No abstract

The objective of the present experiment was to determine whether increasing plasma insulin by different nutritional regimes affects oocyte quality. Holstein dairy heifers (eight per treatment) were assigned, using a two times two factorial design, to diets containing either low or high dietary leucine and either low or high dietary starch. Each heifer underwent six sessions of ovum pick-up beginning 25 days after introduction of the diets. Oocyte quality was assessed by development to the blastocyst stage in synthetic oviducal fluid following in vitro fertilisation. Feeding diets containing high leucine resulted in significantly higher plasma free leucine and tyrosine concentrations. The high-starch diet significantly increased plasma insulin but not glucagon concentration, whereas high dietary leucine increased plasma glucagon but not insulin. Oocyte cleavage was not influenced by diet. The high-starch diet, which was associated with a high plasma insulin : glucagon ratio, had adverse effects on oocyte quality that were avoided when leucine intake was increased. There was an association between total plasma free amino acid concentration and oocyte cleavage. Therefore, in dairy heifers dietary amino acids and carbohydrates during antral follicle development appear to mediate effects on oocyte quality by different mechanisms. These findings have implications for both diet formulation and feeding regimes.

A key to long-term sustainable enhancement of viable livestock production is the introduction of genetic traits that ensure that fertility and meat quality characteristics are compatible with farming environments and market needs. For example, the sheep industry could benefit if daughters of hill-breed ewes were of a crossbred genotype that enhances both carcass characteristics and fertility traits. Use of sires that confer better conformation is an option but does not significantly boost prolificacy. Introduction of the ‘Inverdale’ fecundity gene could change this. On a flock basis in the Romney breed, mean ovulation is increased by 1.0 and litter size by 0.6 in adult ewes carrying a single copy of this gene (designated as FecXI because it is on the X chromosome; Davis et al. 1992). Carrier males transmit it to all of their female offspring, these being heterozygous carriers of the gene unless it also is maternally inherited. In the latter instance, young would be infertile the homozygous genotype confers an undesirable ‘streak ovary’ phenotype. Although a number of sheep breeds world-wide exhibit significant ‘single gene’ effects on ovulation and litter size (Montgomery et al. 2001), Scottish hill sheep breeds show no evidence of this. Consequently, all ewe lambs generated by crossing these hill ewes with a ram carrying the Inverdale gene should be heterozygous. To ascertain whether such animals exhibit enhanced fecundity, an on-farm study investigated ovulation incidence in cyclic ewe lambs born to Cheviot or Scottish Blackface ewes that had been bred to Texel rams carrying a single copy of the ‘Inverdale’ gene.

The post-fertilisation developmental capacity of bovine oocytes recovered by ultrasound guided transvaginal follicular aspiration (ovum pick-up, OPU) is influenced by diet-induced changes in hormone and metabolite concentrations. The objectives of this experiment were first to determine whether post-prandial changes in hormone concentrations, induced by changing the frequency of feeding, influenced oocyte quality and second whether changes in plasma glucagon concentration were associated with oocyte quality. Using a 2 3 2 factorial design, Holstein heifers (six per treatment) were fed either fibre-or starch-based diets containing either 189 or 478 g starch/kg dry matter. The diets were offered in either two or four equal meals per day and supplied twice the maintenance energy requirement. Blood samples were obtained both at weekly intervals (three samples per heifer, collected before feeding) during the experiment and throughout an entire 24-h period (15 or 17 samples per heifer for twice or four times daily-fed heifers, respectively). Each heifer underwent six sessions of OPU (twice weekly) beginning 25 days after introduction of the diets. Oocyte quality was assessed by development to the blastocyst stage in synthetic oviductal fluid following in vitro fertilisation. Mean weekly plasma insulin concentrations did not differ between diets, but plasma glucagon concentrations were greatest when heifers were fed the starch-based diet twice daily compared with the other diets. When heifers were offered four meals per day, there were no meal-related changes in hormone concentrations. However, when heifers were offered two meals per day, plasma insulin concentration increased after feeding the starch-based, but not the fibre-based diet. Plasma glucagon concentration increased after meals when heifers were fed twice daily and the increase was substantially greater when the starch-based diet was fed. Treatments did not influence (overall mean with mean 6 s.e.) ovarian follicle size distribution or oocyte recovery by OPU (6.2 6 0.4 per heifer), the proportion of oocytes that cleaved following insemination (0.57 6 0.030) or blastocyst yield (0.27 6 0.027 of oocytes cleaved). In conclusion, by feeding diets differing in carbohydrate source at different frequencies of feeding, meal-related changes in plasma hormone profiles were altered significantly, but oocyte quality was not affected. Therefore effects of diet on oocyte quality appear not to be mediated by meal-related fluctuations in hormone concentrations.

The naturally occurring Inverdale fecundity gene (FecXI), first identified in a Romney flock in New Zealand is located on the X-chromosome and is a point mutation of the bone morphogenetic protein-15 (BMP-15) gene. Although homozygous carriers are infertile due to abnormal development (hypoplasia) of the ovaries, heterozygotes exhibit an increase in ovulation rate and numbers of lambs born, thus making the gene a candidate for improving prolificacy of crossbred hill ewes in a stratified hill and lowground sheep industry. Heterozygous Inverdale gene-carrying crossbred (Texel � Cheviot) ewes (n = 76) and noncarrier controls (n = 18) were mated by non-carrier Texel rams at approximately 18 months of age. Ultrasound pregnancy scanning took place at approximately 70 days of gestation. Lambing records comprised litter size and birthweight data and all losses, including mummified fetuses. Regression analysis tested effects of ewe genotype, pre-mating liveweight, and body condition score on litter size. ANOVA and Kruskal-Wallis tests were used to compare genotype and litter size category effects on dam and offspring data. Mean (� SEM) litter size was 2.6 � 0.10 and 1.9 � 0.11 for FecXI carrier and noncarrier ewes (P < 0.001). Although carrier ewes had lower pre-mating liveweights (60 � 5.2 vs. 63 � 3.8 kg; P < 0.05) and body condition scores (3.1 � 0.29 vs. 3.3 � 0.24; P < 0.01) than noncarrier ewes, litter size was not affected by either factor. Ultrasound scanning was a good predictor (r2 = 0.86; P < 0.001) of the eventual lamb crop. Incidences of singletons, twins, triplets and higher multiples were 8, 38, 42 and 12%, respectively, among FecXI carrier dams. Corresponding incidences among noncarriers were 17, 78, 5, and 0%. Peri- and neonatal losses increased with litter size. Of lambs from single, twin or triplet births, losses were 20% and 6% for FecXI carrier and noncarrier ewe groups, respectively (P = 0.049). Of 32 quadruplets (mean live weight = 2.65 kg), 9 did not survive; the sole set of quintuplets (mean = 1.52 kg) also succumbed. Birth weights of lambs influenced survival (P < 0.001); among quadruplets, for example, survivors were 0.5 kg heavier than counterparts that died. Surviving triplets from FecXI carrier dams were 0.8 kg heavier than non-survivors (3.66 kg vs. 2.86 kg). Overall, in this study mortality was four times greater among lambs below 3 kg live weight than among their heavier counterparts. Consequently, further studies are needed to investigate how Inverdale gene-carrying ewes can be managed during the peri-conception period to optimize litter size, placental function, and prenatal growth for maximum lamb survival. This work was funded by HIE, ANM Group, Britbreed, Ltd., and Harbro Ltd.; F. M. A. is a Genesis Faraday Associate and is sponsored by the SAC Trust, Harbro, Ltd., and Innovis.