Interview: Dr Ajmal Khan on the Weaning transition

LifeStart sat down with Dr Ajmal Khan, Senior Scientist for Ruminant Nutrition at AgResearch, New Zealand, to discuss the weaning transition and how getting it right helps both calf growth and increased lifetime production

LifeStart: Why and how did you first become interested in researching about weaning and the transition post weaning?

Dr Khan: My interest in feeding and caring for young animals started as a child at my family farm. Then, after completing my Ph.D. in Ruminant Nutrition, I realized that the current calf feeding and management practices required a revisit in order to reduce morbidity and mortality at dairy farms. In particular, work from three institutions (the University of British Columbia, the University of Illinois and Cornell University) on calf nutrition and welfare, inspired me to explore alternative feeding and weaning practices for calves.

My team at the National Institute of Animal Science in South Korea, first replicated the work of feeding ad libitum milk to calves and thereby contributed to breaking a long echoed myth that calves should be given restricted amounts of milk. We successfully demonstrated that the calves can ingest and digest milk around 20% of their body weight. Greater amounts of milk feeding can support better body weight gain and reduce the distress hunger creates in young calves.

However, giving greater milk supplies to calves was criticized on both biological and economic grounds. Others thought that greater supplies of milk could potentially delay the rumen development necessary to shift reliance on solid feed, and they thought that feeding greater amounts of milk would be costly for commercial herds. These arguments pushed me to think about (1) What does the transition mean for young ruminants? And, (2) How do on-farm feeding and management practices affect both the weaning transition and the post-weaning performance of calves?

LifeStart: Given that, can you tell us a bit about your latest research?

Dr Khan: The focus of my research is to support the productivity and sustainability of pastoral dairy systems. I am particularly interested in the areas of nutritional needs for young ruminants, improving on-farm feeding management to reduce losses around times of transition, and the evaluation of feeds, feeding systems, and additives to improve dairy animal performance.

LifeStart: Sounds exciting! Dr Khan, why is weaning transition so important?

Dr Khan: A smooth transition from liquid to solid feed allows calves to consume and digest sufficient solid feed to support growth both during and after weaning. Feeding and rearing practices before or around weaning not only affect the health and performance of young calves, but could potentially impact their long-term performance in commercial herds as well.

LifeStart: May we ask why you think that the importance of the weaning transition had been generally overlooked in the past?

Dr Khan: During the last century, it was generally recommended and desired that calves should be fed a limited amount of milk to encourage starter feed intake, for earlier weaning, and to both save milk and generate income. Early weaning systems were thus developed to promote rumen development at the earliest possible time. Therefore, many producers were weaning calves at a young age to reduce costs associated with feeding milk or milk replacer.

But, calves are born with a non-functional rumen and must initially rely exclusively on milk to meet their nutrient demands for maintenance and growth. Initiation of solid feed consumption, acquisition of anaerobic microbes, establishment of rumen fermentation, expansion of rumen in volume, differentiation and growth of papillae, development of absorption and metabolic pathways, maturation of salivary apparatus and development of rumination behaviour, are all needed as the calf shifts from dependence on milk to solid feed. Recent advances in the fields of animal nutrition, immunology, behaviour, microbiology, and physiology along with public pressure for ethical food production have provoked a revisit of calf feeding and weaning systems.

LifeStart: And what are the most important aspects of the transition, after being weaned?

Dr Khan: There are many important considerations that have to be taken into account, post-weaning. We need to look at feed efficiency, continued and consistent growth, maintaining calf health, and the long term performance of heifers, once they begin producing milk.

LifeStart: How does our knowledge about the impact of this transition today differ from what it was in the past?

Dr Khan: The impact of feeding, weaning and rearing systems on young calves is measured the same as it was in the past, in terms of reducing morbidity and mortality in young stock. However, as a society we are now more concerned about animal welfare and ethical food production as well. Furthermore, our vision in animal nutrition is now focused on linking neonatal feeding and rearing systems with the long-term performance of heifers in commercial herds. Certainly, we are continuously improving our understanding and knowledge about the developmental biology of young ruminants. And, as such, I am optimistic in saying that in the future we will be able to use that knowledge to ethically rear efficient and resilient animals for various livestock production systems. One of my research aims is to demonstrate the role of calf nutrition and management on the sustainability of livestock production systems.

LifeStart: Dr Khan, what are the aspects of the weaning transition that you believe we still need to better understand?

Dr Khan: We need to attain more knowledge in terms of immunology, physiology, gut microbiology and the behaviour of animals by using advanced scientific tools, such as sensing technology and molecular biology in both controlled and farm system level studies.

LifeStart: Are there any holes in the current research that you believe we need to, and should, seek answers to?

Dr Khan: There are many; however, I will put forward the following three:

1. We need to look at how rumen and gut micro-biomes develop in young ruminants.

2. We need to look at which factors govern the immune system development in young ruminants.

3. And, we need to look at how isolation on the one hand, and how social facilitation on the other, affect the physiology and behavioural traits in young ruminants.

Want to learn how to put this into practice?

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