Reproduction of the cow herd - PowerPoint by ycy21310

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									Reproduction of the
cow herd
       R. Mark Enns
Department of Animal Sciences
  Colorado State University
Historical perspective on
improving fertility

   Reproductive ability is very difficult to
    improve.

   Lowly heritable traits
       Focused on properly managing cows
        rather than on selection for improved
        fertility
            Appropriate supplementation and body
             condition score before calving
Example traits
      Traits         Heritability
   Calving Date          .06
  Calving Interval       .11
  Conception Rate        .05
   Calving Rate          .09
  Days to Calving        .08
Traditional Perspective on
reproduction
   Lowly heritable
       Focus on managing your cows properly rather
        than on selection and genetic improvement to
        improve fertility

   Difficult to quanitify
       Binary Trait (yes/no)
       If all animals in a contemporary group have the
        same observation, the data is not useful for
        selection
            For example, every heifer comes in pregnant after
             breeding season
New perspective
   Despite low heritabilities we can make
    genetic improvement in reproduction
       Driven by the establishment of large
        databases of performance and pedigree
        information

       New statistical techniques – threshold
        model
            Heritability of the traits tends to be higher (on
             an underlying scale)
    What evaluations for
    reproductive ability are in use?
   U.S. Dairy Industry
       Daughter Pregnancy Rate
           Percentage of nonpregnant cows that become
            pregnant during each 21-day period.
                Bull 1 ―EPD‖= 1
                Bull 2 ―EPD‖= 0
                Bull 1’s daughters are 1% more likely to become
                 pregnant during that estrus cycle
                Each increase of 1% equals a decrease of 4 days open
                Heritability = .04
What evaluations for reproductive
ability are currently in use?
   Australia
       Days to calving
            How do you account for open cows?
       Scrotal circumference
   Why scrotal circumference?
       Highly heritable
       Related to age of puberty in a bull’s
        daughters
            Justification: earlier puberty results in more
             heifers pregnant
More on scrotal circumference
   Early and current research indicates SC is related to
    yearling and lifetime pregnancy rate

       Genetic relationship between SC and heifer pregnancy rate
        = .57
       Genetic relationship between SC and lifetime pregnancy rate
        = .34
       We have done a lot to improve SC since this study:
            Average SC on 13 month bulls was 27.7 cm
            27.7% of heifers did not reach puberty before the breeding
             season
Scrotal Circumference may not
tell the whole story…
         Changing Relationships




Evans et al., 1999
Why are we concerned with
age of puberty in females?
   Heifer pregnancy
       Should explain more of the genetic
        differences in 1st breeding season fertility
        than scrotal circumference (age of puberty)
        alone
Heifer Pregnancy
   Heifer pregnancy EPD – What is the probability that a
    sire’s daughters will conceive in a restricted breeding
    season?

   Heritability
       Angus = .13
       Red Angus = .24
       Limousin = .20

   Challenge – knowing what heifers had the
    opportunity to conceive
What about cow longevity?

 The ability of a cow to produce a
  calf each year on a consistent
                basis
Stayability
   Stayability – Given the female has a calf at
    age one, what is the probability that she will
    stay in the herd and raise a calf at age 6?

   Why 6 years of age?
       Guttierez et al. showed this was typically the
        average age a cow paid for herself (and the cows
        that didn’t make it to that age)
Stayability (continued)
   Challenges – lack of total herd reporting
    systems that have cow disposal information…
       In the perfect world would require the cow to
        have a calf every year

   Heritability estimates (higher than many
    other measures):
       Red Angus = 0.08
       Simmental = 0.11
       Gelbvieh = 0.12
       What evaluations for reproductive
       ability are out there?
U.S. Beef Industry
      Breed                        Traits Evaluated
       Angus         Scrotal Circumference
     Red Angus       Heifer Pregnancy, Stayability
     Limousin        Scrotal Circumference, Stayability**
     Gelbvieh        Stayability
     Simmental       Stayability **
      Brangus        Collecting data for stayability
     Hereford        Scrotal Circumference
How important is reproductive
ability?
   The largest contributor to profitability of
    the cow/calf operation.
       Ponzoni and Newman, 1989; Melton, 1995
Examples of the value associated
with genetic improvement of
fertility
Change in net income as a function of sires’
heifer pregnancy EPD and herd phenotypic heifer
pregnancy level - 1000 cow herd, 18%
replacement rate
 Change in Net Income
Change in net income ($) per 1000
base cow herd -- stayability
Net Income


                             Herd Stayability




Stayability EPD
Change in number of mature
cows– stayability
Challenges of stayability EPD
   Getting ―reasonably‖ high sire
    accuracies at early ages
       For a cow to have an observation she must
        be 6 years of age


   Strategies for overcoming this challenge
       Find genetically correlated traits
Correlated traits
   Body Condition Score
       Questions:
            Devori Beckman, PhD student
            Is it heritable? (requirement)
            Is it genetically related to stayability?
                 Phenotypically??—yes!
Observations on BCS
   Balancing management and genetic
    improvement…

   Contemporary groups must have
    variation.
   Variability in BCS
3000

2500

2000

1500                                               2 Year-old
                                                   3 Year-old
1000                                               4 Year-old
 500

   0
       BCS 2 and BCS 4   BCS 5   BCS 6 BCS 7 and
          3                               8
BCS – is it heritable?
Age BCS                      Is it heritable?
recorded   Heritability
                                 YES!!!

 2 Years       .20
                             Is it genetically
 3 Years       .17            related to
                              stayability?
 4 Years       .23
     Our theory—genetic optimum
     for fertility

Heifer pregnancy
rate




                   BCS < 3 BCS 4 to BCS 6+
                             6
Another option
   Use earlier measures of fertility to
    increase accuracy of stayability EPD
       Heifer pregnancy
       Stayability at earlier ages
            Stayability to 3 years of age
Summary
   Historically reproductive ability of the
    cow herd has been difficult to improve
   Large breed association databases have
    given us the opportunity to develop
    tools for genetic improvement of fertility
       Stayability (length of productive cow life)
       Heifer pregnancy
Questions?

								
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