Effects of differential ewe body condition at mating and early post-mating nutrition on embryo survival Public Deposited

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  • Two trials were conducted over consecutive years to examine the effects of ewe body condition and post-mating nutrition on ovulation rates and embryo survival. Trial 1 used 146 Polypay ewes ranging in age from 5 to 8 years in a 3 x 2 factorial array of pre-mating (high-H, low flushed-LF and low unflushed-L) and post-mating nutrition (high and low) treatments. Trial 2 was a 2 x 2 x 2 factorial array of 60 Polypay and 60 Coopworth x Polypay (C x P) three year old ewes, two pre-mating (H and LF) and two post-mating (high and low) treatments. To estimate timing and extent of embryo loss, two methods of embryo detection were employed during Trial 2. Real-time ultrasound was performed on all ewes at 21, 28, 34 and 45 days post-mating. Blood samples were also collected on these days for analysis of Pregnancy-specific Protein B (PSPB) levels. There was no effect of pre-mating treatment or ewe age on ovulation or conception rates for Trial 1. Pre-mating treatment was significant in Trial 2, with H ewes having higher ovulation rates than LF ewes. Pre-mating treatment, post-mating treatment, ewe age (for Trial 1) and genotype (for Trial 2) had no effect on mean litter size in either trial. Analysis of litter size among ewes with twin and triple ovulations showed pre-mating treatment to be significant among triple ovulators in Trial 1, where L ewes had much lower litter size (1.86) than LF (2.37) or H (2.60) ewes. In Trial 2, post-mating treatment was significant among the ewes with triple ovulations, with ewes on low nutrition having lower litter size (2.01) than ewes on high nutrition (2.59). Two-way interactions were significant among twin and triple ovulators in Trial 2. Breed x pre-mating interaction among twin ovulating ewes showed C x P LF ewes to have lower litter size (1.43) than the H ewes (1.87), while the opposite was true for Polypay ewes. Pre- x post-mating treatment interaction among triple ovulators showed LF ewes on low post-mating nutrition had lower mean litter size. This effect is largely due to lower litter size in the C x P triple ovulators on low post-mating nutrition. Data available from the ultrasound diagnosis showed little indication of treatment effects on amount or time of embryo loss. Ewes bearing single or multiple embryos differed in PSPB level at day 45, but not at earlier times. However, there were no differences in PSPB levels in ewes with twin or triple embryos at any of the trial days. Assay for PSPB failed to facilitate detection of the amount or time of embryo loss, as determined by ultrasound.
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