1. Sheep Breeding and Reproduction
Dr. Randy Harp

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 = 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+

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 ( # 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 days (med wool less)
heat periods - 20 to 42 hours (no signs)

31. Sheep Breeding and Reproduction
ovulation occurs late in heat cycle
day cycle ave 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
Ewe lambs 70 85
Twin lambs 40
Tw lambs > ave. in WW 20 35
Ewe lambs exposed 30
Preg. Ewes

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 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