Pak Dairy Info
Pakistan's 1st Online Dairy Farming Guide

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Contents

Introduction

Breeds

Selection of Animals

Farm Building

Management

Record Keeping

Sanitation & Hygiene

Nutrition

Reproduction

Breeding

Health

Body Condition Scoring

Milk Quality

Feasibility

Terminologies

Directory

Picture Gallery

Qualitative & Quantitative Traits

Qualitative Traits:
The traits showing the simplest type of inheritance are called as qualitative traits. These involve only one pair of genes. Evident examples of such traits in dairy cattle are hair colour, horned versus polled, some inherited abnormalities and blood antigens. Coat colour is still important from the standpoint of breed requirements. A pair of genes is responsible for hair colour in cattle. A Milking Shorthorn having two genes for red (RR) is actually red in colour, while an animal having two genes for white (rr) is white in colour. A Milking Shorthorn that has one gene for red (R) and one for white (r) is neither red nor white but roan (Rr), which is a mixture of red and white. Thus, red and white matings in Milking Shorthorn cattle usually produce roan offspring. Likewise, white and white matings generally produce white offspring, even though white Milking Shorthorn is seldom pure because the face bristles, eyelashes, and ears usually carry red hairs. Roans, having one gene for red and one for white on the paired chromosomes, never breed true and when mated together produce calves in the proportion of one red, two roans, and one white. The most certain way to produce roan Milking Shorthorns, is to mate red cows with a white bull, or vice versa; this produces all roan calves. If a roan animal is bred to a red one, one-half of the offspring will be red, whereas the other half will be roan. Likewise, when a roan animal is bred to a white one, approximately an equal number of roan and white calves will be produced.


Quantitative Traits:


 

Quantitative traits are also termed as multiple gene inheritance. Relatively a few traits of economic importance in farm animals are inherited in as simple a manner as the coat colour or the polled condition. Most traits of economic importance, such as milk yield and composition, conformation, feed efficiency, disease resistance, are controlled by multiple genes. Because such traits may be expressed in all possible gradations, from high to low performance, they are known as quantitative traits. Estimates of the number of pairs of genes affecting each economically important characteristic vary greatly, but the majority of the geneticists agree that ten or more pairs of genes are involved for most such traits. In addition to being influenced by many pairs of genes, quantitative traits differ from qualitative traits because they are frequently strongly influenced by the environment.

Factors Governing Heritability of Traits in Dairy Animals:
Thee phenotypic expression of a trait, such as milk production, depends on two factors: Inheritance (the genetic potential for expression of a particular trait) and environment (the opportunity to express the inherited trait). Heritability is 100% when the expression of the trait varies solely because of inheritance. A trait that varies solely because of environment has a heritability zero.

Variation in the expression of most traits is neither totally environmental nor completely hereditary. The heritability of some important dairy animal traits is given in Tables below. Traits with higher heritabilities allow more rapid genetic progress. In addition, traits with high heritabilities increase the value of the animal's own phenotype as an estimator of genotype. Even with the most highly heritable production traits, however, at least 50% of the population variation is attributable to environment or heredity-environment interactions. Although some environmental variables are not easily managed (weather or climate, season of calving), many are directly management influenced (feeding, housing, reproductive handling, health care). Most traits of economic importance are primarily controlled by a combination of both management skills and genetics.

The following example shows how heritability can be computed: assume that a herd averages 10,000 litres of milk on a mature basis. A sire used in that herd is capable of transmitting inheritance for 12,000 litres of milk production. He is mated to select animals in the herd with production records averaging 12,000 litres of milk in a normal lactation of 305 days. Because heritability is 30%, we expect only 3/10th of the apparent superiority of the parents to be expressed in the offspring. The selected parents averaged 2,000 litres of milk higher than the herd. Three-tenths of the 2,000 equals 600 litres of milk. Thus, the offspring are expected to average 10,600 litres of milk in this herd when given the same opportunity (environmental effects) as the parents.

Heritabilities of Various Production and Type Traits of Cattle:

Traits

Heritability (h2)

Traits

Heritability (h2)

Milk yield

0.3

Fat yield

0.25

Fat percentage

0.5

Protein percentage

0.50

Reproduction

0.07

Milking rate

0.3

Stature

0.42

Feet and legs score

0.17

Strength

0.31

Fore attachment

0.29

Body depth

0.37

Rear udder height

0.28

Dairy form

0.29

Rear udder width

0.23

Rump angle

0.33

Udder cleft

0.24

Thurl width

0.26

Udder depth

0.28

Rear legs-side view

0.21

Front teat placement

0.26

Rear legs-rear view

0.11

Teat length

0.26

Foot angle

0.15

Final score

0.29


Genetic control (heritability, h2) for various economic traits in Nili-Ravi buffaloes:

Traits

h2 (%)

305-day milk yield (kg)

20

Lactation length (days)

10

Dry period (days)

3

Age at first calving (days)

10

Calving interval (days)

5

Service period (days)

5

Service per conception (number)

3

Gestation period (days)

3

Lifetime milk yield (kg)

15

Herd life (days)

5

Productive life (days)

20

Breeding efficiency (%)

3


Genetic control (heritability, h2) for various economic traits in Sahiwal cattle

Traits

h2 (%)

305-day milk yield (kg)

15

Lactation length (days)

12

Dry period (day)

10

Age at first calving (days)

12

Calving interval (days)

10

Service period (days)

15

Gestation period (days)

5

Lifetime milk yield (kg)

15

Herd life (days)

2

Productive life (days)

2

 

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