Agriculture Reference
In-Depth Information
9.7
Proteins
Proteins in mammary secretions are often determined indirectly by quantification of total
nitrogen in the sample and then multiplying by an adjustment factor (such as N% × 6.38).
Therefore, milk protein is usually reported as total protein or crude protein based on the
nitrogen content of the sample. Mammary secretions contain other non-protein forms of
nitrogen such as free amino acids, peptides, amino-sugars, and nucleotides.
9.7.1
Stage of lactation
Concentrations of total protein in sow mammary secretions are highest at parturition
(Table 9.2). Similar protein concentrations are observed through 4 h after parturition, and
then decline by over 50% by 24 h. These changes in total protein concentrations mirror
the changes in immunoglobulin concentrations (discussed below). Total protein content
of milk typically is in the 5.0 to 6.5% range (Table 9.3).
9.7.2
Other factors
Milk protein content generally is not affected by diet. Fahmy (1972) did not find an effect
of sow breed on milk protein content, however, Shurson and Irvin (1992) did observe that
Landrace sows have higher protein percentage than Duroc sows at day 21 of lactation.
Zou et al. (1992) noted that Yorkshire sows have higher milk protein content at day 7
and day 21 than Meishan sows. However, comparison of milk from Meishan sows with
crossbred sows representing several breeds of European origin does not show significant
differences in milk protein content (Alston-Mills et al. , 2000) and milk protein content
from 50% Meishan sows was similar to that of Yorkshire sows on day 23 of lactation
(Farmer et al., 2001). Total protein concentrations of sow milk are not affected by parity
(Baas et al. , 1992; Goransson, 1990: Klobasa et al. , 1987).
9.7.3
Protein bound amino acids
Table 9.4 summarizes the average percentages of amino acids contained in the protein
fraction of colostrum and milk. Glutamate accounts for 17 to 22% and proline 10 to 12%
of the protein-bound amino acids. Branched chain amino acids (isoleucine, leucine and
valine) collectively account for another 18 to 19% of the protein bound amino acids.
9.7.4
Major milk proteins
Estimates of the proportion of casein in total protein of colostrum at or immediately after
parturition range from 9 to 32% (Brent et al. , 1973; Csapo et al. , 1996). The proportion
of total protein that is casein increases to about 30 to 45% by 24 h postpartum during
the period when immunoglobulin concentrations are significantly declining (Brent et
al. , 1973; Csapo et al. , 1996). Most reports of casein content in sow milk are generally
in the range of 50 to 55% of total protein throughout the remainder of lactation (Brent
et al. , 1973; Csapo et al. , 1996; Mahan et al. , 1971; Richert et al. , 1997), however, higher
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