3 October 2009

8 minute read

Minimising calf mortality through monitoring the health and weights of calves will save costs of replacements later on, the Nottingham Feed Conference 2009 heard. By ensuring calves have adequate colostrum and a healthy environment, producers can significantly reduce calf mortality.

Furthermore, monitoring growth during the first six months and ensuring optimal growth, will allow heifers to be bred earlier, which not only increases the amount of milk produced over the course of the cows life but also increases fertility, helping the cow concieve at the desired time. Over their life, cows successfully bred earlier will also produce more calves.

Above all, producing a healthy heifer results in a healthy and productive cow. Having a comprehensive management plan and knowing the true costs of heifer rearing will allow producers to realise the full potential of their dairy herds.

The average lifespan for Holstein cows is currently around three lactations, with the average cull rate per lactation as high as 25 per cent in some cases. During their lifetime each cow will therefore only produce a maximum of two heifer calves. This type of system is inefficient and unproductive - should the focus be on producing cows that provide a longer and economically more beneficial service period?

Professor Claire Wathes and her group performed a prospective cohort study for Holstein-Friesian heifers born on UK commercial farms to determine their survival and productivity on 29 dairy herds.

Of 506 live heifer calves recruited into the study, each heifer was monitored throughout their life at one, six and 15 months of age, as well as one week prior and after calving and eight weeks post calving. Fertility, milk production and survival were the main attributes monitored.

As a calf, birth weight, crown-rump length, height and average daily growth rate were monitored as well as blood measurements including IGF-I, glucose, urea, insulin and BHB (a ketone produced from non-esterified fatty acids and volatile fatty acids).

With regards to fertility, days until the first service were counted, days open, calving parameters and age at each calving as well as reasons for culling

Table 1 shows that of the 506 heifer calves born alive, 14 per cent failed to reach their first lactation.

The research carried out by Prof Wathes and her team looked at how this figure can be improved so that all heifer calves born reach the first lactation and beyond.

Influences on Neonatal and Calf Mortality

Colostrum feeding
Calves rely on a passive immune system during the first month of their life, which is provided through colostrum and the transfer of IgG until their own immune system becomes active. Colostrum mainly influences growth through its effect on health and therefore good management should consider quality and quantity on colostrum. Calves must receive colostrum quickly within the first six hours of life to gain maximum benefit

Failure of passive transfer (FPT) (FPT, less than 10g/ litre of IgG in blood), say Prof Wathes, is one of the most likely causes of calves contracting enteric disorders and pneumonia. Studies in the USA have found that on some farms up to 50 per cent of calves tested had FPT. Prof Wathes sugessted testing for FPT at 1-2 days of age, this allows calves that require extra attention to be identified. If  FPT is evident (less than 10g/litre of Ig) then serum Ig should be measured into calves for the following few days - this prevents loss of life. If there is a high incidence of FPT among calves, producers should review their procedures of providing colostrum to improve calf survivial.

Feeding calves
A number of factors on how calves are fed will influence the success rate in rearing. These include type of milk fed (whole or milk replacer), the temperature and the amount (including quantities of protein/ fat).

Weaning
The age and size at weaning and how weaning is carried out will effect the stress on young stock. If they are stressed they are more likely to have a weaker immune system.

Housing
Calf housing is critical for good health. Adequate ventilation is needed, but calves exposed to lower temperatures may require more feed. If housing is in individual hutches, animals can receive individual care and attention - however hutches can often be located behind sheds or in hidden locations and so the stockman may neglect to check on young stock. Group housing is often associated with poor cleanliness and housing with older animals which can both spread diseases.

Throughout the 19 herds, a mean of 14.5 per cent of live born heifers failed to calve for the first time.

Growth Rates of Replacement Heifers

Prof Wathes and her team researched the growth rate of heifers on dairy farms as well as what factors influence growth rates and whether growth rates influence subsequent performance. On the farms investigated, very few farmers had previously monitored birth weights or continued to measure calves as they grew. The mean growth rate between one and six months was 0.77 kg/day. However this was very variable between calves. The lowest measured gain was 0.23 kg/day whilst the highest was 1.25 kg/ day.

Insulin-like growth factor (IGF-1) is mainly secreted by the liver as a result of stimulation by growth hormones and is an important regulator of growth and development. By taking regular measurements of IGF-1, the research team found that levels of IGF-1 peak around puberty (9-15 months) and from then until first calving levels of IGF-1 will fall as growth rate slows. Measuring weight and IGF-1 at one month of age showed that calves with lower weights and levels of IGF-1 were at higher risk of mortalitiy between one and six months of age.

Do Growth Rates Affect Fertility?

Poor conformation and poor growth are associated with poor fertility, says Prof Wathes. By monitoring calves' weight and condition at an early age, there is the opportunity to correct the problem before the service period is reached - if a heifer requires five services to conceive, this delays first calving and producers should consider whether it would be more economical to cull.

In the UK, the mean age at first calving (AFC) in this study was 26 months, in America and Italy it can be 27-28 months of age. Calving at an earlier age not only reduces rearing costs but allows cows to reach first lactation sooner and over the course of their life provide more economic benefit. The research also carried out showed that the cows calving between 22 - 25 months were more successful in conceiving at first service and survived longer. Studies showed that conception rates for first service were significantly higher in heifers than in lactating cows.

At time of first service animals should have achieved 55-60 per cent of their mature body weight.  In order to achieve the target weight of 350 kg - 380 kg at time of breeding, the optimum growth rate would be between 0.6 kg - 0.8 kg/ day advised Prof Wathes. Prof Wathes said that calves must not be allowed to gain weight too fast during these first six months as it will cause problems later on.

Table 2 shows examples of two calves with different growth rates between one and six months of age. The faster growing animal achieved a first calving age much before that with the lower growth rate and this difference persisted at second calving.

Bodyweight at breeding should be about 420 kg for Holsteins, this will obviously be lower for other breeds, according to DairyCo. At time of first calving animals are expected to be around the 600 kg mark, 85-90 per cent of their mature body weight. Body condition scoring (BCS) at nine months of pregnancy should be between 2.5 - 3.0. Cows with a BCS above this are more likely to encounter problems at calving such as dystocia or a displaced abomasum, said Prof Wathes.

Although the research carried out showed that milk yield at the time of first calving was slightly lower for cows bred sooner, in the long term they actually spent a higher per cent of their life in milk production.

Studies show that one third of all heifers fail to calve for a second time, which is often due to an inability to conceive again during their first lactation.

Genetic Indices

Prof Wathes believes that successful heifer rearing is the key to successful milk production. Currently selection indices are all based around the milking cow, as the above research has shown, heifer rearing has important influences on future survival and fertility. Could futures breeding indices include information concerning heifer growth rates?

Genomic selection could be used to identify those heifers with good early growth and fertility which develop into profitable and healthy cows.

Conclusion

Dairy units need to have comprehensive management strategies to suit their individual circumstances. Farmers can calculate the true costs of heifer rearing (including the costs of heifers which do not survive!) by using the DairyCo heifer rearing calculator.

By being aware of mortality rates, producers can address and identify the main causes and prevent the losses happening the following year. Measuring growth (which can be tied in with vaccinations, worming etc.) can help identify problems and corrective measures can be made prior to breeding.

Increased growth rates during the rearing period are associated with better heifer fertility, and so a decreased age at first breeding and first calving. A pre-pubertal growth rate of 0.7-0.8 kg/ day should be achieved to allow an age of first calving between 23-24 months for optimal subsequent fertility, milk yield and longevity.