Whole Milk Versus Milk Replacer For Calves

The detailed survey carried out across Northern Ireland farms indicates that most dairy producers (77%) reared their calves on predominately whole milk with only 23% using predominately milk replacer.  Whilst it is recognised that to minimise waste, discard milk needs to be used for calf rearing, it appears that a significant amount of saleable milk may also be used.  There are significant cost implications – £14/calf if all milk fed is saleable.

Opinion on feeding discard milk is mixed.  As expected, numerous studies have demonstrated higher levels of bacteria and/or antibiotic residues in waste milk.  There are concerns that feeding mastitic milk may increase the risk of scours and some research has shown that calves fed infected milk had mastitis as fresh calvers, caused by the same genotype of bacteria.  However, most of the common organisms that cause mastitis are found all over the body, so even a calf suckling from it’s mother is likely to ingest potentially mastitis-causing organisms.  Feeding whole milk increases the risk of Johnes transmission.  For this reason, herds infected with Johnes should not pool colostrum or feed milk from infected cows to calves.

Where large numbers of calves are being fed whole milk, on-farm pasteurisation should be considered to reduce the bacterial loading of waste milk.

As for antibiotic milk, it has been highlighted that most cows have had dry cow therapy, and colostrum therefore contains antibiotics.  Consequently, it is difficult to argue against the use of whole milk solely on this basis.  However, the variation in quality of whole milk should be recognised.  Within farms, the whole milk fed to calves can vary from 2.9-5.0% butterfat and 3.0-5.0% protein. In view of (a) possible disease transmission (b) inconsistent quality, discard milk should be fed, wherever possible, to bull calves only.

Feeding level and protein content of milk replacer

Over the last 20 years recommendations for the pre-weaned calf (up to 8 weeks of age) have been to offer 500-600 g per calf per day of a milk replacer (approximately 1.1 lb per day) containing 20-23% crude protein, together with access to ad libitum concentrates and water.  The aim has been to achieve growth rates from 450 to 600 grammes per day.

Recently, research from North America has questioned the approach of restricted milk feeding and proposed that higher feeding levels should be adopted in a bid to accelerate growth (up to 1 kg per day) in the pre-weaning period.  These higher growth rates can theoretically be achieved by feeding 900 to 1200 g of high protein (up to 30%) milk replacer.  To evaluate the merits of such feeding systems, which have significant cost implications, a series of collaborative studies have been undertaken at AFBI Hillsborough and Teagasc, Grange to compare the performance of dairy-bred calves offered milk replacer containing 23% or 30% crude protein at two feeding levels (600 grammes per day or 1200 grammes per day).

Relative to calves offered 600 g milk replacer per day, calves offered 1200 g milk replacer per day grew significantly faster during the milk feeding period (birth to 8 weeks) (Table 1).  However, differences in live weight and body size recorded at weaning for calves on the higher level of milk replacer had disappeared by 6 months and there were no beneficial effects on milk production during the first or second lactation.  Increasing the protein content of the milk replacer above 23% had no short or long-term effects on performance.

Table 1.  Performance of Holstein calves offered 600 or 1200 g milk replacer per day containing 23% or 30% crude protein (AFBI Hillsborough)

Weaning

On average, calf rearing systems in Northern Ireland wean calves at 8 weeks of age, although there is considerable variation with over 20% of producers surveyed delaying weaning to between 9 and 12 weeks

Previous research has shown that, provided calves are at least 5 weeks of age, concentrate intake is the key factor on which to base when to wean.  Concentrate intake is very important in preparing the calf for a solid food diet as the fermentation of the ingredients promotes rumen development.  As a general rule, the calf should be consuming approximately 0.7 kg concentrate/head/day to minimise a post-weaning check on growth.  A recent study at AFBI Hillsborough found no difference in the performance of calves weaned on age at 8 weeks, compared with those weaned as soon as concentrate intake went above 0.5 kg per day, with calves totally off milk when concentrate intake was above 1.5 kg per day.  Average weaning age for the latter group was 6 weeks.

Provided the rumen has developed sufficiently prior to removal of milk feeding, there is limited evidence to indicate any difference between abrupt weaning and gradual reduction in milk intake.  However, if feeding high levels of milk, studies have shown gradual weaning over a 7-10 day period can prevent the associated slump in growth the week after weaning, compared with abrupt weaning.

The recent survey of Northern Ireland heifer rearing enterprises has shown that on farms where concentrate is offered as soon as the calf enters the calf rearing accommodation, rather than later (11 days plus), heifers are served earlier resulting in a lower age at calving.  For every day delay in offering calves concentrate, the associated age at first calving increased by 4 days.