lecture 27: manipulating domestic animal reproduction 1 Flashcards
1
Q
What can we increase fertility?
A
manipulating reproduction
- breeding at younger ages
- advancing breeding season
- more frequent pregnancies
- synchronisation of ovulation
- induction of multiple ovulations
- genetic improvement
- artificial insemination
- improved pregnancy rate
- embryo transfer and associated techniques
- pregnancy testing
- control of birth timing
increasing economy, decreasing labour
2
Q
What is the relationship between nutrition, energy and reproduction?
A
- starvation
- anovulation
- inability to maintain pregnancy
- inability to maintain lactation
- suppressed sperm production
- altered behaviour
- intense exercise
- amenorrhea
- obesity
- inhibition of ovulation
- inhibition of sperm production
- behavioural modification
- altered foetal nutrition
- parturition issues
3
Q
What is the influence of nutrition?
A
- influence HPG axis acute and chronic effects
- patterns of LH secretion in a rhesus monkey on a normal day of feeding, during a day of fasting, and during refeeding
- nutrition/stress interaction
- LH surge
- ovulation number and egg quality “flush feeding”
- sex ration of offspring
4
Q
What is the relationship between nutrition and puberty?
A
- timing of breeding in sheep fed different diets to manipulate growth rate
- patterns of GnRH secretion in a rapidly growing (top) and in a slowly growing (bottom) lamb
5
Q
What happens with resumption of cycles after calving and subsequent pregnancy rate?
A
- 1st heat BUT then continued cyclicity affected
- conception rate - bell-shaped distribution
- leptin, kisspeptin, ghrelin and other hormones
- metabolic substrates
- direct effect of nutrients
6
Q
What is the role of micronutrients?
A
- e.g. vitamin E and selenium
- antioxidant - free radical scavenger
- deficiency causes infertility in both males and females but by different mechanisms and effects vary between species
- reduced sperm motility and maturity
- rats: normal ovulation/mating but foetal loss after day 7
- cattle: silent heat, delayed conception, reduced fertilisation, cystic ovaries, retained foetal membranes, metabolic disorders
- goats (control vs selenium deficient)
- conception rate: 93% vs 64%
- infertile does: 7.4% vs 36%
- weaned kids/doe: 0.89% vs 0.36%
- milk fat (g/day): 41 vs 36
- milk protein (g/day) 32 vs 28
7
Q
What is the impact of nutritional factors?
A
- impact on females
- ovarian/oocyte
- energy (fat) content/ratio of the oocyte or zona pellucida
- uterine
- sperm swimming/signalling - viscosity + pH “inhospitable”
- modulated lumen histotroph (nutrients - glucose, proteins)
- embryonic loss
- glucose main substrate for embryo development
- modulated embryo-maternal communication (MRP)
- placentation failure - foetal reabsorption or abortion
- ovarian/oocyte
- impact on males
- testis development
- hormone regulation altered
- testicular mass and function
- sperm
- sperm fatty acid composition
- characteristics - abnormal morphology
- testis development
8
Q
What is manipulating the breeding season?
A
- why?
- marketing - lambs
- survival or young
- convenience
- to fit artificial constraints (e.g. horses)
- methods
- photoperiod
- melatonin-implants
- pheromones
9
Q
What is the “ram effect”?
A
- pheromones from ram induce increased LH pulsatility in ewes
- synchronisation of ewes and lambing
- earlier breeding onset (seasonal) (varies with breed)
- allows maximisation of use of valuable stud rams
10
Q
What is artificial insemination?
A
- first performed in 1800s
- widespread commercial use began in 1950s when semen freezing developed
- facilitates genetic improvement of herds
- global frozen genetics - avoids some quarantine restrictions for studs
- “insurance” against death or injury
- cost/benefit determines usage ($10-$100 straw)
- “heat” detection - timing
- visual, tailpant, KAMAR, paedometer
- e.g. cows are in heat for about 18h; best fertilisation rate after insemination 12 h after onset of heat
11
Q
What are aspects of semen to consider in AI?
A
- collection
- artificial vagina; teaser
- bull ~12 billion sperm per ejaculate
- evaluation
- motility, morphology
- dilution
- specialised media containing cryoprotectants, egg yolk, fructose etc
- need 10-25 million sperm per straw
- pack in “straws” (~20 million sperm)
- cool and freeze
- store in liquid nitrogen
- thaw
- inseminate via cervix
- sexed semen (recently available)
12
Q
Are semen collection requiremnets all the same?
A
- no, semen collection requirements vary by species
13
Q
What is improving herd genetics?
A
- desired improvements in productivity
- milk, meat, wool production etc
- limited availability and high cost of top-quality sires
- e.g. top-quality bull may be able to service 3-4 cows per day during breeding season
- proving Bulls for AI at genetics australia (progeny testing)
- year 0-1 source best bulls and best cows, mate and rear bull calves
- year 2 - and collect and distribute semen for test programme (500-1000)
- year 3 - calves born
- year 4 - daughters mated
- year 5 - daughters start milking and sires obtain genetic ranking (BV)
- year 6 - sires of best daughters chosen for use (~1 in 30)
- large numbers → more accurate genetic diagnosis
- faster time scale than with natural breeding
14
Q
What does AI with frozen semen make possible?
A
- makes careful genetic selection of sires possible
15
Q
What are pros and cons of AI?
A
- advantages
- increased production e.g. need 3 rams per 100 randomly cycling sheep to maintain good pregnancy rates
- disease control
- sire availability (global)
- safety (e.g. dangerous bulls)
- long-term supply
- disadvantages
- cost of semen
- technical skill
- can have lower success
- potential for uterine injury or infection
17
Q
What is the normal oestrous cycle in a cow?
A
- use of
- prostaglandin
- CIDR (progestins)
- ovulation inducers (GnRH/hCG/eCG)
18
Q
What is use of prostaglandin in cow oestrous cycle?
A
- can use any time after day 4 of cycle, when CL is responsive → luteolysis and synchronisation
19
Q
What is use of prostaglandin x 2 ?
A
- can use any time after day 4 of cycle, when CL is responsive → luteolysis and synchronisation
- 2nd treatment 11 days later: sensitive CL → luteolysis and = tighter synchrony
20
Q
What is use of prostaglandin and CIDR?
A
- can use an initial PGF2alpha injection
- insert CIDR in late luteal phase for 7-12 days
- PGF2alpha injection 1-2 days before CIDR removal → luteolysis = tighter synchrony
- heat observed and AI or time mated
- CL already regressed by PG injection, but high progesterone suppresses ovulations until CIDR removal
21
Q
What is use of prostaglandin, CIDR, and GnRH?
A
- CIDR and PGF2a injection = luteolysis
- injection of GnRH also synchronises timing of ovulation = very tight synchrony
- heat observed and AI or time mated
25
Q
What is decreasing fertility?
A
- why?
- suppression of behaviour (e.g. male aggression)
- management and stop in-breeding
- improved growth rates, taste (Boar-taint)
- androstenone and skatole in fat
- domestic, companion and wild animals
- desexed e.g. castration
- vaccination - GnRH, GDF-9/BMP-15
- immunocastration
- GnRH agonists (Deslorelin)
