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Nutritional effects on ovulation, embryo development and the establishment of pregnancy in ruminants

Published online by Cambridge University Press:  18 August 2016

D. O’Callaghan  and
M. P. Boland
D. O’Callaghan
Affiliation:
Faculty of Veterinary Medicine, University College Dublin, Ireland
M. P. Boland
Affiliation:
Faculty of Agriculture, University College Dublin, Ireland
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Abstract

The effects of high and low dietary dietary intake on reproduction in female cattle and sheep will be considered at the level of the pituitary gland, ovary and uterus. In sheep, increased dietary intake for a relatively short time will increase ovulation rate, by increasing gonadotropin secretion. Dietary intake can affect steroids such as progesterone and also intra-follicular concentrations of some growth factors such as IGF-1 and IGF-2. The effects of altered energy intake on gonadotropins and steroids in cattle are not as repeatable as those in sheep but follicular growth rates can be altered. High nutrition has a negative effect on oocyte quality, with animals on ad-libitum high energy diets particularly at risk. Overfeeding can decrease embryo quality in both sheep and cattle and it appears that this results from changes primarily at the level of the follicle or oocyte. Restricted nutrition for a short time will enhance pregnancy rates in cattle; most of this benefit appears to occur if food is restricted before insemination. Thus feeding levels before mating are particularly important to subsequent reproductive success. High dietary crude protein may decrease pregnancy rate in lactating cows. In ewes and heifers supplementation with urea failed to have any effect on pregnancy rates when good quality embryos were transferred to recipient animals exposed to high dietary crude protein. In donor ewes there were adverse effects on early embryo development following urea treatment, suggesting that the mechanism affecting the reproductive process was primarily operating at the level of the oocyte. Collectively, these data identify the overall deleterious effects of high dietary intake and excess crude protein on fertility and highlight the importance of dietary intake before ovulation on the likelihood of establishing a viable pregnancy.

Keywords

embryonic developmentnutritionovulationpregnancy
Type
Research Article
Information
Animal Science , Volume 68 , Issue 2 , March 1999 , pp. 299 - 314
Copyright
Copyright © British Society of Animal Science 1999

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References

Abecia, J. A., Rhind, S.M., Bramley, T. A. and McMillen, S. R. 1995. Steroid production and LH receptor concentrations of ovarian follicles and corpora lutea and associated rates of ova wastage in ewes given high and low levels of food intake before and after mating. Animal Science 61: 57–62.CrossRefGoogle Scholar
Assey, R. J., Hyttel, P., Roche, J. F. and Boland, M. P. 1994. Oocyte structure and follicular steroid concentrations in superovulated versus unstimulated heifers. Molecular Reproduction and Development 39: 8–16.CrossRefGoogle ScholarPubMed
Barash, I. A., Cheung, C. C., Weigle, D. S., Ren, H., Kabigting, E.B., Kuijper, J. L., Clifton, D. K. and Steiner, R. A. 1996. Leptin is a metabolic signal to the reproductive system. Endocrinology 137: 3144–3147.Google Scholar
Blanchard, T., Ferguson, J., Love, L., Takeda, T., Henderson, B., Hasler, J. and Chalupa, W. 1990. Effect of dietary crude-protein type on fertilization and embryo quality in dairy cattle. American Journal of Veterinary Research 51: 905–908.CrossRefGoogle ScholarPubMed
Butler, W. R., Calaman, J. J. and Beam, S. W. 1996. Plasma and milk urea nitrogen in relation to pregnancy rate in lactating dairy cattle. Journal of Animal Science 74: 858–865.Google Scholar
Cameron, J.L. 1996. Regulation of reproductive hormone secretion in primates by short-term changes in nutrition. Reviews of Reproduction 1: 117–126.Google Scholar
Cameron, J. L. and Nosbisch, C. 1991. Suppression of pulsatile luteinizing hormone and testosterone secretion during short-term food restriction in the adult male rhesus monkey (Macaca mulatta) . Endocrinology 128:1532–1540.Google Scholar
Canfield, R. W. and Butler, W. R. 1990. Energy balance and pulsatile LH secretion in early postpartum dairy cattle. Domestic Animal Endocrinology 7: 323–330.CrossRefGoogle ScholarPubMed
Canfield, R. W., Sniffen, C. J. and Butler, W. R. 1990. Effects of excess degradable protein on postpartum reproduction and energy balance in dairy cattle. Journal of Dairy Science 73: 2342–2349.CrossRefGoogle ScholarPubMed
Cooke, D. J., Crowe, M. A. and Roche, J. F. 1997 Circulating FSH isoform patterns during recurrent increases in FSH throughout the oestrous cycle of heifers. Journal of Reproduction and Fertility 110: 339–345.CrossRefGoogle ScholarPubMed
Coop, I. E. 1966. Effect of flushing on reproductive performance of ewes. Journal of Agricultural Science, Cambridge 67: 305–323.CrossRefGoogle Scholar
De Sousa, P. A., Betts, D. H., O’Callaghan, D., Boland, M., Overstrom, E. W. and Watson, A. J. 1997. Localization of Na/K-ATPase oc-subunits and comparison of oc-subunit transcript levels in single cultured and in-vivo bovine blastocysts. Theriogenology 47: 316 (abstr.).CrossRefGoogle Scholar
Downing, J. A., Joss, J., Connell, P. and Scaramuzza, R. J. 1995a. Ovulation rate and the concentrations of gonadotrophic and metabolic hormones in ewes fed lupin grain. Journal of Reproduction and Fertility 103:137–145.CrossRefGoogle ScholarPubMed
Downing, J. A., Joss, J. and Scaramuzzi, R. J. 1995b. Ovulation rate and the concentrations of gonadotrophins and metabolic hormones in ewes infused with glucose during the late luteal phase of the oestrous cycle. Journal of Endocrinology 146: 403–410.Google Scholar
Downing, J. A. and Scaramuzzi, R. J. 1997. The effect of the infusion of insulin during the luteal phase of the estrous cycle on the ovulation rate and on plasma concentrations of LH, FSH and glucose in ewes. Theriogenology 47: 747–759.Google Scholar
Driancourt, M. A. and Thuel, B. 1998. Relationships between oocyte quality and follicle function. Reproduction in Domestic Animals 33: 113–117.CrossRefGoogle Scholar
Dunne, L. D., Diskin, M. G., Boland, M. P., O’Farrell, K. J. and Sreenan, J. M. 1997. Nutrition and embryo survival in cattle. Irish Journal of Agricultural and Food Research 36: 95 (abstr.).Google Scholar
Dyer, C. J., Simmons, J. M., Matteri, R. L. and Keisler, D. H. 1997. Leptin receptor mRNA is expressed in ewe anterior pituitary and adipose tissues and is differentially expressed in hypothalamic regions of well-fed and feed-restricted ewes. Domestic Animal Endocrinology 14: 119–128.CrossRefGoogle ScholarPubMed
Elrod, C. C. and Butler, W. R. 1993. Reduction of fertility and alteration of uterine pH in heifers fed excess ruminally degradable protein. Journal of Animal Science 71: 694–701.Google Scholar
Elrod, C. C., Van Amburgh, M. and Butler, W. R. 1993. Alterations of pH in response to increased dietary protein in cattle are unique to the uterus. Journal of Animal Science 71: 702–706.Google Scholar
Fahey, J., Boland, M. P. and O’Callaghan, D. 1998. Effects of dietary urea on embryo development in superovulated donor ewes and on embryo survival following transfer in recipient ewes. Proceedings of the British Society of Animal Science, 1998, p. 182 (abstr.).CrossRefGoogle Scholar
Findlay, J.K. and Clarke, I. J. 1987. Regulation of the secretion of FSH in domestic ruminants. Journal of Reproduction and Fertility, Supplement 34: 27–37.Google Scholar
Furnus, C. C., de Matos, D. G., Martinez, A. G. and Matkovic, M. 1996. Glucose and embryo quality. Proceedings of Techniques for gamete manipulation and storage’, June 22-23, 1996, Hamilton, New Zealand, abstract no. 20.Google Scholar
Gath, V. P., Lonergan, P., Boland, M. P. and O’Callaghan, D. 1999. Effect of diet type on establishment of pregnancy and embryo development in heifers. Theriogenology 51: 224 (abstr.).Google Scholar
Gong, J. G., Bramley, T. A. and Webb, R. 1993. The effect of recombinant bovine somatotrophin on ovarian follicular growth and development in heifers. Journal of Reproduction and Fertility 97: 247–254.Google Scholar
Gutierrez, C. G., Oldham, J., Bramley, T. A., Gong, J. G., Campbell, B. K. and Webb, R. 1997. The recruitment of ovarian follicles is enhanced by increased dietary intake in heifers. Journal of Animal Science 75: 1876–1884.CrossRefGoogle ScholarPubMed
Jordan, E. R., Chapman, T. E., Holtan, D. W. and Swanson, L. V. 1983. Relationship of dietary crude protein to composition of uterine secretions and blood in high producing postpartum dairy cows. Journal of Dairy Science 66: 1854–1862.Google Scholar
Jordan, E. R. and Swanson, L. V. 1979a. Serum progesterone and luteinizing hormone in dairy cattle fed varying levels of crude protein. Journal of Animal Science 48: 1154–1158.Google Scholar
Jordan, E. R. and Swanson, L. V. 1979b. Effect of crude protein on reproductive efficiency, serum total protein, and albumin in the high-producing dairy cow. Journal of Dairy Science 62: 58–63.CrossRefGoogle Scholar
Kaim, M., Folman, Y., Neumark, H. and Kaufmann, W. 1983. The effect of protein intake and lactation number on post-partum body weight loss and reproductive performance of dairy cows. Animal Production 37: 229–235.Google Scholar
Kane, M.T., Morgan, P. M. and Coonan, C. 1997. Peptide growth factors and preimplantation development. Human Reproduction Update 3: 137–157.Google Scholar
Kruip, T. A. M., Meijer, G. A. L., Rukkwamsuk, T. and Wensing, T. 1998. Effects of feed in the dry period on fertility of dairy cows post partům . Reproduction in Domestic Animals 33: 165–168.Google Scholar
Larson, S. F., Butler, W. R. and Currie, W. B. 1997. Reduced fertility associated with low progesterone postbreeding and increased milk urea nitrogen in lactating cows. Journal of Dairy Science 80: 1288–1295.Google Scholar
Leese, H. J. and Barton, A. M. 1984. Pyruvate and glucose uptake by mouse ova and preimplantation embryos. Journal of Reproduction and Fertility 72: 9–13.CrossRefGoogle ScholarPubMed
McCann, J. P. and Hansel, W. 1986. Relationship between insulin and glucose metabolism and pituitary-ovarian functions in fasted heifers. Biology of Reproduction 34: 630–641.Google Scholar
McEvoy, T. G., Robinson, J. J., Aitken, R. P., Findlay, P. A., Palmer, R. M. and Robertson, I. S. 1995. Dietary-induced suppression of pre-ovulatory progesterone concentrations in superovulated ewes impairs the subsequent in vivo and in vitro development of their ova. Animal Reproduction Science 39: 89–107.CrossRefGoogle Scholar
McEvoy, T. G., Robinson, J. J., Aitken, R. P., Findlay, P. A. and Robertson, I. S. 1997a. Dietary excesses of urea influence the viability and metabolism of preimplantation sheep embryos and may affect fetal growth among survivors. Animal Reproduction Science 47: 71–90.Google Scholar
McEvoy, T.G., Sinclair, K. D., Staines, M. E., Robinson, J. J., Armstrong, D. G. and Webb, R. 1997b. In-vitro blastocyst production in relation to energy and protein intake prior to oocyte collection. Journal of Reproduction and Fertility, Abstract Series 19: 51 (abstr.).Google Scholar
Mackey, D. R., Sreenan, J. M., Roche, J. F. and Diskin, M. G. 1997a. Effects of acute change in energy intake on plasma FSH concentration in beef heifers, with or without endogenous steroid influence. Journal of Reproduction and ‘Fertility, Abstract Series 19: 26 (abstr.).Google Scholar
Mackey, D. R., Sreenan, J. M., Roche, J. F. and Diskin, M. G. 1997b. The effect of acute changes in energy intake on follicle wave turnover in beef heifers. Irish Journal of Agricultural and Food Research 36: 95–96 (abstr.).Google Scholar
Macmillan, K.L., Lean, I. J. and Westwood, C. T. 1996. The effects of lactation on the fertility of dairy cows. Australian Veterinary Journal 73: 141–147.CrossRefGoogle ScholarPubMed
Mann, G. E., Lamming, G. E. and Fisher, P. A. 1998. Progesterone control of embryonic interferon tau production during early pregnancy in the cow. Journal of Reproduction and Fertility, Abstract Series 21: 20 (abstr.).Google Scholar
Mantovani, R., Enright, W. J., Keane, M. G., Roche, J. F. and Boland, M. P. 1993. Effect of nutrition and dose of follicle stimulating hormone (FSH) on superovulatory response in beef heifers. Proceedings of the 9th meeting of the Association Europeenne de Transfert Embryonnaire, Lyon, September 1993,> abstract no. 234.Google Scholar
Martin, R., Moscoso, G., Scaramuzzi, R. J., Loughna, P. T., Johnson, P. and Leigh, A. J. 1998. The effects of maternal hyperglycaemia on embryonic development in the ewe. Journal of Reproduction and Fertility, Abstract Series 21: 37 (abstr.).Google Scholar
Meisterung, E. M. and Dailey, R. A. 1987. Use of concentrations of progesterone and estradiol-17ß in milk in monitoring postpartum ovarian function in dairy cows. Journal of Dairy Science 70: 2154–2161.Google Scholar
Miller, D. W., Blache, D., Boukhliq, R., Curlewis, J. D. and Martin, G. B. 1998. Central metabolic messengers and the effects of nutrition on gonadotrophin secretion in sheep. Journal of Reproduction and Fertility 112: 347–356.Google Scholar
Moley, K.H., Chi, M. M.-Y., Manchester, J. K., McDougal Jr, D. B. and Lowry, O. H. 1996. Alterations of intraembryonic metabolites in preimplantation mouse embryos exposed to elevated concentrations of glucose: a metabolic explanation for the developmental retardation seen in preimplantation embryos from diabetic animals. Biology of Reproduction 54: 1209–1216.CrossRefGoogle ScholarPubMed
Moley, K. H., Vaughn, W. K. and Diamond, M. P. 1994. Manifestations of diabetes mellitus on mouse preimplantation development: effect of elevated concentration of metabolic intermediates. Human Reproduction 9: 113–121.CrossRefGoogle ScholarPubMed
Monget, P. and Martin, G. B. 1997. Involvement of insulinlike growth factors in the interactions between nutrition and reproduction in female mammals. Human Reproduction 12: (supplement 1) 33–52.CrossRefGoogle ScholarPubMed
Murphy, M. G., Enright, W. J., Crowe, M. A., McConnell, K., Spicer, L. J., Boland, M. P. and Roche, J. F. 1991. Effect of dietary intake on pattern of growth of dominant follicles during the oestrous cycle in beef heifers. Journal of Reproduction and Fertility 92: 333–338.Google Scholar
Nebel, R. L. and McGilliard, M. L. 1993. Interactions of high milk yield and reproductive performance in dairy cows. Journal of Dairy Science 76: 3257–3268.CrossRefGoogle ScholarPubMed
Nolan, R., Duffy, P., Wade, M., O’Callaghan, D. and Boland, M. P. 1998a. Effect of quantity and type of diet and frequency of trans-vaginal ovum aspiration on in-vitro embryo development in heifers. Theriogenology 49: 402 (abstr.).Google Scholar
Nolan, R., O’Callaghan, D., Duby, R. T., Lonergan, P. and Boland, M. P. 1998b. The influence of short-term nutrient changes on follicle growth and embryo production following superovulation in beef heifers. Theriogenology 50: 1263–1274.Google Scholar
O’Callaghan, D., Wade, M. G. and Boland, M. P. 1997. Effect of urea and an ammonia-binding agent in-vivo on subsequent development of bovine oocytes cultured in-vitro . Irish Journal of Agricultural and Food Research 36: 123–124 (abstr.).Google Scholar
O’Callaghan, D., Yaakub, H., Spicer, L. J. and Boland, M. P. 1998. Effect of nutrition and superovulation on steroids, insulin-like growth factors and insulin-like growth factor binding proteins in pre-ovulatory follicles of ewes. Journal of Reproduction and Fertility, Abstract Series 21: 24 (abstr.).Google Scholar
Ørskov, E.R. and Ryle, M. 1992. Manipulation of rumen fermentation and associative effects. In Energy nutrition in ruminants, pp. 28–42. Elsevier Applied Science, London.Google Scholar
Padmanabhan, V., Lang, L. L., Sonstein, J., Kelch, R. P. and Beitins, I. Z. 1988. Modulation of serum follicle-stimulating hormone bioactivity and isoform distribution by estrogenie steroids in normal women and in gonadal dysgenesis. Journal of Clinical Endocrinology and Metabolism 67: 465–473.CrossRefGoogle Scholar
Pantaleon, M. and Kaye, P. L. 1996. IGF-I and insulin regulate glucose transport in mouse blastocysts via IGF-I receptor. Molecular Reproduction and Development 44: 71–76.Google Scholar
Rhind, S.M., McMillen, S., McKelvey, W. A. C., Rodriguez-Herrejon, F. F. and McNeilly, A. S. 1989a. Effect of the body condition of ewes on the secretion of LH and FSH and the pituitary response to gonadotrophin-releasing hormone. Journal of Endocrinology 120:497–502.Google Scholar
Rhind, S.M., McMillen, S., Wetherill, G. Z., McKelvey, W. A. C. and Gunn, R. G. 1989b. Effects of low levels of food intake before and/or after mating on gonadotrophin and progesterone profiles in greyface ewes. Animal Production 49: 267–273.Google Scholar
Rhodes, F. M., Entwistle, K. W. and Kinder, J. E. 1996. Changes in ovarian function and gonadotropin secretion preceding the onset of nutritionally induced anestrus in Bos indicus heifers. Biology of Reproduction 55: 1437–1443.Google Scholar
Rhodes, F.M., Fitzpatrick, L. A., Entwistle, K. W. and De’ath, G. 1995. Sequential changes in ovarian follicular dynamics in Bos indicus heifers before and after nutritional anoestrus. Journal of Reproduction and Fertility 104: 41–49.Google Scholar
Roche, J. F. and Diskin, M. G. 1995. Hormonal regulation of reproduction and interactions with nutrition in female ruminants. In Ruminant physiology: digestion, metabolism, growth and reproduction (ed. W. von, Engelhardt, S., Leonhard-Marek, G., Breves and Giesecke, D.), pp. 409–428. Delmar Publishers, Albany, Germany.Google Scholar
Rodriguez Iglesias, R. M., Ciccioli, N. H., Irazoqui, H. and Giglioli, C. 1996. Ovulation rate in ewes after single oral glucogenic dosage during a ram-induced follicular phase. Animal Reproduction Science 44: 211–221.Google Scholar
Ropstad, E. and Refsdal, A. O. 1987. Herd reproductive performance related to urea concentration in bulk milk. Acta Veterinaria Scandinavica 28: 55–63.Google Scholar
Rubio, J. M., Hallford, D. M. and Hawkins, D. E. 1997. Effect of glucose administration during the estrous cycle on serum hormone profiles, mRNA for steroidogenic enzymes, and breeding performance of ewes. Journal of Animal Science 75: 775–780.Google Scholar
Ryan, D. P., Spoon, R. A., Griffith, M. K. and Williams, G. L. 1994. Ovarian follicular recruitment, granulosa cell steroidogenic potential and growth hormone / insulin-like growth factor-I relationships in suckled beef cows consuming high lipid diets: effects of graded differences in body condition maintained during the puerperium. Domestic Animal Endocrinology 11:161–174.Google Scholar
Savio, J. D., Boland, M. P. and Roche, J. F. 1990. Development of dominant follicles and length of ovarian cycles in post-partum dairy cows. Journal of Reproduction and Fertility 88: 581–591.Google Scholar
Scaramuzzi, R. J., Adams, N. R., Baird, D. T., Campbell, B. K., Downing, J. A., Findlay, J. K., Henderson, K. M., Martin, G.B., McNatty, K. P., McNeilly, A. S. and Tsonis, C.G. 1993. A model for follicle selection and the determination of ovulation rate in the ewe. Reproduction, Fertility and Development 5: 459–478.Google Scholar
Schwartz, M. W., Seeley, R. J., Campfield, L. A., Burn, P. and Baskin, D. G. 1996. Identification of targets of leptin action in rat hypothalamus. Journal of Clinical Investigation 98: 1101–1106.CrossRefGoogle ScholarPubMed
Sirard, M.-A., Richard, F. and Mayes, M. 1998. Controlling meiotic resumption in bovine oocytes: a review. Theriogenology 49: 483–497.CrossRefGoogle ScholarPubMed
Smith, J. F. 1991. A review of recent developments on the effect of nutrition on ovulation rate (the flushing effect) with particular reference to research at Ruakura. Proceedings of the New Zealand Society of Animal Production 51: 15–23.Google Scholar
Snijders, S. E. M., Dillon, P., Sreenan, J., Diskin, M., O’Callaghan, D., Boland, M. P. and O’Farrell, K. 1997. Effect of genotype on follicular dynamics and subsequent reproductive performance. Irish Journal of Agricultural and Food Research 36: 96 (abstr.).Google Scholar
Snijders, S. E. M., O’Farrell, K., Boland, M. P., Dillon, P., Diskin, M., O’Callaghan, D. and Mee, J. F. 1998. Effect of genetic merit on postpartum follicular development, milk production, body weight, and insulin and glucose levels in dairy cows. Proceedings of the British Society of Animal Science, 1998, p. 188 (abstr.).Google Scholar
Spicer, L. J., Crowe, M. A., Prendiville, D. J., Goulding, D. and Enright, W. J. 1992. Systemic but not intraovarian concentrations of insulin-like growth factor-I are affected by short-term fasting. Biology of Reproduction 46: 920–925.Google Scholar
Spicer, L. J., Enright, W. J., Murphy, M. G. and Roche, J. F. 1991. Effect of dietary intake on concentrations of insulinlike growth factor-I in plasma and follicular fluid and ovarian function in heifers. Domestic Animal Endocrinology 8: 431–437.Google Scholar
Spicer, L. J. and Francisco, C. C. 1997. The adipose obese gene product leptin: evidence of a direct inhibitory role in ovarian function. Endocrinology 138: 3374–3379.CrossRefGoogle ScholarPubMed
Spitzer, J. C., Niswender, G. D., Seidel, G. E. and Wiltbank, J. N. 1978. Fertilization and blood levels of progesterone and LH in beef heifers on a restricted energy diet. Journal of Animal Science 46: 1071–1077.Google Scholar
Sreenan, J. and Diskin, M. 1992. Factors affecting calving rate. In Breeding the dairy herd, pp. 37–46. Teagasc. Ireland.Google Scholar
Stagg, K., Diskin, M. G., Sreenan, J. M. and Roche, J. F. 1995. Follicular development in long-term anoestrous suckler beef cows fed two levels of energy postpartum. Animal Reproduction Science 38: 49–61.Google Scholar
Steiner, R. A. 1996. Editorial: lords and ladies leapin’ on leptin. Endocrinology 137: 4533–4535.Google Scholar
Villa-Godoy, A., Hughes, T. L., Emery, R. S., Enright, W. J., Ealy, A. D., Zinn, S. A. and Fogwell, R. L. 1990. Energy balance and body condition influence luteal function in Holstein heifers. Domestic Animal Endocrinology 7: 135–148.Google Scholar
Williams, S. A., Yaakub, H., O’Callaghan, D., Boland, M. P. and Scaramuzzi, R. J. 1997. Effect of energy intake from diet or infusion of glucose on ovulation rate in ewes. Journal of Reproduction and Fertility, Abstract Series 19: 57 (abstr.).Google Scholar
Wrenzycki, C., De Sousa, P., Herrmann, D., Watson, A. J., Niemann, H., O’Callaghan, D. and Boland, M. P. 1999. Effect of diet type and quantity fed during superovulation on the relative abundance of mRNA in bovine embryos. Theriogenology 51: 195 (abstr.).Google Scholar
Yaakub, H., O’Callaghan, D. and Boland, M. P. 1997a. In-vitro embryo development from oocytes recovered from follicles in cattle on different diets. Proceedings of the 3rd Agricultural Research Forum, pp. 267–268.Google Scholar
Yaakub, H., O’Callaghan, D., Duffy, P., Duby, R. T. and Boland, M. P. 1996. Effect of concentrate type and quantity on superovulation in cattle. Proceedings of Techniques for gamete manipulation and storage’, June 22-23, 1996, Hamilton, New Zealand, p. 37.Google Scholar
Yaakub, H., O’Callaghan, D., O’Doherty, J. V. and Hyttel, P. 1997b. Effect of dietary intake on follicle numbers and oocyte morphology in unsuperovulated and superovulated ewes. Theriogenology 47: 182 (abstr.).Google Scholar
Yaakub, H., Williams, S. A., O’Callaghan, D. and Boland, M. P. 1997c. Effect of dietary intake and glucose infusion on ovulation rate and embryo quality in superovulated ewes. Journal of Reproduction and Fertility, Abstract Series 19: 57 (abstr.).Google Scholar