SPECIAL REPORT
Feeding the cow and the rumen How much and what nutrition does a cow need for superior milk production? Sue Macky finds out.
F
eeding dairy cows is complicated as two entities with differing nutrient needs are involved; the cow and the rumen microbiome. It is the health and function of the rumen that determines what actually feeds the cow, in what form, and how
efficiently. Determining nutrient requirements for milk production is usually determined backwards, i.e., if we want a cow to produce 35 litres of milk or 2.5 kgs MS per day, what amount of energy, protein, minerals does she need to be fed? Most ration software programmes attempt to balance those needs against feeds available. There is an underlying assumption that ‘this’ ration is what the cow consumes in every mouthful, i.e. a total mixed ration (TMR). When grazed pasture is fed, true balance rarely occurs. Pasture is a living changing feed, not of consistent composition or supply. Any supplements fed to make a complementary balanced diet are only fed once or twice a day, in conjunction with milking. It is not possible to have true synergy between all nutrients in the rumen at all times, so balance may be on paper only. If the diet has the required amount of energy/ kg DMI (MJME/kg DM), this is no guarantee of the outcome. ME is not a nutrient – it is a mathematical equation that allows us to determine whether a certain outcome is possible or not. It is how the rumen microbes deal with feed that determines what
66
energy and nutrients the cow gets. Maximising daily dry matter intake (DMI) is the first priority. For lactating cows, we should aim to at least offer the equivalent of 4% of DM on a liveweight basis (20kg DM for a Kiwicross, 500kg mature cow). Cows can eat much more than this, but most NZ cows don’t get this much. Cows cannot regularly collect even 18 kgs DMI from grazed pasture, and much less in many parts of the country, for much of the year. This only meets the intake needs of a small Jersey cow. Feeds must meet the needs of an optimally functioning, healthy, high capacity rumen – a system developed to extract nutrients from the tough bits of plants that we humans cannot digest, and which performs best as designed if it gets enough physically effective fibre and has synergy between crude protein and fermentable carbohydrate.
Sue Macky.
A BALANCED DIET An important component of ‘balance’ is ensuring that what is fed promotes the largest possible, hardest working, rumen microbial population, and delivers nutrients to the cow she can use. She will get most of her ‘fuel’ from glucose made in the liver from the volatile fatty acid byproducts (VFAs) of the rumen microbial fermentation of fibre, sugar, and starch, but
Dairy Exporter | www.nzfarmlife.co.nz | August 2021
