Spring is one of the busiest times of year on a dairy farm. Cows are calving, heifers need to be trained into the parlour and calves have to be looked after. Although it is an extremely busy time of year, it is still worth putting a big effort into rearing your calves to the best of your ability. After all, the calves you rear today will be the herd of 2013.
If replacement heifer calves are to reach the specified critical weight targets throughout the rearing process, you need to start aiming to achieve these weights from the day the calf is born. Of course, it is also essential to minimise mortality and illness levels on the farm. This will give greater scope to cull more cows from the milking herd in two years' time or will allow expansion and growth of the herd, but ultimately it will reduce costs incurred due to illness.
At birth, a calf's immune system is not fully developed. Colostrum (biestings) contains antibodies and growth factors, and is superior in nutritional value when compared with whole milk. Colostrum imparts passive immunity from the dam to the newborn calf via intestinal absorption of antibodies and should be fed for the first three days after birth.
Calves are dependent on adequate consumption of good-quality colostrum to boost initial levels of vitamins such as A, D and E. Most of the essential minerals and vitamins are substantially more concentrated in colostrum than in milk. For example, colostrum usually contains 6-10 times the amount of vitamin D present in ordinary milk. Inadequate feeding, or quality, of colostrum is a primary cause of low immunity in calves. In addition, deficiency of trace elements and vitamin E in the diet of the cow in late pregnancy can compromise the immune system of the young calf. This may increase susceptibility to scour, pneumonia, navel-ill, joint-ill, etc.
On farms, colostrum management is the single most important factor in determining calf health and survival. A failure of passive transfer of antibodies from colostrum contributes to excessively high pre-weaning mortality rates and other short- and long- term losses associated with animal health, welfare, and productivity. A successful colostrum management programme requires farmers to consistently provide calves with a sufficient volume of clean, high-quality colostrum within the first few hours of life.
As time from birth increases, the ability of the calf to absorb antibodies is reduced. Absorption is greatest in the first few hours of life and starts to decline progressively after four to six hours, and ceases after 24 hours from birth. Therefore, it is critical to feed colostrum as soon as possible after calving to ensure maximum immunity is acquired, as the most critical time in a calf's life is during the first few days, when morbidity and mortality are greatest.
The ideal source of colostrum is the calf's dam, for two main reasons. The first is centred on concerns about the potential spread of Johne's Disease, while the second is that by drinking its mother's milk, the calf will acquire immunity to fight pathogenic organisms encountered on the home farm.
Ideally calves should be given 2-3 litres of colostrum by oesophageal tube or by nipple feeding within four hours of birth, with a total of four litres within 12 hours of birth. Leaving calves to suckle colostrum from their dam is not recommended as there is no guarantee that they will have a sufficient intake. The amount of colostrum that calves drink voluntarily does not change within the first four hours after birth, so there is no benefit in delaying first feeding.
Although individual housing of calves, either indoors or outdoors, is generally linked with improved calf health, it is not really feasible in a seasonal calving system where large numbers of calves are being born in a short space of time. Thus, group housing systems predominate in Ireland due to the reduced labour input required compared to individually housed calves.
However, successful group housing of calves is dependent on factors such as feeding regime and hygiene.
Calves are often individually penned for the first few days after birth in order to ensure that adequate colostrum is received, and are then subsequently group penned. If calving patterns are not compact, there is a temptation to mix younger calves with older animals for ease of management.
However, older calves are considered to be the source of respiratory infection in younger calves and, therefore, farmers should be mindful of the difference in ages when grouping calves. Furthermore, research has found disease incidence of calves to be highest during their second week of life, so it is not ideal to group calves at this stage.
The optimum group size that calves should be reared in is frequently queried. Previous studies demonstrated that calves in larger groups (16 vs four) are generally more active, and move other calves away from the feed barrier less frequently.
However, previous studies have reported increased competition between calves in groups of 24 when compared to sets of 12. The increased competition in the larger groups resulted in increased drinking speed and less time spent at the feeding area. Thus, in scenarios where calves are in larger groups, it is important to group similar-sized calves and to ensure that any slow drinkers are removed as they will not thrive in there.
'All-in, all-out' systems, although not common in dairy calf-rearing systems may stop disease transmission from older animals, contribute to better hygiene, due to total emptying of the pens, and a more uniform feeding due to more homogeneous groups.
A recent study compared groups in six large commercial dairy herds, where new calves were continuously introduced to and exited group housing (dynamic groups), to calves in stable groups, where all calves were introduced and exited group housing simultaneously ('all-in, all-out', ie stable groups).
Calves in stable groups had significantly higher daily liveweight gain than calves in dynamic groups (870 v 810g/ day) and the prevalence of diarrhoea and respiratory disease were more than twice as high in dynamic groups calves compared to those in stable groups.
For indoor-reared calves, the quality of bedding material is crucial in minimising heat loss.
Deep straw bedding is superior to other bedding material in its efficacy as an insulator. It allows calves to nestle into it, which can have a preventive effect against calf respiratory disease in naturally ventilated calf barns. Good ventilation is a critical aspect of calf management and can profoundly affect respiratory health. Therefore, ensure that all indoor housing facilities are well ventilated but draught free.
Before this year's calving season starts, check all equipment is in working order. For example, change worn teats on feeders, and locate and clean any stomach tubes/nipple feeders. Also, ensure that housing facilities are thoroughly cleaned. The importance of hygiene when rearing healthy calves can not be underestimated. Remember, the simple systems are often the best, especially when basic calf rearing principles are adhered to.
Dr Emer Kennedy is a researcher at the Animal and Grassland Research and Innovation Centre, Teagasc Moorepark