74
Beef Breeder MANUAL
3.5. Feed Management
3.5.1. Feed Testing
Testing the quality of individual feedstufs used to prepare rations for cattle is a fundamental requirement
to being able to formulate eicient and cost efective rations for cattle, particularly during winter when energy
requirements are critical to manage animal health and welfare.
Feeds vary considerably in the concentration of individual nutrients, both between and amongst the
same feed types. For example, high quality pasture silage would be expected to contain in excess of 10.5
MJ of metabolisable energy per kg of dry matter, and at least 15 crude protein. However the same pasture cut
for silage just a week later may look exactly the same, but only contain 8.5 MJ of energy and 10 protein.
In addition, excess moisture in hays, or too little in high dry matter silages - in excess of 45 dry matter, can
result in heating which binds some proteins to sugars and turns them into a condensed but indigestible ‘syrup’.
Whilst cattle may eat heat damaged forages very readily because of this syrup efect, they perform very poorly
due to the very low quality of the feed.
Low quality feed comes at a very high cost to both the business, in terms of lost energy and protein, and the
animal eating the feed, in terms of lower growth and productivity.
The key nutrients to quantify in feed are metabolisable energy ME – megajoules per kg, crude protein CP - ,
or gkg, and neutral detergent ibre NDF - , or gkg. With these three nutrient concentrations known in the
feeds on hand, a balanced diet can be formulated to meet the weight and body condition targets set for the
herd.
When the quality of the feed is known, several high quality computer programs can be used to help calculate
balanced, least-cost rations, e.g. Cowbytes Alberta Ag and Rural Development, Canada, and Grazfeed CSIRO,
Australia.
3.5.2. What to Feed
Grasses Grasses, which comprise perennial and annual species
as well as many of the human food plants like sugar cane and the cereal grains, are the most common source of
ruminant feed. The feeding value of temperate grasses is highest when the plants are young and leafy, and declines
progressively as the plants mature. Consequently, while it is tempting to leave grass longer before cutting or
grazing to allow maximum accumulation of forage, it is best, in terms of animal production, to use the grass
before it becomes too mature, as this will only increase the percentage of indigestible ibrous stems andor seed
heads Refer Fig 3.3. Legumes
Legumes are a diverse group of plants ranging from low growing herbaceous species, through creeping and
twining types, to shrubs and large trees. The one aspect they all have in common is that they all set their seeds
in pods. While there are three families of legumes, all the
common temperate legumes belong to the family, Fabaceae, distinguished by a pea-shaped lower Fig.
3.6. Legumes generally have higher feeding value than
grasses at a similar stage of growth, due largely to the fact that many legumes have the ability to extract nitrogen
from the atmosphere and convert it to plant available nitrogen in nodules attached to their roots. This leads
to plants having high crude protein levels in their leaves and stems. By contrast, grasses rely on soil availability of
nitrogen to supply their protein requirements. In mixed pastures, legumes perform as a valuable energy
and protein supplement to grasses in the pasture sward that together provide the bulk of the animal’s diet in a
grazing situation. The extent of the impact of feeding legumes to cattle is related to the proportion of legume
in the diet, the quality of both grass and legume, and the total amount of forage available to the animal.
When feeding poor quality grasses, even an additional 5 legume can produce a signiicant beneit to animal
performance, although higher amounts will have greater impacts. Feeding pure legume diets is wasteful
of protein, and in some cases may be detrimental to animal health and reduce animal performance, for
example young, leafy alfalfa may cause bloating in cattle and eventual death if untreated.
In general, considerable beneit can be gained from feeding between about 30 and 50 legumes in the
total forage diet, on a dry matter basis.
75
Cold Winter Climates
The value of feeding legumes increases with the onset of the dry season as grasses mature and their feeding
value declines.
Crop Residues Crop residues are commonly available sources of feed
in mixed farming systems. They may be those parts of the plant remaining after a grain or pulse crop has been
removed e.g. cereal straw, maize stems, pea vines. Grain crop residues usually have very low feeding value
and need to be supplemented with other forages to maintain animals or achieve higher production levels.
This low quality results partly from the increase in lignin in the plant tissues with age, and partly from the fact that
the plant mobilises nutrients from the vegetative part of the plant to concentrate them in the grain.
Crop By-products Many extraction processes involving plant products
result in the production of considerable amounts of by- product e.g. brewer’s grains, potato waste. Many of
these by-products can be used as livestock feeds, often constituting a concentrated source of one or more
essential nutrients. When using crop by-products, particularly those that
have been through a post-harvest manufacturing process e.g. potato skins care needs to be taken to
ensure that no chemical residues that may be harmful to animal or human health remain in the by-products
when they are fed to animals. Conserved Feeds
The basic principle in fodder conservation is to preserve feeds from a period of excess production to feed to
animals at a time of feed shortage Fig. 3.7. The most common methods of fodder conservation are drying
haystraw and ensiling silagehaylage, and additional detail on forage conservation for beef cattle enterprises
in cold climate countries is discussed in Section 8.
AlfalfaLucerne Medicago sativa.
White clover Trifolium repens. Figure 3.6. Examples of pea
lowered forage legumes. Birdsfoot trefoil Lotus uliginosus.
76
Beef Breeder MANUAL
3.6. Moulds and Mouldy Feeds
Kategori