Control of ovine/caprine reproduction Flashcards
Table of measureable parameters during ovine reproduction
Define marking rate.
What is the critical marking weight to maintain a self-replacing flock?
Marking rate (%) = # lambs marked / # ewes mated (x100)
≥65% for a self-replacing flock
Why can pregancy rate not be accurately inferred from lamb marking percentage?
Due to high fecundity of sheep - twins/triplets are common TF [m]arking % > 100%] ≠ [pregancy rate = 100%]
What are the potential sources of dead lamb disappearance? What rate will this influence?
Predation (foxes, birds, dingoes)
Disappeared lambs affects lambing rate
Table of physiological values relating to reproduction in sheep & goats
Describe what physiology is occurring at each of the numbered steps in the diagram of the endocrinology of the ovine oestrous cycle
- Short day length → melatonin (pineal gland) → GnRH (HT) → FSH (AP)
- FSH waves stimulate follicular growth/development
- Mature follicles produce E2
- → +FB on AP = LH secretion
- → stims sexual behaviour/oestrus
- E2TH → LH surge → OV → follicle becomes a CL
- P4 (from CL) → –FB on HT/AP → suppresses GnRH/FSH
- 5a = P4 promotes uterine environment for pregancy
- Mature foetus outgrows uterus → cortisol release → uterine PGF2a production
- PGF2a → luteolysis → initiates parturition
What chemical interventions are available to manipulate the ovine oestrous cycle?
What is the main goal of each?
Ovastim/Fecundin = increases twin/triplet %
Regulin = bring ewes in seasonal anoestrus into oestrus
PGF2a = luteolytic (return to oestrus/termination of pregancy)
CCS = induce parturition
Describe the mechanism of action of Ovastim
Dose regime?
What is a major mitigating factor preventing common used of this drug?
Decreases –FB by ovarian androgens on HT → more FSH → more follicles are stimulated/grow to maturity
Dose = 2 initial doses (2mo + 1mo prior to joining) + 12mo booster
High neonatal mortality rate → need good BCS of ewes to facilitate lamb survival.
What physiological chemical is in Regulin?
How does is this used to control the oestrous cycle in ewes?
What alternative to Regulin is available to start seasonally anoestrus ewes cycling?
Melatonin
Exogenous melatonin → increases GnRH secretion during off-season of season breeds → ewes start cycling
- Doesn’t work in deep anoestrus in highly seasonal breeds
Alternative = teaser rams (vasectomised)
What is the correct timing of use for PGF2a to induce luteolysis in a non-pregnant ewe?
What is the correct timing of use for PGF2a to terminate pregancy in a pregnant ewe or a pregnant goat?
Luteolysis: admin ≥d5 post-OV → oestrus 2-3d later
Termination: luteolytic ≤ d50 of pregnancy (before placental takeover of P4 production)
- in goats: effective through whole pregancy
What is the ideal timing of use of CCS to induce parturition in ewes?
Dosage?
Aim to admin ≥ d144 (last 10d of pregancy) to increase lamb survival
Dose = 10mg dexamethasone IM
What is the ram effect?
What is the protocol for inducing this effect?
When are effects seen, in what % of ewes?
The ram effect: exposure to males induces oestrus
- separate F/M (>500m) for 3-4 wks
- introduce ram (d1)
- → most ewes OV but silent heats (as no p4-priming of brain) TF no mating
- early CL regression in 50% of ewes following silent heat
- Normal oestrus/OV 19-23d post-ram introduction
What options are able to be used as teaser rams/bucks?
Vasectomised rams
Testosterone-tx’d wethers (registration issues)
Regulin (melatonin)-tx of ewes
What method & timing of pregancy dx in sheep?
US dx
d50-100
