MANAGEMENT MATTERS PROTEIN YIELD
Exploiting milk protein yield is vital to all Holstein breeders whether you are signed up to a compositional contract or chasing milk constituents to add value to saleable heifers. Advanced Nutrition’s Bryn Davies explains what milk protein is all about and goes on to discuss how you can maximise yield effi ciently and cost effectively
Bryn Davies
ilk protein is split in two portions: ‘true’ and ‘not true’. The true type makes up approximately 94% of milk protein composition and comprises between 75% and 85% caesin; 7% to 12% beta- lactoglobulin and 2% to 5% alpha- lactalbumin. True protein affects the moisture, texture, fl avour and yield of cheese. In the cheese making process fat is ‘bound’ to the true protein portion of milk therefore the higher the protein content, the greater the fat
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level that can be yielded. The remaining milk protein composition comprises not true protein of between 2% and 10% urea which is no value whatsoever to the processor or consumer. Over 90% of the true proteins are made in the udder from amino acids, glucose and acetate. Production tends to be limited by the amino acid in shortest supply, often methionine. So how do we infl uence true protein yield? Firstly genetics - 55% of milk composition is heredity while the remainder is infl uenced by environment and management factors including health and nutrition. Also the cow herself, her stage of lactation, level of milk production, age and the number of heifers within the herd. While we can all select genetics more carefully for protein for the medium to long term, the one factor we can all get to grips with virtually immediately is nutrition and the real pointers are:
• avoiding a negative energy balance in the fi rst six weeks of lactation
• manipulating the diet’s starch content
• feeding the correct level bypass protein and focusing on the amino acids supplied
Remember, you need to feed the rumen what it needs, don’t waste space with cheap feeds that are of no value. If we insult the rumen with digestive upsets, the yield of microbial bugs is depressed and yield drops.
1. Negative energy balance can reach a low two weeks post calving: it’s an issue that should and can be avoided at all costs in order to minimise fertility issues, improve milk yields as well as improve milk solids - the true protein milk component.
The major infl uence on energy defi ciency is DM intake, not milk yield. As a rule of thumb, dry cows should consume approximately 14 kg DM per day at 40 days pre-calving and this will reduce to 12.5 kg DM per day in the fi nal 10 days to calving. Immediately after calving, DM should be increasing to over 19 kg per day.
2. Starch content: during early lactation, starch energy increases milk yield and also protein production; however it has little effect on milk protein %. In contrast, during late lactation, starch does increase concentration of protein percentage. However, high starch content diets are accompanied with risk. If acidosis or SARA are to be avoided, then starch degradation in the rumen has to be balanced on an hourly basis. Once the rumen pH plummets, the rumen output drops along with amino acid production.
3. Bypass protein: amino acids are in huge demand – they’re essential for the functioning of gut, liver and other tissues. Amino acids arrive in the small intestine from two sources – between 50% and 75% from rumen microbes and the remainder from dietary bypass protein. The amino acid profi le of rumen microbes is very similar to that of milk protein so it comes as no surprise that cows can convert them very effi ciently into milk protein. Dietary bypass protein can make up the shortfall, however it is very expensive and to be honest, we’re struggling in the UK for sources.
There are more infl uencing factors, and the cow’s environment is an obvious one. She needs suffi cient trough space and heat stress must be avoided otherwise appetites become depressed, and acidosis and mastitis kick in. Both mastitis and SCC greater than 200,000 depress milk proteins due to the production of high levels of plasmin and plasminogen - enzymes that degrade milk proteins especially casein and therefore quickly depress milk protein percentage. To sum up, to maximise milk true protein, feed your cows accurately, eliminate negative energy balances, maximise feed intakes, record DM intake and body condition scoring as a minimum level of monitoring, add starch safely and gradually, and trial additional amino acids in the diet.
THE JOURNAL DECEMBER 2010 99
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