Sheep Breeding and Reproduction

1. Sheep Breeding and
Reproduction

2. Sheep Genetics
• 27 pairs of Genes
• Two genes that form a gene pair may be the same
(Homozygous)
• If they are different = Heterozygous
• If Heterozygous, then one allele of the gene pair
may express itself over another = dominance
• This dominance can vary from complete to co-
dominance
• A hidden gene expression is called recessive

3. Sheep Genetics
• Some are sex linked
• Examples
• Genotype vs Phenotype
• Estimated phenotypic variance of the flock
(pg BRD 19)
• Heritability

4. Heritability
• Proportion of the total phenotypic variation that is
due to the variation in additive gene effects
• In other words, the proportion of differences due
to genetic effects and is important in the prediction
of response rates from selection.
• The square root of the variance is the standard
deviation, which is the ave. deviation of each
indiv. in the pop. from the pop. Average
• Heritability est. – handout BRD 33

5. Correlation
• Quantifies a relationship between two
variables
• Measured between zero and one
• Positive versus negative correlations
• Multiple effects (Regression models)

6. Animal Identification
• Accurate identification
• Written records
• Accurate measurements of economic
importance
• ??? Registered or not
• Two ID nos. , one for flock or indiv. ID and
the other for registration ID (if reg.)

7. Record Keeping
• Determine clear goals
• Allow for records such as pedigree, birth
weight, singles or twins, weaning weight,
etc.
• Five categories of records:
– REPRODUCTION, MATERNAL , GROWTH,
WOOL AND CARCASS

8. Estimated Breeding Value (EBV)
• EBV = b (P- ave.P), where b is the
heritability of a particular trait
• Example; Ram A has a grease fleece weight
of 15 # and the ave. flock grease fleece
weight is 11 #, then 15-11 = selection
differential [4]
• 4 x .4 (h) = 1.6 # of grease fleece advantage
for breeding Ram A

9. EPD’s (Expected Progeny
Differences)
• Simply ½ of the EBV
• The ave. EPD in a population is + or – from
the average of the population. A comparison
• Ex. If a ewe has a +.3 for no. of lambs born,
then one would expect the progeny to
produce .3 more lambs per lambing than the
progeny of average ewes.

10. EPD’s
• Another ex. is two rams A and B
• +.5 and +1.1 for fleece weight, respectively
• Ram B progeny would be expected to have
.6 pounds heavier fleeces than Ram A
• Example 3; Ram has +1.0 and Ewe has +.5
for weaning weight, then the progeny will
be 1.5 # more than the pop. ave. for WW

11. EPD’s
• Accuracy
• Gives an idea of reliability of the estimat
• Measured from 0-1
• An accuracy of .45 is not very reliable,
whereas > .9 is considered reliable
• Low accuracies are a result of limited
information known about the parents or low
numbers of progeny occur

12. Generation Interval
• The time lapse between birth of an animal
and the birth of its replacement – usually 3-
4 years for sheep
• A measurement of progress or rate of
improvement
• Genetic Improvement per year = heritability
x selection differential divided by the
generation interval

13. Methods of Selection for Single
Traits
• Individual selection-selection on their own
performance
• Family selection-selection based on
bloodlines; useful when (h) is low
• Pedigree selection-similar to family and is
dependent upon how closely related the
ancestors. Useful when considering same
sex

14. Methods of Selection for Single
Traits
• Progeny Test- observing the performance of
the offspring. Must be mated to several
ewes and then look at the offspring. Best
when looking at carcass traits
• Combined Selection- uses more than one of
the above mentioned methods

15. Methods of Selection for
Multiple Traits
• Tandem Selection- focuses on multiple
traits, yet one at a time. After the
performance of one is achieved, then move
to the next trait
• Independent Culling- Set minimum
standards for more than one trait at a time
for the indiv. Cull any that does not meet
the min. stds for any trait

16. Methods of Selection for
Multiple Traits
• Selection Index- rank indiv. animals for two
or more traits based on a combination effect
• One the farm testing:
• Primary focus is on the ewe flock
• Therefore, traits such as prolificacy,
weaning weight and fleece weight

17. National Sheep Improvement
Program
• Oversees the promotion, funding, development
and implementation of a national genetic
evaluation program for sheep
• Minimum criteria for record keeping
• Lamb records: ID #, sire and dam ID, date of
birth, sex, type of birth, & type of rearing.
• Additional records are reproductive, growth and
fleece traits

18. NSIP
• Focuses on:
• Number of lambs born per ewe lambing
• Body weight at 30,60,90,120 & 240 days
• Grease &/or clean fleece wt.
• Staple length
• Fleece grade
• Pounds of lamb weaned per ewe exposed per year

19. Adj. Factors for No. of lambs born per
lambing to a common ewe
Age of Dam Adj. Factor
1 1.45
2 1.15
3 1.05
4 1.00
5, 6, & 7 .96, .96 & .95
8 .98
9+ 1.00

20. Major Economically Important
Traits
• Reproductive Efficiency
• Carcass Merit
• Milk Production
• Total Ewe Production- # lamb/ewe exposed
• Mature Size
• Hardiness & Adaptability
• Wool Production
• Growth Rate

21. Selection for Growth
• Growth is a very important trait, esp. for
meat breeds
• Adjusted 90 day weaning weight
• If birth weight is known:
• [Actual wt. - birth wt. x adj. Days (90)/
actual age ]+ birth wt.
• If birth wt. is not known:
• Actual wt. X adj. Age in days/age

22. Selection for Fleece Traits
• Grease and Clean Fleece Wts
• Yield
• Staple length- at least 3”/yr.
• Fiber diameter
• Crimp
• Color
• Density
• Belly Wool-undesirable on sides

23. Importance of Genetic
Improvement in Seedstock
Flocks
• Most produce their own replacements
• Therefore, genetic improvement from outside is
by the Ram purchased
• Theoretically, Genetic merit increases at the same
rate as the genetic merit of the rams, yet because
of generation intervals and replacement
production usually improvement lags two
generations behind

24. Mating Systems
• Purebreeding- common genetic group
• Outbreeding- unrelated within a breed
• Inbreeding-closely related with one or more
common ancestors (more than 50% related)
• Linebreeding-common ancesters, but not 50%
related
• Crossbreeding- mating of different breeds
• Grading Up-enhanced concentration of
crossbreeding to rams of a single breed

25. Inbreeding Coefficients
• Full brother mated to sister = .25
• Sire on daughter = .25
• Half brother to half sister = .125
• Sire on Mother = .5
• Therefore; > .5 has to be compounded over
time and added generation to generation

26. Crossbreeding
• Heterosis or Hybrid Vigor
• Superiority of the crossbred indiv. Relative
to the average performance of the parents
• Maximized when parents have no breed
ancestry in common (3 breed terminal X)

27. Crossbreeding Systems
• Two Breed Terminal(50% Heterosis)
• Three Breed Terminal (100%)
• Three Breed Rotational (86 %)
• Four Breed Rotational (93 %)
• Two Breed Rotational
• Roto-Terminal- combination of rotational and
terminal systems. The poor ewes would still be
used in a terminal crossing manner

28. Inherited Defects
• Many defects are recdessive in nature
• Selection pressure is exercised against certain
traits, esp. lethals and fleece defects
• Dwarfism, Spider Syndrome, Jaw Defects,
Rectal Prolapse, Inverted Eyelids,
Cryptorchidism, Horns or Scurs, Face covering,
Color, Skin Folds, Silky, Britch fibers, grey color,
paralyzed limbs, earless, etc.

29. Sheep
Breeding and Reproduction
• Improved lamb production
• More lambs per lambing
• More frequent lambing
• Increased percent of total sheep nos.
• Reducing death losses

30. Sheep
Breeding and Reproduction
• breed dependent - seasonal breeding
• Puberty-weight and age (70-100 # or 5-9 months)
• Breed to lamb as 2 year olds, yet can breed as a
yearling, but with less efficiency
• Actually, greater production per lifetime from
yearlings; Ramb. is later maturing and less effic.
• gestation - 144-152 days (med wool less)
• heat periods - 20 to 42 hours (no signs)

31. Sheep
Breeding and Reproduction
• ovulation occurs late in heat cycle
• 14- 20 day cycle ave. 16-17 days
• Prolifacy - > 100% lamb crop
• flushing ewes works in sheep, too
• Factors affecting reprod.
– daylight (<14 hrs/da), temp. ( <74 F or > 100),
nutrition

32. Hormonal Control
• Progesterone (Progestins)- produced by the corpus
luteum
• Prostaglandins- induces the regression of the
corpus luteum (ineffective in normally cycling
ewes); lutalyse
• Estrogen
• Gonadotropins- GnRH, HCG, FSH & LH
• Melatonin- regulatory of the seasonal breeder;
produced by the pineal gland
• ACTH

33. Sheep
Breeding and Reproduction
• Lambing
– > 4 sq. ft. pen for ewes, clean & dry
– presentation of front legs
– orphan lambs is not uncommon
– 25% death loss is common
– Feed ewes small amounts of water at first with
oats, wheat bran and hay (small amounts)

34. Sheep
Breeding and Reproduction
• Ram management
• mating guide
– ram lamb hand (20-25) pasture (25-35)
– yearling or > hand (50-75) pasture (35-60)
– use marker rams to detect bred ewes both at
breeding and 60 days after breeding

35. Replacement Ewe Selection
Item 140 % Prolif 170 % Prolif
No. ewes 100 100
Ewe lambs 70 85
Twin lambs 40 70
Tw lambs >
ave. in WW
20 35
Ewe lambs
exposed
20 30
Preg. Ewes 20

36. Physiological changes of
reproduction in the ewes
• REPRO – 4 chart
• Ewes in the south have longer breeding
patterns
• Sheep near the equator are less likely to
have seasonal breeding

37. Factors affecting reproduction in
the ewe
• Heredity
• Age
• Photoperiod (seasonal)
• Temperature and humidity
• Nutrition and Exercise
• Parturition and lactation
• Disease and parasites
• Fertility of & assoc. with the ram

38. Pregnancy Testing
• Breeding Marks
• Ultrasonic Scanning- best detected between
70 & 120 days
• Bagging or Udder Palpation
• Blood Progesterone- at the time of the next
expected heat
• PSPB- a protein called pregnancy-specific
protein B after day 21 of breeding.

39. Factors affecting the reproduction
in the Ram
• Breeding soundness exam
• Palpation of the testicles, epididymis, and
penis and visual appraisal of feet, legs, eyes
and jaws.
• Semen evaluation
• Disease prevention
• Heat stress

40. Semen Collection
• Components- seminal fluid and sperm
• Quality of sperm – morphology and
viability (percent live)
• Methods- artificial vagina and
electroejaculation
• Semen handling-dilution characteristics:
glucose or fructose, egg yolk, citrate or
phosphate, antibitotics, glycerol

41. Insemination
• Natural- 3-5 billion sperm inseminated
• AI – vaginal approach – 200 million “
• AI – cervical approach- 100 million “
• AI - Intruterine insemination via lapraroscopic
surgery- 20 million
• Time of insemination – vaginal or cervical = 12 to
18 hrs after onset of estrus
• Synchronizing with progesterone sponge should
be 48-58 hrs after removal

42. Accelerated and Out-of-Season
Lambing
• Day length control (natural or artificial)
• Considerations
• Produce lambs when feeding conditions are
favorable (growth rate and cost of feed)
• Market lambs when lamb supply is low
• Fertility and prolificacy

43. Desirable traits for accelerated
lambing
• Ewes can breed year round
• Ewes that can mate while lactacting
• Ewes that have a good lambing rate (ie
twinning)
• Sires that produce a desirable market lamb
and have the libido and fertility for
conception year round