Hostname: page-component-cd9895bd7-7cvxr Total loading time: 0 Render date: 2024-12-24T14:01:00.444Z Has data issue: false hasContentIssue false
  • English
  • Français

Interactions between nutrition and reproduction in the management of the mature male ruminant

Published online by Cambridge University Press:  07 January 2010

G. B. Martin ,
D. Blache ,
D. W. Miller  and
P. E. Vercoe
G. B. Martin*
Affiliation:
UWA Institute of Agriculture M082, The University of Western Australia, Crawley, Western Australia 6009, Australia School of Animal Biology, The University of Western Australia, Crawley, Western Australia 6009, Australia
D. Blache
Affiliation:
UWA Institute of Agriculture M082, The University of Western Australia, Crawley, Western Australia 6009, Australia School of Animal Biology, The University of Western Australia, Crawley, Western Australia 6009, Australia
D. W. Miller
Affiliation:
School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, WA 6150, Australia
P. E. Vercoe
Affiliation:
UWA Institute of Agriculture M082, The University of Western Australia, Crawley, Western Australia 6009, Australia School of Animal Biology, The University of Western Australia, Crawley, Western Australia 6009, Australia
*
†E-mail: [email protected]
Get access

Abstract

In mature male sheep and goats, changes in feed intake seem to have little effect on gonadal endocrine function but induce profound changes on sperm production. These outcomes are due to changes in size of the seminiferous tubules and in spermatogenic efficiency. Except with severe underfeeding, there are only minor changes in the endocrine function of the testis (testosterone production) unless season-long treatments are imposed. For cattle, nutrition clearly affects testicular development and the production of spermatozoa in young bulls, as it does in other species but, after the period of rapid growth has ended, there appears to be little or no response to nutrition. We are developing a clear picture of the metabolic signals, neuroendocrine processes and hormonal control systems that are involved, particularly for the mature male sheep. The energetic components of the diet, rather than protein, seem to be responsible, so we have envisaged a model of the relationship between energy balance and reproduction that has 4 ‘dimensions’: genotype, structure (organs), communication (chemical and neural signals, nutrient sensing) and time (dynamics, metabolic memory, programming). We have linked these perspectives to ‘resource allocation theory’ and incorporated them into strategies for ‘clean, green and ethical animal production’. In contrast to the clear outcomes with respect to spermatogenesis, the effects of nutrition on sexual behaviour are more difficult to define, perhaps because the behaviour is affected by a complex mix of physiological factors and because of flawed methods for quantifying male behaviour. For example, sexual behaviour is compromised by severe feed restriction, but male sexual behaviour requires intensive motor activity so a decline in libido could be caused by general weakness rather than specific nutritional limitations. The interaction between sexual activity and feeding behaviour also complicates the issue under field conditions. At the other end of the scale, overweight males can show reduced sexual success because they have difficulty courting and mounting. For this reason, exercise can enhance the fertilising capacity of rams. This will be important in extensive mating systems where males need to assemble and guard a harem and then mate many times for several weeks. For artificial insemination centres, there seems to be very few data on the nutritional management of males, but problems with overfed animals appear to be a risk. Future research should concentrate on the intra-testicular systems mediating the effects of nutrition on the production of spermatozoa.

Keywords

testis, spermatogenesis, nutrition, hormones (reproductive, metabolic), behaviour
Type
Full Paper
Information
animal , Volume 4 , Issue 7: XIth International Symposium on Ruminant Physiology (ISRP), 6–9 September, 2009 Clermont-Ferrand (France) , July 2010 , pp. 1214 - 1226
Copyright
Copyright © The Animal Consortium 2009

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Adam, CL, Archer, ZA, Miller, DW 2003. Leptin actions on the reproductive neuroendocrine axis in sheep. Reproduction Supplement 61, 283–297.Google ScholarPubMed
Ahima, RS 2005. Central actions of adipocyte hormones. Trends in Endocrinology and Metabolism 16, 307–313.CrossRefGoogle ScholarPubMed
Alkass, JE, Bryant, MJ, Walton, JS 1982. Some effects of level of feeding and body condition upon sperm production and gonadotropin concentrations in the ram. Animal Production 34, 265–277.Google Scholar
Amann, RP 1970. Sperm production rates. In The testis, vol 1, development, anatomy and physiology (ed. WR Gromes, NL Van Demark and AD Johnson), pp. 433–481. Academic Press, London, UK.Google Scholar
Banks, EM 1964. Some aspects of sexual behavior in domestic sheep, Ovis aries. Behaviour 23, 249–279.Google Scholar
Barth, AD, Brito, LF, Kastelic, JP 2008. The effect of nutrition on sexual development of bulls. Theriogenology 70, 485–494.CrossRefGoogle ScholarPubMed
Bell, AW 1984. Factors controlling placental and fetal growth and their effects on future production. In Reproduction in sheep (ed. DR Lindsay and DT Pearce), pp. 144–152. Cambridge University Press, Cambridge, UK.Google Scholar
Bielli, A, Pérez, R, Pedrana, G, Milton, JTB, Lopez, A, Blackberry, MA, Duncombe, G, Rodriguez-Martinez, H, Martin, GB 2002. Low maternal nutrition during pregnancy reduces the numbers of Sertoli cells in the newborn lamb. Reproduction, Fertility and Development 14, 333–337.Google Scholar
Blache, D, Adam, CL, Martin, GB 2002. The mature male sheep: a model to study the effects of nutrition on the reproductive axis. In Large mammals as neuroendocrine models (ed. DC Skinner, NP Evans and C Doberska) Reproduction Supplement 59, pp. 219–233. Society for Reproduction and Fertility, Cambridge, UK.Google Scholar
Blache, D, Chagas, LM, Blackberry, MA, Vercoe, PE, Martin, GB 2000. Metabolic factors affecting the reproductive axis in male sheep. Journal of Reproduction and Fertility 120, 1–11.CrossRefGoogle ScholarPubMed
Blache, D, Chagas, LM, Martin, GB 2007. Nutritional inputs into the reproductive neuroendocrine control system – a multidimensional perspective. In Reproduction in domestic ruminants VI (ed. JI Juengel, JF Murray and MF Smith), pp. 123–139. Nottingham University Press, Nottingham, UK.Google Scholar
Blache, D, Zhang, S, Martin, GB 2003. Fertility in males: modulators of the acute effects of nutrition on the reproductive axis of male sheep. In Reproduction in domestic ruminants V (ed. BK Campbell, R Webb, H Dobson and C Doberska), pp. 387–402. Society for Reproduction and Fertility, Cambridge, UK.Google Scholar
Blache, D, Zhang, S, Martin, GB 2006. Dynamic and integrative aspects of the regulation of reproduction by metabolic status in male sheep. Reproduction, Nutrition, Development 46, 379–390.Google Scholar
Boukhliq, R, Martin, GB 1997. Administration of fatty acids and gonadotrophin secretion in the mature ram. Animal Reproduction Science 49, 143–159.Google Scholar
Boukhliq, R, Martin, GB, White, CL, Blackberry, MA, Murray, PJ 1997. Role of glucose, fatty acids and protein in the regulation of testicular growth and the secretion of gonadotrophin, prolactin, somatotrophin and insulin in the mature ram. Reproduction, Fertility and Development 9, 515–524.Google Scholar
Boukhliq, R, Miller, DW, Martin, GB 1996. Relationships between the nutritional stimulation of gonadotrophin secretion and peripheral cerebrospinal fluid (CSF) concentrations of glucose and insulin in rams. Animal Reproduction Science 41, 201–204.Google Scholar
Braden, AWH, Turnbull, KE, Mattner, PE, Moule, GR 1974. Effect of protein and energy content of the diet on the rate of sperm production in rams. Australian Journal of Biological Sciences 27, 67–73.CrossRefGoogle ScholarPubMed
Bronson, FH 1985. Mammalian reproduction: an ecological perspective. Biology of Reproduction 32, 1–26.Google Scholar
Brown, BW 1994. A review of the nutritional influences on reproduction in boars, bulls and rams. Reproduction Nutrition Development 34, 89–114.CrossRefGoogle ScholarPubMed
Budak, E, Fernández Sánchez, M, Bellver, J, Cerveró, A, Simón, C, Pellicer, A 2006. Interactions of the hormones leptin, ghrelin, adiponectin, resistin, and PYY3-36 with the reproductive system. Fertility and Sterility 85, 1563–1581.Google Scholar
Cameron, AWN, Murphy, PM, Oldham, CM 1988. Nutrition of rams and output of spermatozoa. Proceedings of the Australian Society of Animal Production 17, 162–165.Google Scholar
Celi, P, Miller, DW, Blache, D, Martin, GB 2009. Interactions between nutritional and opioidergic pathways in the control of LH secretion in male sheep. Animal Reproduction Science (on line doi:10.1016/j.anireprosci.2009.03.011).Google Scholar
Celi, P, Walkden-Brown, SW, Széll, AZ, Blache, D, Wilkinson, HM, Martin, GB 2007. Twin efficiency for reproductive variables in monozygotic twin sheep. Theriogenology 68, 663–672.CrossRefGoogle ScholarPubMed
Chilliard, Y, Delavaud, C, Bonnet, M 2005. Leptin expression in ruminants: nutritional and physiological regulations in relation with energy metabolism. Domestic Animal Endocrinology 29, 3–22.CrossRefGoogle ScholarPubMed
Clark, RT 1934. Studies of reproduction in sheep I. The ovulation rate of the ewe as affected by the plane of nutrition. Anatomical Record 60, 125–134.Google Scholar
Combrink, GC, Schoeman, SJ 1993. The influence of exercising rams on the lambing performance of a Merino ewe flock. South African Journal of Animal Science 23, 24–25.Google Scholar
Coulter, GH, Carruthers, TD, Amann, RP, Kozub, GC 1987. Testicular development, daily sperm production and epididymal sperm reserves in 15-mo-old Angus and Hereford bulls: effects of bull strain plus dietary energy. Journal of Animal Science 64, 254–260.CrossRefGoogle ScholarPubMed
Da Silva, P, Aitken, RP, Rhind, SM, Racey, PA, Wallace, JM 2001. Influence of placentally mediated fetal growth restriction on the onset of puberty in male and female lambs. Reproduction 122, 375–383.CrossRefGoogle ScholarPubMed
Davies, DV, Mann, T, Rowson, LEA 1957. Effect of nutrition on the onset of male sex hormone activity and sperm formation in monozygous bull-calves. Proceedings of the Royal Society of London, Series B, Biological Sciences 147, 332–351.Google Scholar
Diez, JJ, Iglesias, P 2003. The role of the novel adipocyte-derived hormone adiponectin in human disease. European Journal of Endocrinology 148, 293–300.Google Scholar
Fernandez-Fernandez, R, Tena-Sempere, M, Aguilar, E, Pinilla, L 2004. Ghrelin effects on gonadotropin secretion in male and female rats. Neuroscience Letters 362, 103–107.Google Scholar
Flier, JS, Harris, M, Hollenberg, AN 2000. Leptin, nutrition, and the thyroid: the why, the wherefore, and the wiring. Journal of Clinical Investigation 105, 859–861.Google Scholar
Flipse, RJ, Almquist, JO 1961. Effect of total digestible nutrient intake from birth to four years of age on growth and reproductive development and performance of dairy bulls. Journal of Dairy Science 44, 905–914.Google Scholar
Fourie, PJ, Schwalbach, LM, Neser, FWC, Van der Westhuizen, C 2004. Scrotal, testicular and semen characteristics of young Dorper rams managed under intensive and extensive conditions. Small Ruminant Research 54, 53–59.Google Scholar
Gauthier, D, Berbigier, P 1982. The influence of nutritional levels and shade structure on testicular growth and hourly variations of plasma LH and testosterone levels in young Creole bulls in a tropical environment. Reproduction, Nutrition, Développement 22, 793–801.Google Scholar
Henry, BA, Goding, J, Tilbrook, A, Dunshea, F, Clarke, I 2001. Intracerebroventricular infusion of leptin elevates the secretion of luteinising hormone without affecting food intake in long-term food restricted sheep, but increases growth hormone irrespective of bodyweight. Journal of Endocrinology 168, 67–77.Google Scholar
Hiroe, K, Tomizuka, T 1965. Effects of nutrition on the characteristics of goat semen. Bulletin of the National Institute of Animal Industry 8, 17–24.Google Scholar
Hochereau-de Reviers, MT, Perreau, C, Delouis, C, Chemineau, , Courot, M 1986. Effects of photoperiod during foetal life and age on total number of Sertoli cells per testis between birth and adulthood in the goat. Biology of Reproduction (suppl. 234), 369 (abstract).Google Scholar
Hochereau-de Reviers, MT, Perreau, C, Lincoln, GA 1985. Photoperiodic variations of somatic and germ cell populations in the Soay ram testis. Journal of Reproduction and Fertility 74, 329–334.Google Scholar
Hötzel, MJ, Markey, CM, Walkden-Brown, SW, Blackberry, MA, Martin, GB 1998. Morphometric and endocrine analyses of the effects of nutrition on the testis of mature Merino rams. Reproduction, Fertility and Development 113, 217–230.Google Scholar
Hötzel, MJ, Walkden-Brown, SW, Blackberry, MA, Martin, GB 1995. The effect of nutrition on testicular growth in mature Merino rams involves mechanisms that are independent of changes in GnRH pulse frequency. Journal of Endocrinology 147, 75–85.CrossRefGoogle ScholarPubMed
Hötzel, MJ, Walkden-Brown, SW, Fisher, JA, Martin, GB 2003. Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: response to a nutritional stimulas in the breeding and non-breeding season. Journal of Reproduction and Fertility 15, 1–9.CrossRefGoogle Scholar
Irwig, MS, Fraley, GS, Smith, JT, Acohido, BV, Popa, SM, Cunningham, MJ, Gottsch, ML, Clifton, DK, Steiner, RA 2004. Kisspeptin activation of gonadotropin releasing hormone neurons and regulation of KiSS-1 mRNA in the male rat. Neuroendocrinology 80, 264–272.Google Scholar
Knight, TW 1977. Methods for the indirect estimation of testes weight and sperm numbers in Merino and Romney rams. New Zealand Journal of Agricultural Research 20, 291–296.CrossRefGoogle Scholar
Knight, TW, Gherardi, S, Lindsay, DR 1987. Effects of sexual stimulation on testicular size in the ram. Animal Reproduction Science 13, 105–115.Google Scholar
Komatsu, T, Itoh, F, Mikawa, S, Hodate, K 2003. Gene expression of resistin in adipose tissue and mammary gland of lactating and non-lactating cows. Journal of Endocrinology 178, R1–R5.CrossRefGoogle ScholarPubMed
Leatham, JH 1975. Nutritional influences on testicular composition and function in mammals. In Handbook of physiology (Exec ed. SR Geiger) Section 7, Male reproductive system (Section ed. RO Greep and EB Astwood) vol 5, Endocrinology (Vol ed. DW Hamilton and RO Greep), pp. 225–232. American Physiological Society, Washington, USA.Google Scholar
Lincoln, GA, Short, RV 1980. Seasonal breeding: nature’s contraceptive. Recent Progress in Hormone Research 36, 1–52.Google ScholarPubMed
Lindsay, DR 1991. Reproduction in the sheep and goat. In Reproduction in domestic animals, 4th edition. (ed. PT Cupps), chapter 15, pp. 491–515. Academic Press, San Diego, USA.Google Scholar
Malagon, MM, Rodriguez-Pacheco, F, Martinez-Fuentes, AJ, Tovar, S, Pinilla, L, Tena-Sempere, M, Dieguez, C, Castano, JP 2006. Regulation of pituitary cell function by the adipokine adiponectin. Frontiers in Neuroendocrinology 27, 35.CrossRefGoogle Scholar
Mann, T, Rowson, LEA, Short, RV, Skinner, JD 1967. The relationship between nutrition and androgenic activity in pubescent twin calves, and the effect of orchitis. Journal of Endocrinology 38, 455–468.Google Scholar
Mann, T, Walton, A 1953. The effect of underfeeding on the genital functions of a bull. Journal of Agricultural Science (Cambridge) 43, 343–347.CrossRefGoogle Scholar
Martin, GB 1984. Factors affecting the secretion of luteinizing hormone in the ewe. Biological Reviews 59, 1–87.CrossRefGoogle ScholarPubMed
Martin, GB, Blache, D, Williams, IH 2008. Allocation of resources to reproduction. In Resource allocation theory applied to farm animal production (ed. W Rauw), pp. 169–191. Oxford University Press, Oxford, UK.CrossRefGoogle Scholar
Martin, GB, Durmic, Z, Kenyon, PR, Vercoe, PE 2009. Landcorp farming limited lecture: ‘clean, green and ethical’ animal reproduction: extension to sheep and dairy systems in New Zealand. Proceedings of the New Zealand Society of Animal Production 69, 140–147.Google Scholar
Martin, GB, Hötzel, MJ, Blache, D, Walkden-Brown, SW, Blackberry, MA, Boukliq, R, Fisher, JA, Miller, DW 2002. Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: modification of response to photoperiod by annual cycle of food supply. Reproduction, Fertility and Development 14, 165–175.CrossRefGoogle ScholarPubMed
Martin, GB, Milton, JTB, Davidson, RH, Banchero Hunzicker, GE, Lindsay, DR, Blache, D 2004. Natural methods of increasing reproductive efficiency in sheep and goats. Animal Reproduction Science 82–83, 231–246.Google Scholar
Martin, GB, Sutherland, SRD, Lindsay, DR 1987. Effects of nutritional supplements on testicular size and the secretion of LH and testosterone in Merino and Booroola rams. Animal Reproduction Science 12, 267–281.Google Scholar
Martin, GB, Tjondronegoro, S, Blackberry, MA 1994a. Effects of nutrition on testicular size and the concentrations of gonadotrophins, testosterone and inhibin in plasma of mature male sheep. Journal of Reproduction and Fertility 101, 121–128.Google Scholar
Martin, GB, Tjondronegoro, S, Boukhliq, R, Blackberry, MA, Briegel, JR, Blache, D, Fisher, JA, Adams, NR 1999. Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: modification of endogenous rhythms by photoperiod. Reproduction, Fertility and Development 11, 355–366.CrossRefGoogle ScholarPubMed
Martin, GB, White, CL, Markey, CM, Blackberry, MA 1994b. Effects of dietary zinc deficiency on the reproductive system of young male sheep: testicular growth and the secretion of inhibin and testosterone. Journal of Reproduction and Fertility 101, 87–96.CrossRefGoogle ScholarPubMed
Messager, S, Chatzidaki, EE, Ma, D, Hendrick, AG, Zahn, D, Dixon, J, Thresher, R, Malinge, I, Lomet, D, Carlton, MBL, Colledge, WH, Caraty, A, Aparicio, SAJR 2005. Kisspeptin directly stimulates gonadotropin-releasing hormone release via G protein-coupled receptor 54. Proceedings of the National Academy of Sciences (USA) 102, 1761–1766.Google Scholar
Miller, DW, Blache, D, Boukhliq, R, Curlewis, JD, Martin, GB 1998. Central metabolic messengers and the effects of diet on gonadotrophin secretion in sheep. Journal of Reproduction and Fertility 112, 347–356.CrossRefGoogle ScholarPubMed
Miller, DW, Blache, D, Martin, GB 1995. Insulin stimulates LH secretion in rams when infused into the third cerebral ventricle: comparison with the effect of improved nutrition. Journal of Endocrinology 147, 321–329.CrossRefGoogle Scholar
Miller, DW, Findlay, PA, Morrison, MA, Raver, N, Adam, CL 2002. Seasonal and dose-dependent effects of intracerebroventricular leptin on LH secretion and appetite in sheep. Journal of Endocrinology 175, 395–404.CrossRefGoogle ScholarPubMed
Miller, DW, Harrison, JL, Bennett, EJ, Findlay, PA, Adam, CL 2007. Nutritional influences on reproductive neuroendocrine output: insulin, leptin and orexigenic neuropeptide signaling in the ovine hypothalamus. Endocrinology 148, 5313–5322.CrossRefGoogle ScholarPubMed
Miller, DW, Harrison, JL, Brown, YA, Doyle, U, Lindsay, A, Adam, CL, Lea, RG 2005. Immunohistochemical evidence for an endocrine/paracrine role for ghrelin in the reproductive tissues of sheep. Reproductive Biology and Endocrinology 3, 60.Google Scholar
Monet-Kuntz, C, Hochereau de Reviers, MT, Terqui, M 1984. Variations in testicular androgen receptors and histology of the lamb testis from birth to puberty. Journal of Reproduction and Fertility 70, 203–210.Google Scholar
Mori, A 1959. Studies on the reproductive failure of ram caused by underfeeding. I. On the effects of underfeeding upon the mating potency of ram, and the effects of normal feeding upon its recovery from impotence. Tohuku Journal of Agricultural Research 10, 263–281.Google Scholar
Moule, GR 1963. Postpubertal nutrition and reproduction by the male. Australian Veterinary Journal 39, 299–304.CrossRefGoogle Scholar
Mwansa, PB, Makarechian, M 1991. The effect of postweaning level of dietary energy on sex drive and semen quality of young beef bulls. Theriogenology 35, 1169–1178.Google Scholar
Nogueiras, R, Barreiro, ML, Caminos, JE, Gaytan, F, Suominen, JS, Navarro, VM, Casanueva, FF, Aguilar, E, Toppari, J, Dieguez, C, Tena-Sempere, M 2004. Novel expression of resistin in rat testis: functional role and regulation by nutritional status and hormonal factors. Journal of Cell Science 117, 3247–3257.Google Scholar
Nogueiras, R, Gallego, R, Gualillo, O, Caminos, JE, Garcia-Caballero, T, Casanueva, FF, Dieguez, C 2003. Resistin is expressed in different rat tissues and is regulated in a tissue- and gender-specific manner. FEBS Letters 548, 21–27.Google Scholar
Okolski, A 1975. Effect of different amounts of protein in the diet on sexual behaviour and properties of semen in rams. Acta Agraria et Silvestria, Zootechnica 15, 101–121.Google Scholar
Oldham, CM, Adams, NR, Gherardi, PB, Lindsay, DR, Mackintosh, JB 1978. The influence of level of feed intake on sperm producing capacity of testicular tissue in the ram. Australian Journal of Agricultural Research 29, 173–179.Google Scholar
Parker, GV, Thwaites, CJ 1972. The effects of undernutrition on libido and semen quality in adult Merino rams. Australian Journal of Agricultural Research 23, 109–115.Google Scholar
Pénicaud, L, Cousin, B, Leloup, C, Lorsignol, A, Casteilla, L 2000. The autonomic nervous system, adipose tissue plasticity, and energy balance. Nutrition 16, 903–908.CrossRefGoogle ScholarPubMed
Popa, SM, Clifton, DK, Steiner, RA 2008. The role of Kisspeptins and GPR54 in the neuroendocrine regulation of reproduction. Annual Review of Physiology 70, 213–238.Google Scholar
Raadsma, HW, Edey, TN 1985. Mating performance of paddock-mated rams. II. Changes in sexual and general activity during the joining period. Animal Reproduction Science 8, 101–107.CrossRefGoogle Scholar
Rekwot, PI, Oyedipe, EO, Akerejola, OO, Kumi-Diaka, J 1987. The effect of protein intake on body weight, scrotal circumference and semen production of Bunaji bulls and their Friesian crosses in Nigeria. Animal Reproduction Science 16, 1–9.Google Scholar
Rhind, SM, Archer, ZA, Adam, CL 2002. Seasonality of food intake in ruminants: recent developments in understanding. Nutrition Research Reviews 15, 43–65.CrossRefGoogle ScholarPubMed
Ritar, AJ, Adams, NR, Sanders, MR 1984. Effect of lupin feeding on LH, testosterone and testes. In Reproduction in sheep (ed. DR Lindsay and DT Pearce), pp. 76–78. Cambridge University Press, UK.Google Scholar
Robinson, JJ, Ashworth, CJ, Rooke, JA, Mitchell, LM, McEvoy, TG 2006. Nutrition and fertility in ruminant livestock. Animal Feed Science and Technology 126, 259–276.CrossRefGoogle Scholar
Salamon, S 1964. The effect of nutritional regimen on the potential semen production of rams. Australian Journal of Agricultural Research 15, 645–656.CrossRefGoogle Scholar
Scaramuzzi, RJ, Campbell, BK, Downing, JA, Kendall, NR, Khalid, M, Munoz-Gutiérrez, M, Somchit, A 2006. A review of the effects of supplementary nutrition in the ewe on the concentrations of reproductive and metabolic hormones and the mechanisms that regulate folliculogenesis and ovulation rate. Reproduction, Nutrition and Development 46, 339–354.CrossRefGoogle ScholarPubMed
Schwartz, MW 2006. Distribution of insulin receptor substrate-2 in brain areas involved in energy homeostasis. Brain Research 1112, 169–178.Google Scholar
Setchell, BP 1986. The movement of the fluids and substances in the testis. Australian Journal of Biological Sciences 39, 193–207.Google Scholar
Setchell, BP 1990. Local control of testicular fluids. Reproduction, Fertility and Development 2, 291–309.Google Scholar
Setchell, BP, Hinks, NT 1967. The importance of glucose in the oxidative metabolism of the testis of the conscious ram and the role of the pentose cycle. Biochemical Journal 102, 623–630.Google Scholar
Setchell, B, Waites, GMH, Lindner, HR 1965. Effect of undernutrition on testicular blood flow and metabolism and the output of testosterone in the ram. Journal of Reproduction and Fertility 9, 149–162.Google Scholar
Smith, JT, Clay, CM, Caraty, A, Clarke, IJ 2007. KiSS-1 messenger ribonucleic acid expression in the hypothalamus of the ewe is regulated by sex steroids and season. Endocrinology 148, 1150–1157.Google Scholar
Smith, JT, Coolen, LM, Kriegsfeld, LJ, Sari, IP, Jaafarzadehshirazi, MR, Maltby, M, Bateman, K, Goodman, RL, Tilbrook, AJ, Ubuka, T, Bentley, GE, Clarke, IJ, Lehman, MN 2008. Variation in kisspeptin and gonadotropin-inhibitory hormone expression and terminal connections to GnRH neurons in the brain: a novel medium for seasonal breeding in the sheep. Endocrinology 149, 5770–5782.Google Scholar
St-Pierre, DH, Wang, L, Tache, Y 2003. Ghrelin: a novel player in the gut-brain regulation of growth hormone and energy balance. News in Physiological Sciences 18, 242–246.Google ScholarPubMed
Steppan, CM, Bailey, ST, Bhat, S, Brown, EJ, Banerjee, RR, Wright, CM, Patel, HR, Ahima, RS, Lazar, MA 2001. The hormone resistin links obesity to diabetes. Nature 409, 307–312.CrossRefGoogle ScholarPubMed
Sugino, T, Hasegawa, Y, Kurose, Y, Kojima, M, Kangawa, K, Terashima, Y 2004. Effects of ghrelin on food intake and neuroendocrine function in sheep. Animal Reproduction Science 82–83, 183–194.CrossRefGoogle ScholarPubMed
Sutama, IK, Edey, TN 1985. Reproductive development during winter and spring of Merino ram lambs grown at three different rates. Australian Journal of Agricultural Research 36, 461–467.Google Scholar
Tanaka, T, Nagatani, S, Bucholtz, DC, Ohkura, S, Tsukamura, H, Maeda, KI, Foster, DL 2000. Central action of insulin regulates pulsatile luteinizing hormone secretion in the diabetic sheep model. Biology of Reproduction 62, 1256–1261.CrossRefGoogle ScholarPubMed
Tarulli, GA, Stanton, PG, Lerchl, A, Meachem, SJ 2006. Adult Sertoli cells are not terminally differentiated in the Djungarian hamster: effect of FSH on proliferation and junction protein organization. Biology of Reproduction 74, 798–806.Google Scholar
Tegegne, A, Entwistle, KW, Mukasa-Mugerwa, E 1992. Gonadal and extragonadal sperm reserves and testicular histometric characteristics in Zebu and crossbred bulls: effect of dry season nutritional supplementation. Animal Reproduction Science 29, 25–33.Google Scholar
Tena-Sempere, M 2005. Exploring the role of ghrelin as novel regulator of gonadal function. Growth Hormone and IGF Research 15, 83–88.CrossRefGoogle ScholarPubMed
Thwaites, CJ 1995. The comparative effects of undernutrition, exercise and frequency of ejaculation on the size and tone of the testes and on semen quality in the ram. Animal Reproduction Science 37, 299–309.Google Scholar
Tilbrook, AJ, Cameron, AWN 1990. The contribution of the sexual behaviour of rams to successful mating of ewes under field conditions. In Reproductive physiology of Merino sheep – concepts and consequences (ed. CM Oldham, GB Martin and IW Purvis), pp. 143–160. School of Agriculture, The University of Western Australia, Perth, Australia.Google Scholar
Tilton, WA, Warnick, AC, Cunha, TJ, Loggins, PE, Shirley, RL 1964. Effect of low energy and protein intake on growth and reproductive performance of young rams. Journal of Animal Science 23, 645–650.Google Scholar
Van Demark, NL, Fritz, GR, Mauger, RE 1964. Effect of energy intake on reproductive performance of dairy bulls. 2. Semen production and replenishment. Journal of Dairy Science 47, 898–904.Google Scholar
Van Demark, NL, Mauger, RE 1964. Effect of energy intake on reproductive performance of dairy bulls. 1. Growth, reproductive organs, and puberty. Journal of Dairy Science 47, 798–802.Google Scholar
Walkden-Brown, SW, Martin, GB, Restall, BJ 1999. Role of male-female interaction in regulating reproduction in sheep and goats. Journal of Reproduction and Fertility Supplement 52, 243–257.Google Scholar
Walkden-Brown, SW, Restall, BJ, Norton, BW, Scaramuzzi, RJ, Martin, GB 1994. Effect of nutrition on seasonal patterns of LH, FSH and testosterone concentration, testicular mass, sebaceous gland volume and odour in Australian cashmere goats. Journal of Reproduction and Fertility 102, 351–360.Google Scholar
Zhang, S, Blache, D, Blackberry, MA, Martin, GB 2004. Dynamics of the responses in secretion of LH, leptin and insulin following an acute increase in nutrition in mature male sheep. Reproduction, Fertility and Development 16, 823–829.Google Scholar
Zhang, S, Blache, D, Blackberry, MA, Martin, GB 2005. Body reserves affect the reproductive endocrine responses to an acute change in nutrition in mature male sheep. Animal Reproduction Science 88, 257–269.Google Scholar
Zieba, DA, Amstalden, M, Macie, MN, Keisler, DH, Raver, N, Gertler, A, Williams, GL 2003. Divergent effects of leptin on luteinizing hormone and insulin secretion are dose dependent. Experimental Biology and Medicine 228, 325–330.CrossRefGoogle ScholarPubMed