Resultado final
Two experiments were conducted: (1) to evaluate the effects of protein level and acidogenicity value (AV) of concentrates on performance of lactating cows offered diets based on grass and maize silages, and (2) to evaluate the effects of dietary protein content and amino acids profile of metabolisable protein on voluntary intake and milk production of dairy cows fed maize silage based diets. The consortium aims to disseminate these results by publication in international scientific journals.
Experiment 1: Despite large differences in concentrate ingredients, the main nutritional characteristics of the four concentrates used were similar apart from the designed differences in crude protein (CP) concentration. Neutral detergent fibre (NDF) concentration varied to balance the differences in CP among the concentrates. The concentrate AV pHs, as measured following incubation of samples in rumen fluid (starting pH 7.20) for 24 hours at 39°C, were very similar for all concentrates, with an overall mean value of 5.26. Similarly, the maize/grass silage mixtures used were reasonably consistent throughout the duration of the experiment. Despite differences in feeds offered, there were only small differences in feed intake and milk production performance of the cows. The inclusion of a buffer in the concentrate significantly reduced forage dry matter (DM) intake, and significantly reduced milk fat concentration, although in both cases the numerical difference was small. However, increasing the concentrate CP concentration had no effects on milk protein concentration or yield. Milk fatty acids were affected in various ways by the treatments, most specifically by the time of collection (from morning or afternoon milking).
The biohydrogenation theory of milk fat depression, seen in this experiment with the incorporation of buffer into the concentrate, suggests that milk fatty acid production is reduced by the presence of certain fatty acid biohydrogenation intermediates, such as C18:1 trans-10. However, in this case, there was no effect of buffer on the concentration of C18:1 trans-10 in milk. The main conclusion of this work is that concentrate composition (CP concentration, acid load, and inclusion or not of a buffer) had very little effect on feed intake and milk composition, and no significant effects on milk yields.
Experiment 2: The four concentrates used differed in the CP, ether extract (EE) and sugar concentrations, the metabolisable energy (ME) density being similar across concentrates. Concentrates based on maize by-products had higher concentrations of the fatty acid C18:2 n-6 and of the amino acids Leu and Met, and a lower concentration of Lys. Diets with higher CP concentrations increased feed DM intake, milk production, milk protein and lactose productions, but decreased the efficiency of conversion of dietary N into milk N. Diets based on maize by-products increased milk production, milk lactose production and tended to increase DM intake, milk lactose content, and crude efficiency of milk production. Diets based on soybean meal increased milk fat and protein concentrations. Rumen protected Lys and Met only tended to increase milk fat and protein concentrations. Plasma urea concentration was higher in diets with 16% CP and in diets based on soybean meal. Plasma glucose concentration was higher in diets based on soybean meal. Milk fatty acids were mainly affected by dietary CP and main protein source in the concentrate. Plasma free amino acids were mainly affected by the main protein source in the concentrate. Plasma Leu was increased in diets with higher CP content and in diets based on maize by-products, reflecting the higher inclusion of maize dry distillers grains. Plasma Met was increased in diets based on maize by-products (reflecting their ingredient composition) and by adding rumen protected Lys and Met. Plasma Lys was only affected by the main protein source in the concentrate, and increased with concentrates based on soybean meal.
These results show that diets with lower CP concentration (14% vs 16% CP) decrease DM intake and milk production, but improve the efficiency of conversion of dietary N into milk N, thus contributing to a reduction in N pollution. Concentrates based on maize by-products increased milk production and decreased milk protein and fat concentrations. The lower milk protein concentration was probably a consequence of a great imbalance of amino acids in the absorbed protein, as these concentrates had a lower Lys content. The lower milk fat concentration probably reflect an inhibition in the de novo synthesis of fatty acids in the mammary gland (short and medium-chain fatty acids) and by rumen bacteria (odd and branched-chain fatty acids) due to the inhibitory effect of a lipid supplementation. The effects of adding rumen protected Lys and Met on milk composition reflect a better balance of amino acids in the protein absorbed and the role of Met in lipid metabolism.
New raw material matrices were generated incorporating the new feed information into existing commercial rationing models from the SME partners. The new feed information comprised (1) the amino acid content in undegradable protein of the main protein sources and the effects of protein supplements on rumen buffering capacity; and (2) the acidogenicity value (AV) of the principal protein and energy sources as well as the main forages used in dairy cow feeding.
The work showed that the amino acid profiles of microbial protein are not constant as assumed in the past (e.g., differences between solid- and liquid-associated bacteria, and protozoa); the amino acid profiles of nylon bag residues are different from those of the original feeds (affected by: rumen exposure time, differential degradation by rumen microbes, microbial contamination, and losses of particles by nylon bags); and the dietary inclusion of yeast supplements (which are in widespread commercial use) could affect the duodenal amino acid profile. Principal component analysis and biplot analysis further showed differences between amino acid composition of some protein supplements and of their rumen residues. Microbial protein was clearly associated with milk protein, supporting the need to formulate diets that maximize microbial protein supply. Within the feeds studied, fish meal was the most strongly associated with microbial protein and milk protein.
However, the use of this feed in ruminant diets is prohibited in the EU. Maize, sorghum and maize by-products were clustered away from the other feeds. Therefore, it is currently difficult or even impossible to formulate diets with legal and commercially available feeds that allow the absorption of a mix of amino acids similar to that found in milk protein. This has implications for the excretion of nitrogen from the animal, because amino acids available in excess of utilisation requirements are largely deaminated and excreted; supplying amino acids in a mixture that is close that required for milk protein synthesis increases the efficiency of their utilisation. The use of rumen- protected amino acids could contribute to improving the balance of absorbed amino acids for milk production.
Samples of the main forages and the most common energy- and protein-rich supplements collected by SME partners were analysed for chemical composition. Dry matter (DM) and N degradability after 0 and 12h rumen incubation were also measured. These data were also used to generate new raw material matrices.
The work on buffering capacity of ruminant feed ingredients confirmed the suggestion that high-protein feeds may contribute to increase buffering in the rumen. Samples of maize silage, protein and energy sources and dietary ingredients that do not ferment (mineral and fat supplements and buffers) were analysed for Acidogenicity Value (AV) followed the procedure of Wadhwa et al. (2001), except that the final pH was recorded instead of the dissolution of calcium from calcium carbonate. The information generated was incorporated into rationing software.
All the information referred to above is being used in practice by SME partners. Indeed, all of the SME partners are heavily involved in the dairy cow feed market and have benefited from the exploitation of the new protein supplementation concept. This is allowing them to generate new products more competitively (at lower cost) and which contribute to a reduction both in the need for protein sources (mainly imported from United States) and in nitrogen pollution.
Therefore, this result contributes for achieving prime industrial/economic objectives, namely:
- Better utilisation of protein sources that are produced in the European Union.
- Reduction in protein supplementation needs and, consequently, the costs of dairy cow diets.
- Less dependency on imported protein sources (mainly from United States).
- New market opportunities.
In addition, social objectives were achieved:
- Reduction in nitrogen environmental pollution.
- Increased incomes for dairy farmers.
- Improvement of quality of life, health and safety.
- Improved skill levels for people formulating and monitoring rations for dairy cows.
- Improved utilisation of low quality feeds for more sustainable animal production systems.
This result is pre-competitive and significant implementation will require further development and evaluation within the SMEs, which will now make decisions about their commercial development.
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