Reproduction in Domestic Animals

Reprod Dom Anim 43 (Suppl. 2), 129–136 (2008); doi: 10.1111/j.1439-0531.2008.01152.xISSN 0936-6768The Importance of Interactions Among Nutrition, Seasonality and Socio-sexualFactors in the Development of Hormone-free Methods for Controlling FertilityRJ Scaramuzzi 1,2 and GB Martin 31 UMRPhysiologie de la Reproduction et des Comportements, L’Institut National de la Reproduction, Nouzilly, France; 2 Department of VeterinaryBasic Sciences, Royal Veterinary College, Hertfordshire, UK; 3 Animal Production Systems, UWA Institute of Agriculture, The University ofWestern Australia, Crawley, WA, AustraliaContentsAround the world, consumers are demanding animal productsthat are produced to agreed standards for human health,environmental management and animal welfare. This has led tothe development in Australia of the concept of ‘clean, green andethical’ (CGE) animal production based on the manipulation ofnutrition (‘focus feeding’) and the application of phenomena,such as the ‘male effect’, to provide ‘natural’ methods formanaging small ruminant production systems. With respect tothe management of fertility, CGE involves utilization of theinherited responses of animals to environmental factors tomanipulate their reproductive processes. The successfuldevelopment and implementation of this new generation ofmanagement tools depends on a thorough yet holisticunderstanding of the interactions among environmental factorsand the ways these interactions affect reproductive physiologyand behaviour of the animal. For sheep and goats, a centralaspect of CGE management is the way in which ovarian functionis affected by three major factors (nutrition, photoperiod andsocio-sexual signals) and by interactions among them. Nutritioncan exert two profound yet contrasting types of effect on ovarianactivity: (i) the complete inhibition of reproduction by undernutritionthrough the hypothalamic mechanism that controlsovulation and (ii) the enhancement of fecundity by nutritionalsupplementation, through a direct ovarian mechanism, infemales that are already ovulating. A similarly profound controlover ovarian function in female sheep and goats is exerted by thewell-known endocrine responses to photoperiod (seasonality)and to male socio-sexual signals. The ‘male effect’ already has along history as a valuable technique for inducing a synchronizedfertile ovulation during seasonal and post-partum anoestrus insheep and goats. Importantly, experimentation has shown thatthese three major environmental factors interact, synergisticallyand antagonistically, but the precise nature of these interactionsand their significance to reproductive outcomes are not wellunderstood. Most research to date has been with smallruminants but CGE principles can be applied to any species ina managed environment. For example, a male effect has beenreported for lactating cattle and, in the horse, the pattern ofseasonality of oestrus can be altered by nutrition. Well-fed mareshave a longer breeding season and some animals become nonseasonal.Similar observations have been reported for sheep andgoats. By working towards a holistic perspective of the physiology,nutrition, genetics and behaviour of our animals, we willbe able to formulate ways to manipulate the animals’environment that will improve management, productivity andprofitability and, simultaneously, promote a CGE industry.IntroductionAnimal industries around the world are being challengedby changing attitudes in the market place, andconsumers are increasingly demanding products that areproduced to agreed standards for human health,environmental management and animal ethics andwelfare. This is particularly evident in high-profit,discerning markets that are influenced by discretionaryspending power. Our challenge is to turn these developmentsto advantage, improve productivity and profitabilityand, simultaneously, promote ‘clean, green and ethical(CGE) production’ (Martin et al. 2004a; Kadokawa andMartin 2006; Martin and Kadokawa 2006). Importantly,these issues need not pose difficulties or increase costs – onthe contrary, they offer excellent opportunities. Forextensively managed sheep and goats, we are developingmanagement tools, such as ‘focus feeding’ and the ‘maleeffect’, for controlling reproduction and quantitativebreeding values for improving temperament (Martinet al. 2004a).This paper reviews current information, mainly forsheep and goats, on a central aspect of the CGE system –the way in which ovarian function is affected by threemajor factors (nutrition, photoperiod and socio-sexualsignals) and by interactions among them. We review theway in which nutrition can influence the ‘decision toreproduce’ through the hypothalamic mechanism thatcontrols ovulation and the ‘decision for fecundity’through a direct ovarian mechanism in females that arealready ovulating. In addition, we review the ways inwhich the endocrine responses to photoperiod(seasonality) and to male socio-sexual signals interact,synergistically and antagonistically, with nutritionalinputs. It is increasingly clear that the multi-dimensionalnature of these interactions are often far more importantthan the responses to the individual environmental input(Blache et al. 2007).Most research to date has been with small ruminantsbut the ‘CGE principle’, in which manipulation of theenvironment is used to control reproductive processes,can be applied to all species. For example, a male effecthas been reported for cattle (review: Ungerfeld 2007)and, in this review, we will describe nutrition–reproductioninteractions in the horse.Thus, the aim of this review is to outline the state ofour knowledge on the interactions among environmentalfacts that affect reproductive processes, and to pointout research that is needed for refining CGE managementof farm animals, particularly with respect tomanagement of the nutritional inputs.Nutrition and Ovarian FunctionAll major measures of reproductive performance (prolificacy,fertility and fecundity) are affected by geneticsÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag