Effect of periconceptional nutrition on the growth, behaviour and survival of the neonatal lamb.

Periconceptional nutrition (PCN) can influence foetal hypothalamo-pituitary adrenal (HPA) axis function and alter cortisol secretion with possible consequences for maturation and growth of major organs, gestation length and behaviour. We examined effects of PCN on phenotype and survival of the neonatal lamb in 466 Merino ewes allocated to treatments providing 70%, 100% and 150% respectively, of maintenance requirements for 17 days prior and 6 days after insemination. Gestation length and birth weight for lambs in PCN treatment groups was similar (P > 0.05) but low PCN decreased the size of the neonate (crown-rump-length and metacarpal length P < 0.05). A subset of lambs euthanased at 5 days of age further showed that low PCN decreased the amount of peri-renal fat (P < 0.05) and increased liver mass (P < 0.05) while high PCN increased neck thymus and ovary mass (P < 0.05). Neonatal lambs from low PCN ewes returned faster to their mothers after release (P < 0.05) and contacted the udder in the shortest time (P < 0.05). Significant interactions between PCN treatment and sex (P < 0.05) and between PCN treatment and ewe age (P < 0.05) were also observed for time lambs took to follow the ewe. Survival of lambs was similar but potential differences may have been masked by favourable weather conditions. In conclusion, this study provides evidence of significant changes in lamb growth and development dependent on PCN and, for the first time, links these changes with significant changes in behaviour of the neonate. The impact of these effects on lamb survival and potential reproductive capacity of female offspring remains to be determined.

Effect of nutrition during pregnancy on fetal growth and survival in Fec(B) Booroola x South Australian Merino ewes.

The effect of nutritional manipulation during mid and late pregnancy on fetal growth and survival in high fecundity (Fec(B) Fec(+)) Merino ewes was examined. A total of 4 treatment groups was utilized in each of 3 years (1987, 1988 and 1989); and 2 groups were given low nutrition during mid pregnancy while 2 groups received high nutrition during this period. One group from each of these treatments subsequently received a high protein diet 1 to 2 weeks prior to term. Differential feeding during mid pregnancy resulted in the high and low treatment groups varying by 7.5 and 5.0 kg liveweight at Days 100 and 135 of pregnancy, respectively. Fetal survival was not improved by variation in nutritional intake during mid pregnancy (P>0.05) and neither were placental and fetal growth (P>0.05), as indicated by observations on cotyledon diameter and fetal head width, respectively. However, fetal survival during late pregnancy was reduced by a high level of nutrition during both mid and late pregnancy (P<0.05).

Exogenous progesterone and embryo survival in Booroola-cross ewes.

To investigate if exogenous progesterone improves embryo survival, 209 multiparous Booroola Merino x South Australian Merino ewes, heterozygous for the F gene (F+) were allocated to seven treatment groups and inseminated at a synchronized oestrus. Six groups received progesterone from controlled internal drug release G dispensers on the following days after ovulation: 4-7, 4-11, 4-14, 7-11, 7-14 and 11-14. Concentration of peripheral progesterone increased (P less than 0.05) in most supplemented groups, but there were no significant differences in pregnancy rates between treatments. However, the number of fetuses per pregnancy was increased for progesterone treatments starting on Day 4 (Days 4-7, 4-11 and 4-14 combined v. control; P less than 0.05) and for all supplemented treatments compared with the control (P less than 0.05).

Fertilization and embryo loss in Booroola Merino x South Australian Merino ewes: Effect of the F gene.

The effects of Booroola genotype (F+, ++); the number of ovulations per ewe (one, two or three); and the age of a ewe (2.5 yr vs 3.5 to 6.5 yr) on the percentage of ova fertilized, embryo loss and fetal loss were examined in Booroola x South Australian Merino ewes slaughtered on Days 4, 21 and 90 after insemination. Ewes slaughtered on Day 90 were examined by real-time ultrasound imaging (RUI) on Day 45. Fertilization failure was independent of ewe genotype, ovulation rate and age of ewe, and it was not an important source of wastage (F+, 9.4%; ++, 6.7%). Most embryo loss occurred during the first 21 d (F+, 54.7%; ++, 40.3%). Interpretation of the effects of genotype and ovulation rate on embryo wastage measured on Days 21, 45 and 90 was obscured by significant (P < 0.05) genotype and ovulation rate interactions with the day of slaughter/RUI. The effect of age on embryo loss was not significant (P > 0.05). Reasons for the high rate of wastage observed in this experiment require further study.

Uterine presensitization and embryo survival and growth in Booroola Merino x South Australian Merino ewes.

The fertility enhancing effects of semen were examined following the intra-uterine insemination of killed spermatozoa plus seminal plasma 17 d prior to insemination with viable spermatozoa. Three experiments were conducted: two on 1.5-yr old and 2.5 to 5.5 yr-old Booroola Merino x South Australian Merino ewes in 1986 and one on 1.5 yr-old ewes in 1987. Differences between treatment and control groups for the percentage of ewes exhibiting estrus by Days 21 and 35 following fertile insemination, the percentage of ewes with viable embryos at Day 35, the number and weight of viable embryos per ewe, the nubmer of caruncular implantation sites and the progesterone level were not statistically significant (P>0.05). There were no statistically significant treatment by experiment interactions for any of the variables examined. Inflammation and edema of the endometrial tissue was not observed following the presensitization treatment.