*3.2.2 Out crossing*

It is usually applies only to mating within a pure well-defined breed. If two lines within the same breed are separated for 4 or 5 generations and the sire from one herd is used in another herd that accounts to out crossing. It is used when the genetic variability and there is lack of selection response [3]. It introduces new genes in the population with reference - color, horn type, etc.

#### *3.2.3 Top crossing*

It refers to the use of highly inbred sires to the dams of the base population or non-inbred population within the same breed. It usually refers to the best sire in a pedigree. It also refers to the continued use of sires to different families within a pure bred, same breed or different breed [3, 5].

#### *3.2.4 Up-grading*

Grading up or upgrading is the repeated use of pure breed sire (or sires) over females of non-descript population. There is a noticed improvement in crosses if sires from a particular breed (A) are repeatedly back crossed to another breed/non-descript animals (B). Five generations are sufficient to raise the level of inheritance of breed A to 96.9% (0.969) in the fifth generation. After five generations of repeated back crossing to a particular breed, the animals after the end of fifth generation become eligible to be registered as purebred. After 7 to 8 generations of continuous grading up the non descript population will be transferred into well defined purebreed [3, 4].

The level of inheritance (%) of pure-bred male and non-descript in different generation under upgradation program is summarizes below in the [4, 5] (**Table 4**).

**Table 4** [4, 5] summarizes the change in the per cent level of inheritance of pure-bred male and non-descript female in different generation under upgradation program. By the successive backcrossing from one population into another population over generation after generation (7–8 generations), the non-descript population can be substituted by pure bred population.

The representative model for upgrading the local cattle by frozen semen and nucleus breeding unit is summarized in [4, 5] (**Figure 5**).
