Natural methods for increasing reproductive efficiency in small ruminants
Introduction
Our animal industries are nowadays strongly influenced by a new set of societal constraints that are inevitably leading to changes in the marketplace: consumers worldwide are beginning to demand products that are “clean, green and ethical”. Effectively, for sheep and goat producers, this means moving into practices that minimise or completely avoid chemical and hormonal treatments of animals, and practices that do not compromise the welfare of the animals. In many countries, regulatory authorities have already imposed these conditions on local producers, importers and exporters. The evidence suggests that this is a long-term phenomenon so it makes sense for animal producers in all countries to begin to move towards clean, green and ethical practices. This need not be difficult because, as we shall discuss below, such practices are based on a better understanding of the physiology and behavior of the animals, and are therefore likely to improve productivity and profitability. To prepare for this future, our industries need a long-term vision with clear goals, supported by research and development programs that will lead to these goals. In this paper, we propose strategies that should promote the development of such a vision.
The productivity and profitability of our meat and milk industries effectively depend on reproductive performance for which the goals have not changed since the early stages of domestication. We still need to be able to accomplish the following:
- (1)
Accurately control the timing of reproductive events—first, by controlling the season of birth so as to benefit from opportunities in seasonal markets and in seasonal peaks in pasture supply; second, by acquiring accurate knowledge of the time of ovulation and parturition so we can provide precisely-timed nutritional supplements, a major factor in the second goal.
- (2)
Maximise the number of animals born—maximising the potential litter size by maximising ovulation rate and minimising post-fertilisation wastage by ensuring successful embryonic and fetal development.
- (3)
Ensure the survival of the new-born, and their ability to grow and mature into productive life efficiently, by good management and by genetic selection for behavior.
These same goals have been addressed by reproductive biologists for at least 100 years and in that time we have made great advances, especially in endocrinology and reproductive technology. The practical outcomes of this research have often been to control reproduction with exogenous hormone regimens. However, we now need to find alternative approaches. As a vehicle for discussion, we will use the example of a major animal enterprise in Australia—the breeding of Merino ewes for lamb production. Since this industry is mostly run under extensive management, options for controlling reproductive performance are heavily constrained. Ruminant production systems worldwide are mostly extensive and there is increasing pressure, from the clean, green and ethical movement, to disband intensive systems. The Australian Merino is, in fact, a good genotype for focussing on many of these issues because it has been almost exclusively selected for wool production for two centuries. Consequently, its reproductive performance is relatively poor and provides scope for improvement. Our focus may be on Merino lamb production, but most of the principles that we describe here can be extended to any production system for sheep and goats.
Section snippets
Our approach
In addressing the issue of clean, green and ethical production, we will concentrate initially on the natural control systems that the animals themselves use to cope with environmental challenges and ensure reproductive success, as previously proposed (Martin, 1995). These endogenous control systems underpin breeding patterns that have evolved to ensure that abundant food supply coincides with late pregnancy and lactation. The typical view is that this is achieved by linking sexual activity to
Control over the timing of reproductive events
In the absence of exogenous hormones, we can use the male effect for control of the estrous cycle and ultrasound for knowledge of the stage of pregnancy and fetal development.
Focussed feeding
For all animal enterprises, feed is the primary limiting resource and there is constant economic pressure to reduce the amount used and then to ensure that, when used, it provides the greatest benefit. Strategic use of nutritional supplements has long been an important management tool in production systems but, in the light of recent research, we can extend the list of points of focus:
- (a)
boost sperm production before mating;
- (b)
maximise potential litter size (ovulation rate);
- (c)
avoid early embryo loss;
- (d)
Selection of animals for “temperament”
In the last four decades, the intense interest in endocrinology, technology and molecular biology has often diverted attention away from the contributions that management of animal behavior can make to production enterprises. Perhaps the major exception has been the sustained research done on mother–young interactions. In Australia, this was driven by the very high rates of lamb mortality that were typical for Australian Merino sheep in the 1980s—it was estimated that we were losing 10–11
Conclusions
Understanding the reproductive responses of animals to exteroceptive factors such as photoperiod, nutrition and socio-sexual signals is an obvious step towards the use of “biostimulation” in place of exogenous hormones and drugs to control and improve the productivity of our sheep and goats (Martin, 1995, Rekwot et al., 2001). In addition, we can easily select and breed animals that have a calm temperament and this greatly improves their mothering ability and the survival of their lambs. The
Acknowledgements
We thank the German Academic Exchange Service (DAAD) for supporting GEBH during her studies at The University of Western Australia. Much of the work from our laboratory was funded through the Australian Research Council and the National Health and Medical Research Council (Australia).
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