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Accelerated growth

Agriculture

Accelerated growth

In recent years significant research has been carried out on the birth to weaning period, with areas such as colostrum feeding/management, calf nutrition and environment to name a few. One research of particular interest is the pre weaning period, with elevated milk or milk replacer feeding leading to accelerated growth in calves.

Traditionally, milk feeding programmes consist of calves being fed 4-5 litres (L) of milk or 750 grams (g) of milk replacer per day. However, this feeding programme results in relatively low daily live-weight gains (DLWG’s) of 300-500g per day and may not be exploiting the full genetic potential of the animal. In contrast, on elevated milk feeding programmes, calves are fed more than 8 L of milk per day or ≥ 1.2kg of milk replacer per day. Research has showed that by increasing the nutrient supply early in life (milk or milk replacer), this can lead to improved production performance in lactation.

Figure 1- Higher milk allowances result in increased body weight (Rosenberger et al, 2017)
Accelerated growth

As shown in Table 1 the evidence from a review of research studies would suggest that calves managed on elevated milk feeding programmes have increased DLWG’s, along with additional milk produced during their 1st lactation.  Across the research studies, the average DLWG for calves on conventional milk feeding was 0.54 (range 0.34-0.8kg) and on elevated feeding 0.76kg per day (range 0.50-0.90kg), with an additional milk yield response of 675kg of milk per first lactation (range 0-1,405kg).  Due to the low number of animals in these studies, the additional milk yield in some cases was not statistically significant.  However, when the data from the research studies in Table 1 was pooled together, the review model found that DLWG and 1st lactation yield are closely associated when nutrient intake is increased from milk or milk replacer.

Table 1– Production response (DLWG & yield) to increasing nutrient supply from either milk or milk replacer pre weaning – a worldwide review of 13 individual research studies.

Number of animals DLWG of control (kgs) DLWG of increased milk feeding (kgs) Milk yield of control (kgs) Additional milk 1st lact (kgs)
30 n/a n/an/a 1,405
20 0.56 0.859,171 453
20 0.60 0.90 7,716 519
14 0.44 0.73 6,100 700
20 0.59 0.88 10,784 981
10 0.52 0.75 9,245 1,332
14 0.56 0.71 8,796 342
26 0.56 0.79 12,962 718
30 0.80 0.90 9,888 624
38 0.34 0.50 6,862 0
23 0.73 0.80 9,150 732
40 0.44 0.64 9,778 416
400 0.32 0.70 10,605 552
Average 0.54 0.76   675
Epigenetics

Further recent research also suggests that pre weaning DLWG increases both 1st lactation milk yield and milk solids, however this research found that intake of concentrates along with liquid milk was important. The consensus of the research evidence suggests that by increasing milk or milk replacer intake early in life, the calf’s genetics are somehow altered, known as epigenetic programming, which has a positive effect on the heifers’ subsequent milk yield. The whole area of epigenetics requires further research. 

Fertility

In relation to heifer fertility research papers are limited. However, two authors have showed that calves fed elevated planes of nutrition reached puberty and conceived earlier. The data also suggested a numerical reduction in age at first calving (14 to 27.5 days earlier).

Disease immunity

It has been suggested that increasing the total energy and protein supply can effect immune response, thus leading to calves better able to cope with disease challenges. However, it is thought improved health is a result of the increase in supply of nutrients as opposed to any specific changes in the animal’s immune system.

Weaning management

One aspect that requires careful consideration in calves on accelerated growth programmes is weaning management. During the first three weeks of life calves on elevated levels of milk or milk replacer feeding benefit from higher intakes of milk/milk replacer.  Concentrate starter feed intakes are almost negligible in the first three weeks. However, after this three week period, research has shown calves fed higher levels of milk or milk replacer can have their concentrate feed intake reduced, particularly before weaning. If weaning is poorly managed, a check in growth can occur, thus losing some of the advantages gained from accelerated growth. Recent research has suggested the optimal age to reduce milk or milk replacer and stimulate increase solid food intake is around 45 days of age.

Conclusion

The aim of the CAFRE heifer rearing enterprise is to rear heifers cost effectively to the point of calving into the main herd at 24 months of age or earlier at a calving weight of around 90% of mature weight. Calving at 24 months or earlier is optimum for economic performance as it reduces the number of replacement heifers on the farm and reduces the number of non-productive days of life. In addition to reducing costs, earlier calving will also reduce greenhouse gas emissions per litre of milk produced through reducing the number of unproductive animals releasing greenhouse gases on the farm. In order to achieve this age at first calving (AFC) careful management is required in all three of the heifer rearing stages (birth-weaning/weaning-conception/conception to calving). The research evidence suggests that animals on accelerated growth programmes during the birth to weaning stage reach puberty and conceive earlier, which leads to a reduced AFC. This combined with other production performance data suggests that accelerated growth pre weaning, can have a positive effect on the long term productivity of heifer calves and the dairy herd.