Part I - Instructor's notes:

1. Colostum is not milk. As opposed to the definition of colostrum presented in the reading, calf experts have recently revised its definition as the mammary gland secretion collected at the first milking after calving.


2. Intestinal “openings” really refers to the passage of macro-molecules through the intestinal epithelial cells.


3. By the way, if the concentration of IgG in colostrum averages 59.8 mg/ml (or 0.0598 g/ml) and colostrum specific gravity is 1.05, (i.e., 1.05 g/ml), then colostrum contains 0.0598 g of IgG per 1.05 g of colostrum; or 0.0569 g per g; or 5.69 g per 100 g. In other word colostrum contains 5.7% IgG.


4. Notice that there were some discrepancies between the “extension publication (Ch 3) and the NRC, as to the amount of starter consumption recommended to wean a calf successfully.


5. Contrarily to the statement at the bottom of page 26, a calf is NOT born a ruminant. Chewing activity in a calf begins when the rumen has developed to a point at with the ingestion of solid feeds contributes to nutrient supply.


6. Average numbers are “dangerous” to use. The study of Levieux and Ollier (1999) showed the colostrum IgG in 60 Holstein cows averaged 59.8 mg/ml, but the standard deviation was 28.5 mg/dl. Large variations were recorded for IgG concentrations (15.3–176.2 mg/ml) and yields (0.2–925 g).

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Part II - Understanding Variation (Importance of understanding a standard deviation):

The three figures below have been constructed to describe expected variation in concentration of IgG in colostrum based on the research of Levieux and Ollier (1999) [D. Levieux and A. Ollier (1999). Bovine immunoglobulin G, [beta]-lactoglobulin, [alpha]-lactalbumin and serum albumin in colostrum and milk during the early post partum period. Journal of Dairy Research, 66:421-430] who reported an average IgG concentration of 59.8 mg/ml and a standard deviation of 28.5 mg/ml. The frequency distribution indicates the probability of occurrence of any particular IgG concentration (for a single observation), whereas the cumulative frequency graph provides the probability that IgG concentration is above / below any particular value. The bottom graph shows the range of values expected for 68% (means ± 1 standard deviation) and 95% (means ± 2 standard deviations) of the colostrum “population”. In the graphs below, the means is 59.8 mg/ml but the standard deviation was either 28.5 mg/ml (solid lines) (i.e., a standard deviation about half the size of the mean), but for purpose of comparison, the frequencies and the ranges were also calculated assuming a much narrower standard deviation: 5.98 mg/ml (one tenth of the value of the mean). Using the information presented in the graphs above, answer the following questions

Question 1: What is the probability that a colostrum sample contain more than the average of 59.8 mg/ml of IgG?

50%

Question 2: What is the probability that a colostrum sample contain less than 25 mg/ml of IgG?

About 10%

Question 3: What is the probability that a colostrum sample contain more than 100 mg/ml of IgG?

About 10%

Question 4: Compare the probability for a colostral IgG test to return a value of 59.8 (say 60) mg/ml (i.e., the mean) when the standard deviation is either 28.5 mg/dl (about half the mean) or 5.98 mg/ml (i.e., about one tenth of the mean)? Explain your finding.

As the standard deviation decreases from 28.5 mg/ml to 5.98 mg/ml, the probability of “landing” on the mean for any particular sample increases from 0.015 (1.5%) to 0.065 (6.5%).

Question 5: Compare the probabilities of finding a colostrum with less than 40 mg/ml if the standard deviation is 5.98 mg/ml versus 28.5 mg/ml)

With a standard deviation of 5.98 mg/ml there is almost no chance whatsoever to find a colostrum with less than 40 mg/ml of IgG, however with a standard deviation of 28.5 mg/ml, the probability is about 25%.

Question 6: Given the standard deviation of 28.5 mg/ml, what the expected range that will include 68% of the samples?

68% of the population is included in the range defined by the mean ± 1 standard deviation. Thus, the lower limit is: 59.8 – 28.5 = 31.3 mg/ml and the higher limit is 59.8 + 28.5 = 88.3 mg/ml. These values can be observed in the bottom graph and in the cumulative graph for the cumulative probability of 0.16 (16%) [i.e., 50 - (68/2)] and the cumulative probability of 0.84 (84%) [i.e., 50 + (68/2)].