The length of time dairy heifers survive in a herd and the longevity of dairy cattle, declined significantly throughout the 1980’s.  In fact, the average UK cow survives only three lactations.  A recent survey of UK herds showed that 8.1% of calves were born dead and a further 3.4% died within their first month. Potential heifers are also lost pre-natally due to early embryonic death (about 40%), later embryo loss (at 1-2 months, 20%) and abortion (about 5%).  Another 6.2% had died or been culled before reaching their first service period at 15 months due to either disease or accident, further losses are seen when some heifers served at this stage fail to conceive.  After calving a total of 3.3% were removed from the herd within 8 weeks, predominantly as a result of difficult calvings and mastitis. With replacement rates of up to 40% in some herds, it is taking as long to rear a heifer as she eventually spends in the herd.

Herds, in which heifers calve young, have high yields and low replacement rates; will achieve the best milk per year of life figures.  According to NMR results, the best herds are achieving 7637 litres per cow per year of life, whereas the worst have 3108 litres.  There is considerable work to be done in terms of rearing dairy heifer replacements on farm.

Growth rates

Heifer weight rather than age determines when puberty occurs and oestrus cycling begins.  The key to successful heifer rearing for two-year calving is to maximise weight gains without creating over-fat animals. The first signs of oestrus usually appear when heifers reach 40% of their mature body weight, at around 12 months of age.

Growth rates of 0.7 – 0.8 kg/day are recommended for Holstein Friesian heifers to achieve a BCS of 2.75 – 3.0 at first calving, the key being to avoid getting heifers over-fat.  In fact, current work shows that it is not detrimental to grow heifers at 1 kg/d for at least part of the growth period, provided heifers do not deposit fat.  However, frame size (assessed by height at the withers) is the most valuable measure of heifer growth.

	Wither height (cm)
Age (months)	Holstein	Friesian	Jersey
12	124	118	109
24	140	134	122

Enhanced calf growth systems, feeding a high level of protein, can result in much heavier heifers at weaning and better development of udder secretory tissue.  Feeding quality bypass protein e.g. soya will help grow large frame heifers. Feeding 1kg/day of concentrates though the summer (May to August), will cost you around £27/head.

For heifers less than 6 months, 3-4 kg of concentrates should be fed with ad lib straw. Under nutrition during the first 12 months will restrict the growth of the pelvis.

Feeding at bulling

Bodyweight at breeding should be about 420kg for Holsteins; at calving they will be around 600kg, 85-90% of mature body weight.  Fertility increases up to the third oestrus cycle after puberty, heifers need to be grown to reach puberty at least 6 weeks before the start of serving.  To ensure implantation of the embryo after service, feeding level should be maintained for 6 weeks after service.

Pre calving

There is evidence that magnesium chloride can reduce feed intake more in heifers than cows, however this is not a problem as heifers will not suffer from milk fever.

Udder oedema can be a problem in heifers, particularly if they calve on high protein, high potash pastures or are receiving diets containing a high percentage of grass silage containing potash.  Also, less oedema occurs on maize and straw-based diets.

To minimize lameness problems, heifers should be fed dry diets (greater than 30% DM silage).

Excess condition, which is far more likely to occur in older heifers, will increase calving problems; reduce feed intake after calving; increase fatty liver and ketosis; and reduce subsequent fertility.

After calving

Where possible, heifers should be kept as a separate milking group, allowing heifers to access the feed troughs and supporting continued growth and helping to get them back in calf with having to compete with older animals.  Where separate heifer group is not possible, they should not be mixed with the herd until 5 days after calving and they should be introduced after the evening milking when cows are less socially active.