Nutritional value of milk protein is a high protein, its amino acid content, the ratio is basically the ratio of the number of amino acids needed by the body similar. However, dairy cattle breeding in China has long been over-emphasized both milk yield and milk fat production performance at the expense of milk protein of breeding, therefore has a lower concentration of cow milk protein.With the deepening of research in recent years, it was found that milk contains large amounts of highly unsaturated fatty acids contribute to circulating levels of cholesterol and increased incidence of cardiovascular disease, while it also found that milk protein in addition to the new animal and human provide protein, amino acids, the digestion of some milk proteins and peptides produced by active substances also have specific physiological functions. Currently many countries the proportion of low-fat milk sales are increasing every year and milk prices in many countries in the world system of the value of milk protein in the first place regarded in some countries milk protein and milk fat price ratio of 1.5:1 or even up. Our standard of pasteurized milk (GD5408.1-1999) is also to milk protein (≥ 2.9%) as a key indicator included.Take into account the consumers and producers on dairy milk composition changes in demand, improve the yield of milk protein concentration and milk production will be the inevitable trend of development.
Milk protein secretion depends mainly on genetic factors, other nutrition, environmental factors are also important factors affecting milk protein secretion. From the nutritional point of view, to improve measures of milk protein in milk, mainly to meet the cow mammary gland under the premise of total nitrogen requirements for mammary synthesis of milk protein needed to provide the best amino acid pattern that is “ideal amino acid” mode. However, there are cows and other ruminant animals, the ideal of amino acids in monogastric animals significantly behind, and now most of the ideal amino acid of the cow milk protein are used based on amino acid composition, to control the rear of the digestive tract to reach protein cows the amount of amino acids.
A cow’s limited amino acids and ideal amino acid pattern
The concept of limiting amino acids in monogastric animals on the initial set up. Microbial protein production when the cows are required to limit or host on the amino acid increases, the host needs some amino acids appears limited. In recent years, limiting amino acid in dairy research has attracted attention. Limiting amino acids in lactating cows by stage and the impact of dietary components. Boisen et al (2000) studied the different diet of the first limiting amino acid, rapeseed meal and fish meal on the run, is the first limiting amino acid leucine; on the grain feed is the first limiting amino acid lysine; soybean Methionine is the first limiting amino acid; from barley, corn, rapeseed meal, fish meal and dry mixture of leather preparation is the first limiting amino acid lysine, is illustrated in table 1.
Table 1 cow feed with different protein sources in rumen the first limiting amino acids in g / d
Amount of microbial amino acid for the lack of barley seed meal of corn meal soybean meal mixed day Knight
Volume of a grain c egg b
Lysine (Lys) 99.781.817.9b17.9f17.9d26.621.528.717.9d
Methionine (Met) 31.425.46.08.713.16.0d8.010.57.5
Threonine (Thr) 68.458.69.816.921.516.717.516.113.5
Isoleucine (Ile) 66.664.12.517.920.920.615.315.412.6
Leucine (Leu) 113.185.128.034.874.033.428.0d28.0d28.9
Valine (Val) 75.968.57.425.632.220.620.418.917.0
Phenylalanine (Phe) 59.456.43.025.228.621.415.614.414.4
Note: a +3.2% to maintain milk yield of milk protein (protein body composition does not change)
b. full set of energy needed to reach the amount of microbial protein in duodenal microbial
c. Composition: 10% barley, maize 30%, Lesotho 30% seed meal, fish meal 20%, 10% hay
d. first limiting amino acid
Fraser et al (1991) using casein as the sole nitrogen source results show that lactating dairy cows, lysine, methionine and histidine were the first, second and third limiting amino acid; phenylalanine also potentially restrictive . Schwab et al (1992) with a dairy cow test that is the first limiting amino acid lysine, methionine peak in milk production for the second limiting amino acids, and these two kinds of amino acids in milk medium term play a coordinating role. King et al (1990) reported that the corn gluten feed, threonine, methionine and lysine for the first 3 limiting amino acids. Short. Current limiting amino acids in lactating dairy cows in the identification of most of the work that lysine and methionine is a metabolic protein (MP) first limiting amino acid, methionine and lysine for other than the identification of amino very restrictive Co. (2001 NRC). But in recent years, following the cow after methionine and lysine amino acids of other restrictive has become a hot spot, mainly arginine, histidine, phenylalanine and branched-chain amino acids (leucine, isoleucine acid and valine).
Cow ideal amino acid pattern monogastric animals are fundamentally different. Dietary protein or amino acid in the rumen after the time in the form of fundamental changes have taken place, from dietary protein into microbial protein. This protein is to reach the duodenum and rumen microbial protein from the protein composition of the mixture, so make an ideal protein to duodenal protein must balance the rumen microbial protein and protein pattern. Further to enter, to make the protein to reach breast milk proteins ideal for the synthesis of protein, must be based on different proteins or amino acids and dietary absorption and utilization of other nutrients to balance the level of circumstances. At present the ideal amino acid pattern of dairy cows is far behind the monogastric animals, the ideal amino acid for monogastric animals, models and more according to research purposes, choose a reference protein for the growth of animals, mostly muscle or carcass amino acid composition as the reference protein. Storm (1982) suggested that the milk protein or microbial protein amino acid model as the ideal amino acid pattern cows. By dietary factors as microbial protein and endogenous protein, and now most people to cow milk protein model of the ideal protein amino acid amino model. Specific milk protein amino acid pattern in Table 2.
Table 2 Amino acid profile of milk protein (in 1ys as 100%)
Egg + cystine tryptophan amino acid lysine threonine valine leucine isoleucine Phe + Tyrosine Histidine Arginine
Content 100 47.6 17.1 61 124.4 120.7 36.6 48.8 90.2 68.3
Boisen et al (2000) According to Table 1, designed for the 32% milk protein, milk yield was 30 kg / d + lactating cows to maintain the ideal protein to the duodenum, and to the model-based measurement, analyze the a 33 amino acid diets to reach the duodenum of restrictive pattern and extent of different amino acids in Table 3.
Table 3 cows ideal protein (AA/100g AA, in order to reach the duodenum acid ammonia stupid date)
Amino acid LysMetThrIleLeuValPhe
Ideal protein 6.72.05.24.88.65.34.4
Endogenous protein 6.004.43.76.35.52.6
Duodenal protein 6.95.91.45.68.16.45.0
Relative lack of degree 34681508905
Can see from Table 3, 33 diets in accordance with the lack of the extent that the first, second and third limiting amino acids were leucine, methionine, lysine.
Two limiting amino acids and ideal amino acid pattern of the cow milk protein secretion.
Limiting amino acids on cow milk protein secretion of research reports focused on lysine and methionine. Koch et al (1996) give the only protein of soybean meal as feed for 42 cows (18 primiparous, 24 by the middle) diet supplemented with ruminally protected methionine or methionine 10.9g 11.7 g, lysine 14.6 g, was found early milk protein yield were increased by 1.8%, 3.9%, beef production increased by 2.5%, 3.5%. Kampl et al (1996) made use of Simmental test showed that adding 15g / head d) the protection of methionine can increase milk yield 2.19 kg / d and milk protein by 0.27 percentage points. Currently the milk cow rumen methionine and lysine on the reaction of the literature has been reviewed (Rulquin and Verite, 1993; Schwab, 1995b, 1996a; Garthwaite, 1998). Overall Summary and recent reports of these (Piepenbink etc., 199; Nocek, etc., 1999; Sniffen, etc., 1999a, 1999b; Freeden, etc., 1999; Rode, etc., 1999; Wu, etc., 1999, Nichol, etc., 1998; Rulyn and Delasby, 1997) suggest that: ① milk protein on rumen supplementary methionine and lysine very sensitive, especially dairy cows after the peak; ② milk protein percent were not related ③ casein milk yield is affected by milk protein The main sections. Methionine and lysine in addition to rumen on milk protein synthesis, there are reports on the improvement of milk fat. After rumen infusion or added ruminally protected methionine or methionine plus lysine to improve the milk fat were observed in the case (Socha, etc., 1994b; Bremer, etc., 1997; Canale, etc., 1990; Xu, etc., 1998; Brunchwig and Augeers, 1994), but the exact mechanism is unclear.
Vanhatalo et al (1999) does not contain corn and protein supplement to feed cows in summer love from Finland abomasum infusion 6.5g / d of histidine, found that milk yield, milk protein were increased by 3.1%, 3.7%, but milk protein content has not changed. Mackle et al (1999) reported on alfalfa hay, corn and soybean product-based diet of early lactation Holstein cows abomasum infusion branch chain amino acids (leucine, isoleucine do acid were 55.5,39, 0.55,5 g / d), found that milk yield and milk composition did not change.
Further study the contents of the 3
In short, the ideal cow limiting amino acids and amino acids pattern of research has made great progress, but from the true ideal of proteins still have a long journey. To this end, many in-depth research needs to be improved. Such as lysine and methionine cow other than limiting amino acid research; of different limiting amino acids on milk protein secretion and gene expression; limiting amino acids lysine and methionine increased serum concentration of the mechanism of milk fat; small intestine of different amino acid uptake, utilization and utilization and turnover mechanism; breast tissue ideal amino acid pattern of milk; cows of different varieties and physiological state of amino acid requirements and ideal amino acid pattern of the study. After completion of these studies, according to the specific needs of amino acids under physiological models for different amino acids in dietary protein restriction and Rumen volume, determine the limiting amino acids, amino acids of the restrictive regulation, and ultimately achieving the ideal amino acid pattern, so that optimal level of milk protein secretion.