovulations and ovulation rate on Day 10, estrous cycle length in ewes that returned to estrus and non-return rate to estrus up to Day 22, fertility, prolificacy and fecundity on Day 70 were analyzed. Ewes having ovulations, ovulation rate, estrous cycle length and prolificacy did not differ between groups (P>0.05). However, non-return to estrus, fertility and fecundity was decreased in Synchrovine®+GnRH24 (P<0.05) and similar between Synchrovine® and Synchrovine®+GnRH36 (P>0.05). It was concluded that the reproductive performance obtained by Synchovine® TAI protocol was impaired by GnRH at 24h and not improved by GnRH administered at 36h after the second PG injection.

Alternatives to improve a prostaglandin-based protocol for timed artificial insemination in sheep.

The objective was to improve the reproductive performance of a prostaglandin (PG) F(2α)-based protocol for timed artificial insemination (TAI) in sheep (Synchrovine®: two doses of 160 µg of delprostenate 7 d apart, with TAI 42 h after second dose). Three experiments were performed: Experiment 1) two doses of a PGF(2α) analogue (delprostenate 80 or 160 µg) given 7 d apart; Experiment 2) two PGF(2α) treatment intervals (7 or 8 d apart) and two times of TAI (42 or 48 h); and Experiment 3) insemination 12 h after estrus detection or TAI with concurrent GnRH. Experiments involved 1131 ewes that received cervical insemination with fresh semen during the breeding season (32/34 °S-58 °W). Estrous behaviour, conception rate, prolificacy, and fecundity (ultrasonography 30-40 d), were assessed. In Experiment 1, ewes showing estrus between 25 and 48 h or at 72 h after the second PGF(2α) did not differ between 80 and 160 µg of delprostenate (73 vs 86%, P = 0.07; and 92 vs 95%, P = NS, respectively). Conception rate and fecundity were lower (P < 0.05) using 80 vs 160 µg (0.24 vs 0.42, and 0.27 vs 0.47, respectively). In Experiment 2, giving PGF(2α) 7 d apart resulted in higher (P < 0.05) rates of conception (0.45 and 0.51) and fecundity (0.49 and 0.53) than treatments 8 d apart (conception: 0.33 and 0.29; fecundity: 0.33 and 0.34) for TAI at 42 and 48 h, respectively. In Experiment 3, rates of conception, prolificacy and fecundity were similar (NS) between Synchrovine® with TAI at 42 h (0.50, 1.13, and 0.56) and AI 12 h after estrus detection (0.47, 1.18, and 0.55), and Synchrovine® plus GnRH at TAI (0.38, 1.28, and 0.49). However, all TAI treatments had lower (P < 0.05) prolificacy and fecundity compared to AI following detection of spontaneous estrus (1.39 and 0.83, respectively). In conclusion, the Synchrovine® protocol was: a) more successful using 160 vs 80 µg delprostenate; b) more successful with a 7 d than 8 d PGF(2α) interval; c) similarly effective for TAI versus AI 12 h after estrus detection; and d) not improved by giving GnRH at TAI.

Effects of prostaglandin administration on ovarian follicular dynamics, conception, prolificacy, and fecundity in sheep.

Two experiments were conducted to determine the effects of prostaglandin administration on ovarian follicular dynamics, conception, prolificacy, and fecundity in sheep. During the breeding season, multiparous Corriedale ewes were randomly allocated to two groups: 1) PG group (n = 15 and n = 135 in Experiments I and II, respectively): synchronized with two injections of DL-Cloprostenol (125 µg) given 7 d apart, and inseminated at a fixed time (Day 0), 48 h after the second injection; and 2) Control group (n = 15 and n = 73 in Experiments I and II): ewes in spontaneous estrus inseminated at detected estrus. Ewes received 100 × 10(6) sperm by intrauterine AI. Ultrasonography was used to evaluate growth of the ovulatory follicle, ovulation rate (OR), conception rate, and prolificacy on Days 30 and 60. Ewes from the group PG had a larger (4.8 ± 0.5 mm, mean ± SEM; P < 0.05) ovulatory follicle that grew faster (1.2 ± 0.3 mm/d, P = 0.08), and a lower OR (1.37 ± 0.1, P < 0.05), compared to ewes from the Control group (3.9 ± 0.2 mm, 0.7 ± 0.2 mm/d, and 1.61 ± 0.1 respectively). Plasma progesterone concentrations from Days -6 to 1 were lower in the PG group (P < 0.05), but plasma estradiol concentrations were similar between groups (P > 0.05). Progesterone concentrations were similar between groups during the early luteal phase and on Days 12 and 17 (P > 0.05). The embryo recovery rate (Day 7) tended to be lower in the PG group (39 vs 64%, P = 0.08), but embryo quality did not differ between groups. Conception, prolificacy and fecundity, were lower in the PG than in the Control group (P < 0.05). Cumulative reproductive losses were similar between groups, but more twins were lost in the PG group (P < 0.05). We concluded that in ewes synchronized with PGF(2α) given twice, 7 d apart, lower reproductive performance was associated with an environment dominated by lower progesterone concentrations that stimulated the preovulatory follicle to grow faster and become larger; this was associated with lower rates of ovulation, conception, prolificacy, and fecundity.

Comparison of prostaglandin- and progesterone-based protocols for timed artificial insemination in sheep.

The objective was to compare the reproductive performance of a new PGF(2α)-based timed artificial insemination (TAI) protocol in sheep (Synchrovine®: two doses of PGF(2α), 7 d apart) to a traditional progesterone-eCG (P4-eCG) protocol, considering the effects of seminal state, AI-times, and AI-pathway. Three experiments involving 1297 multiparous Australian Merino ewes were done during the physiologic breeding season (location 32 °S-57 °W). Reproductive performance was assessed as non-return rate to service 21 d after AI (NRR21d), based on detection with androgenized wethers, as well as Fertility (pregnant/inseminated ewes), Prolificacy (fetuses/pregnant ewe), and Fecundity (fetuses/inseminated ewe), which were based on transabdominal ultrasonography 50 d after TAI. In Experiment 1, Synchrovine® treated ewes TAI cervically with fresh semen at 42, 48, or 54 h had similar NRR21d (0.51, 0.46, 0.57), Fertility (0.27, 0.31, 0.26), and Fecundity (0.29, 0.32, 0.27), all of which were lower (P < 0.05) than in a control P4-eCG group inseminated at 54 h (0.61, 0.48, 0.52, NRR21d, Fertility and Fecundity respectively). In Experiment 2, using chilled semen and cervical TAI, Synchrovine® treated ewes inseminated at 42 h yielded lower (P < 0.05) NRR21d, Fertility and Fecundity (0.28, 0.06, 0.06) compared to 48 (0.43, 0.24, 0.24) and 54 h (0.44, 0.22, 0.23). In Experiment 3 with chilled semen, Synchrovine® treated ewes TAI into the cervix at 51 or 57 h were similar in NRR21d (0.16 vs 0.20), Fertility (0.12 vs 0.14), and Fecundity (0.12 vs 0.15), respectively; but lower (P < 0.05) than P4-eCG treated ewes TAI at 54 h (0.34, 0.28, and 0.33 for NRR21d, Fertility and Fecundity respectively). Synchrovine® treated ewes intrauterine TAI at 51 or 57 h yielded similar NRR21d (0.51 vs 0.58), Fertility (0.43 vs 0.51), and Fecundity (0.45 vs 0.56) respectively, but lower (P < 0.05) results compared to P4-eCG treated ewes (0.75, 0.71, and 0.88 for NRR21d, Fertility and Fecundity respectively). In conclusion, AI-time in Synchrovine® treated ewes with fresh semen might be extended (42 to 54 h after the second PGF(2α)), but should be delayed to 48-54 h with chilled semen and cervical AI. Independent of the seminal state, AI-time or AI-pathway, Synchrovine® yielded lower reproductive results than a conventional P4-eCG protocol.

Chilled storage of ram semen improves with the addition of egg yolk and glycerol to milk-based extenders.

This study aimed at comparing in vitro, ultra-heat-treated (UHT) skim milk and INRA-96(®) -based extenders supplemented or not with 5% egg yolk and/or 2% glycerol on sperm quality parameters along 72 h of preservation at 5 °C, using a factorial design. Semen from six healthy mature Merino rams was pooled and extended in each medium using a split sample procedure (six replicates) and chilled. Subjective motility (SM) (%), membrane integrity (MI) (%) and uncapacitated spermatozoa (US) (× 10(6) spermatozoa/AI dose) were used to assess the semen quality at 0, 12, 24, 48 and 72 h of preservation. UHT-based extenders yielded better (p<0.05) SM and MI than INRA-96(®) -based extenders (59.7% vs 57.9%; 60.2% vs 55.8%, respectively) but similar numbers of US (64.2% vs 62.3 × 10(6) sperm/AI dose, respectively) along the preservation time. Egg yolk-glycerol or just egg yolk as additives improved (p<0.05) the results compared with the base extenders without additives or just with glycerol. The sperm parameters assessed decline slowly from 0 to 48 h, with a sharp decline (p<0.05) at 72 h of preservation. In conclusion, UHT and INRA-96(®) were similar as base extenders, and the addition of 5% egg yolk plus 2% glycerol or just 5% egg yolk improved the quality of ram semen preserved at 5 °C, at least for 48 h. The combination of egg yolk-glycerol might provide extra protection in case of fluctuation of temperatures below 5 °C, commonly seen under field conditions.

Conception rates in ewes after AI with ram semen preserved in milk-egg yolk extenders supplemented with glycerol.

This study aimed at comparing the effect of ram semen preserved at 5 °C on two milk-based extenders (UHT skim milk or INRA-96(®) , 5% egg yolk) supplemented with 2% glycerol, and the preservation time (24 and 48 h) on conception rates after cervical AI of ewes. In two field trials, 1198 Merino ewes were cervical AI in spontaneous oestrus. In Experiment 1, pooled semen (6 rams) was extended in UHT-base (fresh, control) or chilled for 24 h in UHT5Y (UHT-base 5% egg yolk), INRA5Y (INRA-96(®) 5% egg yolk), UHT5Y2G (UHT5Y 2% glycerol) or INRA5Y2G (INRA5Y 2% glycerol). In Experiment 2, AI was performed with pooled semen (7 rams) used fresh (extended in UHT-base or UHT5Y2G, control groups) or chilled (extended in UHT5Y2G) for 24 or 48 h. Conception rate was determined by ultrasound 40 days after AI. INRA-96(®) - had similar conception as UHT-preserved semen (56.7 vs 55.4%, p>0.05). Addition of 2% glycerol did not modify the results (56.8 vs 55.2%, p>0.05). Fresh semen extended in UHT-base, and UHT5Y2G yielded similar conception rates (60 vs 64%, p>0.05). Preservation for 24 or 48 h in UHT5Y2G gave similar results (49 vs 47%; p>0.05). In conclusion, ram semen chilled for 24 h in UHT- or INRA-96(®) -based extenders yielded similar results, and glycerol addition did not have a detrimental effect. UHT5Y2G might be used to extend ram semen for fresh AI, or to preserve it for 24 or 48 h with acceptable results.