Feed conversion efficiency (FCE) is optimum in young animals – that’s a fact.
Heifer replacement FCE is highest in the first eight weeks of life after which it rapidly tails off – check out the graph.
In the first two weeks, 100g of feed will give approximately 50 – 60g of growth, after which it dramatically falls during the first 12 months of life, by when 100g feed will only give approximately 9g of growth.
Heifer feed efficiency
* (Average daily gain) / (dry matter intake) x100
Feeding for growth has also proved to be cost effective according to research findings from the Institute of Research and Technology in Agrifood (IRTA). To achieve average age at first calving at 23 months and a body weight of 650kg, feeding a total six litres of milk per day to weaning at two months resulted in the lowest total rearing feed costs.
The data in the following table confirms that heifers fed four litres during the same period had some catching up to do later on when FCE is lower. In other words it is cheaper to put weight on heifers earlier.
Milk volume fed and the impact on total heifer rearing costs
(calving 23 months, 650kg body weight)
|Volume milk fed (l/day) during first two months||Average weight gain during first two months (kg/day)||Total rearing feed cost (£)|
Three reasons why FCE is the highest in early life
- Milk is more digestible and nutritious than concentrate to a young calf.
- Calves fed concentrate utilise the ME that they consume less efficiently than the energy derived from milk or calf milk replacer. This is because at least some of the carbohydrate and protein in starter feed must be fermented in the rumen prior to being digested by the calf. As rumen activity increases, the amount of heat produced by the animal also increases which can be considered a loss as it cannot be utilised by the animal.
- Before puberty, growth is mainly bone and muscle, after which heifers gain more fat relative to bone and muscle, consequently they are less feed efficient.