Too late to act if cows are thin or butterfat is low

Irish rugby star Rob Kearney at the Aviva Stadium in Dublin with National Dairy Council Marketing Manager Jeanne Spillane, supporting the European Milk Forum/NDC campaign to encourage consumers to drink more milk. Kearney said, “Growing up on our family farm, milk and dairy was always an important part of our diet.” 2019 is year one of a three-year EU-funded milk promotion campaign implemented locally in Ireland, France, Denmark, Belgium and the Netherlands (see www.ndc).

By Independent dairy and beef nutrition consultant, Brian Reidy

Buffer feeding simply means filling the feed gap between the energy requirement of a cow and the energy consumed by her in grazed grass. If there is a deficit, the feed you give her is a buffer feed, regardless of whether that is fed in the parlour, from a bale, out of a pit or through a mixer wagon.

As spring (hopefully) approaches, after a blip in the excellent start to 2019, the prospect of warmer weather and cows remaining outside full time becomes a reality.

The annual questions around what a dairy cow needs in addition to grass begin to surface.

Obviously, it is cheaper and simpler to graze cows with little or no supplementation, but it’s also far less reliable to maintain intakes, milk production, milk solids, return on investment in genetic improvement, and cow fertility.

So, what is the answer to this annual debate?

What is sensible for a 5,000-litre herd certainly is not realistic for one at 8,000 or even 7,000 litres. Different genetics require different nutrition management.

If you under-feed a cow, it is not her fault when she has poor solids and doesn’t go back in calf. This does not make her a bad cow!

In an Irish dairy system, optimising grass intake must be the number one priority, once grazing is possible.

The table, above, right, shows the grass dry matter intakes required at various milk yields and body tissue changes.

It highlights a significant problem if intakes cannot be measured; the energy balance of the cow only becomes apparent when cows ‘go thin’ over a period of weeks rather than days, and the possibility of early corrective action has been lost. The information in the table also confirms the requirement for buffer feeding strategies if high-yielding cows are to be managed successfully at grass.

Obviously, at the upper end of intake requirements, these figures are physically impossible on a consistent basis, and supplementary feeding is essential.

Excessive energy loss will delay the onset of oestrus and greatly reduce conception rates. Early introduction of a well-designed buffer feed will reduce live-weight loss at grass.

Potential of grass

So, what is the potential of grass? At its best, grazed grass can support about 25 litres/cow/day. Some would claim rather more, but it’s not common, and requires excellent management. To support 25-litre production, intakes of about 120kg of fresh grass per cow per day (17kg of DM) are needed. In poor weather, the cows graze and eat less, intakes drop, often to 10kg of dry matter per cow per day, or less, which will support about 10 litres per cow, at best.

However, this is not an exact science, indeed quite the opposite, as breed, stage of lactation, stage of gestation and many other factors will need to be considered.

Strategic buffer feeding

Buffer feeding is used to complement grass, to maintain intakes, milk production, body condition and fertility.

The main difficulty is in judging how much buffer feed should be offered.

Some guidelines can be offered, depending on target milk production, grass quality and availability.

Some key points:

  • Turnout to grass should be gradual, starting with 3-4 hours per day.
  • Continuing with winter ration, but 50g of cal mag added (25g of magnesium per cow).
  • Followed by grazing all day, feeding less supplement, especially less protein.
  • At no point should any buffer or complementary feed reduce intakes of grazed grass. It should be designed to improve grazed grass digestion and animal performance.
  • For higher yield potential cows, depending on the level of production, cows can be offered a fibrous buffer feed via a mixer wagon, or a straight alternative forage (5-7kg of dry matter per cow per day), ideally before or after the morning milking.

    Any complementary forage or mix should ideally be fed in the morning so that cows can return to pasture in the evening with a strong appetite, to consume the highest dry matter and highest sugar content grass of the day.

    Lack of dietary energy often the main cause of infertility

    It is essential to meet the cow’s energy demands for both maintenance and production in the early lactation.

    Invariably, these demands are often not met, and to compensate, the cow begins to milk off her back, by mobilising her own energy reserves to make up the deficit.

    It is the amount of energy that the cow pulls from her reserves that is the key to managing subsequent fertility rates in the herd.

    Why worry about the energy status of the herd?

    Simply put, because as the cow breaks down its energy reserves at or around calving time, and in early lactation, ketone production associated with fat break down in the body increases.

    This increase in ketone production will depress luteinising hormone (LH) pulse frequency, which in turn leads to poor or zero follicular development, and a delay in ovulation.

    The earlier the first ovulation, the greater the number of oestrus cycles that will occur prior to breeding.

    Cows can tell us their energy status

    Several studies show that the most reliable indicators of energy balance in the herd are overall dry matter intakes, milk protein percentage and body condition score (BCS).

    A herd having a steady milk protein of 3.3% or higher in early lactation is an indication that the energy status of that herd is pretty good.

    We can use the milk protein test to measure the energy status of the herd and the effectiveness of the ration offered.

    In general, it is fair to say that if the milk protein percentage is falling, the cows are in negative energy balance, and they will lose weight as they begin to milk of their back.

    If the milk protein percentage is rising, the cows are in positive energy balance, and gaining weight.

    A rising milk protein, even from a low base, also indicates that the herd is in a positive energy status.

    Don’t get confused between milk protein and the protein content of the cow’s diet.

    As long as a diet is not severely deficient in protein, it will have little influence on the milk protein percentage.

    An extreme excess of dietary protein can result in cows using energy to excrete the surplus, which has been shown to suppress milk protein in extreme cases.

    The excess dietary protein will also increase feed throughput in the digestive system, reducing nutrient absorption.

    How intake influences milk performance and fertility

    Where possible, it is well worth taking note of daily dry matter intakes.

    Modern grassland management and measurement strategies are making intake measurements from pasture much more achievable.

    Any sudden drops in dry matter intake associated with a change in feed quality, or in the quantity offered, along with weather issues, must be acted upon immediately.

    Introduce diet changes slowly, this is particularly important when cows are turned out to grass, as the sudden change in diet will cause digestive upsets leading to reduced overall intakes.

    Introduce a good quality buffer feeding strategy, with sufficient fibre to help reduce any potential digestive upsets.

    High dry matter intakes not only drive milk production, but also reproduction, by stimulating ovarian function and days to first ovulation.

    Research from around the world has shown that there is a measured increase in milk production if cows calve down with a minimum body condition score of 3.25, on the scale of 1.0 to 5.0.

    Herd fertility is reduced when more than 1.0 of condition score is lost, or the overall condition drops below score 2.5 between calving down and breeding.

    Low butter fat

    It is becoming more common to see low butter fats once herds get into the second rotation and beyond.

    What can be done about this?

    What are the main causes?

    How we manage our grass from April onwards will have a big influence on milk fat percentages.

    If grass is very lush, high in protein, low in dry matter and fibre, it can tend to pass through cows too fast and induce sub-acute ruminal acidosis, resulting in sub-optimal butter fats.

    Including quality fibre in diets well in advance of feeding this top-quality grass, to prepare the rumen, can be a very wise strategy.

    It is often too late to act when fats collapse, the damage is already done.

    The quality fibre can be in the form of forages such as straw, maize silage, or whole crop, along with including hulls and pulp in significant proportions through any concentrates being fed.

    Oily by-products tend to suppress fats when cows are on top quality grass, and should be avoided.

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