GB2297485A - Amino acid compositions - Google Patents

Abstract

An amino acid composition suitable for adminstration to an animal and being capable of altering the milk protein yield of that animal comprising at least three (preferably four or all five) amino acids selected from the Group I essential amino acids: methionine, tyrosine, phenylalanine, histidine or tryptophan, and being in a form that when administered to the animal enables it to produce milk having an increased protein concentration. Compositions may further include four or more (preferably five or all six) amino acids selected from the Group II essential amino acids: threonine, valine, isoleucine, leucine, lysine or arginine. Preferably the composition is substantially free of non-essential amino acids, and is protected against metabolism in the gut or liver, particulalarly the rumen.

Description

AMINO ACID COMPOSITIONS TECHNICAL FIELD The present invention relates to amino acid compositions and methods of using them for controlling milk protein synthesis in animals for the purpose of increasing protein levels in milk. The invention further relates to milk produced by such methods and to dairy products such as cheese derived therefrom.

BACKGROUND ART The control of milk protein synthesis has long been of interest to dairy scientists and the dairy industry. In particular, a reliable method for increasing the concentration of protein in milk is of interest to milk manufacturers, especially with respect to cheese making, and to milk producers as a way of increasing the value of milk sales in a climate of strict volume quota management.

Previous attempts to manipulate milk protein content have been largely confined to feeding experiments to examine the effect of specific protein or energy supplements.

One useful investigative tool has been the infusion of the major milk protein, casein, into the abomasum of dairy cows. This technique supplies nutrients directly to the postruminal part of the alimentary tract, and is therefore similar to supplying rumen bypass nutrients in the diet. However, the efficiency with which casein is used by the dairy cow for milk protein synthesis by this route of administration rarely exceeds 20% (output/input), even though it should in theory be the ideal precursor.

Other proteins when infused into the abomasum have even lower efficiency, and dietary proteins, even ones which have been protected against ruminal degradation, only increase milk protein output by approximately 10% of the input. Unfortunately the increases in milk protein output tend to be associated with increased milk yield, with the concentration of protein in the milk unchanged.

Rogers et al (1989) J. Dairy Sci. l, pl800-1817 reported that dietary administration of rumen protected L-lysine and DL -methionine to cows in combination with a variety of feeds results in varying effect on protein concentration in milk. Notably supplementation of soybean meal diets did not result in increases of protein content, whereas supplemel'ltion of a corn gluten meal and urea diet did.

In a different approach, amino acids were infused by an intravascular route (Fisher (1972) Can. J. Animal. Sci. 5X p377). These workers showed a significant increase in milk protein yield in response to methionine, but importantly milk protein concentration was not increased by a statistically significant amount.

In a study similar to the current work carried out in lactating goats (Champredon and Pion (1979) Ann. Rech. Vet. 1Q p379), ten essential amino acids were infused for 6 to 7 days in early lactation without producing any increases in milk yield or milk protein output.

Similarly when a mixture of five essential amino acids was infused close arterially to the mammary gland (Metcalf et al (1991) J. Dairy Sci. 74 p3412) there was no significant effect on milk protein concentration, whilst milk protein yield increased, albeit at a non-significant level.

One further report of intravascular infusion (Metcalf et al (1994) J.

Dairy Sci. 12 Supplement 934) indicated that milk yield was increased by methionine infusion in a close arterial situation, but milk protein concentration was not significantly altered.

Thus it can be seen that no reliable, widely applicable, methodology has been published for increasing milk protein concentration in a predictable manner using amino acids or protein dietary supplements.

In particular a methodology for increasing milk protein concentration based around the efficient conversion of dietary supplements would be a major contribution to the art.

THE INVENTION The present inventors have carried out a number of investigations into this field in order to address some of the issues unresolved in the published literature. The inventors found that the dietary supplementation of protein increases arterial concentrations of essential amino acids (EAA) but not non-essential amino acids (NEAA).

They have further investigated whether or not the infusion of the EAA found in milk protein produces a similar effect to the infusion of total amino acids (TAA) from milk protein ie. EAA and NEAA together.

By 'milk protein' is meant the average protein composition of milk i.e. both casein and other proteins present eg. whey proteins.

In order to remove the effects of digestion and absorption of amino acids in their transfer into the milk protein product, the route of administration of the amino acids they used was primarily intravascular, although other rumen-bypass techniques were also used.

Using such techniques they have now found that milk protein concentration can be stimulated rapidly on a variety of protein diets by intravascular infusion of a mixture of EAA similar in composition to those from which milk protein is partly comprised. The magnitude of this response is not improved, as may be expected, from the inclusion with the EAA of the corresponding NEAA found in milk protein, but indeed appears to be reduced.

The efficiency with which the EAAs are converted into milk protein is high in comparison with direct dietary supplementation, and this may be related to the route of administration as well as the composition of the supplemental amino acid delivered to the mammary gland.

In a first aspect of the present invention there is provided an amino acid composition suitable for adminstration to an animal and being capable of altering the milk protein yield of that animal characterised in that said composition comprises at least three amino acids selected from the Group I essential amino acids and is in a form that when administered to the animal enables it to produce milk having an increased protein concentration.

By 'animal' is meant any animal capable of secreting milk.

Preferably the animal is a bovine female.

By 'Group I amino acids' is meant methionine, tyrosine, phenylalanine, histidine and tryptophan (see Table 1); As demonstrated in the examples below, the compositions of the present invention have utility when used with animals at various stages of lactation and having a wide variety of milk yields and dietary protein inputs. However the effect on protein milk protein concentration is conveniently demonstrated by those of ordinary skill in the art, without undue burden, using a multiparous, moderate yielding cow in mid-lactation fed at its approximate dietary requirement for protein (eg. within +/- 10%) in accordance with the AFRC Metabolisable Protein Scheme (1992) in Technical Committee on Responses to Nutrients Report 9 "Nutrient Requirements of Ruminant Animals"; Protein Nutrition Abstracts and Reviews Series 8: Livestock Feeds & Feeding Vol 62, pp 787-835. The concentration increase can then be measured being with respect to an untreated cow.

TABLE 1: L-amino acid composition (g) of 400 g milk protein (TAA) Group I Group II NEAA Methionine 10.7 Threonine 16.5 Glycine 6.5 Tyrosine 0.4 Valine 24.9 Alanine 12.4 Phenylalanine 36.7 Isoleucine 22.4 Proline 37.6 Histidine 10.2 Leucine 36.7 Serine 23.7 Tryptophan 5.5 Lysine 31.0 Cysteine 2.9 Arginine 12.8 Asparagine 17.6 Aspartate 13.0 Glutamine 35.1 Glutamate 43.4 Prerably at least four Group I amino acids are used, and most preferably all five.The Group I essential amino acids may be the only amino acids present in the composition. Preferably however the compositions comprise the Group I essential amino acids together with at least four of the six Group II essential amino acids.

By 'Group II essential amino acids, is meant threonine, valine, isoleucine, leucine, lysine and arginine (see Table 1).

Preferably the compositions are substantially free of NEAA (i.e NEAA constitute less than 10% of the amino acid content of the compositions) and most preferably NEAA will not be present at all.

In particular compositions containing NEAA in additionn to the EAA will not only be more expensive to produce, but may also be less efficient in increasing the protein concentration of the milk as is demonstrated in the Examples hereinafter.

Indeed it may be desirable to limit the NEAA available to the animal from other sources eg. dietary protein, in order to enhance the efficiency of the EAA based compositions and methods of the present invention. For instance the animal may be fed at eg. between 80 and 95% of its approximate protein requirement in accordance with the AFRC scheme (1992, supra). Feeding at decreased levels, in conjunction with administering the compositions of the present invention, will not only reduce the cost of protein feed, but will also reduce the levels of nitrogen waste entering the environment as the efficiency of conversion into milk protein is increased.

In the light of the findings of the present inventors, the results of the prior art studies may be interpreted as follows: The lack of a consistent improvement in milk protein concentrations using the methods of Rogers et al (1989) is presumably attributable to the nature of the feed consumed by the animals and/or the lack of more than one Group I or Group II amino acid in the supplement. As demonstrated below, the present inventors have demonstrated such an improvement in cows fed on a wide variety of diets, using a variety of administration methods.

Fisher (1972) used only one Group I amino acid (met), levels of which may not have been a limiting with respect to milk protein synthesis.

The lack of response seen in the Champredon and Pion (1979) study may perhaps be seen to be attributable to the decrease in feed intake during infusion, which was reported by the authors. In the present invention it has been found that there was no difference in feed intake between the covariate (i.e. control) and infusion periods.

Metcalf et al (1991) used two Group I (met, phe) and three Group II (lys, leu, thr) amino acids. Again levels of these amino acids may not have been limiting. Also the use of close arterial infusion straight into the mammary gland, rather than a systemic infusion, may have precluded any hormonally induced effects. These considerations apply also to Metcalf (1994).

The amino acids compositions of the present invention may be provided in a precursor form that protects them against metabolism in the gut and/or liver, and/or that enhances their absorption from the gut. In ruminant species it is particularly important to prevent excessive degradation of amino acids in the rumen, thus any form that allows protected passage through the rumen and while allowing free uptake of acid in downstream areas of the gut will be preferred. One such suitable form employs a proteinaceous coating or binder as a carrier for the amino acids wherein the protein has been treated to protect it from digestion in the rumen by, eg., treating it with aldehydes such as formaldehyde (see eg. GB 1099583 and GB 11372214). Examples of amino acids in precursor form are also given in Rogers et al (1989) discussed above.

It will be realised that the amino acids may be provided in the form of peptides which themselves can be embedded in the proteinaceous coat and only split into amino acid components on acid hydrolysis within the intestine.

It may be possible to administer the amino acids in the form of protein itself treateu with a protective agent such as formaldehyde.

Macrae et al (1972) Br. J. Nutr. 21 p39 reported the increased uptake of amino acids in sheep using casein treated with formalin.

Other suitable forms include encapsulation in fats or oils having melting points above that of the rumen but not the stomach. In a still further option the amino acids are provided in a form suitable for parenteral administration, thus allowing their administration via a route avoiding the rumen altogether.

The preferred ratio of the amino acids, or their precursors such as peptides, in the composition is that such that their ratio in milk protein is maintained, that being approximately 10.7: 0.4: 36.7: 10.2: 5.5 for methionine: tyrosine: phenylalanine: histidine: tryptophan Group I amino acids optionally with :16.5: 24.9: 22.4: 36.7: 31.0: 12.8 of threonine: valine: isoleucine: leucine: lysine: arginine Group II amino acids.

Preferably the amino acid compositions of the invention comprise a physiologically acceptable carrier, preferably a physiological saline.

A second aspect of the present invention provides a method of producing milk of increased protein content comprising administering a composition of the invention to an animal fed on feed material over a feed period and subsequently collecting the milk produced corresponding to that feed period; i.e. milk produced by the animal from the nutrients given in that period.

Preferably the method of the invention comprises administering the composition intravenously, preferably via a catheter.

Products produced by the second aspect of the invention form the third aspect of the present invention.

The compositions, methods and products of the present invention will now be described by way of example only with reference to the non-limiting Examples below. Further embodiments of the invention will occur to those skilled in the art in the light of these.

WXAMPIW Example 1: Mid lactation cows: modest protein diet: intravascular (jugular) TAA and EAA METHOD: Four mature Holstein/Friesian cows in mid lactation were prepared with simple jugular vein catheters and infused at a constant rate with physiological saline for four days as a covariate control period. immediately followed by five days of infusion at the same rate of a TAA mixture representing all amino acids found in milk protein (see Table 1) or the alternative treatment where only the EAA were provided. Each amino acid was infused to provide its equivalent in 400g of milk protein in 24 hours. Cows were milked as usual in a 16:8 h split and samples taken of milk at each milking.Cows were fed every hour with grass silage (40X of Dry Matter Intake - DMI) and a barley based concentrate (60% of DMI). The overall diet was relatively low in protein content providing 2.0kg crude protein (CP)/day in an intake of 16.5 kg dry matter (DM)/day. The metabolisable energy (ME) intake of these cows was estimated at 192 MJ/day, with feed intake fixed at a level to ensure minimum feed refusals at 95X of ad libitum intake. The experimental design was a simple cross-over where treatment results could be compared after covariate adjustment by analysis of variance. Effects of infusion were determined using a paired t-test to compare the amino acid infusion period with the covariate period.

Average milk production for the covariate periods was 23.8 and 22.4 kg/d for TAA and EAA respectively. Both infusions caused small (P > 0.05) increases in milk production, equivalent to 0.63 and 1.08 kg/d for TAA and EAA respectively. Changes in fat yield were RESULTS: The results are shown in Table 2: TABLE 2. Comparison of milk production, component output and composition in response to amino acid into the jugular vein.

significance tested by paired t-test TAA Control Infused SEDI Control Infused SED Milk Prodn. 23.8 24.4 0.33 22.4 23.5 0.57 (kg/d) Composition (g/kg) Fat 46.0 43.5 1.09 46.9 46.5 0.50 Protein 32.4 35.0** 0.34 32.5 36.9* 1.02 Lactose 48.4 47.2* 0.23 48.2 46.5 0.57 Urea (mg/d) 256 241 17.5 209 231 30.5 Component Output (g/d) Fat 1066 1046 34.0 1037 1078 22.0 Protein 765 852* 16.3 726 869* 42.9 Lactose 1156 1162 16.4 1084 1094 33.8 1 SE of difference * P < 0.05 ** P < O.01 inconsistent showing a 4% improvement on EAA but a 2% reduction on TAA. On the latter treatment, fat content declined by 2.5 g/kg (P > 0.05) but no effect was seen for treatment with BAA.

Milk protein yield was substantially improved on both treatments (P < 0.05) and it was estimated that 74 and 71% (TAA and EAA respectively) of this increase was due to the increased milk protein concentrations rather than increased milk production.

Infusion of TAA resulted in an increase of milk protein concentration from 32.4 to 35 g/kg (P < 0.01) when compared to the covariate period while the increase in milk protein concentration in response to EAA (32.5 to 36.9 g/kg) was greater, although it only reached the lower level of statistical significance (P < 0.05).

The sustainable increase in milk protein concentration (4.4 g/kg) in a predictable fashion, in a short time span (12 h after commencement of administration) is the first indication that protein concentration can r. manipulated in this way, and to such a high degree. The results may have significant implications for the dairy industry.

The increase in output of milk protein as a proportion of amino acid infused (i.e. a measure of efficiency of conversion) was similar for the intravenous TAA infusion (87/400 = 22%) to that observed with published experiments involving abomasal casein infusion. Using this technique, Clark (1975) J. Dairy Sci 2 p1178 found efficiency values between 10 and 15% for casein. In another published experiment concerned with establishing which amino acids were limiting when fed to cattle on a very low protein diet using intraabomasal infusion, Schwab et al (1976) J. Dairy Sci. 59 pl256 demonstrated 22% efficiency for casein.

Example 2: Earlv lactation cows: modest protein diet: intravascular (mesenteric) TM. NEAA and EAA METHOD: Six multiparous Friesian-Hostein cows were catheterized in early lactation for measurements of nutrient flux across splanchnic tissues (see method of Reynolds et al (1988) 71 p1803), such as to allow infusion of mixtures of amino acids into a mesenteric vein to mimic increased adsorption from the gut via the portal vein and prior to liver metabolism, rather than peripherally as in Example 1. The experiment began at week 10 to 16 postpartum and throughout cows were fed 95X of a libitum dry matter intake at peak lactation to ensure minimal feed refusal.A 40:60 dry matter basis mixture of grass silage: concentrate contained approximately 11% crude protein, showing the cows to be marginally deficient in protein.

Treatments were three day mesenteric vein infusion of saline followed immediately by 3 day mesenteric vein infusion of mixtures of amino acids based on composition of milk protein as in Experiment 1 (Table 1) except that the amount infused was increased to 600g/d for the total mixture (TAA), and the non-essential (NEAA) and essential (EAA) amino acids in the total mixture were both infused as separate treatments (284 and 316 g amino acid/day respectively). Cows were milked in an 16:8 split and milk samples were obtained at each milking during infusions. Two 3X3 Latin Squares with 3 week periods were used in allocating treatments and cows were sampled during the last week of each period.Data from saline and treatment periods and their difference were analyzed for treatment effects using analysis of variance and a model testing effects of square, cow within square, period and treatment against residual error mean squares. When treatment effects were significant, paired t-tests were used to determine if differences between saline and respective treatment periods were significantly different from zero.

RESULTS: Effects of amino acid infusions on milk composition, yield and constituent yield are shown in Table 3.

TABLE 3: Milk yield, composition and constituent yield in lactating cows receiving 3 day mesenteric vein infusions of saline or amino acids equal to 600g/d milk protein (T600) or the essential (E600) or non-essential (N600) amino acids in the total mixture alone Infusion E600 N600 T600 SEM p, Milk yield kg/d Saline 22.0 21.5 21.8 0.5 0.790 Treatment 22.7 20.5 24.7 0.5 0.002 Difference 0.73 -1.0* 2.77"' 0.48 0.005 Table 3 continued.

Infusion E600 N600 T600 SEM P > Protein g/kg Saline 32.4 32.6 32.4 0.4 0.948 Treatment 36.9 31.5 36.2 0.4 0.001 Difference 4.49"' -0.95** 3.46""" 0.38 0.001 Protein yield kg/d Saline 0.709 0.696 0.706 0.020 0.904 Treatment 0.834 0.645 0.902 0.019 0.001 Difference 0.126"' 0.051" 0.183""" 0.021 0.001 Fat g/kg Saline 46.7 48.4 51.0 1.7 0.525 Treatment 47.9 52.2 49.5 2.2 0.424 Difference -0.87 3.85 -0.32 3.12 0.546 Fat yield kg/d Saline 1.06 1.04 1.11 0.03 0.401 Treatment 1.08 1.06 1.23 0.04 0.080 Difference 0.02 0.03 0.14 0.05 0.255 Lactose g/kg Saline 48.8 48.6 48.7 0.3 0.841 Treatment 46.3 49.6 47.2 0.3 0.001 Difference -2.51*** 1.02""" -1.67*** 0.28 0.001 Lactose kg/d Saline 1.08 1.05 1.05 0.03 0.792 Treatment 1.05 1.02 1.17 0.03 0.020 Difference -0.02 -0.03 0.10" 0.03 0.035 tProbability corresponding to the hypothesis of no effect of treatment * Different from zero P < 0.10 ** Different from zero P < 0.05 ***Different from zero P < 0.01 Infusion with TAA increased daily milk yield (P < 0.001) (2.8kg) and fat corrected milk yield (3.2kg; data not shown) and infusion of NEAA decreased daily milk yield (P < 0.08) (-lkg), but not corrected fat milk yield. Infusion of BAA had no effect on milk or fat corrected milk yield.

Milk protein concentration and yield were increased (P < 0.001) by both TAA and EAA infusions and decreased (P < 0.05) by NEAA infusion. The recovery of infused amino acids as increased milk protein yield was 20% and 31% for EAA and TAA respectively. The greater recovery of amino acids for TAA is due to the increase in volume yield as the increase in milk protein concentration was greater when BAA were infused. While data presented in Table 3 are based on means of observations for 6 individual milkings per period, in the present and previous study the response of milk protein increase in milk protein concentration occurred within the 16 hours after beginning EAA or TAA infusions.

There were no treatment effects on milk fat concentration or yield.

Milk lactose concentration was decreased (P < 0;001) by TAA and EAA infusions and increased (P < 0.001) by infusion of NEAA. Milk lactose yield was increased (P < 0.05) by TAA infusion but not affected by BAA and NEAA when infused singly. Increased levels of milk lactose may increase the volume yield of milk thereby leading to a reduction in the concentration of milk protein.

In addition, as milk lactose is surplus to the needs of most milk producers, the effect on lactose levels caused by the compositions of the present invention may provide a further benefit of their use.

The observations above confirm the results from Example 1 where increased vascular availability of a mixture of EAA of the same composition as milk protein increased milk protein concentration and yield.

In addition, data from the present example suggests that, in cows fed at or slightly below requirement for protein, increased availability of NEAA alone is more detrimental than beneficial to milk protein production. This may be attributable in part to costs of disposal of those amino acids. However, when supplied with EAA the presence of NEAA markedly increased total and fat corrected milk yield, suggesting that the presence of BAA, in correct proportions, is required for NEAA to be utilized for milk production.

Example t: Earlv lactation cows: high protein diet: intravascular (Jugularl EAA METHOD: Five Holstein/Friesian cows in early lactation were fed dried lucerne (170 g CP/kg DM): high protein concentrate (190 g CP/ kg DM) in a 1:1 ratio and during weeks 7-10 of lactation received jugular infusions of saline (3 days) followed by an infusion of EAA equivalent to the EAA contained in 600 g milk protein (i.e. 312 g EAA/day) for a further 3 days. All animals were milked twice daily and milk samples were taken at each milking to assess milk protein, fat and lactose contents and yields.

RESULTS: The results are shown in Table 4. The results indicate that milk yield was unaffected by the EAA infusion (mean 31.7 kg/d) although both the protein and lactose content were significantly altered.

Milk protein concentration increased by 2g/kg milk [P < 0.001] and this contributed to an increased net synthesis of milk protein of 83g/d [P < 0.001]. Milk lactose content was reduced by 0.7g/kg [P < 0.01].

Milk fat content was non-significantly increased.

Thus, although the increase in milk protein concentration and decrease in lactose were less than those seen with later lactation cows receiving lower levels of dietary protein (Example 1) the changes were still significant and of considerable potential importance to the dairy industry.

TABLE 4. Comparison of milk production, component output and composition in response to amino acid into the jugular vein.

significance tested by paired t-test Pooled Saline E600 SEM Milk Prodn. 31.4 31.9 1.3 (kg/d) Composition (g/kg) Fat 39.1 39.0 1.0 Protein 31.0 33.0 1.7 Lactose 49.5 48.8 0.4 Component Output (kg/d) Fat 1.170 1.242 0.080 Protein 0.968 1.051 0.045 Lactose 1.557 1.557 0.072 Example 4: Early lactation high yielding cow8: high protein diet: abomasal casein and EAA METHOD: Six high yielding cows in early lactation were fed a diet comprising dried lucerne and grass silage (3:1) and a soya based concentrate containing 190g CP/kg DM, with a forage:concentrate ratio of 1:1. The treatments comprised an intra-abomasal infusion of either casein (800g/d = Treatment C800) or the EAA present in 800g milk protein (416g/d = Treatment E800).All treatments were for 6 days and were preceded by a water infusion control (4 days). The cows were milked twice daily and milk samples were taken for analysis of milk fat, protein and lactose contents.

RESULTS: The results are presented in Table 5.

TABLE 5. Effect of intra-abomasal infusions of casein/EAA on milk production and composition in high yielding dairy cows in early lactation C800 E800 Control Infused Control Infused SEM Milk Prodn. 35.8 36.0 38.8 38.3 0.2 (kg/d) Composition (g/kg) Fat 35.1 35.0 34.6 32.7 0.1 Protein 32.4 33.2 29.4 30.4 0.9 Lactose 48.7 48.5 48.8 48.7 0.1 Component Output (kg/d) Fat 1.238 1.255 1.330 1.247 0.056 Protein 1.134 1.171 1.136 1.163 0.007 Lactose 1.739 1.739 1.898 1.866 0.007 As can be seen, neither infusion had an effect on milk yield, which averaged 37.2 kg/d for all cows on all treatments. Treatment C800 led to a significant [P < 0.001] increase in milk protein content (+0.8 g/kg) with neither milk lactose nor fat content being affected.

Similarly, the E800 treatment stimulated milk protein content (+1.0 g/kg. P < 0.001), with lactose content unaffected. In contrast to C800, the fat content was significantly reduced (-1.9 g/kg). There was also a small but significant increase in milk protein yield for E800.

Thus it appears that both casein and EAA administered intraabomasally can increase milk protein content, although the magnitude of the responses was less than that observed with EAA administered intravascularly. The response in milk protein output was low for both infusions, especially when compared with the respective inputs of protein/amino acids - this would seem to indicate considerable catabolism within gut tissues. It also appears that neither casein nor its constituent EAA in the appropriate ratios lead to a reduction in lactose content when administered by intraabomasal infusion. In this regard, the provision of extra glucose from the catabolism of amino acids may have maintained the levels of lactose synthesis.

Example 5: Mid lactation cows: medium protein diet: duodenal EAA at two concentrations METHOD: The duodenum is the part of the alimentary tract immediately posterior to the abomasum, and thus intraduodenal infusion is similar to intraabomasal infusion. Four cows were fitted with permanent duodenal cannulae to permit the infusion of amino acids. The treatments comprised an infusion of either the EAA present in 600g/d milk protein (312g/d = Treatment E600) or 900g/d milk protein (468g/d = Treatment E900). All treatments were for 7 days and were preceded by a water infusion control (7 days). The cows were fed a diet comprising grass silage and a medium protein concentrate (40:60) and were milked twice daily and milk samples were taken for analysis of fat, protein and lactose contents.

RESULTS: The results are shown in Table 6. As can be seen the average milk yield was 24.4.kg/d, with the mean response to the EAA infusions being +0.75 kg/d tP < O.O1]. On both treatments, milk protein content was increased non-significantly (E600, +1.1 g/kg; E900, +1.9 g/kg, P < 0.001) as was milk protein yield (86 and 74 g/d respectively, P < 0.001). Milk lactose contents were reduced by both treatments (mean -1.25 g/kg, P < 0.05), but overall lactose yields were largely unaffected because of the increase in milk yield.

The study confirmed that significant increases in milk protein content in response to intraduodenal infusions of BAA, similar to those obeserved with intravascular EAA infusions, were only achieved TABLE 6. Effect of intraduodenal infusions of EAA on milk production and composition in dairy cows in mid lactation E600 E900 Control Infused Control Infused SEM Milk Prodn. 23.7 24.6 24.4 25.0 0.2 (kg/d) Composition (g/kg) Fat 43.0 47.6 45.2 45.3 0.2 Protein 36.0 37.1 35.2 37.1 0.2 Lactose 47.9 46.4 47.6 46.6 0.04 Component Output (kg/d) Fat 1.018 1.178 1.080 1.134 0.035 Protein 0.833 0.919 0.857 0.931 0.012 Lactose 1.105 1.143 1.161 1.170 0.018 when the EAA were supplied at the highest level (E900). The reductions in milk lactose concentrations observed with intavascular EAA were also demonstrated to be possible using the intraduodenal route.

Example 6: Mid lactation cows: low and high protein diet: intravascular (jugular) EAA METHOD: Five cow in mid lactation received either a low protein (LP) diet or.a high protein (HP) protein concentrate (110 or 190 CP/kg DM respectively) and chopped lucerne in a 1:1 ratio. The treatments comprised a jugular infusion of the EAA present in 600g/d milk protein (312g/d). All treatments were for 3 days and were preceded by a saline infusion covariate period (3 days). The cows were milked twice daily and milk samples were taken for analysis of milk fat, protein and lactose contents.

RESULTS: The results are shown in Table 7: TABLE 7. Effect of intrajugular infusions of EAA on milk production and composition in dairy cows in mid lactation on low or high protein diets LP HP Control In fused Control Infused Milk Prodn. 22.9 23.6 24.1 24.6 (kg/d) Composition (g/kg) Fat 42.3 43.8 44.4 42.5 Protein 36.7 39.1 36.8 38.0 Lactose 48.6 47.7 48.0 47.4 Component Output (kg/d) Fat 0. 972 1.035 1.071 1.049 Protein 0.841 0.921 0.887 0.936 Lactose 1.113 1.126 1.157 1.166 As can be seen the mean milk yields were 23.3 and 24.4 kg/d for LP and HP respectively with no marked change in response to the amino acid infusions. With LP, the milk protein content was increased from 36.7 g/kg (already a high value) to 39.1 g/kg, the increase for HP being around half of this value (36.8 to 38.0 g/kg).This led to milk protein yield responses of 80 and 49 g/d respectively. This equates to partial efficiencies of 26% and 16% conversion of EAA to milk protein. Lactose concentrations were reduced, by 0.9 and 0.6 g/kg for LP and HP respectively, whilst lactose yields were unaffected by the EAA treatments.

This study confirmed that the previously noted responses in milk protein and lactose content can be achieved with mid lactation cows on both high and low protein diets, although the reposnse was greater in the low protein condition. The increase in milk protein concentration was observed notwithstanding already high control levels.

Example 7: Mid lactation high yielding cows: low and high protein diet: abomasal EM METHOD: Four high yielding cows in mid lactation received either a low protein (LP) diet or a high protein (HP) protein concentrate (110 or 200 CP/kg DM respectively) and forage in a 1:1 ratio. The forage component comprised 3:1 (on a dry matter basis) dried lucerne:grass silage. The treatments comprised intraabomasal infusions of the EAA present in 800g/d milk protein (416g/d). All treatments were for 6 days and were preceded by a water infusion covariate period (4 days).

The cows were milked twice daily and milk samples were taken for analysis of milk fat, protein and lactose contents.

RESULTS: The results are shown in Table 8. As can be seen the mean milk yields were not affected by the treaments (mean 30.8 kg/d).

Equally the level of crude protein in the concentrate did not affect the milk protein content (LP, 34.8; HP, 33.6 g/kg). A significant response to EAA was observed (mean controls 33.9; infused 34.6 g/kg; P < 0.01) although this was smaller than was observed withintravascular infusions. Milk fat contents were unaffected by dietary protein content or EAA infusion. Lactose concentrations were significantly [P < 0.05] reduced by EAA infusions (controls 48.4; infused 47.6 g/kg).

Both diets showed significant [P < 0.01] responses in milk protein yield to EAA infusion (controls 1.022; infused 1.064 kg/d) with the size of the response being largely independent of dietary protein level. Fat and lactose yields were unaffected by the EAA treatments, TABLE 8. Effect of intraabomasal infusions of EAA on milk production and composition in dairy cows in mid lactation on low and high protein diets LP HP Control Infused Control Infused SEM Milk Prodn. 29.7 30.0 31.5 32.0 0.3 (kg/d) Composition (g/kg) Fat 38.1 38.4 38.9 37.7 0.4 Protein 34.5 35.1 33.1 34.0 0.2 Lactose 48.0 47.3 48.8 47.9 0.3 Component Output (kg/d) Fat 1.115 1.141 1.219 1.203 0.01 Protein 1.011 1.048 1.032 1.080 0.01 Lactose 1.424 1.423 1.531 1.527 0.01 though both were marginally higher for the high protein diets.

This study confirmed that the previously noted EAA induced responses in milk protein and lactose content can be achieved with mid lactation cows on both high and low protein diets using an intragastric method although the magnitude of the overall response was less than that observed using intravascular BAA.

Claims (22)

1. An amino acid composition suitable for adminstration to an animal and being capable of altering the milk protein yield of that animal characterised in that said composition comprises at least three amino acids selected from the Group I essential amino acids: methionine, tyrosine, phenylalanine, histidine or tryptophan, and is in a form that when administered to the animal enables it to produce milk having an increased protein concentration.

2. A composition as claimed in claim 1 comprising four or five of the Group I essential amino acids.

3. A composition as claimed in claim 1 or claim 2 further comprising four or more of the amino acids selected from the Group II essential amino acids: threonine, valine, isoleucine, leucine, lysine or arginine.

4. A composition as claimed in claim 3 comprising five or six of the Group II essential amino acids.

5. A composition as claimed in any one of claims 1 to 4 wherein those amino acids which are present in the composition are present at approximately the following relative concentrations: methionine (10.7); tyrosine (0.4); phenylalanine (36.7); histidine (10.2); tryptophan (5.5); threonine (16.5); valine (24.9); isoleucine (22.4); leucine (36.7); lysine (31.0); arginine (12.8).

6. A composition as claimed in any one of the preceding claims being substantially free of non-essential amino acids.

7. A composition as claimed in any one of the preceding claims wherein the amino acids are provided within a physiologically acceptable carrier.

8. A composition as claimed in claim 8 wherein the carrier is a physiological saline or water.

9. A composition as claimed in any one of the preceding claims wherein one or more of the amino acids are provided as precursors that protect the amino acid against metabolism in the gut or liver.

10. A composition as claimed in claim 9 wherein the amino acids are protected against degradation in the rumen of ruminant animals.

11. A composition as claimed in claim 10 wherein the amino acids have been chemically treated to protect them against degradation in the rumen.

12. A composition as claimed in claim 10 or claim 11 wherein the amino acids are coated or bound with a coating or binder which is resistant to rumen degradation.

13. A composition as claimed in claim 12 wherein the coating or binder is proteinaceous and has been treated with an aldehyde.

14. A composition as claimed in any one of the preceding claims wherein one or more of the amino acids are provided in a form capable of enhanced uptake from the gut.

15. A composition as claimed in any one of the preceding claims wherein the amino acids are provided in the form of peptides.

16. A method of producing milk of increased protein concentration characterised in that it comprises the steps of administering a composition as claimed in any one of the preceding claims to an animal fed on feed material over a feed period and subsequently collecting the milk produced corresponding to that feed period.

17. A method as claimed in claim 16 wherein the feed material is a low protein content feed material.

18. A method as claimed in claim 16 or 17 wherein composition is administered via oral or parenteral route.

19. A method as claimed in claim 18 wherein the compound is administered by catheter.

20. A compound or method as claimed in any one of the preceding claims wherein the animal is a bovine female.

21. Milk having increased protein content characterised in that it is obtained from an animal to which a composition as claimed in any one of claims 1 to 15 has been administered.

22. A dairy product characterised in that it is derived from milk as claimed in claim 21.