How to Tell When Finnsheep Will Have Baby

Sheep Reproduction Basics and Conception Rates

Agdex#:	433/30
Publication Date:	July 2012
Lodge#:	12-037
Last Reviewed:	July 2012
History:
Written by:	Delma Kennedy - Provincial Sheep Specialist/Genetics and Reproduction/OMAFRA

Table of Contents

1. Introduction
2. Reproduction Basics
3. Conclusion
4. References

Introduction

To run a assisting sheep operation, producers must sympathise the details of many different disciplines and how they interrelate. One of the basic aspects of a sheep farming operation is to make certain that ewes become pregnant and take lambs. It is important to understand the basic physiology of the reproductive wheel to ensure that management decisions practise not prevent ewes from becoming significant. Conception charge per unit varies between season, age, brood and lambing organization. Agreement the result of these factors volition enable you to determine what a skilful conception rate is for your farm.

Reproduction Basics

Estrous Wheel

The estrous bicycle is divers as the number of days between the start of ii different periods of oestrus, or heat. The estrous wheel is controlled by a circuitous regulatory system involving a number of hormones, as illustrated in Effigy 1. The hypothalamus sends gonadotropin-releasing hormone (GnRH) to the pituitary gland, which sends luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to the ovaries, prompting the ovaries to abound follicles.

As the follicles abound, they create estradiol, which is fed back to the brain and causes the ewe to come into estrus. The amount of estradiol beingness sent to the brain increases as the maturing follicles get larger. When the follicles accomplish 0.5-1 cm in bore, blood concentration of estradiol peaks, and the brain releases a large corporeality of LH, which causes ovulation. After ovulation occurs, the follicle that the egg was in collapses and forms a corpus luteum, which secretes progesterone.

Figure 1. Estrous cycle. Sheep Production Handbook (2002).

This increase in progesterone tells the hypothalamus to decrease product of GnRH, resulting in reduced follicular growth, causing rut and ovulation to exist suppressed as long as the progesterone level is loftier. If a pregnancy is not established (which would proceed the progesterone levels high), the uterus will secrete the hormone prostaglandin F2a(PGFa). This hormone causes the corpus luteum to dice and decreases progesterone. As a result, the hypothalamus starts producing GnRH, and the cycle begins over again.

Duration of Estrus

The length of time that most ewes are in estrus, or heat, is more often than not 24-36 hours.

In a study done in Missouri in 1937, i,235 cycles were observed in 344 different ewes. Effigy ii shows the distribution of the number of ewes exhibiting heat for each fourth dimension period. While nigh ewes showroom estrus over 24-36 hours, many showroom heat for either less or more time. Ewe lambs testify heat for a shorter time than mature ewes. Of the cycles studied, ninety% were betwixt 15 and 45 hours in length.

Figure ii. Frequency distribution of the duration of rut in ewes. Sheep Production Handbook (2002).

Length of Bicycle

The average length of bike used for sheep is 17 days. Figure 3 shows the length of 1,038 estrous cycles for 299 unlike ewes: xc% of the cycles were 14-xix days long, with an boilerplate of nigh 17 days. The start of the estrous cycle is considered to be when ovulation of an egg occurs from the ovary. The stop of the cycle occurs just before the adjacent ovulation.

Ovulation

The list below summarizes the basic reproductive characteristics of ewes. Heat and convenance normally brainstorm prior to ovulation, and as a result the sperm are present in the oviduct by the time the egg reaches information technology. Sperm survive for nigh 30 hours after convenance. Ovulation usually occurs 24-27 hours after the kickoff of heat. The egg can generally exist fertilized for 10-25 hours afterwards ovulation.

Reproductive Characteristics of Ewes

Age at puberty (ewe): 6 - 9 months

Heat cycle length: 17 days (range 14 - 19)

Estrus (oestrus): 24 - 36 hours

Life bridge of corpus luteum: 14 days

Fertilizable life of ova: 10 - 25 hours

Adapted from Hafez, Subcontract Reproduction in Farm Animals (2000).

Variation in Seasonality

Sheep are seasonal breeders. The natural sexual season is positioned so that lambs volition be born in the jump when the weather is warmer and grass is bachelor.

The length of the breeding season varies from one breed to another. Breeds that originated closer to the equator tend to accept longer breeding seasons than those that originated further due north.

Figure iii. Frequency distribution of the length of the estrous cycle in ewes. Sheep Production Handbook (2002).

Each yr, sheep have a natural breeding season and a period of anestrus. Sheep breed in periods of decreasing solar day length. The season tends to vary around the shortest solar day. In the autumn, in days of decreasing daylight, the ewes are in their convenance season. During winter, when days brainstorm to go longer, the ewes are pregnant. They lamb in spring, as the days keep to get longer, and go into anestrus in the summer, with the bicycle repeating itself the following year.

David Thomas (2008) summarized characteristics of many breeds, including length of convenance season. The list below shows mutual sheep breeds and the length of season category that they usually fit into.

Different Breeds and Length of Convenance Season

Long Flavor (6 - 8 months)

• Finn
• Romanov
• Dorset
• Rideau
• Rambouillet
• Polypay

Medium Season (iv - half-dozen months)

• Suffolk
• Hampshire
• Oxford
• Canadian
• Charollais

Brusque Season (< 4 months)

• Northward Country Cheviot
• Leceister
• Scottish Blackface
• Texel
• Shetland

Adapted from Thomas (2008)

Inducing Oestrus

Sheep can be induced to cycle out of season with a treatment of progesterone followed by pregnant mare serum gonadotropin (PMSG). To get good results, a period of progesterone priming is required. The PMSG causes heat and ovulation. Some research projects accept too induced sheep to cycle out of season with a treatment of progesterone followed past the sudden introduction of rams (ram event).

Conception Rates

Formulation is the point in time when the sperm fertilizes the ova. Formulation charge per unit is ordinarily considered to be the number of ewes that lambed compared to the number of ewes exposed to the ram. Using this broad definition of conception rate, more than factors can influence the results, considering both fertility and embryo loss can be included in the outcome.

In Season

Nawaz and Meyer (1992) reported the functioning of ewes of different brood crosses in Oregon betwixt 1984 and 1990.

Ewes were mated for the first time at 18 months of age. Ewes were grouping mated on pasture to Hampshire rams for 42 days starting the tertiary week in August afterward exposure to teaser ram for two weeks. The ram-to-ewe ratio was 1:50 with rams periodically replaced with fresh rams (Table 1).

At that place was no meaning difference in formulation rate between the breeds shown when using the ram upshot and exposing ewes in season for several cycles.

Casas et al. (2004) compared conception rates among ewes of different ages bred in August, October and Dec in Nebraska. The five-yr project was designed to produce 1,800 F1 ewes that lambed at ane, 2 and three years of age. Ewes were grouping mated by Suffolk rams for 35-day periods that began August 5, Oct fifteen and Dec 15. Ewes bred in August were exposed to a teaser ram for 17 days prior to convenance. Tabular array 2 shows that the ewe lambs had significantly lower formulation rates compared to two- and 3-year-old ewes. They too announced to take had a shorter flavor than their older counterparts.

Almanac Out of Flavor

In a follow-up study, Casas et al. (2005) took the same ewes used in Table 2 and bred them annually March 12 and May 14 for 42 days at 4, 5 and half dozen years of age. Ewes were exposed to a teaser ram for sixteen days earlier breeding. Rams were light treated (six weeks of eight-hour days prior to breeding) and semen tested. The results are shown in Table 3.

Overall formulation rates are much lower in May than in March. There is a significant difference between breeds in the May formulation rates. It is interesting to note that the Romanov cross ewes bred likewise in May every bit they did in March.

Table one. Conception Rates of Different Ewe Breeds Exposed to Hampshire Ram

Ewe Breed Composition	# Ewes Bred	# Ewes Lambing	Average Conception Rate
Coopworth Sire	332	320	0.95
Polypay Sire	382	370	0.97
Suffolk Sire	378	354	0.94
Coopworth Dam	390	372	0.95
Polypay Dam	702	672	0.95
Coopworth x Coopworth	99	94	0.94
Polypay 10 Polypay	236	226	0.96
Polypay x Coopworth	146	142	0.97
Coopworthh 10 Polypay	233	226	0.96
Suffolk 10 Coopworth	145	136	0.93
Suffolk x Polypay	233	218	0.94
Overall	1,092	one,044	0.95

Source: Nawaz and Meyer (1992).

Table 2. Conception Rates by Age of Ewe and Month of Breeding

Month of Breeding	Conception %			All Ages
	ane year-old	2year- old	3 year-old
August	40.1	83.6	87.7	lxx.v
October	66.6	93.i	94.3	84.7
Dec	74.7	95.three	93.9	88.0
Overall	60.5	90.7	90.2

Table three. Formulation Rates by Brood Type and Calendar month of Breeding

Ewe Sire Breed	% Conception March	% Formulation May
Dorset	82.6	62.v
Finn	91.5	72.3
Texel	89.6	52.ii
Romanov	92.4	89.two
Montadale	87.7	52.0
All	88.viii	65.6

Source: Casas et al. (2005).

Accelerated Lambing

Notter (1980) evaluated conception rates of crossbred Rambouillet Finn ewes from 1971-73 in Maryland (further south than Ontario, then theoretically better for out-of-season breeding). Ewes were bred on an accelerated lambing schedule in August, Nov and April, exposed to Suffolk rams for 45 days for each convenance. Table iv shows the accelerated lambing results for a organization of three lambings in ii years.

Table 4 also shows significantly lower conception rates out of season compared to in season. The November conception rates are lower than expected rates for ewes bred annually in November. It appears that ewes existence bred on an accelerated lambing schedule may have lower conception rates in season.

Lunstra and Christenson (1981) synchronized ewes with progestogen sponges for sixteen days and injected them with PMSG on day 17. Estrous responses and lambing rates of mature ewes were measured in mid anestrus (May/June) and late anestrus (July/Aug). The results for the 2 groups were not statistically unlike, showing that synchronization worked as well mid anestrus every bit in late anestrus (Tabular array 5).

Formulation rates were highest among ewes that exhibited estrus within 72 hours of the PMSG injection. In the same report, ovulations were actually counted at 40-70 hours after the onset of oestrus. This showed that 98.ii% of the ewes tested had ovulated to the synchronized estrus in both the May/June and July/August groups.

The authors speculated that when ewes are treated to breed out of season, in that location may be greater asynchrony between the time of heat, LH surge and ovulation, especially in those ewes that don't show rut within 72 hours of PMSG injection. This could be one reason for the difference in the number of ewes in oestrus and ewes actually lambing.

Target Conception Rates

Target formulation rates are calculated based on either how many ewes produce lambs or how many ewes are pregnant at scanning. Tabular array 6 targets are based on how many ewes produce lambs. Many factors can affect target conception rates. These will differ depending on the age of the ewes, lambing interval, breed and product system. The post-obit suggestions assume 20% ewe lambs in season, no ewe lambs out of season and a minimum of 80 days since the concluding lambing.

Table four. Accelerated Lambing Results from Lambing Iii Times in Two Years

Month Bred	Conception Charge per unit
Baronial	90.0%
Nov	79.0%
Apr	53.0%
Average	74.0%

Source: Notter (1980).

Table 5. Percentage of Mature Ewes Lambing in Mid and Late Anestrus

Grouping	# Ewes	% Ewes Showing Estrus	% Ewes Lambing
Control May/June	30	ten.0%	n/a
Control July/Aug	30	16.7%	northward/a
Treated May/June	233	82.0%	65.0%
Treated July/Aug	233	78.1%	54.0%

Source: Lunstra and Christenson (1981).

Table 6. Target Conception Rates

Season	Average Conception Rate	Excellent Formulation Charge per unit
In	90%	96+%
Out	50% - 60%	70+%

Factors Affecting Fertility

Many factors affect conception rates in ewes:

• historic period
• ram
• health
• nutrition and body condition
• lambing interval
• genetics
• season
• stress and environment

Each of these factors can have a significant consequence on conception charge per unit; in some cases, a combination of factors causes conception problems. Out of season, every factor must be managed well in order to take a successful consequence. If formulation rates are poorer than expected, review all management factors, including ram management, health, nutrition, lambing interval, historic period, genetics, stress and ecology factors such as heat.

Conclusions

Good conception rates are essential for the profitability of a sheep farm. High rates of fertility can and should be achieved with an annual lambing organization when breeding in season. Breeding out of season well-nigh often results in a broad range of conception percentages. Out of season, manage all factors strictly to achieve satisfactory conception results. If conception rates are not high, consider and review the many factors that influence the number of ewes lambing and the number of lambs born, including age, breed, lambing interval, wellness, nutrition, stress and the ability of the ram.

References

American Sheep Industry Clan Production Education and Inquiry Council. 2002. Sheep Product Handbook. C&M Press, Denver Colorado, United states of america.

Casas, E., Freking, B.A., Leymaster, M.A. 2004. Evaluation of Dorset, Finnsheep, Romanov, Texel and Montadale breeds of sheep: Ii. Reproduction of F1 ewes in fall mating seasons. J Anim Sci 82:1280-1289.

Casas, E., Freking, B.A., Leymaster, K.A. 2005. Evaluation of Dorset, Finnsheep, Romanov, Texel and Montadale breeds of sheep: Five. Reproduction of F1 ewes in jump mating seasons. J Anim Sci 83:2743-2751.

Castonguay, F. 2010. La reproduction chez les ovins. world wide web.ovins.fsaa.ulaval.ca/publications-ovins.html (downloaded October 2011).

Hafez, B., Hafez, E.Southward.E. 2000. Reproduction in subcontract animals. seventh Edition. Lippincott Williams & Willkins, Baltimore, Maryland, U.s..

Lunstra, D.D., Christenson, R.K. 1981. Synchronization of ewes during anestrus : Influence of fourth dimension of year and interval to onset of estrus on conception rate. J Anim Sci 53:448-457.

Nawaz, 1000., Meyer, H.H. 1992. Performance of Polypay, Coopworth and crossbred ewes: I. Reproduction and lamb production. J Anim Sci, 70:62-69.

Notter, D.R., Copenhaver, J.S. 1980. Performance of Finnish Landrace crossbred ewes nether accelerated lambing: I. Fertility, prolificacy and ewe productivity. J Anim Sci 51:1033-1042.

Thomas, D.L. 2008. Breeds of sheep in the U.Southward. and their uses in production.

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Source: http://www.omafra.gov.on.ca/english/livestock/sheep/facts/12-037.htm

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