3 Flashcards
is probably the single most important factor affecting the economics and
profitability of beef cattle breeding operations. For bulls, reproduction is all about the capacity and ability
to sire a large number of viable offspring in each mating year.
Reproduction
one generation to the next and can greatly influence genetic gainforms the basis of livestock improvement as it allows the transfer of genetic
material from
Reproduction
Improved management of
reproduction can increase economic returns to cattle producers. In severe environments where nutrition
is a major stress factor, improvements of 5–10% in weaning rates are possible through improving
nutrition and management.
Notes
/ Measuring reproductive performance
/
Reproductive performance is influenced by a number of independent traits.
Measures for the bulls
Measures for the cow
Measures for the breeder herd
Measures for the bulls include:
• physical and structural soundness
• scrotal size and sperm production capacity
• semen quality, including morphology
• serving ability/serving capacity.
Measures for the cow include:
• weight and age at first estrous cycle
• the inter-calving interval
• lactation status at subsequent pregnancy diagnosis.
Measures for the breeder herd include:
• branding and/or weaning rates
• kilograms of calf weaned per 100 kg of cow mated.
• conception rates determined by pregnancy diagnosis (PD)
Limitations to the above measures include:
- fertility cannot be assessed directly for bulls.
- pregnancy status for cows requires skills in pregnancy diagnosis, which should be coupled with an
assessment of lactation status. - branding and weaning rates (in isolation) do not provide indications of when or where reproductive
losses may be occurring. - unless birth dates are known and a restricted joining period used, a slight ‘creep’ in inter-calving
interval can often be overlooked. - it is important to consider that these rates must be calculated for a standard or specific period of time
(e.g., 12 months) to allow accurate analysis and comparison.
- This is difficult in a herd where controlled mating is not carried out, as distinctions between
calving periods become blurred.
Calculating a number of reproductive rates can
help to identify areas of loss.
A combination of
pregnancy diagnosis, lactation status, branding rates and weaning rates will help to determine stages and
possible causes of low herd fertility and assist in the following:
- identifying the importance of age, weight, body condition and lactation status impacts on herd fertility.
- identifying how management, nutrition and breeding practices can be modified to optimize fertility.
- making an assessment of whether disease status of both cows and bulls may be interfering with herd
fertility.
Bull costs per calf weaned will depend on:
1.) purchase price
5.) number of cows per bull
2.) bull salvage value at ultimate sale
6.) weaning percentage achieved;
3.) number of breeding seasons that involve the bull
7.) bull mortality rates;
4.) whether bulls are checked annually for soundness and fertility.
can be used to distinguish infertile or sub-fertile
bulls from those that meet satisfactory fertility standards.
bull breeding soundness evaluation (BBSE)
Key components of bull fertility:
- Bull breeding soundness evaluation (BBSE)
- Physical (structural) soundness
- Sheath, prepuce and penis.
- Semen and spermatozoa.
- Libido and serving ability.
involves assessing four key components—(i) physical
(structural) soundness, (ii) scrotal size (functional testicles), (iii) semen assessment (including
morphology where appropriate) and (iv) serving ability—to provide an indication of likely fertility.
Bull breeding soundness evaluation (BBSE)
Bull breeding soundness evaluation (BBSE) involves assessing four key components:
i) physical
(structural) soundness,
(ii) scrotal size (functional testicles), (iii) semen assessment (including
morphology where appropriate) and (iv) serving ability—to provide an indication of likely fertility
Assessing a bull’s structural soundness should include a systematic
examination of eyes and surrounding areas, jaws, mouth and teeth, limb structure, joints, stance, gait (at
trot), hoof and claw structure. Common problems (Figure 3.1) include post legs (excessively straight),
sickle hocks (standing under), swollen and puffy hocks, bow legs and cow hocks.
Physical (structural) soundness
structures are moderately
heritable. Likewise, any structural defects are passed
on to offspring.
Leg and foot
The penis is housed
within the
Prepuce and sheath
is the inner
lining of the sheath and is the pink mucosa, seen at the
end of the sheath. Figure 3.2 shows some structural
problems that can occur.
Prepuce
Scrotal size (Table 3.2) is a useful criterion for assessing bull fertility for the
following reasons:
1.) It is easily measured and is repeatable, and can take place at a younger age than most other male traits;
2.) It is related to a bull’s own fertility, and is a highly heritable trait that influences the scrotal size of
male offspring.
3.) Finally, it is genetically correlated—scrotal size in a sire is positively related to scrotal size of his
male progeny, and also earlier puberty and enhanced fertility of his female progeny.
The major factors influencing scrotal size include:
(i) genotype, (ii) age, (iii) liveweight, (iv) nutrition,
and (v) timing of nutritional stress
Common conditions that interfere with fertility and can be diagnosed by palpation of testicles include:
- unequal size of testicles
- hardness of one or both testicles
- thickened scrotal skin.
- softness and flabbiness of testicles and tail of epididymis
sample is often
collected as part of a routine BBSE conducted by a
veterinarian and examined crush-side under a
microscope to assess factors such as volume, color,
density and motility.
Semen
is the sexual
desire of a male to serve a receptive female. Number of mounts, mounts plus serves and libido score of
bulls that had passed a reproductive examination were found to be positively related to calf output in
multiple sire mating.
Libido