Utilising male stimulus to improve the reproductive efficiency of 8-month-old nulliparous ewes and adult parous ewes

We tested whether utilising the male effect to stimulate ewes before the mating period can reduce the time to conception following the introduction of entire rams, and increase fertility, prolificacy, and reproductive rate (number of fetuses per 100 ewes exposed to fertile rams). A retrospective analysis was used to analyse records from 59,716 ewes collected over 34 years (1986-2020) from seven genotypes: Border Leicester, Composite (crossbred), Dorset, Merino, Dorset x Polypay, Rambouillet, White Suffolk. The dataset also included nulliparous young ewes (mated at age 8 months) and adult parous ewes. Vasectomized rams were used to stimulate 20,632 ewes before a mating period that lasted 2 or 3 estrous cycles, and the outcomes were compared with those from 39,084 ewes that had not been stimulated. Independently of genotype, utilising the male stimulus advanced the average conception date by 8 days for young ewes (P < 0.0001) and by 1 day for adult ewes (P < 0.0001). The male stimulus also increased the proportion of ewes that conceived in their first cycle by 33 % for young ewes and by 6 % for adult ewes (P < 0.0001). For the cycle of conception, there were significant (P < 0.0001) effects of two interactions: male stimulus x age at mating and male stimulus x live weight at mating. The male stimulus improved fertility in both adult ewes (99.8 % vs 89 %; P < 0.001) and young ewes (77.7 % vs 81.3 %; P < 0.001). The male stimulus increased the number of young ewes (41.9 % vs 11.1 %; P < 0.001) and adult ewes (16.6 % vs 2.7 %; P < 0.001) that conceived multiple fetuses in the first 17 days of the mating period. The reproductive rate was improved by the male stimulus in young ewes (129 % vs 135 %; P < 0.001) but not in adult ewes (120 % vs 122 %; P = 0.12). When all animals for all breeds were included in the analyses, there were improvements in fertility, prolificacy, and reproductive rate as age and live weight increased at mating (P < 0.0001). We conclude that, independently of genotype, utilising the male stimulus before the mating period reduces the time to conception and improves reproductive performance in both young and adult ewes.

Application of the "echo-synch protocol" to advance pregnancy onset in ewe lambs at the first reproductive season

Introduction

This study assessed the efficacy and economic impact of a reproductive protocol based on repeated ultrasound scanning (US) associated with the use of GnRH to advance pregnancy onset in ewe lambs.

Methods

Prepubertal ewe lambs (n = 133) were divided into three weight groups (High: HW n = 35; Medium: MW n = 65; Low: LW n = 33). Thereafter, animals were randomly allocated into two subgroups: GnRH, ewe lambs treated with GnRH analog and then exposed to rams; CTR, ewe lambs exposed to rams only. CTR groups were joined with rams as a single flock. GnRH groups were kept separate from rams receiving a single dose of gonadorelin (40 μg/head) and then were evaluated after a week of US. Animals showing corpora lutea received an injection of PGF2α analog (100 μg/head) and then were joined with rams. The remaining ewe lambs received a second dose of gonadorelin and were kept separate from the rams. After another week, animals were checked again and the ones showing corpora lutea were injected with the PGF2α analog, while the others received a third injection of gonadorelin. On the same day, all the animals were joined with rams. Pregnancies were confirmed within 30 days by US. The efficacy of the protocol was determined by assessing differences in the number of days required to achieve pregnancy rates of 25, 50, and 75% and in the total costs and incomes from birth to the end of first lactation within the groups.

Results

The GnRH-MW group showed the best performances in reaching the threshold pregnancy rates of 25, 50, and 75%, but the effect of treatment was significant only at the 25% threshold (p < 0.01). Both low groups displayed an overall poorer performance at 50 and 75% thresholds than medium and high-weight groups (p = 0.01 and p < 0.01, respectively). The GnRH administration did not advance pregnancy onset in GnRH-HW compared with CTR-HW. In the balance between costs and income, the HW-CTR and MW-GnRH groups showed higher gross margins than the other groups.

Conclusion

Using the US/GnRH protocol in ewe lambs appears technically and economically effective in animals that have not reached the optimal weight at the first breeding season, advancing ewe lambs' pregnncies and increasing farm profitability.

Breeding Ewe Lambs: An Australasian Perspective

A number of potential advantages have been identified for breeding ewe lambs at 7 to 9 months of age, including increased lifetime productivity and profitability. However, breeding at this young age in extensive pastoral systems, such as in Australasia, can be associated with a number of disadvantages resulting in uptake of this management procedure being relatively low. This review highlights the known differences between ewe lamb and mature ewe reproductive performance, thus differing in their management. The review then summaries the scientific literature of factors that affect ewe lamb reproductive success, with a focus on recent studies conducted under extensive pasture-based conditions in Australasia. In particular, this review outlines the importance of ewe lamb live weight and body condition score on their productivity. The potential long-term consequences of breeding a ewe lamb at a young age in terms of her future success and that of her offspring to weaning are briefly outlined. In addition, the potential impacts of selecting progeny born to ewe lambs as future replacement ewes are discussed. Throughout this review, optimal management guidelines from prior to breeding the ewe lambs until rebreeding at 2 years of age are provided. Lastly, areas requiring future research are identified and discussed.

The effects of birth rank (single or twin) and dam age on the lifetime productive performance of female dual purpose sheep (Ovis aries) offspring in New Zealand

Greater rates of genetic gain can be achieved by selecting animals born to younger parents. However, little is known about the lifetime performance of dual purpose ewes (Ovis aries) that are born to primiparous ewe lambs (8 to 9 months old at breeding). This experiment investigated the effect of being born from either a ewe lamb or mixed age dam as either a single or twin on the lifetime performance of ewe progeny. Lifetime performance was measured in terms of the life time live weights of the ewes, the weight and number of lambs born and weaned, the efficiency of production (kilograms of lamb weaned / predicted pasture intake (kgDM) of the ewes), and ewe survival. The study followed the lifetime production of 17 single and 41 twin female lambs born to mature ewes (M1 and M2, respectively), and 28 single and 29 twin lambs born to ewe lambs (L1 and L2, respectively). Over their lifetime L2 ewes were lighter (P<0.05) but had similar body condition scores to the other three ewe groups. There was no difference in average progeny weaning weight or total progeny litter weaning weights between groups. The M1 ewes had the greatest longevity (P<0.05) of the four groups. Even though L2 ewes were lighter than the other three groups, this was insufficient to increase their lifetime efficiency of production (kg lamb weaned/predicted pasture consumption), relative to the other groups. These results suggest farmers could select replacements born to ewe lambs without sacrificing animal production.

Sexually active bucks are a critical social cue that activates the gonadotrope axis and early puberty onset in does

In rodents, early exposure to adult male is well known to induce an early puberty in females (Vandenbergh effect). This phenomenon has been less studied in other mammals. In goats, despite our extensive knowledge about the "male-effect" phenomenon in adults (i.e. ovulation induced by the introduction of the male during the anestrous), there are few data on the consequences of an early exposure of females to males. Here, we evaluated the puberty onset of young alpine goats when raised since weaning with intact bucks (INT), with castrated bucks (CAS) or isolated from bucks (ISOL). The INT group had the first ovulation 1.5 month before the two other groups. Despite the earlier puberty the INT group of females had normal and regular ovarian cycles. Morphological study of the genital tract showed that at 6 months, uterus of INT goats was 40% heavier than CAS and ISOL goats. Moreover, INT females had a myometrium significantly thicker and INT was the only group having corpora lutea. In our study, INT females were pubescent in the month following the entry of bucks into the breeding season, suggesting that only sexually active bucks provide the signal responsible for puberty acceleration. By removing direct contact with the bucks, we showed that somatosensory interactions were dispensable for an early puberty induction. Finally, no difference in the GnRH network (fiber density and number of synaptic appositions) can be detected between pubescent and non-pubescent females, suggesting that the male stimulations triggering puberty onset act probably on upstream neuronal networks, potentially on kisspeptin neurons.

Intensive sheep and beef production from pasture--a New Zealand perspective of concerns, opportunities and challenges

This paper details current production trends for sheep and beef cattle production in New Zealand and gives some insight into the opportunities for improvement based on New Zealand research at Massey University. Further it outlines some of the challenges the industries face in the near future. The New Zealand climate favours pasture growth and this is the key to sheep and beef cattle production with over 95% of the diet being grazed pasture or crop. Exports are the focus of the industry with 95% of sheep meat and wool, and 80% of beef exported. There have been considerable gains in production over the last 20 years but there still remains a huge opportunity for further intensification through breeding sheep at an earlier age, increasing the weight of lambs weaned per ewe per year and improving beef production systems. These improvements need to occur within a framework of minimal environmental footprint and produce products that are in demand in the high end international markets.