Diet Check appendices
- Pasture plate meter heights
- Pasture mass/Pasture Allowance
- Grazed area
- Nutrients consumed in perennial pastures
- Body condition scoring
- Condition score changes throughout lactation
- Energy requirements of the animal (SCA 1990)
- Pasture Intake
- Marginal response
Appendix 4 Nutrients consumed in perennial pastures
In addition to energy, nutrients required by dairy cows include amino acids, minerals and vitamins. In Diet Check, assessments are made of whether the feeds being consumed (pasture and supplements) will provide sufficient metabolisable energy, crude protein and neutral detergent fibre for dairy cows to achieve a target level of production.
Estimations of the digestibility, metabolisable energy, crude protein and neutral detergent fibre contents of pastures consumed by cows are derived from the Victorian perennial pasture database.The pasture database is essentially a collection of existing pasture data collected as part of the department's dairy program. The data has been sorted to provide nutritive values for pastures based on month of year, pasture mass and pasture type (ie. perennial ryegrass, white clover or paspalum-based).
Pasture mass and pasture nutritive characteristics are generally measured by cutting the pasture to ground level. While cows cannot graze to the bottom of the sward, cutting to ground level removes subjectivity involved with cutting to 'grazing' height and has allowed researchers to standardise methodologies around Victoria.
In this database the values for metabolisable energy, crude protein and neutral detergent fibre in the perennial pasture offered to cows are adjusted to reflect what the grazing cow will consume. This is done by using correction factors, commonly termed 'selection differentials'.
The nutritive characteristics of pastures are variable. In general, the metabolisable energy and crude protein of the leaf is higher than in the stem, while the concentration of neutral detergent fibre is generally lower in the leaf and higher in the stem of the plant. Selection differentials are a ratio which relate the concentration of nutrient consumed by a grazing cow to the concentration of nutrient in the pasture cut to ground level. A selection differential greater than 1.0 implies that the animal will consume more of the nutrient than is measured in pasture cut to ground level – a selection differential less than 1.0 suggests that the animal will consume less of a particular nutrient than is measured in the pasture cut to ground level. For example, the ME consumed by grazing cows in spring is 10% higher than in the pasture cut to ground level. A series of selection differentials have been defined for the perennial pastures in the primary dairying regions in Victoria. These have been included in the Diet Check program.
Energy content of feeds is expressed in terms of metabolisable energy (ME) in megajoules per kilogram of dry matter (MJ/kg DM). As a guide, a pasture with an ME >10.8 MJ (or >75% dry matter digestibility), and concentrates with an ME > 12.5 MJ (or >85% DMD) are desirable for dairy cows. Energy is derived from the digestion and metabolism of carbohydrates, fats and protein. Dairy cows require energy for maintenance, milk production, pregnancy, walking to and from the dairy, for grazing, and for tissue deposition in growth or in adding condition. In early lactation, high producing cows cannot consume enough feed to meet energy requirements and rely on converting body fat and protein to energy. This is almost unavoidable, and one should focus on managing these cows to minimise losses in condition. In mid lactation, as milk production declines, the demand for energy to produce milk is reduced, and cows generally maintain condition. In late lactation, feed management should concentrate on a steady decline in milk production (around 7%) and adding condition to cows in preparation for calving.
Metabolisable energy content of pastures consumed by cows in the principal dairying regions of Victoria varies within and between months (Fig 1). This variation also occurs in other regions and information in the DPI perennial pasture database provides estimates of ME for a particular month and pasture type.
Fig 1. Estimated metabolisable energy content (MJ ME/kg DM) of pastures in the principal dairying regions of Victoria. The values are adjusted to reflect those in the pasture consumed as opposed to those in the pasture on offer. Error bars indicate standard deviation.
Protein, or more precisely crude protein, is expressed as %DM. The term crude protein is used because protein is usually calculated from the nitrogen concentration of the feed which is then multiplied by a factor of 6.25 (assuming that protein contains, on average, 16% nitrogen). Protein used by the cow comes either directly from dietary protein which is not digested in the rumen or from rumen microbial protein. Protein is used primarily to build and repair body tissues, for milk production, growth and pregnancy.
Protein concentration of perennial pastures in the principal dairying regions of Victoria varies between and within months (Fig 2). The Victorian perennial pasture database provides estimates of protein content of pastures within a month based on characteristics of the pastures. These values are adjusted to reflect what the cow consumes.
Fig 2. Crude protein concentration (%DM) of pastures in the principal dairying regions of Victoria. The values are adjusted to reflect those in the pasture consumed as opposed to those in the pasture on offer. Error bars indicate standard deviation.
Neutral detergent fibre is a measure of the cell wall content of feeds and is expressed as %DM. High neutral detergent fibre concentrations are usually associated with lower DM intakes because they slow the rate of passage of feed through the gut. A large proportion of a cow's energy is derived from the digestion and metabolism of neutral detergent fibre, however, the neutral detergent fibre concentration of herbage is inversely related to its energy content.
Variation in neutral detergent fibre concentration of pastures in the principal dairying regions of Victoria (sourced from the Victorian perennial pasture database) is illustrated in Figure 3. These values have again been adjusted to reflect what the cow would consume.
Fig 3. Neutral detergent fibre concentration (%DM) of pastures in the principal dairying regions of Victoria. The values are adjusted to reflect those in the pasture consumed as opposed to those in the pasture on offer. Error bars indicate standard deviation.
NB: Although the program indicates that the user can enter details of their own supplements, this is not an option in the internet downloaded version. The user should select the the supplement/feed that best fits the description of their feed.