- - AGRICULTURE CORE CURRICULUM - - (CLF3000) Advanced Core Cluster: ANIMAL SCIENCE (CLF3250) Unit Title: LIVESTOCK BREEDING AND GENETICS ____________________________________________________________________________ (CLF3258) Topic: ESTROUS CYCLES AND Time Year(s) BREEDING CAPACITIES 2 hours 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (D-14) - List three methods to detect estrus in livestock, explain the importance of detection in a breeding program, and describe the equipment used to detect estrus. (D-17) - Compare and contrast the estrous cycles of the mare, cow, sow, ewe, and doe rabbit and include the seasons of the year in which they cycle. (D-22) - Identify the recommended breeding age for the bull, stallion, buck, boar, and ram and the potential amount of service (years) for breeding males of each species. Special Materials and Equipment: Equipment used for detecting estrus, such as chin-ball markers and heat-mount detectors. Supplemental Handout #4. References: American Breeders Service. A.I. MANAGEMENT MANUAL. Ensminger, M.E. (1983). THE STOCKMAN'S HANDBOOK. Evaluation: Quiz by instructor. TOPIC PRESENTATION: ESTRUS DETECTION AND BREEDING CAPACITIES A. Estrus (heat) Detection 1. Importance: a. to determine when breeding males are to be placed with females, and b. to determine when females should be inseminated if artificial breeding is to be used. 2. Signs of estrus: a. The expression of estrus varies depending on the species. 1) Ewe - a) It is very difficult to detect estrus without using a ram, since there are no outward physical signs or behavioral signs. b) Vasectomized rams with marking harnesses are often used. 2) Sow - Typical signs include: a) swollen, red vulva; b) increased activity and restlessness; c) actively seeks out boars; d) frequent urination; and e) shows the immobility response. (When pressure is applied to the back, the sow or gilt will brace her legs and not move. This response is more obvious when the sow is near the sound or smell of the boar.) 3) Cow - Typical signs include: a) stands to be mounted by her herdmates when in "true heat"; b) swollen vulva showing a thick, clear string of mucus; c) nervousness, restlessness, vocalizations; and d) lack of appetite. 4) Mare - a) squatting with frequent urination and "winking" of the vulva after urination, and raising of the tail; b) nervousness, irritability, and restlessness, c) vocalizations, and d) being more social by seeking out the stallion. 3. Methods used for estrus detection: a. Chin-ball markers - used in cattle on vasectomized bulls. When the bull mounts a cow or heifer, the dye in the chin-ball marker leaves a mark on the cow's rump. b. Marking harnesses - used on vasectomized rams and is similar to the chin-ball marking device except that the harness has the ink in a device on the ram's chest. c. Heat-mount detectors - used on cows and heifers. It is a 2 x 4 1/2 inch fabric base to which is attached a small plastic capsule containing dye. The dye is released by pressure placed on it during mounting. d. Boar sound tapes - used with sows and gilts. A tape recording of boar vocalizations when he is exposed to a sow or gilt in heat is used for sows and gilts. This will often stimulate a sow or gilt to exhibit the immobility response. e. Observation is still the best means for detecting estrus. f. Teasing is the most common method of heat detection in horses. This involves exposing the mare to a stallion using a fence or stall as a barrier. B. Reproductive Terms 1. Estrus (estrous period): The time when the female is most receptive to the male for breeding. 2. Estrous cycle: The number of days between consecutive estrous periods. 3. Breeding season: The time of the year when the female has regular estrous cycles. 4. Breeding seasons by species: a. Mare - Horses are seasonal polyestrous breeders and mares will cycle naturally in the spring and stop cycling in mid- summer. 1) Breed mares on the second day of estrus and every other day for 2-4 days. They ovulate 24-36 hours before going out of heat. 2) Artificial lighting has been used to create an increase in daylight hours and cause mares to start cycling earlier in the season. 3) January 1st is the official birthday of all race horses, so most breeders want their foals born as close to this date as possible for greater maturity before racing. b. Cow or heifer - 1) Cattle will breed throughout the year (polyestrous), although most cattle ranchers restrict breeding to 90 days either in the fall or spring, so that the calves will be born together. 2) Breed after heat is detected because cows ovulate 1-2 hours into their estrus. c. Ewe - Sheep are seasonal polyestrous breeders and breed during the late summer and early fall in order to lamb in the winter or early spring. 1) An exception to this is the Dorset breed which is known for being less seasonal than other sheep breeds. 2) Hormones have been used successfully to bring ewes into heat at any time of the year. d. Sow or gilt - 1) Hogs are nonseasonal polyestrous breeder, and are usually are bred to have two litters a year. 2) Breed the sow on the first day of heat and 24 hours later, ovulation occurs in last half of estrus. e. Doe rabbit - 1) Domestic rabbits breed most successfully during the spring and fall and they are not seasonal in cool climates. 2) The doe is an "induced ovulator". She will mate any time when not pregnant or lactating, and will ovulate and conceive following mating. C. Breeding Capacities 1. See Supplemental Handout #4. __________________________________________________________ ACTIVITY: 1. Discuss the difference between "estrus period" and "estrous cycle". (Note the spelling differences.) 2. Discuss the differences in breeding capacities, why are fewer matings suggested in a pasture breeding situation? __________________________________________________________ Supplemental Handout #4 "ESTROUS CYCLES AND BREEDING CAPACITIES" ============================================================================ Species Age at Puberty Duration of Heat Heat Interval ____________________________________________________________________________ Cow 8 - 15 mos. 12 - 20 hrs 21 days Ewe 5 - 9 mos. 24 - 30 hrs 15 - 17 days Sow 4 - 8 mos. 2 - 3 days 21 days Mare 12 - 15 mos. 4 - 6 days 21 days ============================================================================ "MALE BREEDING CAPACITIES" ============================================================================ Species Age Handmatings*/Year Pasture matings/Yr. ____________________________________________________________________________ Bull yearling 10 - 12 8 - 10 2 year old 25 - 30 20 - 25 3 yrs and older 40 - 50 25 - 40 Ram lamb 20 - 25 0 yearling and older 50 - 75 35 - 60 Boar 8 - 12 mos. 24 12 yearling and older 50 35 - 40 Stallion 2 yr.old 10 - 15 0 3 yr old 20 - 40 0 4 yr old 30 - 60 0 Mature 80 -100 25 - 50 Over 18 yrs 20 - 40 0 * Handmating refers to matings observed by the livestock handler, the male is removed after breeding. ============================================================================ 4/16/90 sg/gv #%&C