Investigation of relationship between vitamin D status and reproductive fitness in Scottish hill sheep.

There is a growing interest in the influence of vitamin D on ovine non-skeletal health. The aim of this study was to explore the relationship between pre-mating vitamin D status, as assessed by serum concentrations of 25-Hydroxyvitamin D [25(OH)D; comprising D2 and D3] and subsequent reproductive performance of genetically unimproved Scottish Blackface (UBF), genetically improved Scottish Blackface (IBF) and Lleyn ewes kept under Scottish hill conditions. 25-Hydroxyvitamin D2 (25(OH)D2) and 25-Hydroxyvitamin D3 (25(OH)D3) concentrations were determined in serum samples harvested in November from ewes grazed outdoors. There were no significant differences in 25(OH)D2concentrations amongst the 3 genotypes. Lleyn ewes had significantly higher 25(OH)D3 and 25(OH)D concentrations than both Scottish Blackface ewe genotypes, whereas these vitamin D parameters did not differ significantly between the UBF and IBF ewes. Concentrations of 25(OH)D3 and 25(OH)D were positively associated with subsequent birth weights of singleton and of twin lamb litters. No significant associations between vitamin D status and number of lambs born or weaned per ewe were found. This study demonstrates that concentrations of cutaneously-derived 25(OH)D3, but not of orally consumed 25(OH)D2, differed between breeds. The positive association between ewe vitamin D status and offspring birth weight highlights the need for further investigations.

Effects of cobalt/vitamin B12 status in ewes on ovum development and lamb viability at birth.

Scottish Blackface ewes from cobalt-deficient farmland were fed a diet containing 0.06 mg cobalt per kg dry matter from approximately 30 days before embryo recovery/transfer until lambing. Ewes remained untreated (-Co; n = 82) or were given an intraruminal cobalt-containing bolus to compensate for the dietary deficit (+Co; n = 82). Ewes used as embryo donors (-Co, n = 17; +Co, n = 16) were artificially inseminated with semen from a single Suffolk sire. Day 6 embryos obtained from -Co and +Co donors were transferred in singleton to -Co and +Co recipients in a 2 x 2 factorial-designed experiment to determine the effects of cobalt/vitamin B12 status during the periconception period (factor 1) and pregnancy (factor 2) on lamb viability at birth. Mean (+/- s.e.m.) circulating concentrations of vitamin B12 in -Co and +Co donors at ovum recovery were 182 +/- 10 and 1288 +/- 64 pmol L(-1), respectively (P < 0.001), and the number of corpora lutea per ewe ovulating was 9.9 +/- 1.6 and 14.4 +/- 1.3, respectively (P < 0.05). Treatment did not affect the proportion of recovered ova that contained >32 cells (viable) or the median stage of development (late morula), but viable ova recovered from -Co v. +Co ewes had a better morphological grade (2.0 +/- 0.1 v. 2.20 +/- 0.04, respectively; P < 0.01). There was no effect of treatment on the proportion of recipient ewes that became pregnant. Circulating concentrations of vitamin B12 were lower in -Co than +Co ewes during pregnancy (P < 0.001) and at birth in lambs born to -Co ewes compared with those born to +Co ewes (P < 0.001). There was no effect of donor or recipient cobalt/vitamin B12 status on lamb birthweight, neonatal vigour or neonatal rectal temperatures, but lambs derived from +Co v. -Co embryo donors were more active in the first 3 days after birth (P < 0.05). Results show that sub-clinical cobalt/vitamin B12 deficiency reduces ovulatory response in superovulated ewes and that periconception nutrition can affect neonatal lamb behaviour.

Large offspring syndrome and other consequences of ruminant embryo culture in vitro: relevance to blastocyst culture in human ART.

In vitro production of embryos from domestic animals is used to augment conventional genetic improvement programmes in agriculture and to facilitate advances in gene transfer and cloning. However, production of embryos in vitro exposes them to hazards not normally encountered in vivo and, as a result, there have been unforeseen consequences including the large offspring syndrome. This syndrome is manifest as abnormal growth and development at fetal, neonatal and later stages after transfer of embryos cultured in vitro for up to 1 week after fertilization. Our embryo culture and fetal development studies have begun to characterize many of the genetic, metabolic and developmental features associated with the syndrome. This review considers the findings of these studies in the context of blastocyst production in vitro, emphasizing the impact of culture strategies on ruminant (cattle and sheep) embryo composition and developmental competence. The need to alter in vitro production strategies to safeguard oocytes and embryos during culture is discussed. Finally, the implications of experiences gained in domestic animal studies are considered in the context of current options for human embryo culture. The need for an appreciation of the sensitivity of the embryo to its environment and the possible short- and long-term consequences of inappropriate in vitro production strategies are considered.