Comparison between the reproductive performance of ewe hoggets and mature ewes following a progesterone-based oestrus synchronization protocol

Successful induction of oestrus, ovulation and pregnancy in adult ewes and ewe lambs out of the breeding season using a GnRH+progesterone oestrus synchronisation protocol

“…Oestrus rates in adult ewes (ranging from 71.9% to 77.8%) were similar to those reported in New Zealand studies during the non-breeding season (deNicolo et al, 2008a) and slightly lower than those in the breeding season (deNicolo et al, 2008a;Mulvaney et al, 2013), which ranged from 75% to 100%, respectively. The proportion of adult ewes with corpora lutea after treatment with the U-synch protocol (83.0% in Experiment 1) was also comparable with those from previous studies performed in the non-breeding season (deNicolo et al, 2008a).…”

“…The higher fertility found in mature ewes in comparison to that in ewe lambs of Experiment 3 has also been reported in progesterone-synchronised sheep during the breeding season (Quirke, 1979;Mulvaney et al, 2013). This difference in fertility has been recognised as a result of decreased competence of oocytes from ewe lambs to produce early embryos capable of developing to term compared to mature ewes (Quirke and Hanrahan, 1977).…”

“…These ranged from 48.0% to 97.3% of ewe lambs marked by rams after the use of synchronisation protocols consisting of the standard treatments with a 11-to 12-day progestin device with or without eCG treatment at device removal (Ch'ang et al, 1968;Quirke, 1979;McMillan, 1986;O'Doherty and Crosby, 1990;Kenyon et al, 2012;Mulvaney et al, 2013). Variation in the oestrous response can be attributed to season (deNicolo et al, 2008a), breed (Quirke, 1979), age and length of the period of joining (Mulvaney et al, 2013). In the current studies, variability in oestrus rates of untreated Control groups was observed with the proportion of ewe lambs marked by rams being 8.6% or 42.1% after 7 or 21 days, respectively, after joining with rams for Experiments 3 and 4.…”

“…This standard protocol has been used to synchronise oestrus during the breeding season in sheep (Clarke and McDonald, 1975;Allison and Kelly, 1978;Fenton et al, 1997;Wildeus, 2000;Mulvaney et al, 2013). While progesterone induces "priming" of areas of the brain involved with cyclicity, eCG stimulates the final stages of follicular growth.…”

Effect of breeding season on fertility of sheep following estrus synchronization and fixed-time artificial insemination under field conditions in semi-arid tropical region

“…Martinez et al (Martinez et al 2015) also reported estrus rates in adult ewes (ranging from 71.9 to 77.8%) in accordance with our findings. However, deNicolo et al (2008) reported slightly lower estrus percentage during non-breeding season than those in the breeding season (Mulvaney et al 2013) which ranged from 75 to 100%, respectively. It may be due to deep anestrus during non-breeding season that reduced the estrus percentages slightly (deNicolo et al 2008) even with the use of progesterone and eCG.…”