Study Objectives
1. Understand why different breeds developed within
domestic animal species
2. Describe and contrast the growth and development of
small and large framed cattle breeds
3. Learn what frame scores are and how they are calculated
and interpreted
4. Describe the differences in growth between breeds of
cattle, sheep and pigs selected for different purposes
5. Describe the different growth patterns between male,
female and castrated animals
6. Learn how and why muscle, fat and bone development
differs between the sex classes
Genetics — Breeds
Genetic factors affecting growth
Breeds
• Within a species, animal breeders have placed selection pressure
on different traits that have led to many different breeds
Strength
Disease resistance
Meat
Milk
Domestication
~8,500 B.C.
Cattle breeds
Chianina
Holstein
Angus
Jersey
• Within breeds selected for meat and milk production, cattle have
also been selected for size
• As a result some breeds have very large skeletons and are called
large-framed cattle
• Breeds with small skeletons are so-called small-framed breeds
Distribution of cattle frame size
Holstein
Jersey
Frame score
• To determine the frame size of an individual animal,
a frame score is given for a particular age range
• Frame score is based on the height over the hips
Frame score
How to evaluate body/frame type
• The height or 'frame' of cattle of a given age is closely
related to maturity type
Maturing type
Early
Moderate
Late
Very-late
Frame score
1 and 2
3, 4 and 5
6, 7 and 8
9, 10 and 11
growth potential
Low/Lack
rapid
Average
high
extreme
Muscle
good
good
Lean
extremely lean
Carcass weights
150–180 kg
200–350 kg 350–450 kg
Framed
>450
Frame type - growth and fattening
relationships
• Large framed cattle reach heavier weights at a given
compositional or physiological maturity, e.g. slaughter
weight
• Large-framed cattle
take longer to reach
their mature weight
and are therefore
considered latermaturing animals
• Because small framed
animals grow relatively
quickly they are called
Frame type - growth and fattening
relationships
• At the same chronological age, large-framed animals are
physiologically younger than small-framed animals
• If comparisons are made
at the same chronological
age or same weight, later
maturing (large-framed)
animals are leaner, while
earlier maturing (small
framed) animals are
fatter and more
physiologically mature
Small-framed
Large-framed
Frame type - growth and fattening
relationships
• Cattle can be compared at
the same physiological or
compositional endpoint, i.e.
1. Puberty
2. 5% intramuscular fat in
the longissimus muscle
3. 19% fat trim
• In this case, large-framed, later-maturing cattle can be
compositionally equivalent to small-framed cattle
Frame type - growth and fattening
relationships
Effect of Frame Size and Breed on Beef Carcass
Composition at a Constant Maturity (19% Fat Trim)
% Lean
% Fat trim
% Bone
Hereford
Angus X
Red
Poll X
Maine
Anjou X
Chianina
X
68.8
68.4
68.6
69
-
-
-
-
12.3
12.7
12.5
12.1
Small-framed
Large-framed
Frame type - growth and fattening
relationships
Effect of Frame Size and Breed on Beef Carcass Composition
at a Constant Quality Grade (5% Fat in Longissimus)
Hereford Limousin Simmental Charolais
Angus X
X
X
X
% Lean
67.1
69.6
69.7
70.9
% Fat trim
20.3
18.5
17.2
16.2
% Bone
12.6
11.9
13.1
12.9
Small-framed
Large-framed
Cattle breeds - Beef vs Dairy
Holstein
Hereford
Cattle breeds - Beef vs Dairy
• Selection for muscle is inversely related to milk production
• Animals used for milk production are less muscular
• Reduction in muscle fiber numbers in milk breeds, which occurs
prenatal
• Selection has not changed muscle distribution
Cattle breeds - Beef vs Dairy
Muscle : Bone Ratios
• Changes in muscle to bone ratios are primarily responsible for
muscling differences across breeds
• Mature muscle to bone ratios range from 4:1 to 7:1 for dairy
cattle and double-muscled cattle, respectively
Weight of muscle plus bone (kg)
Effect of breed types
on fat distribution
• Selection for milk production
has shifted the fat distribution
on the carcass
• As stated earlier, in mature
meat cattle, carcass fat is
generally evenly distributed
between the intermuscular
and subcutaneous depots
• However, dairy cattle have less
subcutaneous fat but more
prerenal fat than beef cattle
500
Sheep breeds - Wool vs Meat
• Selection for muscle is
inversely related to wool
production
• Meat breeds have superior
conformation as measured by
muscle:bone ratios = amount
of meat per unit of bone
• Wool breeds are larger
framed, fatten at heavier
weights than meat breeds
Marino - wool
Suffolk - meat
Pig Breeds - Maternal vs Meat
Yorkshire -maternal
• Selection for muscle is
inversely related to ability to
conceive and produce milk
for young
• Pietrian pigs are extremely
muscular compared to
maternal breeds like
Yorkshire and Landrace
Pietrian - meat
Genetics — Sex
Genetic factors - Sex
Growth and composition are dependant on the sex of
the animal
• Intact males are capable of > body weights than
castrates and females
• Intact males attain compositional maturity at later
chronological ages than castrates and females
• Intact males are generally heavier at any given
chronological age
• Intact females mature earliest of sex classes,
whereas castrates are intermediate
Genetic factors - Sex
Onset of maturity
Barrow = castrated boar
Gilt = female pig that has not
produced a litter
Wether = castrated ram
Capon = castrated rooster
Pullet = young hen
Heifer = young female cow
Genetic factors - Sex
Exception are pigs:
• Gilts (females that have not been bred) mature later
and reach heavier weights than barrows (male
castrates)
• Gilts are leaner than barrows at same chronological
age; “why” is unclear
• Maybe associated with estrogen secretion
enhancing muscle development
Genetic factors - Sex
Sex – Muscle differences
• Intact males have greater
Bull
proportion of muscle located in
forequarter, specifically in neck and
thorax, which are associated with
secondary sex characteristics
• Increased androgen binding
receptors in these tissues
• Females have increased proportion
of muscle in pelvic limb and
abdominal wall – support for fetus
and udder (mammary gland)
• Castrates are intermediate
Cow
Steer
Genetic factors - Sex
Sex – Muscle differences
• Males have larger muscle fiber diameters than females and
castrates
• Differences are hormonally driven (Testosterone)
• Male >> Castrate >> Female
Genetic factors - Sex
Sex – Skeleton differences
• Estrogen stimulates epiphyseal plate closure
• Therefore intact males tend to be taller than females because
their long bones grow more before closure
• Both estrogens and androgens increase periosteal bone growth
(bone thickening) but androgens more.
Genetic factors - Sex
Sex – Fat differences
• Lipogenesis and lipolysis are hormonally regulated through sex
steroids with dramatic effects
• E.g. animals at equal slaughter weights, from leanest to fattest
1. Cattle: male, castrate, female
2. Sheep: male, castrate, female
3. Swine: male, female, castrate
Genetic factors - Sex
Sex – Fat differences
• Gender effects drive nutrient partitioning
• Why do females fatten sooner?
- Decreased long bone growth due to increased estrogen
- Muscle growth starts to decrease and more nutrients available
for fat
Epiphyseal
plate closes