Effects of short and long - term nutrition and progesterone supplementation on the success of fixed - time artificial insemination in the ewe.

The success of fixed - time artificial insemination (AI) in the ewe is variable due to poor synchrony of estrus. We examined the effects of long-term nutrition (LTN; low, medium, high - 6 months), short-term nutrition (STN; 1.0 M, 1.5 M - 14 days) and progesterone supplementation (P; single pessary, replacement on Day 9) on synchrony and reproductive outcomes. High LTN advanced (P < 0.05) estrus, increased (P = 0.06) pregnancy (range 71.1 - 81.1%) and improved (P < 0.01) litter size (range 1.30 - 1.50). STN increased (P < 0.05) pregnancy (79.0 versus 72.3%) but not litter size or timing of estrus. A LTN x STN interaction (P < 0.01) for time of estrus indicates that the effects of LTN were moderated by STN depending on the level of LTN. Pessary replacement delayed (P < 0.05) the onset of estrus, improved synchrony but did not affect pregnancy or litter size. High LTN increased (P < 0.05) the number of large (≥ 3.8 mm) and medium - size follicles (2.0 - 3.7 mm) but the diameter of large follicles tended to be reduced (P = 0.08) on Day 12. STN did not affect follicle number or size whilst P reduced (P < 0.05) the diameter of large follicles on Day 12 (4.83 versus 5.10 mm) and increased the number of medium - size follicles (3.56 versus 2.74 mm). In conclusion, both LTN and STN are major sources of variability in AI programs whilst pessary replacement has potential to reduce variability.

Split weaning improves pregnancy rate and embryo survival in sows mated in lactation.

Increasing piglet weaning age while maintaining the reproductive efficiency of the breeding herd depends on the ability to stimulate sows to ovulate during lactation without reducing subsequent pregnancy rates and litter sizes. The aim of this study was to determine if a reduction in piglet suckling load, either prior to or immediately after mating in lactation, altered ovarian follicle development and increased embryo survival to day 30 of gestation. Fifty-nine multiparous Large White x Landrace sows were allocated to one of three treatments; litter size maintained at 11 piglets (control); litter size reduced to seven piglets on day 18 of lactation (split wean (SW)); or litter size reduced to seven piglets at expression of lactation oestrus (oestrus split wean (OES SW)). The percentage of sows that expressed lactation oestrus did not differ between treatments (79.7 %; P > 0.05) and split weaning had minimal effects on ovarian follicle development. Pregnancy rates were higher for SW and OES SW sows, compared to control sows. Embryo survival to day 30 of gestation was higher for SW sows (73.7 %) compared with control (56.4 %) and OES SW sows (49.5 %; P < 0.05). In summary, weaning a portion of the litter prior to mating in lactation improved pregnancy rates and embryo survival.

Heat stress from current and predicted increases in temperature impairs lambing rates and birth weights in the Australian sheep flock.

Livestock heat stress threatens production, particularly in semi-arid, arid and tropical regions. Using established temperature thresholds for sheep, we modelled +1 °C and +3 °C temperature increases over the historical baseline, estimating that 2.1 million potential lambs are lost annually due to heat stress alone, increasing to 2.5 and 3.3 million, respectively, as temperatures rise. Heat stress poses risks at key periods of the reproductive cycle, with consequences across the Australian sheep flock.

Effect of split weaning on follicle development and oocyte quality in multiparous sows.

Increasing piglet weaning age while maintaining the reproductive efficiency of the breeding herd depends on being able to stimulate sows to ovulate during lactation without reducing subsequent pregnancy rates and litter sizes. Embryo survival is affected by the quality of the oocytes shed at ovulation, and oocyte quality is profoundly impacted by the follicular environment in which the oocyte matures. This study determined the effect of reducing suckled litter size from 11 to 7 piglets on day 18 of lactation on the ovarian follicular environment and oocyte developmental competence at day 21 of lactation. Thirty-nine, Large White X Landrace sows (parity 3.2 ± 0.2; mean ± SEM; range 2-6) had their litter size either maintained at 11 piglets (control); or reduced to seven piglets on day 18 of lactation (split wean (SW)). Sows were slaughtered on day 21 of lactation and ovaries were collected for analysis of follicular fluid composition and in vitro blastocyst development rates. There was no effect of split weaning on fertilisation rate and development to blastocyst stage; however, a greater proportion of blastocysts from control sows were classified as early blastocyst stage. Furthermore, follicular fluid concentrations of oestradiol were higher in SW sows. Together, these results indicate split weaning prior to mating in lactation alters the ovarian follicular environment and while blastocyst development rates were unaffected, embryos from control sows may be of poorer quality as indicated by a delay in development.

Strategies to improve the success of fixed-time artificial insemination in the ewe.

During the sheep breeding season, ovulatory follicles vary widely in age at pessary removal impacting both the timing of oestrus and pregnancy rates following artificial insemination (AI). Ovulatory follicles that emerge between days 7 to 9 of the pessary period are associated with higher fertility whilst those that emerge earlier or later are associated with lower fertility. In this study, two strategies to improve the success of AI by controlling the development of the ovulatory follicle were examined. In the first, ewes were treated with PGF2α at either -12 and/or +6 days (experiment 1) or -27 days (experiment 2) relative to pessary insertion to control the time of emergence of the ovulatory follicle. In the second, ewes were treated with eCG (400 IU per ewe) at either 0 h, -6 h or -12 h relative to pessary removal (experiment 3) to improve the development of young ovulatory follicles. PGF2α administered on day -27 increased the percentage of pregnant ewes by 17.8% and the number of foetuses per 100 ewes inseminated by 33.9%. PGF2α treatment at other times had either no effect or reduced fertility. During the breeding season, treatment with eCG at -12 h improved the synchrony of oestrus, reduced the size of the ovulatory follicle but did not improve pregnancy rate compared with other treatments. Treatment had no effect during the non-breeding season, supporting earlier findings that the quality of young ovulatory follicles differs during the year. In conclusion, PGF2α treatment 27 days before pessary insertion provides a new and cheap strategy to improve the success of fixed-time AI programs.

Ovarian follicle dynamics in ewes treated with intra-vaginal progesterone pessaries. 2. Factors affecting timing of estrus and reproductive outcomes following artificial insemination.

This study extends observations on the effects of intra-vaginal progesterone treatment on the relationships between the time of luteolysis, emergence of the ovulatory follicle, timing of estrus and ewe fertility. Observations were made in progesterone - treated ewes in autumn, the spring equinox and late spring (Experiment 1, Data set 1) and in progesterone - treated ewes and naturally cycling ewes in autumn and the spring equinox (Experiment 1, Data set 2). In Data set 1, the day of emergence of both the first and second ovulatory follicle was positively related to the day luteal regression within each season. In turn, the day of emergence influenced the timing of estrus by means of a season by day of luteal regression interaction (P < 0.001) indicating that the relationship was positive in autumn and the spring equinox but negative in late spring. In autumn, older ovulatory follicles were associated with an earlier onset of estrus compared with younger ovulatory follicles. In late spring, this relationship was reversed and was influenced by whether or not ewes were cycling at the time of pessary insertion. In Data set 2, the relationship between the day of follicle emergence and luteal regression was influenced by a treatment by day of regression interaction indicating the relationship was positive in treated ewes and negative in naturally cycling ewes. Timing of estrus was positively related (P < 0.001) to both the day of luteal regression and the day of follicle emergence (P < 0.05), with both relationships being stronger in naturally cycling ewes than in treated ewes. In Experiment 2, pregnancy rate following artificial insemination in autumn was highest (90.2%) when luteolysis occurred during Days 7-9 of the pessary period compared with Days 1-6 (77.8%, P = 0.16), 10 to 12 (68.8%, P < 0.05) or Days ≥13 (71.2%, P < 0.05). Timing of estrus was not affected. The mean diameter of ovulatory follicles that emerged during Days 7-9 was larger on Day 12 (5.8 ± 0.13 mm) compared with other periods (range 4.7 ± 0.05 to 5.6 ± 0.14 mm). This study provides two potential strategies to improve the success of AI programs. Firstly, appropriately timed treatment with PGF2α to control the time of emergence of ovulatory follicles and, secondly, earlier treatment with eCG to improve the development of ovulatory follicles that emerge late in the pessary period. Each is likely to be influenced by season and the cyclical status of the ewe.

Ovarian follicle dynamics in ewes treated with intra-vaginal progesterone pessaries. 1. Follicle waves and parameters of the estrous cycle.

Progesterone treatment for synchrony of estrus is standard in sheep artificial insemination (AI) programs but can be associated with poor outcomes. Potential for improvement exists through a better understanding of the interactions between follicle development, luteal regression, emergence of the ovulatory follicle and timing of estrus. These interactions were examined by comparing progesterone-treated (Day 1 = day of pessary insertion) and naturally cycling ewes (Day 1 = day after estrus) at three times of the year (Autumn, Spring equinox and late Spring). Observations were made from Day 1 until the day of ovulation. Compared with the natural cycle, progesterone treatment (300 mg intra-vaginal pessary for 14 d) reduced the number of follicle waves (2.2 ± 0.18 versus 2.8 ± 0.12; P < 0.05) and increased the length of the ovulatory wave (8.6 ± 0.45 versus 6.6 ± 0.42 d; P < 0.05). The number of follicles per wave, the inter-wave interval and ovulation rate were not affected. However, progesterone treatment induced (P < 0.05) an earlier luteolysis (9.7 ± 0.51 versus 15.4 ± 0.49 d after Day 1), an earlier emergence of the ovulatory follicle (7.5 ± 0.48 versus 11.4 ± 0.46 d after Day 1) and an earlier onset of estrus (26.1 ± 2.95 versus 53.3 ± 2.84 h after Day 14). Time of year also influenced the response to progesterone treatment. In Autumn compared with the Spring equinox and late Spring, there was a reduction (P < 0.05) in follicle wave number (2.4 ± 0.21 versus 2.5 ± 0.29 versus 3.0 ± 0.20 respectively), follicles per wave (2.6 ± 0.27 versus 3.5 ± 0.25 versus 3.2 ± 0.20 respectively), ovulation rate (1.6 ± 0.12 versus 1.9 ± 0.12 versus 2.0 ± 0.10 respectively) and the inter-wave interval was longer (5.3 ± 0.40 versus 4.0 ± 0.32 versus 3.8 ± 0.27 d respectively; P < 0.05). Time of year also influenced (P < 0.05) the time of luteolysis (earliest in late Spring), emergence of the ovulatory follicle (earliest in Autumn) and onset of estrus (earliest in Autumn). It is concluded that (1) the effects of progesterone treatment on follicle waves are relatively minor, (2) the effects of treatment on timing of luteolysis, emergence of the ovulatory follicle and onset of estrus are all significant although the effects on AI outcomes remain to be determined and (3) time of year has a minimal effect on follicle waves but a more significant effect on other parameters of the estrous cycle. A better understanding of these complexities will assist in the development of improved protocols for synchrony of estrus.

Supplementary Tryptophan Fed to Sows Prior to and after Farrowing to Improve Piglet Growth and Survival.

Tryptophan indirectly increases plasma calcium levels, which may improve sow health, and melatonin production, which may improve piglet survival when supplemented during late gestation and lactation. It was hypothesised that tryptophan would increase piglet survival and increase sow circulating melatonin and calcium. Seventy-two multiparous (Landrace x Large White) sows were allocated to either control (0.16% tryptophan; n = 24), low tryptophan (0.42%; n = 24) or high tryptophan (0.56%; n = 24). Piglet viability measures consisted of weights, behaviour, meconium staining, rectal temperature, blood glucose and serum immunoglobulin G concentration. Blood samples collected from sows were analysed for melatonin (two daytime and three night-time samples; n = 17) and calcium (two samples pre- and post-farrowing; n = 14). Both tryptophan treatments increased piglet survival compared to the control group (p < 0.001). Tryptophan had no effect on piglet viability (p > 0.05) and no effect on sow plasma melatonin and calcium concentrations compared with the control group (p > 0.05) except at 21:00 when low tryptophan sows had higher melatonin concentration compared with high tryptophan (p = 0.011). Further research to understand the mediating effects of tryptophan (particularly 5-hydroxytryptophan) on piglet survival, including sow behaviour, is warranted.

Review of the impact of heat stress on reproductive performance of sheep.

Heat stress significantly impairs reproduction of sheep, and under current climatic conditions is a significant risk to the efficiency of the meat and wool production, with the impact increasing as global temperatures rise. Evidence from field studies and studies conducted using environmental chambers demonstrate the effects of hot temperatures (≥ 32 °C) on components of ewe fertility (oestrus, fertilisation, embryo survival and lambing) are most destructive when experienced from 5 d before until 5 d after oestrus. Temperature controlled studies also demonstrate that ram fertility, as measured by rates of fertilisation and embryo survival, is reduced when mating occurs during the period 14 to 50 d post-heating. However, the contribution of the ram to heat induced reductions in flock fertility is difficult to determine accurately. Based primarily on temperature controlled studies, it is clear that sustained exposure to high temperatures (≥ 32 °C) during pregnancy reduces lamb birthweight and will, therefore, decrease lamb survival under field conditions. It is concluded that both ewe and ram reproduction is affected by relatively modest levels of heat stress (≥ 32 °C) and this is a concern given that a significant proportion of the global sheep population experiences heat stress of this magnitude around mating and during pregnancy. Despite this, strategies to limit the impacts of the climate on the homeothermy, behaviour, resource use and reproduction of extensively grazed sheep are limited, and there is an urgency to improve knowledge and to develop husbandry practices to limit these impacts.

Neonatal lamb mortality: major risk factors and the potential ameliorative role of melatonin.

High incidences of pre-weaning mortality continue to limit global sheep production, constituting a major economic and welfare concern. Despite significant advances in genetics, nutrition, and management, the proportion of lamb deaths has remained stable at 15-20% over the past four decades. There is mounting evidence that melatonin can improve outcomes in compromised ovine pregnancies via enhanced uterine bloodflow and neonatal neuroprotection. This review provides an overview of the major risk factors and underlying mechanisms involved in perinatal lamb mortality and discusses the potential of melatonin treatment as a remedial strategy. Supplementing pregnant ewes with melatonin enhances uterine bloodflow and fetal oxygenation, and potentially birthweight and neonatal thermogenic capacity. Melatonin freely crosses the ovine placenta and blood-brain barrier and provides neuroprotection to the fetal lamb during periods of chronic and acute hypoxia throughout gestation, with improved behavioural outcomes in hypoxic neonates. The current literature provides strong evidence that maternal melatonin treatment improves outcomes for lambs which experience compromised in utero development or prolonged parturition, though to date this has not been investigated in livestock production systems. As such there is a clear basis for continued research into the effects of maternal melatonin supplementation during gestation on pre-weaning survival under extensive production conditions.

Supplementing Merino ewes with melatonin during the last half of pregnancy improves tolerance of prolonged parturition and survival of second-born twin lambs.

High preweaning mortality rates continue to limit sheep production globally, constituting a major economic and welfare concern. Greater losses in twin lambs (≥30%) compared with singletons (≥10%) are attributed primarily to lower birth weight and increased risk of intrapartum hypoxia, leading to impairment of thermoregulation, neuromotor activity, and maternal bonding behavior. Previous intensive studies demonstrated that supplementing pregnant ewes with melatonin reduced the adverse effects of fetal growth restriction and perinatal hypoxia on the neonatal brain via increased umbilical blood flow, placental efficiency, and antioxidant actions. The current study examined the effects of supplementing pregnant ewes with melatonin on lamb survival, birth weight, and behavior under intensive conditions. From gestational day (gD) 80 until parturition, pregnant singleton and twin-bearing ewes were supplemented with melatonin via a 2-mg capsule fed daily (Mel-FED, n = 61) or 18 mg subcutaneous implant (Regulin), with one implant administered at gD80 and another at gD125 (Mel-IMP, n = 60). Control ewes received no supplementation (CTL, n = 60). Ewes and lambs were monitored via video throughout parturition. Postpartum measures were taken from lambs at 4 and 24 h (live weight [LW], rectal temperature, serum immunoglobulin G, and latency to stand and suck after birth) and LW at 72 h, 7 d, marking (49.7 ± 0.2 d), and weaning (124.2 ± 0.8 d). Chi-square analysis was used to compare lamb survival between treatment groups. There were no treatment effects on singleton lamb survival. Melatonin supplementation tended to increase the proportion of twin lambs surviving from birth to weaning (Mel-FED = 85.5%; Mel-IMP = 85.9%; CTL = 72.9%; each P < 0.1). Survival of first-born twins did not differ between treatment (each ~90%, P = 0.745) but within second-born twins, survival of Mel-FED was greater than CTL (81.6 vs. 57.1%, P = 0.023), and Mel-IMP (78.1%) tended to be greater than CTL (P = 0.068). Similarly, in second-born twins exposed to prolonged parturition (≥ 90 min), survival of lambs from Mel-FED ewes was greater than CTL (86.7% vs. 42.9%, P = 0.032), while Mel-IMP was intermediate (66.7%). These data suggest that the neuroprotective actions of melatonin may improve twin lamb survival by increasing tolerance of prolonged parturition and provide a sound basis for continued testing in extensively managed sheep flocks.

Maternal melatonin implants improve twin Merino lamb survival.

High preweaning mortality rates cost the Australian sheep industry an estimated $540 million annually in lost production, with losses significantly greater in twin (≥30%) compared with singleton lambs (≥10%). Previous intensive studies demonstrated that supplementing pregnant ewes with melatonin reduces adverse effects of fetal growth restriction and perinatal hypoxia on the neonatal brain via increased umbilical blood flow, placental efficiency, and antioxidant actions. The current study examined the effects of supplementing ewes with melatonin on the survival of twin Merino lambs under extensive grazing conditions. Pregnant mixed age ewes were implanted with 1 (M1, n = 50) or 2 (M2, n = 53) slow-release melatonin implants (18 mg, Regulin) at gestational days 70 to 90. Control ewes received no supplementation (CTL, n = 54). Ewes were monitored twice daily throughout the lambing period. Lamb survival, weight, and rectal temperature were recorded on the day of birth. Lamb blood samples were taken the following day for serum immunoglobulin G (IgG) analysis. Lamb survival and weight were recorded again at marking (30.6 ± 0.6 d postpartum) and weaning (70.7 ± 0.6 d postpartum). Lamb survival was increased in both melatonin treatments to 3 d postpartum (M1 = 98.0%; M2 = 95.3%; CTL = 83.3%; each P < 0.01), and this improvement was maintained to weaning (M1 = 94.0%; M2 = 92.5%; CTL = 79.6%; each P < 0.01). Melatonin did not affect lamb birthweight, rectal temperature, or growth rate. However, the rates of parturition-related death (dystocia, stillbirth, and birth injury) were greater in CTL lambs than M1 (P = 0.009) and M2 (P = 0.035). This suggests that improved survival is primarily due to melatonin-induced neuroprotection, although further studies are required to clarify the underlying mechanisms. These data provide evidence that supplementing pregnant twin-bearing Merino ewes with melatonin may be a practical strategy to reduce neonatal mortality and improve weaning rates in extensively managed sheep flocks. Although the present data are promising, this study is limited by small sample size and requires further replication.

Maternal Supplementation with Dietary Betaine during Gestation to Improve Twin Lamb Survival.

Betaine increases the synthesis of creatine, an energy-rich amino acid that increases adenosine triphosphate (ATP) and has neuroprotective properties which may improve post-natal lamb survival. This study determined whether maternal betaine supplementation during gestation would improve body weight, thermoregulation, time to stand and suck, colostrum intake and survival to weaning of twin lambs. Twin-bearing Merino ewes received dietary betaine at either 0 g/day (Control, CTL), 2 g/day from ram introduction to parturition (Early betaine, EB) or 4 g/day from Day 80 of gestation to parturition (Late betaine, LB). Ewes were housed individually during parturition and measures were collected at 4, 24 and 72 h and Day 7 post-partum, and at marking (53.2 ± 0.2 days of age) and weaning (99.3 ± 0.2 days of age). The EB treatment resulted in heavier lambs at weaning compared with CTL and LB lambs (p < 0.05). Time to stand and suck from birth was longer in EB lambs (p < 0.05), whereas, the interval from birth to first suck was shorter for LB lambs (p < 0.05). Lamb survival rate was the highest for LB lambs at 72 h and Day 7 (p < 0.05), and lowest for EB lambs on Day 7 (p < 0.05). These data indicated that betaine supplementation at 4 g/day during the second half of pregnancy improved twin lamb survival to Day 7 and shortened the interval from birth to first suck; whereas feeding ewes 2 g/day of betaine for the duration of pregnancy increased twin lamb body weight at weaning, but increased both the time to attain behavioural milestones and mortalities before Day 7.

Controlling lactation oestrus: The final frontier for breeding herd management.

Lactation anoestrus limits the flexibility of modern pig production systems such that any increase in lactation length reduces farrowing frequency, and thus profit. This review focuses on post-partum development of the sow's reproductive system, the physiology of lactation anoestrus and how it can be overcome, as well as the fertility of sows mated while lactating. The propensity for sows to ovulate spontaneously while lactating is high (24-31%), and a high proportion of sows will ovulate rapidly and synchronously in response to combinations of altered suckling (split weaning, interrupted suckling), daily boar contact, exogenous gonadotrophins, and group housing. The apparent ease with which lactation anoestrus can be overcome represents an opportunity to uncouple sow mating from weaning, thus reducing the impact of lactation length on productivity. This is especially true when considering the benefits of the described stimulation methods on the reproductive performance (i.e., shorter weaning to oestrus intervals and higher litter sizes) of the low proportion of sows that maintain lactation anoestrus.

Effects of lactation length and boar contact in early lactation on expression of oestrus in multiparous sows.

The ability to stimulate a fertile oestrus during early lactation provides an opportunity to increase piglet weaning age whilst maintaining 2.4 litters per sow per year. This study evaluated the effects of boar contact beginning on day 7 of lactation and lactation length on lactation oestrus induction and subsequent reproductive output in multiparous sows (parity 2.9 ± 0.16; mean ± SEM; range 2-6). Large White × Landrace multiparous sows were allocated to one of four treatment groups; weaning at 26 days post-partum and no boar contact (control); weaning at 26 days and boar contact (BC); weaning at 7 days and boar contact (BC+short lactation (SL)); and weaning at 7 days and no boar contact (SL). Control and SL sows were taken for a short walk daily during which a backpressure test was performed in the absence of a boar. Oestrus expression within 26 days of farrowing was significantly higher in BC (67%) and BC+SL (93%) sows than control (11%) and SL (13%) sows (P<0.05). Of sows mated within 26 days of farrowing, there was no difference in the number of piglets born alive or stillborn. Therefore, boar contact is an effective method to stimulate oestrus within 26 days of farrowing in both lactating and weaned sows.