Summary of the Consultants Meeting on compensatory growth in animals during periods of restricted feeding or under-nutrition, 12 – 14 October 2009, VIC, Vienna, Austria

Purpose:
To develop a Coordinated Research Project (CRP) to investigate the biology of the digestive system and nutrient requirements of livestock during compensatory growth and restricted periods of growth and how to take advantage of the compensatory growth to maximize output.

Overall conclusion:
Five experts in animal growth, ruminant nutrition, muscle biology and lactational biology from Agricultural Research Organisations and Universities in Australia, Germany, India and USA attended the meeting, along with IAEA staff to discuss the potential of using the compensatory growth phenomenon to augment animal productivity. The experts recognized the advantages the Joint FAO/IAEA Division had in coordinating integrated technical and research programmes through its CRP programme that bring together research institutes in both developing and developed Member States to collaborate on the research topic of interest. They agreed on the possibility of initiating a new CRP on “Use of the compensatory growth phenomenon to improve livestock productivity in regions with fluctuating quantity and quality of available feed resources”.

Such an initiative is strongly supported by the growing need to secure sufficient supply of balanced feed resources for sustainable development of the livestock sector from resources, which do not compete with human food e.g. the use of tree leaves, agro-industrial by-products, and aquatic sources to bridge the gap between supply and demand of feeds. This initiative will build upon the expertise already developed through the IAEA supported projects. The overall objective of the CRP is to improve livestock productivity using the compensatory growth phenomenon in environments with fluctuating feed supply. The first phase of the CRP would be to understand how animals lose and gain weight during periods of dramatic shifts in nutrient supply. Once the biological phenomenon that controls “compensatory growth” has been elucidated, the second phase would develop management strategies to exploit and harness this highly efficient growth process to improve livestock production.

Background Situation Analysis:
The main constraint to livestock production in many regions of Africa, Asia and Latin America is the scarcity and/or fluctuations in quality and quantity of year-around supply of feed. For example, ruminants in the tropics and sub-tropics experience marked seasonal fluctuations in feed supply and quality characterized by the imbalanced protein/energy ratio of the native grasses and crop residues, which form the basis of the diets in these regions. This is particularly quite pronounced during the dry seasons which results in a drastic cyclic patterns of wet-season weight gain and dry-season weight loss. The problems are aggravated by the tendency of 2 to 3 year droughts to occur at fairly regular intervals. For example, Maasai elders in Kenya have said the current drought (October 2009) was the worst they had seen since 1961, when they lost almost all their cattle. On the other extreme, on, for example the Qinghai-Tibetan plateau, animal productivity is greatly humped by a different type of weather pattern ? winter. Due to the high altitude, agricultural cultivation is not possible on most alpine plateaux. The only way the land can be used is for grazing livestock. Therefore, ruminant (yak and Tibetan sheep) farming plays the most important role in the socio-economic and environmental systems of the Plateau. However, animal performance in these systems is reflected by low milk production, low calving rates, poor survival of calves associated with low birth weights and low growth rates, all considerably limited by the poor levels of nutrition especially during the winter months.

Compensatory growth or “catch-up growth” is a period of increase weight gain following a period of nutritional deprivation and is a common feature amongst animals. During this period of compensatory growth, animals exhibit greater body weight gain, increased efficiency of energy utilization, reduced maintenance requirements because of depression of the basic metabolic rate, enhanced appetite and feed intake capacity, changes in endocrine status, and altered body tissue composition compared with animals fed conventionally. Studies have shown that an animal’s ability to compensate for prior periods of restricted feeding or under-nutrition is affected by severity and duration of the under-nutrition period, the animal’s stage of development, genotype and sex, level of feed intake during re-alimentation, duration of re-feeding, and composition of the diet during re-alimentation. Because of the dramatic fluctuations in the quality and quality of feedstuffs available for feeding animals year-round, compensatory growth is often of considerable practical significance to grassland livestock production. Even so, however, the physiological reason for the “catch-up growth” has not been fully elucidated. In particular, little is known regarding the factors involved in partitioning nutrients following periods of under-nutrition or restricted feeding. Moreover, the requirements for maximizing output at this period of exaggerated growth are unknown. The principles of matching animal requirements to nutrient availability need to be applied when devising feeding strategies and diet composition for defined production systems..