THE OESTRUS AND HEAT PERIOD



OESTRUS CYCLE

(i) Oestrus cycle is the interval from the end of one heat period to the beginning of another
(ii) It is also the period of ’heat” or “oestrus” for coitus or mating
(iii) It is followed by a long period in which female animals will not show desire to mate
(iv) It is under the influence of hormone called oestrogen
(v) The oestrus cycle varies among farm animals
e.g Cow = 20 – 21 days
Ewe = 17 – 21days
Sow = 14 – 28days
Doe (Goat) = 17 – 21 days
Doe (Rabbit) = Spontaneous

REASONS WHY OESTRUS DETECTION IS IMPORTANT IN FARM ANIMALS

(i) It enables the farmer to know when best his animals can be serviced
(ii) It enables the farmer to properly manage the animals
(iii) It also helps the farmer to start preparation for the impending pregnancy


HEAT PERIOD

(i) The heat or oestrus period is the time when the female animal shows signs of its readiness to mate
(ii) It is the period of sexual receptivity in female animal, when the ovum or ova are released. That is, the period when ovulation takes place
(iii) It occurs within the oestrus cycle and controlled by oestrogen
(iv) Heat period varies from one animal to another e.g
Cow = 5 – 2hours
Ewe = 35 – 36 hours
Sow = 40 – 48 hours
Doe (Goat) = 40 – 50hours





SIGNS OF HEAT IN FARM ANIMALS

(i) The vulva becomes large, red and swollen
(ii) There is undue noise making or granting
(iii) A clear viscous secretion comes from the vigina and this arouse and excites the mates
(iv) The animal becomes restless
(v) It shows tendency to be ridden or mounted by other animals
(vi) There is loss of appetite
(vii) The animal has abnormal high body temperature
(viii) Frequent urination
(ix) Standing still to be mounted
(x) Frequent tail shaking as in goat



The majority of mammals become sexually-receptive (express estrus) and ovulate spontaneously at defined intervals. The female will only allow the male to mate during a restricted time coinciding with ovulation. Inefficiency of reproduction is attributable in part to prolonged periods of estrus; thus, the female might need to be bred several times to augment the chances of conception (eg., the mare and dog).

Differences in lengths of estrous cycles among species (Table 4-4) are determined primarily by duration of the luteal phase. Luteal phases of larger mammals are long compared to species of lesser body stature. Many small animals are subject to predation, and cannot afford the luxury of lengthy nonpregnant cycles (moreover, they are usually litter-bearing, have short gestations, abbreviated or no lactational anestrus, and their young attain puberty quickly). Extinction can quickly besiege those species with extended reproductive cycles (eg., rhinoceroses and elephants).

Stages. The estrous cycle can be divided into four stages: proestrus, estrus, metestrus, and diestrus. During proestrus the CL regresses (progesterone declines) and a preovulatory follicle undergoes its final growth phase (estradiol increases). Ovulation usually occurs during estrus (cows ovulate during metestrus). Proestrus and estrus comprise the follicular phase. Corpora lutea develop during metestrus and function at optimum during diestrus. Metestrus and diestrus make up the luteal phase.




Reproductive tract. Changes in contractility and development of the reproductive tract are regulated by cyclic alterations in secretory patterns of steroid hormones. The oviducts and uterus are motile under the influence of estradiol; progesterone has the opposite effect. The endometrium undergoes proliferation during the follicular phase in response to rising circulatory titers of estradiol. Progesterone causes endometrial glands to become branched and secretory (Figure 4-43). Estradiol primes the endometrial response to progesterone (expressed during the luteal phase) by stimulating synthesis of receptors for progesterone (which inhibits synthesis of receptors for estradiol). The cervix becomes dilated in the follicular phase and constricted in the luteal phase; correspondingly, cervical mucus is of either a watery or more dense consistency (Figure 4-44). Each of the noted changes in the reproductive tract of the female have relevance to gamete transport and pregnancy - topics discussed in the next chapter.

Because structural integrity of the endometrium requires steroidal support, regression of the CL (or ovariectomy) leads to atrophy. An ebb and flow of degeneration, growth, and remodeling of the endometrium occurs in all mammals (necrosis and sloughing are pronounced in menstrual animals).

The vagina also presents cyclic changes according to hormonal fluctuations. Epithelial cells exfoliated from the vaginal wall can be collected onto a swab, smeared onto a slide, and examined under the microscope; the presence of cornified cells is indicative of estrus (Figure 4-45). Keratinization of the mucosal lining helps to minimize irritation to the vagina during copulation. With a drop in circulatory estradiol, cornified epithelia is sloughed and the vaginal mucosa becomes very thin; phagocytic leukocytes can then readily migrate into the vaginal lumen (Table 4-5).

Cows sometimes exhibit a bloody vaginal discharge during estrus or metestrus; the bleeding originates from essentially intact uterine vessels - diapedesis or pseudomenstruation. Diapedesis also occurs in the proestrous bitch. In some species (eg., murine rodents), conspicuous uterine intraluminal water imbibition at estrus occurs without overt loss of blood cells. Vessels apparently become leaky in response to an acute elevation in circulatory estradiol. Diapedesis is not the result of hormonal withdrawal, and therefore from a mechanistic standpoint is not comparable to menstruation. Possible local mediators of diapedesis are histamine, catecholamines, and arachidonate metabolites. Eosinophils infiltrate the uterus in response to estradiol.




Synchronization of estrus. There are advantages of being able to synchronize the timing of estrus and ovulation in livestock. Synchronization techniques result in a uniform animal crop and labor can be concentrated at parturition. Furthermore, efficient use of an AI technician is maximized when animals are synchronized to estrus. Estrous synchronization technologies are costly, laborious, generally yield lower rates of conception than natural service, and require skill and specialized facilities. The decision to implement a new system of management should be made only after it is deemed feasible and will solve more problems than it creates.

Two basic approaches to synchronization of estrus and ovulation have evolved from an understanding of female reproductive endocrinology - progestin and prostaglandin. Progestins mimic the luteal phase. Estrus and ovulation follow removal of the progestational influence. Prostaglandin F2a causes luteal regression, thereby synchronizing the onset of a follicular phase.

The Syncro-Mate-B system (history) involved placing a norgestomet-releasing implant between the skin and cartilage of the ear of a cow for nine days. At the time of implant insertion, the cow was injected with estradiol valerate to induce endogenous uterine production of luteolysin - so when the implant is removed, there was no natural source of progesterone to prevent a prompt return to estrus. Animals can be either observed for estrus (Table 4-6) and bred 12 hours later or bred-by-appointment 48 hours following implant removal. Advantages of the Syncro-Mate-B system were that some anestrous animals respond and synchrony of estrus was tight (timed insemination is practical). The system was expensive and labor intensive (animals must be handled twice). It was approved for use in beef animals and dairy heifers. A new alternative for (intravaginal) progesterone delivery is the Eazi-Breed CIDR (controlled internal drug-releasing), which is inserted for 7 days; Lutalyse is given on Day 6.

Orally-active progestins (eg., melengestrol acetate or altrenogest) have been incorporated into livestock rations. Feeding progestins is effective for induction of estrus, but has not met with widespread application because of cost, unequal consumption, and poor synchrony following cessation. Ewes can be induced to estrus by treatment with progestin (eg., two weeks by vaginal sponge impregnated with MPA or flurogestone acetate) and PMSG (at pessary removal); however, because of low corporate profits, these products are no longer readily available in the US marketplace.

Naturally-occurring PGF2a as the tromethamine salt (Lutalyse, Upjohn; ProstaMate, Phoenix Scientific), and synthetic analogs of PGF2a such as cloprostenol (Estrumate, Haver), are sold for synchronization of estrus in nonlactating cattle (Figure 4-46) and horses. The cost of a single-injection prostaglandin program is less than that of a progestin system and not as laborious. Animals must be in diestrus to respond to PGF2a (the young CL is insensitive to treatment), return to estrus is somewhat variable (semen is wasted if breeding-by-appointment), and treatment of pregnant females can cause abortion. Porcine CL will not respond to PGF2a until about Day 12 of the estrous cycle. Gonadotropin-releasing hormone (to induce ovulation and CL formation) is being used in cattle in combination

HERE YOU WILL FIND EVERY AVAILABLE TOPICS ABOUT AGRICULTURAL SCIENCE AND BIOLOGY. AND THE LINKS TO THEIR VARIOUS SOURCES.
1. DEVELOPMENT OF AGRICULTURE
2. IMPORTANCE OF AGRICULTURE
3. SUBSISTENCE AGRICULTURE
4. COMMERCIAL AGRICULTURE
5. PROBLEM OF AGRICULTURAL DEVELOPMENT
6. SOLUTIONS TO POOR AGRICULTURAL DEVELOPMENT
7. AGRICULTURAL LAWS AND REFORMS
8. ROLES OF GOVERNMENT IN AGRICULTURAL DEVELOPMENT
9. AGRICULTURAL POLICIES
10. PROGRAM PLANNING IN AGRICULTURE
34.
FORESTRY
35. WILDLIFE CONSERVATION
36. FACTORS AFFECTING LAND AVAILABILITY
37. TOPOGRAPHY
38. SOIL
39. BIOLOGICAL FACTORS
40. SOCIAL-ECONOMIC FACTORS
41. ENVIRONMENTAL FACTORS AFFECTING AGRICULTURAL PRODUCTION
42. CLIMATIC FACTORS AFFECTING AGRICULTURAL PRODUCTION
43. TEMPERATURE
44. RAINFALL
45. WIND
46. SUNLIGHT
47. SOLAR RADIATION
48. BIOTIC FACTOR AND AGRICULTURAL PRODUCTION
49. PESTS
50. BIRDS
51. DISEASES
52. SOIL MICRO-ORGANISMS
53. SOIL PH
54. ROCK FORMATION
55. IGNEOUS ROCK
56. SEDIMENTARY ROCKS
57. METAMORPHIC
58. SOIL AND ITS FORMATION
59. FACTORS OF SOIL FORMATION
60. LIVING ORGANISM
61. PARENT MATERIALS
62. SOIL FORMATION TOPOGRAPHY
63. PROCESS OF SOIL FORMATION
64. WEATHERING
65. PHYSICAL WEATHERING
66. CHEMICAL WEATHERING
67. PRESSURE
68. WATER
73. BIOLOGICAL WEATHERING
74. CHEMICAL AND BIOLOGICAL COMPOSITION OF THE SOIL
75. SOIL WATER
76. MICRO AND MACRO NUTRIENTS
77. SOIL MICRO ORGANISM
78. PROPERTIES OF SOIL
79. SOIL STRUCTURE
80. SANDY SOIL
81. CLAY SOIL
82. LOAMY SOIL

83. SOIL TEXTURE
84. IDENTIFICATION OF SOIL TYPES THROUGH EXPERIMENTS
85. RETENTION OF WATER BY VARIOUS SOIL TYPES
86. DETERMINATION OF SOIL PH REACTION
87. COLORIMETRIC DETERMINATION OF SOIL PH LEVEL
88. PH SOIL TEST
89. PLANT NUTRIENTS
90.
MACRO NUTRIENTS IN GENERAL
112.
THE MAINTENANCE OF SOIL FERTILITY
113. CROP ROTATION
114. APPLICATION OF ORGANIC MANURES
115. FARM YARD MANURE
116. APPLICATION OF INORGANIC MANURE

117. LIMING
118. FARMING PRACTICES
119. BUSH BURNING
120. CLEARING

121. FERTILIZER APPLICATION
122. ORGANIC MANURING
123. FARM YARD MANURE

124. HUMUS
125. COMPOST
126. CROP ROTATION
133. FARM POWER AND MACHINERY
134. SOURCES OF FARM POWER
135. HUMAN SOURCE
149.
PLOUGHS
142.
FIELD MACHINES
157.
PLANTERS
164.
SIMPLE FARM TOOLS
165. AGRICULTURAL MECHANIZATION
166. THE CONCEPT OF MECHANIZATION


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