Basic Nutrition
We've repeated it over and over
again that for the cow to perform efficiently we have to meet
her basic nutrient requirements. That means appropriate levels
of protein, energy, minerals and vitamins based on her size,
age, breed and so on. Research and practice has also shown that
feeding increased levels (~30 percent increase) of protein,
energy, minerals and vitamins (a practice known as flushing), 30
to 45 days prior to target breeding dates can enhance cycling
and conception. We'll discuss some of these in particular as we
go along.
One particular nutritional component that has shown to be very
beneficial to reproductive function when fed correctly is fat.
In the most basic of terms, fat is an energy source. The effects
of feeding fat sources to cattle, as a source of increasing
energy status, is well documented. Recent research into the
effects of fat inclusion in the diet on reproduction have shown
positive results. As early as the mid 1980's work was done
comparing the reproductive status and return to cycling of cows
in optimal condition and cows in poor condition receiving
supplementation with whole cottonseed (which will run 18 to 22
percent fat on a dry matter basis). The reproductive performance
receiving the whole seed supplementation was similar to that of
the cows in better body condition. More recent studies have
compared various fat types from different plant and animal
(non-ruminant) sources as well as investigated the actual
physiological changes that take place when fat is used as an
energy supplement.
Various studies have shown the positive response noted. Several
hypotheses currently exist for why this response is seen.
1) The feeding of the additional energy in the form of fat
improves the cow's overall energy status so that she returns to
estrus sooner after calving and therefore conceives earlier.
2) Cows fed fat secrete more progesterone, a hormone necessary
for implantation and nutrition of the newly formed embryo. One
of the effects seen from the feeding of fat is an increase in
the size of follicles produced on the ovaries. A review of a
series of studies investigating this concept showed that
follicle size increased an average of 27.13 percent. The
increase in follicle size also resulted in an increase in corpus
luteum (CL) size. The CL is the structure which produces
progesterone.
3) Specific individual fatty acids (components of fats) inhibit
the production of PGF2Ą by the uterus. This prevents the
regression of the (CL) on the ovary so that the newly formed
embryo survives. In other words, the CL has a longer lifespan
which increased the length of the estrus cycle. This means that
a cow has a longer period of time in which to be bred when she
is in heat. Certain fat types have been shown to be especially
effective in creating this result. Fats higher in linoleic acid
(a specific long-chain fatty acid) have been shown to be
especially useful in this area
4) Higher dietary fat levels may increase the concentration of
cholesterol in the blood stream which acts as precursors or
building blocks for reproductive hormones such as progesterone.
Regardless of the exact mechanism, the use of fat in
supplementation of brood cows has proven very effective in
improving reproductive performance. More research is needed to
identify specific feeds or grains that possess the necessary
fatty acid profile to produce an optimal response (or at least
the best improvement. Cows should receive supplements higher in
fats just prior to calving and in the early postpartum period to
enhance this effect. Feeding a higher fat supplement which
results in the cow receiving 3 to 5 percent fat in her overall
daily diet should improve reproductive rates in most cases. Be
sure not to exceed 6.5 to 7 percent fat in the daily diet since
this can result in reduced fiber digestion in the rumen and
prove counter productive.
The nutritional quality of feeds and forage can have a tremendous
influence on the reproductive performance of cattle. Although
reproductive failure may occur for several reasons, management and the
environment are often important contributing factors. Part of the
environment and management of any animal is nutrition.
Producers must be aware of daily changes in a cow's feed requirements if
they want to wean calves from at least 90 per cent of cows exposed to
the bull. For instance, cows in the last third of pregnancy or those
producing milk have special needs. If these needs are not met,
reproduction is the first body function that is sacrificed.
This document describes the effect of deficiencies and imbalances of
both macro and micro nutrients.
Energy
Energy is probably the most important nutritional consideration in beef
cattle production. Animals require energy to grow and to keep the body
functioning. Cows need energy to maintain milk production as well as to
initiate and maintain pregnancy. Carbohydrates and fats are the primary
source of energy in the diet. Besides being a source of energy,
carbohydrates are building blocks for other nutrients. The excess energy
in a diet is deposited as fat, which provides insulation and protection
for the body.
Energy in the diet must meet the needs of production and in all animals
there is a priority for nutrient use. The most economically important
function of the beef cow, reproduction and the initiation of pregnancy,
is the last function to be supplied with energy. In addition, energy
requirements increase significantly during the last third of pregnancy
and while the cow is producing milk.
Low energy intake during late pregnancy can result in:
-
slightly lowered birth weights
-
higher death rates in newborn calves
-
lower milk production
-
lower weaning weights
-
increased days to first heat
-
reduced conception rates
Overconditioning due to high energy intake over a long period can also
affect reproduction. Animals with "fat cow syndrome" have reduced
fertility, which contributes to long calving periods.
Body condition scoring is a good method for assessing energy
requirements and should be used for adjusting diets throughout the year
(See Body Condition: Implications for Managing Beef Cows, Agdex
420/40-1).
Protein
Protein is the second limiting nutrient in most rations. It is the
principal building block of most tissues. The amount of crude protein in
an energy sufficient diet ranges from 8 to 12 per cent. If dietary
energy is not adequate to meet demands, it can be supplied by the
breakdown of body fat and muscle. However, there is no way for the body
to compensate for prolonged low levels of dietary protein. Therefore,
diets deficient in energy, protein or both can result in a protein
deficiency and a loss of body condition.
Without adequate amounts of protein in the diet, daily feed consumption
drops off, feed passage rates decrease and overall digestive efficiency
declines. Reduced feed intake results in both a protein and energy
deficiency; therefore, the clinical signs that are seen are those of an
energy deficiency listed on page 1. A lack of protein in a diet can
create a cyclical problem that magnifies itself (Figure 1).
Figure 1. Low protein intake results in reduced feed intake
which, in turn results in lower dietary protein.
Large excesses of protein in the diet may also depress fertility. The
process by which this happens is still unclear, but recent research has
shown that dairy heifers have lower conception rates when fed rations
with extremely high protein levels.
Water
Water is the least expensive nutrient in the diet and should always be
available to livestock. It makes up about 50 to 70 per cent of body
weight. A mature cow drinks between 35 and 120 liters of water a day,
depending on the temperature and humidity. Animals will lose their
appetite, dehydrate and can possibly die if not enough water is
available.
Water quality is also an important consideration - for example, high
sodium and sulphate levels can affect free choice salt intake and the
use of other trace minerals (See Water Requirements for Livestock, Agdex
400/716-1 and Water Analysis Interpretation, Agdex 400/716-2).
Minerals and Reproduction
Minerals are loosely classified as macro or micro minerals depending on
the relative amounts needed or present in the body. Macro minerals
include calcium, phosphorus, magnesium, potassium, sulphur, sodium and
chloride. Cobalt, copper, iodine, iron, manganese, molybdenum, selenium
and zinc are considered micro or trace minerals. Rations that contain a
high percentage of forage usually supply adequate amounts of calcium but
may be low in phosphorus. However, rations high in grain contain
adequate phosphorus but may be deficient in calcium and other minerals.
Micro or trace mineral deficiencies are associated with soil type and
are usually geographically related.
Abnormal levels of some minerals such as iron and cobalt do not usually
cause a problem with reproduction. Others mineral, including those which
follow, can significantly affect reproduction.
Calcium
Cattle need calcium for skeletal growth and milk production. From mid to
late pregnancy, a bred cow's requirement for calcium increases by 22 per
cent and after calving by an additional 40 per cent. A deficiency can
lead to "milk fever" around the time of calving particularly in high
milk producing beef breeds. A greater incidence of calving difficulty,
retained placenta and prolapsed uterus may also occur.
Calcium interacts directly with phosphorus and Vitamin D. If dietary
calcium levels are extremely high, phosphorus availability is reduced.
Conversely, high levels of phosphorus impair calcium absorption. In
addition, other complex macro and micro mineral interactions occur: high
levels of phosphorus and magnesium reduce calcium absorption, while high
levels of calcium reduce the absorption of iron, magnesium, manganese,
phosphorus, zinc and iodine.
Phosphorus
Phosphorus has more known functions in the animal body than any other
mineral. It is required for bone and tissue development, energy
utilization and milk production. Phosphorus requirements increase by 12
per cent from mid pregnancy to the last month of gestation. After
calving, phosphorus requirements increase by 50 per cent.
Phosphorus is commonly referred to as the "fertility" mineral. A
deficiency can severely affect reproductive performance and may be
expressed as delayed puberty (associated with poor appetite and growth
rate) and increased number of services required per conception.
Insufficient amounts of phosphorus in the ration results in reduced milk
production and consequently lower calf weaning weights.
Selenium
Selenium is an important component of enzyme systems and interacts with
vitamin E to prevent tissue damage. Selenium deficiency has been
associated with significantly reduced fertility in affected cattle, a
higher than expected number of retained placentas, occasional abortions,
premature or weak calves, reduced ability to resist disease and "white
muscle disease" in calves. Selenium is the trace mineral that gets the
most attention in Alberta because selenium toxicity can also be a
problem. The levels at which selenium can be added to feeds are
regulated due to the narrow range between deficiency and toxicity.
Copper
Connective tissues, red blood cells and key enzymes in the body need
copper. The most important reproductive effects of copper deficiency are
similar to deficiencies of other minerals and include delayed puberty
and poor fertility. Other signs of copper deficiency include repeat
breeding and a higher than expected number of retained placentas. Bulls
may have reduced libido and poor semen quality. If the deficiency is
severe, the bull can become sterile because of damage to testicular
tissue.
Affected animals may be anemic and have an unthrifty appearance and, in
severe cases, a bleached hair coat.
Both high sulphate levels in water and high molybdenum levels in feeds
reduce the availability of copper.
Manganese
The amount of manganese required for reproduction is at least 30 per
cent higher than the requirement for growth. Manganese plays an
important role in the process of energy metabolism and enzyme
activation. A deficiency seriously affects reproductive performance.
Cows with a manganese deficiency do not show heat, have decreased
conception rates, higher abortion rates and low birth weight calves.
Calves are generally born weak and may be deformed with twisted legs and
enlarged joints.
Zinc
Low zinc diets affect the testicular development of bulls and therefore
can affect fertility in a herd. A zinc deficiency results in reduced
sperm production and delays maturation of sperm. in addition, cows may
have low conception rates even though the bulls are normal. Calves grow
slowly and reach puberty at a later age than normal. Zinc deficiency
also results in reduced Vitamin A utilization and signs of a Vitamin A
deficiency may be seen. In addition, high calcium and phosphorus levels
decrease zinc absorption from the intestine.
Iodine
Cattle need iodine for the formation of two hormones that are produced
by the thyroid gland. The thyroid gland is responsible for controlling
the metabolic rate of the body. A lack of iodine indirectly influences
growth rate, milk production and feed consumption. Iodine deficient
animals may have delayed puberty and frequently do not show signs of
heat. Other deficiency symptoms include poor conception rates,
abortions, longer gestation periods and the birth of dead, weak or
hairless calves. Goiters develop when an iodine deficiency is severe.
High nitrate feeds reduce the uptake of iodine in the digestive tract.
Grazing on pastures containing many plants belonging to Brassica spp. (i.e., kale, forage rape, cabbage or turnips) can also cause goitre
by interfering with iodine utilization.
Cobalt
Cobalt is required for the synthesis of Vitamin B12, which in
turn is required for energy metabolism. Animals deficient in cobalt have
a poor appetite, loose body condition and are weak. The conception rate
of cows in an affected herd may decline.
Low cobalt levels reduce the storage of copper in the liver and can
interfere with the activity of manganese, zinc and iodine.
Sodium and Chloride
Sodium and chloride, the components of salt, are essential nutrients.
Salt is required to regulate body fluid levels. In addition, sodium
affects the absorption of sugar and proteins from the digestive tract.
Salt deficiencies can affect the efficiency of digestion and indirectly
the reproduction performance of cows.
The Role of Vitamins
Vitamin A
Vitamin A is found in actively growing green plants and properly
preserved hay. The level of Vitamin A in stored feeds decreases with
time and therefore deficiencies are most often observed in late fall and
winter.
Vitamin A is involved in the maintenance of body tissues so requirements
of the pregnant cow are higher in the last third of pregnancy and
immediately after calving. Cows that have a vitamin A deficiency may
have night blindness, excessive tear production and problems moving.
Pregnant animals may abort, retain their placenta or develop uterine
infections after calving. Calves may be born weak and blind, or dead.
Cows with a vitamin A deficiency conceive normally but return to heat
due to the early death of the embryo. Bulls affected by a vitamin A
deficiency produce fewer and abnormal sperm which contributes to
infertility problems.
Vitamin D
Cattle usually form adequate amounts of Vitamin D through exposure to
the sun and consumption of forages. This vitamin interacts with calcium
and phosphorus in bone development and maintenance. A deficiency is
rarely seen, but if it develops the animal will have a stiff gait,
labored breathing, weakness and possibly convulsions. Swollen knees and
hocks can also occur. Calves may be born dead, weak or deformed. Cows
may not show heat when expected.
Vitamin E
The best source of vitamin E is fresh green forage. Although vitamin E
requirements for beef cattle are not clearly defined, deficiencies are
rarely recognized in adults. Vitamin E interacts with selenium and the
two together work to prevent damage to body tissues. Deficiency in
calves is seen as "white muscle disease."
Summary
Unbalanced and nutrient deficient rations are an important
cause of poor reproductive performance. Problems associated with
protein/energy malnutrition as well as calcium, phosphorus, selenium,
zinc, manganese, copper and vitamin A deficiency are frequently
encountered. Trace mineral deficiencies occur in 75 to 95 per cent of
the feeds grown in Alberta. Because symptoms of various deficiencies can
be similar, the exact problem is sometimes difficult to identify.
Diagnosis may require the help of a veterinarian and the provincial
laboratory system. Better yet, imbalances and deficiencies can be
prevented by nutrient analysis of all forages and grains every year and
using these results to formulate the best ration for each class of
livestock in a herd.
Prepared by:
Cornelia Kreplin and Barry Yaremcio
Alberta Agriculture
1992
Source: Agdex 420/51-1. Revised March 2000.
