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5.4. Cows
A breeding cow’s productivity is dependent on her ability to cycle, conceive, carry a pregnancy, calve unassisted,
provide adequate milk for her calf, and return to cycle while still lactating. The environmental conditions under
which a cow lives i.e. access to suicient nutrition, protection from extreme climatic conditions, protection
from pests, diseases and predators, exposure to fertile bulls, etc. combine with her genetic potential to
determine the actual level of productivity achieved.
The objective of a proitable breeding enterprise is to have all cows calving on or about the same date each
year known as a 365-day calving interval. Achieving such a high level of herd productivity requires careful
management of all females throughout the annual breeding cycle. Cows that do not calve every year are
a cost to the enterprise, and eliminating these from the herd should be the primary focus for all beef breeding
enterprise managers. A sound understanding of the basics of a cow’s reproductive system and how to
manage it assists managers to reduce the number of cows that do not calve every year.
5.4.1. Reproductive Organs
The ovaries are the primary reproductive organs of the cow and have two important functions:
• Production of the female reproductive cell, the egg or ovum
• Production of two hormones, oestrogen and progesterone.
The secondary sex organs are a series of tubes which receive the semen from the bull, transport the sperm to
the egg so it can be fertilised, nourish the fertilised egg embryo, and expel the ofspring. These organs include
the vagina, cervix, uterus, uterine horns, and oviducts also called Fallopian tubes Fig. 5.10.
The ovary produces eggs by a process called oogenesis. In contrast to sperm production in bulls, which is
continuous, oogenesis in the female is cyclic. This cycle, called the oestrus cycle, is of a characteristic
length and consists of a deinite sequence of events, both of a physiological and a behavioural nature. These
are described below.
Figure 5.10. The reproductive tract of a cow. Source: http:www.iowabeefcenter.orgBeef20Cattle20Handbook Reproductive_Anatomy-Cow.pdf.
Uterus Cervix
Vagina Vulva
Uterine Horns Oviduct
Bladder Blind Pouch
Ovary
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5.4.2. Oestrus Cycle and Heat Detection
The oestrus cycle in cows irst occurs during puberty and normally continues at regular intervals until conception.
The oestrus cycle begins when the British breed heifer is between 6 and 11 months of age, but weight is a
more signiicant factor than age in triggering puberty in young cattle. For young British breed heifers, cycling will
generally commence when they reach about 285kg.
The average interval between heat periods, i.e. the period of time where the cow is receptive to the bull, is
21 days, but this may range from 18 to 24 days. It tends to be shorter in heifers than in older cows.
The most reliable sign a cow is in heat is standing to be mounted by bulls if present or by other cows Fig.
5.11. Each stand lasts only 4 to 6 seconds. Cows are in heat for only 6 to 8 hours, a little more than a third of
a day and only spend a total of 3 to 5 minutes actually standing to be mounted on each occasion.
Under natural mating conditions, bulls detect and serve the cows when they come into heat and no input by
Figure 5.11. Standing heat. Source: Irish Farmers Journal.
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people is required. However, in an artiicial breeding program, cows must be observed for oestrus to
determine the ideal time for insemination. Apart from exhibiting the desire to stand while being mounted,
other signs of heat include:
• Clear mucous discharge from the vagina Fig. 5.12 left
• Rubbed patches over the pin-bones and tail area resulting from having being mounted
• Swollen red vulva, frequent urination • Ruled lanks and tail head
• Bawling, restlessness, sniing behaviour Fig. 5.12 right.
5.4.3. Joining
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