To Feed or Not To Feed
The impact of milk restriction in calves
In the dairy industry, it is common practice to restrict a calf’s access to milk - on the one hand, to save money, on the other hand it is believed that restrictive feeding of milk encourages the calf to eat more solid feed, thus beginning the weaning process earlier. This approach was recommended and accepted as a standard industry practice. However, these recommendations have been challenged with new findings.
If the natural food intake behaviour of calves with their dam is examined though, a huge discrepancy is seen with the scenario described above. New born calves feed from their dams up to 10 times a day, ingesting between 8 and 16 litres of milk per day.
So what is the milk restriction being well-established in the practise doing to calves?
Short term, when compared to calves fed milk ad libitum, restricted calves never reach satiety, do not grow to their potential, vocalise more and play less. When examined in this way, it has been recognised that this practice represents underfeeding of calves and therefore poses a significant well-being issue.
In addition, numerous recent studies have now shown that nutrition in the early days, weeks and months of an animal’s life influences the metabolic programming of that animal for the rest of their lives. This is because the release of hypothalamic neuropeptides are permanently affected, controlling feed intake and long-term weight gain. The metabolic programming effect causes modifications of non-imprinted genes as an effect of the developmental environment. Put simply, life-long gene expression of these animals is modified without any alteration to the DNA sequence.
Practically, these effects manifest themselves in a wide variety of ways:
- Development of the mammary gland – intensive feeding (no restriction of milk) in week 2-8 of life stimulates the development of the mammary gland. This time frame of influence seems to close after weaning.
- Milk yield – calves fed well pre-weaning demonstrate higher milk yields in their first lactation (this may partly be explained by better mammary development described above)
- Glucose metabolism – calves fed intensively in the first few weeks of life exhibited improved pancreatic insulin response later in life
- Somatotrophic axis – restricted feeding in calves has been shown to lead to decoupling of the somatotropic axis, characterised by high GH concentrations in face of low IGF-1 levels in the blood. This decoupling is also observed in fresh cows suffering metabolic disturbances - however, it remains to be tested whether the two are linked
- Immune function – a direct effect of restrictive feeding on immune function is unclear, but studies have shown lower plasma fibrinogen in intensively compared to restrictively fed calves, suggesting effects on the acute phase response
- Fertility - higher weight gains during the pre-weaning period may affect the fertility traits, such as onset of puberty and age at first calving.
Interestingly, effects of metabolic programming in early life do not automatically persist in later life but are at least partly reversible. Disease, for example, seems to represent an important factor that can erase the effects of developmental programming in calves. For example, those calves which were fed well in the first weeks of life but suffered from a severe pneumonia later on, lost their potential for subsequent superior growth. This reinforces the need to ensure appropriate environmental conditions, as well as consider nutrition, when rearing calves.
More important considerations for chosen calf feeding protocols have been discussed as part of the Bayer Dairy Cattle Summit educational programme.