Ruminants placenta avoids immunoglobulins transfer from the mother to the fetus (passive immunity). Calves are not protected against infections until they develop their own active immunity, except for antibodies received through colostrum (Figure 1).

Figure 1: Bovine maternal, innate, and acquired immunity scheme.

Colostrum production begins some weeks before calving and its composition changes starting from the second milking until it becomes proper milk (from the 4^th onwards, Table 1). Immunoglobulins are big molecules (about 150 kDa) absorbed through protein transport only before intestinal mucosa maturation. During these firsts 24 hours from birth, the calf intestine has a non-selective absorption and is able to absorb immunoglobulins. Immunoglobulin G (IgG or γ-globulins) are about 75% of the total: they stimulate phagocytosis, activates the complement, and faces bacterial toxins. It is important that newborn calves receive more than 100 g of IgG within 12 hours from calving through the colostrum.

Calves that receive low concentrations of immunoglobulins have a failure of passive transfer (FPT) of these proteins (less than 10 g/l of blood during the first days of life). FPT is really frequent (> 50% of calves) and causes about 65 €/animal economic loss due to high mortality, increased pathologies prevalence, and low performance during the whole productive life. Good quality colostrum contains more than 50 g/l immunoglobulins (IgG). In 2012, Morrill et al. evaluated that only 30% of the colostrum produced in 67 US farms had these concentrations. FPT has 2 main causes: 1) calves did not receive enough good quality colostrum during the first hours of life, and/or 2) the colostrum contained low IgG concentration. The first cause is the most frequent one: calves receive colostrum too long after birth and the more time passes, the fewer globulins are absorbed (the absorption is null after 24 h of life). It is suggested to give to the newborn Holstein calves at least 3 kg (or the 5-10% of its body weight, Table 2) of good quality colostrum during the first 2 hours of life.

Table 1: Analytic composition of colostrum, transition milk, and proper milk for Holstein cows (Hammon et al., 1987).

Table 2: Estimated colostrum requirements for a 40 kg calf to reach the blood concentration of 10 g/l IgG 24 hours after birth.

The colostrum IgG content is easily detectable both in the laboratory and on-farm. Radial immunodiffusion (RID) is the gold standard laboratory analysis: it is highly accurate, but not usable in the field. The colostrometer is a useful tool to evaluate colostrum quality on-farm, as well as the first milking volume and the Brix refractometer. Using the colostrometer, good quality colostrum has a specific weight > 1050 mg/ml (equal to Ig > 50-140 mg/ml). At the refractometer, good quality colostrum has a Brix value > 22%. Thanks to the National Animal Health Monitoring System (NAHMS) of the USDA, in 2014 was published the situation for 76.7% of the US dairy farms (80.3% of total dairy cows in the US). An average of 12.7% of farmers considered the first milking volume as colostrum quality indicator, 11.4% (average data) used colostrometer, while refractometry was the less used method for the smaller farms (an average of only 0.3%) but reached 22.2% in the bigger ones. For the calf, the first 24 hours of life, there is a correlation (0.71) between the serum protein and the colostrum IgG. The refractometer is useful to determine herd risk factors for FPT measuring the total serum proteins. Results indicate no risk if more than 90% of calves have ≥ 5.2 g/dl or if 80% of calves have ≥ 5.5 g/dl total serum protein. NAHMS data revealed that in 2014 only 6.2% of the farms (the 35.3% of total calves) measured serum proteins (38.3% of the bigger farms, 53.9% of total calves).

As described, colostrum quality is extremely important for newborns’ protection against pathogens. Here below are reported several factors that modify the IgG colostrum content.

Breeding

Colostrum immunoglobulins content is strictly related to animal breeding. For example, Holstein cows have 5.6%, Guernsey 6.3%, Brown Swiss 6.6%, Ayrshire 8.1%, and Jersey 9.0%.

Age of the mother

The older the cow, the higher the colostrum quality and its immunoglobulins content.

Calving season

Heat stress during the last part of the pregnancy is associated with a low colostrum quality. It contains only a few immunoglobulins (IgG and IgA), but also a low percentage of protein, casein, lactoalbumin, fat, and lactose. These variations are due to lower feed intake and reduced blood flow to the udder under heat stress.

Dry period lenght

Immunoglobulins transfer to the milk begins about 5 weeks before parturition. If there is no dry period or if it lasts less than 21 days, the IgG colostrum content is very low; less than 40 days of dry period affects the colostrum volume but not its IgG content; 57.5 ± 11 days dry period does not interfere with colostrum IgG concentration.

Nutrition

Dietary protein, energy, and antioxidant molecules (such as vitamin E and selenium) can improve colostrum quality and immunoglobulins content, even if there are only a few related scientific research. Unbalanced amino acid dietary content negatively affects the immunoglobulin colostrum content. Table 3 reports the results of Burton experimentation: low protein intake caused low immunoglobulins colostrum concentration.

Table 3: Ingestion, heifers average daily gain (ADG) during the last 3 months of pregnancy, and immunoglobulins concentration in calves serum 24 hours after the first colostrum ingestion. Cows/heifers were fed low protein diets. From: Burton et al., 1984. Can. J. Anim. Sci. 64:185-186)

There are only a few references about the relationship between dietary energy and colostrum: the reduction of the available energy (70% of the requirements) reduced colostrum volume in ewes, but not its immunoglobulin content.

Among vitamins and trace elements, vitamin E and selenium are the most important and studied. About selenium, the NRC (2001) suggested 0.3 mg/kg of DM in the diet for dairy cows. However, this review is not updated and, nowadays, the soil selenium content is lower than in 2001 in most of the geographic areas, with the concrete risk of selenium dietary deficiency. The immune system is sensitive to antioxidant deficiency and the reduced selenium (ad selenoproteins, i.e. glutathione peroxidase) availability can affect IgG production. Dairy cows’ dry period diets are commonly supplemented with selenium (sodium selenite) up to 0.3 ppm of the DM. This inorganic form of selenium may be poorly absorbable and during the last few days before calving, there is a huge increase in selenium requirement. These two conditions can negatively affect colostrum quality: it is suggested to supplement animal diets with different and highly bioavailable sources of selenium.

Vitamin E is a powerful antioxidant that protects all cellular membranes (also the immune cells ones) against polyunsaturated lipids peroxidation due to free radicals. This vitamin is commonly supplemented in ruminant diets during the last period of pregnancy with higher dosages than the NRC 2001 suggestion to protect animals from oxidative stress and to improve immune system activity.

Conclusion

• Too late colostrum administration can affect calves health as well as their whole life performance;
• It is highly suggested to control colostrum and calves serum immunoglobulins content to determine if there is FPT risk;
• Good quality colostrum has > 1050 mg/ml specific weight and immunoglobulins concentration > 50 g/L;
• 10 g/L serum immunoglobulins concentration in calves during the first days of life indicates good passive immunity transfer through colostrum administration;
• Avoid heat stress and overcrowding during the last period of pregnancy;
• Include > 900 g/day metabolizable protein in the dry period diets for dairy cows;
• Include at least 1200 mg of rumen-protected vitamin E and 0.3 mg/kg of dry matter of highly bioavailable selenium.

For more information: marketing@vetagro.comOriginal article here: part #1 and #2.