Feeding for Target Growth

30 March 2012

1.       Feeding for Target Growth

Energy and protein supplied to the calf is first used for maintenance (such as body temperature), then growth and finally immune function. If maintenance energy requirements are not met by that supplied in feed, then the calf will mobilise body energy reserves, resulting in low or even no growth. The amount of solids fed to the calf each day is key to its potential growth. For example, increasing the amount of solids from 500g per day (4L per day at 125g/L) to 900g per day (7L per day at 125g/L) will increase growth, as long as the protein content is not limiting.   

2.       Monitoring Growth Rate  

Why: Growth rate targets need to be set based on the target age and weight at first calving for your farm. For example, if a calf has a birth weight of 40kg, in order for it to calve at 24 months of age with a body weight of 550kg, it will be necessary for heifers to gain 510 kg over 730 days. Thus it must achieve an average daily gain of 0.7 kg per day throughout the entire rearing period. But in practice growth rates are not consistent. A study at the Royal Veterinary College, London, based on 19 farms across southern England found that body weight gain ranged from 0.23 to 1.3 kg per calf per day during the first 6 months of life. The effect of growth rate during the first 6 months remained significant at 15 months resulting in animals reaching first service without adequate body size. 

Table 1. Suggested target body weights for Holstein-Friesians

#85-90% mature body weight 

The only way to ensure calves are reaching targets, and to reduce the variation between calves, is to regularly monitor calves.  

How: The easiest way to measure growth is to weigh calves through a race. Alternatively, heart girth is closely correlated with weight, so measuring heart girth in cm, or using a weigh band will provide a reliable measure. The key is to be consistent – if using a weigh band, use the same one throughout the year, and between years. 

When: As a minimum, calves should be weighed at birth, and again at 6 months. Calves are often vaccinated or wormed before turn out at around 6 months of age, so weigh calves at a time to coincide with another management practice. If calves are too small at 6 months, use the check list below to identify the main cause of poor growth. Changes can then be made to ensure all calves reach the target body weight and age at first breeding. Alternatively, if animals are not handled until the time of first service – weigh them at this point. If heifers are smaller than desired – make corrective changes to subsequent groups of heifers to ensure all heifers have adequate body size at the time of first service. 

Check List for Ensuring Adequate Growth:

• Colostrum feeding
• Milk feeding (type, amount, system)
• Housing (ventilation, drainage, bedding, pen design)
• Weaning management
• Post-weaning nutrition (concentrate, roughage, grazing)
• Vaccination / disease management

3.       Adequate body size for first service at 13 months

If heifers are to calve for the first time at 24 months – they must be in calf at 15 months of age. Although fertility in maiden heifers is often superior to that of lactating cows, the RVC study found that heifers require on average 1.4 services per conception (range 1 to 5), and only 67% of heifers were pregnant to first insemination. First breeding must therefore start before 15 months of age, so set target growth rates to help ensure heifers have adequate body size for first service at 13 months of age.

4.       Well grown and well equipped heifers to join the herd at 24 months

Although most farms aim for first calving at 24 months, heifers are often calving at greater than 24 months. The RVC study found that the mean age at first calving was 26 months, ranging from 21 to 51 months. Growth has a direct effect on age at first calving – larger calves with faster growth rates were younger at first calving.

5.       Good fertility, multiple lactations

A short herd life span is a significant economic loss to the dairy industry. On average 19% of heifers are culled during lactation 1, and 24% are culled during lactation 2 (RVC study). Only 55% of live born replacement heifers calved successfully for a third time. Calving at 23 to 25 months of age can help to increase the productive lifetime of dairy cows; in the RVC study these animals had better fertility, higher milk yield per day of life, and improved longevity (Table 2).

Table 2. Data from Royal Veterinary College Study (part funded by DairyCo and Defra) led by Professor Claire Wathes and Dr Jessica Cooke

Source: RVC
 

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