Target pre-weaning growth

By Dairy News

PRE-WEANING GROWTH of calves is the most expensive period of growth an animal will undergo in its lifetime. However, it is also the time at which feed conversion efficiency is greatest.

Traditionally, it is recommended to provide calves with about 10 per cent of bodyweight (4 — 4.5 litres/day) in milk or milk replacer during the pre-weaning period.

Importantly, this is less than a calf would naturally receive if left suckling with its mother, where it would generally consume 8–10 litres/day in the first 3–4 weeks of life.

The theory behind this strategy is that restricted feeding of milk will accelerate rumen development and function, intake of solid feed and thus allow for early weaning at about six weeks to reduce costs.

Successful calf rearing should target an average daily gain (ADG) of 0.7 kg/day, which equates to a target weight of about 100 kg at 12 weeks of age (for a 40 kg calf at birth). However, recent data suggests it is very difficult to achieve this under conventional feeding practices described above. Restricted milk provision, especially in the first 3 weeks of life, generally results in lower growth rates, increased susceptibility to stress and disease and higher mortality levels.

This is why concentrate provision is critical in early life.

Calves should have access to concentrates within 3–5 days of age, to assist rumen development and function. It should contain about 17 per cent crude protein, have a high energy density (>13.0 MJ/kg DM) and be somewhat coarse in nature, to maintain rumen papillae in optimum condition.

Unlimited access to clean drinking water is essential, and a limited amount of good quality fibre is also important as concentrate intake increases.

However, large amounts of poor quality hay or straw will reduce the energy density of the overall diet, slow down growth rates and can often result in an undesirable “pot belly” condition.

Weaning is a very stressful period for calves and the age of calves should NOT be the sole criteria determining weaning date.

Instead a solid feed intake of about 1.4 per cent of bodyweight (minimum of 1 kg DM/day solid feed) should be targeted before gradual removal of liquid feed over a seven day period.

Poorly functioning rumens at weaning will stunt the growth rate of the calf post-weaning regardless of how they performed pre-weaning; hence adequate intake of solid feed pre-weaning will help reduce this effect and improve health and wellbeing of the calf.

Accelerated feeding is an alternative feeding strategy that has received significant research interest in recent years.

This involves providing higher amounts of milk or milk replacer in the first 4 weeks of life, (15–20 per cent of bodyweight or 8–10 litres/day for an average calf), before stepping down to conventional levels from about 5 weeks of age until weaning.

This results in a higher ADG, but slower rumen development in the first 4 weeks due to reduced solid feed intake during this period.

However research has shown if this strategy is managed correctly through weaning and post weaning, calves will have a higher bodyweight at 12 weeks of age (115–120 kg).

The benefits of this strategy include calves being able to express more natural feeding behaviour, reduced signs of hunger, improved growth and improved health and welfare.

Longer term benefits of higher growth rates in heifers pre-weaning include a reduced age to first calving, and greater lifetime milk yields.

A recent review of 12 experiments in the Journal of Dairy Science showed that first lactation milk yield increased by 155 kg of milk for every additional 100 g of pre-weaning ADG as heifers.

It has also been estimated that 22 per cent of the variation in first lactation milk yield can be traced back to the average daily gain of heifers.

To place this in context, this is a far larger effect on milk production than the heifer’s genetics which often receives much more attention on many farms.

Accelerated growth rate feeding results in increased costs in terms of extra milk consumed, but so far, data indicates that the long term benefits to the animal more than compensate this, although it is a topic of ongoing research.

• Ruairi McDonnell is a GippsDairy regional extension officer.

• This article first appeared in GippsDairy’s How Now Gippy Cow.

Key points for successful calf rearing

• Ensure every calf gets good quality colostrum (greater than 22 per cent Brix) — 2 litres within 2 hours of birth and another 2l in the next 10 hours.

• If using milk replacer, ensure consistent mixing of powder and delivery. For fresh milk and milk replacer, feed it at a consistent temperature every day.

• If using fresh milk, try and avoid feeding mastitic or antibiotic residue milk. Never feed this milk to sale calves or calves destined to become replacement heifers.

• It might sound boring, but HYGIENE is a critical factor. Clean, fresh drinking water, clean teat buckets and equipment, clean milk (free from contaminants and organic matter), clean sheds with sufficient bedding.

• Monitor growth rates — measure weight & height of a sample of calves so as to keep a close eye on whether weight targets are being met.

• Refer to Dairy Australia’s Rearing Healthy Calves manual for a full overview on best practice management.