In general, 25-30% f the herd must be replaced every year. A restocking plan aims to rear healthy heifers to replace, two years later, the culled cows, with improved production and genetic value of the herd. High-quality heifers at the best cost possible are essential to put in place this plan and maximize income. However, newborn calves are often not given much thought.
Dairy cows’ production and reproduction performance are monitored every day, while we control heifers’ health and growth less frequently. Too often heifer rearing is not considered as an opportunity to improve the future income, because of their short-term unproductivity. But a high-producing dairy cow comes from a well-reared heifer. Even if the heifer is not of excellent genetic value, she can become a high-producing dairy cow if we take care of her growth and health starting from the first day of life. On the contrary, obstacles to the physiological development of a high genetic value calf during the first part of her life will prevent the full expression of her genetic potential. It was proven that a mortality rate of up to 22% of pre-weaned calves affects 38% of the herd net income, taking into account mortality, morbidity, lower growth rate, lower feed efficiency, and lower milk production along the whole rearing cycle (Martin and Wiggins, 1973).
But which “obstacles” are we talking about? The ruminant placenta does not allow the passage of the antibodies from the mother to the fetus so that the calf is without active immunity up to 5 weeks of age. Colostrum is the only source of immunoglobulins for the newborn calf and this is the basis of its immune system.
The failure of passive transfer (FPT) is the cause of the high morbidity and mortality among calves (respectively over 50% and 11%) during the firsts 3 weeks of life, the reduced health status, and lower longevity of the animals. Calves that do not receive enough immunoglobulins (IgG, IgM, IgA) after birth have higher mortality and lower longevity than the others. The IgG cut-off value in calves plasma 24-48 hours after birth to ensure an effective passive immunity is 10 mg/ml. Lower IgG values mean that the calf has a 50% more chance of dying than other calves. An effective passive transfer gives benefits both in the short and long term. Calves have lower pre-weaning mortality and morbidity but there are many advantages even later in life. Better health status, higher feed efficiency, reduced age at the first parturition, improved milk production during the first and second lactation, higher fertility, and the consequent lower restock rate are among the aspects of the productive life of the animal that begin to take root in the first hours after birth and the optimal colostrum ingestion and quality.
The plasma IgG cut-off value (10 mg/ml) and the optimal colostrum management require four fundamental criteria to be observed: timeliness, quality, quantity, and cleanliness. At 24 hours old the intestinal mucosa of the calf loses the ability to absorb macromolecules such as the immunoglobulins. Some researches demonstrated that already after 6 hours they absorb only 66% of the colostral IgG. Only the ingestion of at least 3 liters of colostrum with an IgG concentration equal to or greater than 50 mg/ml (22° Brix) during the firsts 2 hours of life can ensure an effective transfer of passive immunity (Faber et al., 2005).
Table 1: Benefits given by the administration of 2 or 4 liters of colostrum referred to health, veterinary costs, and productive and reproductive performance (from Faber et al., 2005).
|Colostrum 2 l||Colostrum 4 l|
|Pathology incidence %||21,6||16,1|
|Veterinary costs ($)||24,51||14,77|
|Daily gain (kg)||0,8 ±0,02||1,03±0,03|
|Age at conception (months)||13,97||13,54|
|EVM ME (kg) * 1° lactation||8 952||9 642|
|EVM ME (kg) * 2° lactation||9 907||11 294|
Bacterial contamination of the colostrum, especially by coliforms, is a potential source of infections and hurts the effectiveness of the transfer of passive immunity. Bacteria can link free immunoglobulins along the gastrointestinal tract, lowering the absorption through the intestinal barrier. To meet the standards of good quality, colostrum has to contain less than 100.000 CFU/ml of total bacterial count (TPC, total plate count) and less than 10.000 CFU/ml of coliforms (TCC, total coliforms count). To reduce as possible the risk of bacterial contamination, during the colostrum collection it is necessary an adequate cleaning of the nipple as well as the cleaning of the equipment used to collect and administer the colostrum. Colostrum that will not be administered immediately must be refrigerated or frozen within 30-60 minutes from the collection. This allows the reduction of bacterial contamination preserving the colostrum IgG content. Pasteurization (60°C, 60 minutes) can be an additional tool to reduce bacterial contamination but not the IgG concentration.
So far we have seen how to manage colostrum and its intake by the calf. Although its characteristics are often considered as a fact, much can be done to improve its quality acting on the management of the cows. Individual factors (i.e. the health of the cow at calving, parturition duration, the management and the alimentation during the dry period) and environmental conditions (i.e. overcrowding, heat stress) can greatly affect the immunoglobulin and nutrient content of the colostrum with direct consequences on calf performance. The transfer of immunoglobulins from the maternal circulation to the mammary secretions begins a few weeks before delivery and then stops abruptly at calving. Therefore, a too-short dry period, marked negative energy balances, ketosis, or too low calcium levels will also harm the colostrum quality. The good management of the dry period is an investment for the future health of the calves that will be born.
Thanks to the variety of nutrients that contains, the right colostrum intake has more positive effects than the immunoglobulin transfer, with optimal growth of the calf. As an example, colostrum has a high amount of choline (0.7 mg/ml, Fauley et al., 1978; Waugh et al., 1947), suggesting a high requirement for the newborn. The mechanism of action is not completely clear yet but it seems that the exposition to choline in the uterus and its intake with colostrum, plays a key role in calf immunity and live performance. A plausible hypothesis is that calves born to mothers whose diet has been supplemented with rumen-protected choline during the dry period have better development and faster maturation of the gastrointestinal tract. In addition, the intestinal mucus layer, the first barrier against pathogens, contains phosphatidylcholine. The high availability of choline improves nutrient transport (lipids and liposoluble vitamins) and the chylomicrons synthesis (lipoproteins). Immunoglobulins can link chylomicrons; a higher amount of chylomicrons means better IgG transport and improved absorption. Moreover, it seems that the ingestion of choline through the amniotic fluid causes the better development of the fetal intestinal mucosa. A recent study was aimed to evaluate the effect of the administration of rumen-protected choline to dairy cows during the last 3 weeks of pregnancy on their calves’ live performance. Cows receiving the supplementation with rumen-protected choline had a numerically higher amount of IgG than the control and produced the same colostrum volume. Calves from supplemented cows had higher milk and cereals intake than the control group and higher growth in the first 21 days of life. During the first 36 hours of life calves fed with the colostrum from the supplemented group of cows demonstrated a better Apparent Efficiency of Absorption (AEA, the efficiency in IgG absorption), a higher IgG serum level, and an improved survival rate compared to those fed with the control group colostrum.
A good immune system function depends even on a correct selenium intake. A dietary integration with selenium during the dry period of the cow is useful not only to the mother but also to the calf. Selenium can pass through fetal membranes and is transferred also in colostrum and milk. An increase in the mother’s plasma selenium level at calving means an increase of this value also in the newborn, both in blood and liver. Moreover, the dietary supplementation of the maternal diet causes an increase in colostrum IgG and their better absorption by the calf. Higher bioavailability of selenium in calves has different positive effects:
- Improved immunity;
- Improved reactiveness against stressors and pathogens;
- Reduced mortality during the firsts weeks of life;
- Improved thermoregulation of the newborn: selenium is a co-factor of the selenium-dependent enzymes that activate thyroid hormones.
To have a successful restock it is mandatory to take care of calves even before they are born. The correct supplementation of the diet of the mother with functional nutrients is useful both for the cow and the calf, which already benefits in the womb. The perfect management of the transition period assumes even more importance: it has repercussions on the maternal but also on the daughter’s future lactation performance.
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Original article here.