Dairy nutrition is about understanding the nutrient requirements of dairy cows at various stages of lactation and combining various feed alternatives to meet those needs in a cost-effective manner.

cows_feedingThe nutrients required by dairy cows are energy, fibre, protein, water, vitamins and minerals.

Pasture provides a balanced feed source and generally only provides a profitable response to supplementation if there is a pasture deficit.

Energy is the key driver of milk production. It determines milk yield, milk composition (fat and protein content) and body weight. Energy is measured as megajoules (MJ) of metabolisable energy (ME).

The main feed energy sources are soluble carbohydrates (starch, sugar) and fibre. Protein and fats in feeds can also be used for energy sources.

  • Soluble Carbohydrates (starch and sugars)

    If cows have sufficient feed (i.e. target residuals are 1500 – 1600 kg DM/ha with good pasture utilisation), supplementing with starch-based concentrates is unlikely to improve reproduction.

    If a pasture deficit exists, it is most important to increase the energy (MJ ME) available to the cow. The type of supplement used to achieve this is secondary.

    Related information

    • FeedRight InfoSheet: Feeding starch or sugar after calving to mating will reduce empty rates – true or false?
    • Inside Dairy (October 2011) – Myth Buster page 21
  • Fibre

    Fibre is the primary source of energy for grazing animals, but is also required to stimulate chewing and saliva production.

    Neutral Detergent Fibre (NDF) is the most common measure of fibre used for animal feed analysis. It measures more than 90% of the structural components in plant cells (i.e. lignin, hemicellulose and cellulose).

    For cows grazing only high quality pasture the minimum NDF requirements are 28-32%.

    There is no benefit of feeding additional fibre (i.e. straw or hay) to lactating cows when pasture makes up more than 60 % of the diet. 

    In diets containing large amounts of finely ground grain and by-products or precision chopped silages, recommended fibre levels have been further refined to include the term ‘effective fibre’ (eNDF). This term is used to describe the fibre that is most effective at promoting chewing. For example, the fibre in fresh pasture or silage (pasture, cereal or maize) is very effective and the fibre in cereal grains is 0% effective in promoting chewing. However, currently there is no accurate way to measure eNDF of long forages (fresh pasture, or grass or cereal silage), hence eNDF figures have not been included in the feed table.

    Counting cud chews to evaluate dietary fibre and rumen function is not necessary in a Kenya pasture-based system as Kenyan pastures will always provide sufficient fibre.

    Related information

    FeedRight InfoSheet: Do lactating cows on pasture require additional fibre?

  • Protein

    In practice high protein pastures meet the protein requirements for high milksolids production. The table below shows when protein may limit production for cows fed high quality pasture.

    Nutrients first-limiting milk production on high quality pasture diets

    kg milk/cow/day Approx. kg MS/cow Nutrient first limiting milk production
    20 1.6 Energy (protein in pasture> 18%)
    25 2.0 Energy (protein in pasture> 24%)
    30 2.4 Energy and protein
    35 2.8 Protein

    It would be rare in Kenya for cows to be deficient in protein unless more than 50 percent of the diet was a low protein supplement (e.g. maize silage at 7.5 % crude protein). Pasture has 50  to 100 percent more protein than is required by the cow.

    Protein to fat (P:F) ratio

    The P:F ratio is calculated by dividing the milk protein % by the milk fat %. There are three main reasons why P:F ratio is considered important:

    • Protein to fat ratio is considered by some nutritionists as an indicator of energy balance, with a lower than average ratio reflecting underfeeding and a higher than average ratio reflective of a well-fed cow.
    • Milk protein is worth approximately twice as much as milk fat in current milk payment systems, primarily because of the value of milk powders relative to butter and cheese. Therefore, a higher P:F ratio will result in a greater milksolids price.
    • Cows with a higher P:F ratio are more likely to get pregnant.

    If using the P:F ratio to determine whether or not to feed cows with supplement, the following points should be considered:

    • P:F ratio can be influenced by diet. In particular, cows consuming starch will have a higher P:F ratio than cows consuming fibre.
    • P:F ratio is not a sensitive measure of energy status and should not be used alone to make decisions on whether or not to supplement cows.
    • P:F ratio can be used in conjunction with postgrazing residuals and milk yield/cow to determine, if it is appropriate to provide cows with a supplement.
    • Although a high P:F ratio is associated with increased pregnancy rates, there is no evidence that increasing P:F ratio through nutrition has this effect; in fact, there is compelling evidence of a negative effect of starch-based feeds on pregnancy rates.

    Related information

    2584.400x400FeedRight InfoSheet: Protein to fat ratio 

    Technical Series (November 2011): Is protein supplementation needed during summer? pages 6-10

  • Fat

    Fat is not limiting in pasture-based diets as fresh pasture contains 3-5% fat.

    Fat supplements can be classed into two categories:

    • Protected or bypass fats: These are either chemically treated (calcium soaps) or saturated fats (e.g. HyFat) that pass through the rumen unaltered.
    • Unprotected fats: These are unsaturated fats that require hydrogenation in the rumen.

    Fat supplements are generally expensive and the gains in milk revenue are rarely profitable.

    Related information

    FeedRight InfoSheet: Feeding Fat Supplements


Nutritional Guidelines

  • Soluble Carbohydrates (starch and sugars)

    Pasture + Supplement, TMR (% diet DM)
    Maximum total soluble carbohydrate 38
    Maximum starch 30
  • Fibre

    As a general rule for all diets

      (% diet DM)
    Minimum NDF 35
    Minimum effective fibre (eNDF) 17

    Pasture + supplements, TMR

      (% diet DM)
    Minimum NDF 27-33
    Minimum effective fibre (eNDF) 20
    Minimum ADF 19-21
  • Protein

    Good quality all-pasture diets

    kg milk/cow/day kg MS/cow/day Protein content of diet required % DM
    20 1.6 18
    30 2.4 24

    Pasture + supplement, TMR

    kg milk/cow/day kg MS/cow/day Protein content of diet required % DM
    20 1.6 16

    (65% degradable, 35% bypass, 32% soluble)

    30 2.4 18

    (65% degradable, 35% bypass, 32% soluble)

    As a general rule for all diets (% diet DM)
    Early lactation 18
    Mid lactation 16
    Late lactation 14
    Dry cow 12
  • Fat

    Pasture + Supplement, TMR (% diet DM)
    Maximum additional unprotected fat 3
    Maximum additional protected fat 3
  • Macro Minerals

    All diets for high production – (2 kgMS/cow/day)

      Mineral content of diet required (%DM)
    Calcium 0.6-0.8
    Phosphorus 0.3-0.35
    Magnesium 0.22-0.28
    Potassium 1.0+
    Sulphur 0.23
    Sodium 0.20
    Chlorine 0.25