Natural methods for increasing reproductive efficiency in small ruminants

doi:10.1016/j.anireprosci.2004.05.014

Animal Reproduction Science

Volumes 82–83, July 2004, Pages 231-245

https://doi.org/10.1016/j.anireprosci.2004.05.014 Get rights and content

Abstract

This paper describes three strategies to improve the reproductive performance of small ruminants in ways that lead to “clean, green and ethical” animal production. The first is aimed at control of the timing of reproductive events for which we turn to the socio-sexual inputs of the “male effect” to induce synchronised ovulation in females that would otherwise be anovulatory. The second strategy, “focussed feeding”, is based on our knowledge of the responses to nutrition and aims to develop short programs of nutritional supplements that are precisely timed and specifically designed for individual events in the reproductive process, such as gamete production, embryo survival, fetal programming and colostrum production. The third strategy aims to maximise offspring survival by a combination of management, nutrition and genetic selection for behavior (temperament). All of these approaches involve non-pharmacological manipulation of the endogenous control systems of the animals and complement the detailed information from ultrasound that is now becoming available. The use of such clean, green and ethical tools in the management of our animals can be cost-effective, increase productivity and, at the same time, greatly improve the image of meat and milk industries in society and the marketplace.

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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Natural methods for increasing reproductive efficiency in small ruminants

Abstract

Introduction

Section snippets

Our approach

Control over the timing of reproductive events

Focussed feeding

Selection of animals for “temperament”

Conclusions

Acknowledgements

Small Rumin. Res.

Liv. Prod. Sci.

Appl. Anim. Behav. Sci.

Small Rumin. Res.

Physiol. Behav.

Anim. Reprod. Sci.

J. Dairy Sci.

Liv. Prod. Sci.

Appl. Anim. Behav. Sci.

Res. Vet. Sci.

Anim. Reprod. Sci.

Anim. Reprod. Sci.

Small Rumin. Res.

Los fenómonos de biostimulatión sexual en ovejas y cabras

Vet.-Mex.

Supplementation of Corriedale ewes with maize during the last week of pregnancy increases production of colostrum

Anim. Prod. Aust.

Fetal and placental size and risk of hypertension

Br. Med. J.

Low maternal nutrition during pregnancy reduces the numbers of Sertoli cells in the newborn lamb

Reprod. Fertil. Dev.

The mature male sheep: a model to study the effects of nutrition on the reproductive axis

Reprod. Suppl.

Fertility in males: modulators of the acute effects of nutrition on the reproductive axis of male sheep

Reprod. Suppl.

The effect of short term fasting on early embryonic survival in ewes

Proc. Aust. Soc. Anim. Prod.

Effect of undernutrition of ewes from the time of mating on fetal ovarian development in mid gestation

Reprod. Fertil. Dev.

A subset of gonadotropin-releasing hormone neurons in the ovine medial basal hypothalamus is activated during increased pulsatile lutenizing hormone secretion

Endocrinology

Effects of stress on ovarian morphology and oestrous cycles in ewes

Aust. J. Agric. Res.

Measurements of temperament and their relationships with performance traits of beef cattle

Anim. Breed. Abstr.

The behavioral, endocrine and immune responses of sheep to isolation

Anim. Prod.

The influence of exercising rams on the lambing performance of a Merino flock

S. Afr. J. Anim. Sci.

Use of teasing in an A.I. programme

Anim. Prod. Aust.

Reproductive performance of Merino ewes supplemented with sweet lupin seed in southern Western Australia

Aust. J. Exp. Agric.

A study of relationships of breed, time of mating, level of nutrition, live weight, body condition and face cover to embryo survival in ewes

J. Agric. Sci. (Camb.)

Influence of placentally mediated fetal growth restriction on the onset of puberty in male and female lambs

Reproduction

Role of fetal and infant growth in programming metabolism in later life

Biol. Rev.

Effects of premating environmental stress, ACTH, cortisone acetate or metyrapone on oestrus and ovulation in sheep

J. Agric. Sci. (Camb.)

Ovulation rate and the concentrations of gonadotrophins and metabolic hormones in ewes infused with glucose during the late luteal phase of the oestrous cycle

J. Endocrinol.

Residual effects of prenatal nutrition on the postnatal performance of Merinos

Proc. N. Z. Soc. Anim. Prod.

Associations between temperament, performance and immune function in cattle entering a commercial feedlot

Aust. J. Exp. Agric.