- -  AGRICULTURE CORE CURRICULUM  - -

(CLF3000)  Advanced Core Cluster:  ANIMAL SCIENCE

  (CLF3250)  Unit Title:  LIVESTOCK BREEDING AND GENETICS

____________________________________________________________________________
  (CLF3262)  Topic:  CROSSBREED             Time          Year(s)
                     IDENTIFICATION        1 hour          3 / 4
____________________________________________________________________________

          Topic Objectives:  Upon completion of this lesson, the
                             student will be able to:

          Learning Outcome #:

            (D-25)  -  Visually identify cross-breeds of commercial
                       livestock and explain the advantages of the
                       cross.

          Special Materials and Equipment:  Slides of examples of
                        common crossbred animals.

          References:  Ensminger, M.E. (1983). THE STOCKMAN'S 
                         HANDBOOK.
                       Bundy and Diggins. (1968). LIVESTOCK AND 
                         POULTRY PRODUCTION.
                       Roediger, Roger D. (1977). LIVESTOCK BREEDING.

          Evaluation:  Correct visual identification of crossbreds
                       using either slides or live animals.


TOPIC PRESENTATION:  CROSSBREED IDENTIFICATION

A.  Definition of Crossbreeding:  The mating of at least two different 
    breeds of animals together.

B.  Reasons Why Crossbreeding is Used:

    1.  Hybrid vigor or Heterosis:

        a.  The biological phenomenon which causes crossbreds to 
            out produce the average of their parents.  For example,

            1)  an average crossbred beef cow will produce more milk 
                and be a better mother than an average purebred cow.

            2)  an average crossbred sow will lactate better and
                produce a larger litter than an average purebred sow.

        b.  The level of hybrid vigor for all traits depends on the
            breeds used.  The greater the genetic difference, the 
            greater the hybrid vigor.  For example,

                crossing Brahma cattle (Bos Indicus) with Hereford 
                cattle (Bos Taurus) shows greater hybrid vigor than 
                crossing Angus cattle with Hereford cattle (both Bos
                Taurus).

        c.  Traits high in heritability show little response in 
            hybrid vigor crosses.  Traits low in heritability show a 
            good response in hybrid vigor crosses.

    2.  Complementarity:

        a.  The advantage of one cross over another cross or over a 
            purebred is so that 2 or more characters combine to 
            COMPLEMENT each other.

        b.  Matching of breeds so that they compensate each other,
            the objective is to get the desirable traits of each. 
            For example,

                in swine, the Landrace breed is known for its 
                prolificacy, but it is light muscled, and the
                Hampshire breed is known for its excellent carcass; 
                by crossing these 2 breeds, the female offspring 
                will produce large litters with adequate conformation.

    3.  Introduce new genes quickly:  New and desired genes are infused at a 
        faster rate by crossbreeding than by just using selection.  For 
        example,

                we can introduce new genes for milk production in a 
                beef cow herd by crossing them with a dairy breed 
                much faster than if we try to improve milk 
                production through selection alone.

C.  Examples of Common Crossbreds:

    1.  Beef cattle -

        a.  Black with a white face or black baldy cattle result 
            from a cross between Hereford cattle and Angus cattle 
            They are:

            1)  Recognized by their white faces and black bodies.

            2)  The resulting offspring from this cross show 
                hybrid vigor in the areas of growth and resistance to 
                disease; and if they are allowed to mature, the 
                females will have above average milk production and 
                mothering abilities.


        b.  Zebu or Brahma are often crossed with British breeds such as the 
            Hereford, Angus, or Shorthorn.

            1)  They are recognized by large, droopy ears, extra leather 
                around the brisket area, a slight hump at the
                crest, and a slight sloping of the rump from hooks to
                pins.

            2)  The resulting offspring from this cross will show hybrid 
                vigor in the areas of heat tolerance, insect 
                resistance, improved rate of gain, and mothering 
                ability.

    2.  Sheep - Crosses between white face wool breeds and black face 
        mutton breeds are common.

        a.  they can be recognized by their spotted faces (brockle 
            face).

        b.  By mating blackface rams to whiteface (range) ewes, we 
            get fast growing lambs with good range hardiness and 
            wool quality.

    3.  Swine - Crosses between swine breeds are very common and most 
        commercial swine producers raise crossbred market animals from 
        crossbred sows.  An example:

                is the "blue - butt", which is a cross between a 
                Hampshire and a Yorkshire (or some other white
                breed).  The advantages of hybrid vigor are present
                in above average growth rate and feed conversion 
                rates.

    4.  Dairy Cattle -

        a.  The crossing of dairy cattle breeds produces hybrid vigor 
            just as in meat animals.  However, crossbreeding has been 
            used little in the dairy industry.  This is because one 
            breed, the Holstein, produces much more milk than any 
            other breed.  The crossbred cow, for example Jersey x
            Holstein, will produce more milk than the average of the 
            two parents, but less than the pure Holstein.

        b.  With the current system of pricing milk and the high 
            yields of milk from the Holstein, we do not have a 
            crossbred that competes economically.



4/16/90  bkm/sg/gv


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