Small Ruminant Medicine - Investigating Lambing Losses

Outline the steps involved in undertaking a flock or herd investigation.

History

Examine the Environment

Examine the Animal

Ancilliary Aids

Data Analysis and Decision Making

Reporting and Further Monitoring

What is the critical lambing % for self replacing Merino Flocks and what is the average marking %?

Critical lambing rate is 60-65%

Average marking rate is 85%

Define ‘lamb marking rates’

It has different meanings so please clarify it with your farmer.

Normally it is the number of **lambs marked per 100 ewes exposed to the rams**

Define the terms ‘fertility’

Ewes that present with a lamb at marking and are pregnant

Define the term ‘fecundity’.

The numbers of lambs produced

The average normal resting heart rate for an adult ewe is?

70-90 beats/min

What is the rule of thumb when joining ewes?

Aim for 3 to 3.5 BCS at joining and keep it short (5 weeks) and maintain this BCS throughout pregnancy to:

* Increase conception rate


* Increase lamb birthweight and surviviability
* Increase lamb weaning weight

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What are the economic drivers of lambing?

1. Stocking Rate → main one!
2. Net Reproductive Rate
3. Nutrition

How can you manipulate onset of oestrus?

1. Ram Effect
2. Intravaginal progestagen + eCG + PMSG
3. Photoperiod Control
4. Melatonin

How many ewes do you expect to be in lamb at scanning from a 5 week seasonal joining?

95% in lamb

What factors can lower % pregnant at scanning?

* Clovers disease → phytooestrogens in subclover and red clover
* Brucellosis
* Nutrition → declines is < 2.5 BCS
* Seasonality can cause gradual smaller losses
* Poor ovulation rates → age, genes, breeds, season and nutrition
* Embyronic Mortality → age, genes, nutrition, stress, Se deficiency, infectious diseases

What % of ewes are expected to lamb?

>98% should lamb as the second half of pregnancy is considered robust (from Day 18-20 onwards)

What are the expected lamb survivial rates?

From days 1-5

Singles: 88%

Twins: 78%

How do breeds differ in ferility?

* British breede except the Poll Dorset have a sharply defined breeding season
* First cross ewes are intermediate
* Merinos are less seasonal
* Dorpers are said to be less seasonal but in practice are pretty seasonal

Phytoestrogens can cause both temporary and permanent infertility. Explain the difference and what plants cause which?

1. Temporary Infertility: **green oestrogenic clover** → watery cervical mucous which impairs sperm transport through cervix
2. Permanent Infertility: **high formonentin** content clovers

* Subclovers (annual)
* Red clovers (perenial)

What is the prime factor that determines lambing rates and lamb survival rates?

Stocking rate

Which is more important BCS or flushing?

BCS

Aim for CS 3 at joining! Flushing can help maintain BCS by giivng a nutrition spike just before mating to increase ovulation but ultimaltely BCS is more important than a push in nutrition.

What are the three common causes abortion in sheep?

In order of most common:


1. Campylobacteriosis (C. fetus fetus & jejuni)
2. Listeriosis (L. monocytogenes & ivanocii)
3. Toxoplasmosis (T. gondii)

N.B: we do not have aborting strain of Salmonella in AUS

How is campylobacteria transmitted?

1. CLOSE CONTACT TRANSMISSION through discharge
2. Oral route → septicaemia

How does Campylobacter fetus fetus or jejuni cause abortion outbreaks?

1. Sporadic outbreaks in early pregannacy
2. Abortion “Snowstorm” within 3 weeks of ewe being exposed to campylobacter → 10-60% lamb loss

How can you diagnosis campylobacteriosis?

* History
* Sample aborted membranes and foetal stomach contents
* PM → **grey-like rosettes (necrotic foci) in foetal livers** are pathognomonic

How is toxoplasmosis transmitted?

Ingestion of feed (open bins or haystacks) or water contaminated with cat faeces containing Toxoplasma oocysts

How would you diagnosis toxoplasmosis?

* History
* Sample the placental cotyledons and foetal brain, lung and liver
* PM → **bright to dark red placental cotyledons** with white foci of necrosis
* **Mummified foetus**

What are the risk factors of pregnancy toxaemia?

1. Very fat or skiny ewes
2. Ewe with twins
3. Older ewes > maidens
4. British crossbreds
5. Shearing
6. Anything that decreases in feed intake

What are the differences in presentation between preg tox and hypocalcaemia?

Preg Tox → gradual onset → low numbers over prolonged period → depressed & down → take the UP & kick the DOWN

Hypocalcaemia → sudden onset → large numbers → BAR & down → can get them back up

What is the main risk factor causing hypocalcaemia?

Stress

What is a big factor contributing to pre-weaning losses?

Perinatal looses contributes to 80-90% of pre-weaning losses

What are the risk factors which affect perinatal lambing loss?

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* Less than 4kg birthweight (4-6kg is optimal)


* Litter size (twinning worse than singles)
* Maternal instinct
* Age of ewe
* Nutrition of ewe
* Predation
* Environmental conditions
* Infectious diseases
* Brown Fat Reserves

How can you distinguish loss before scanning (embryonic mortality) from perinatal losses?

Wet/dry ewe marking

Wet → lambed and successfully reared

Dry → lambed and lost

What are major causes of lamb losses?

1. Starvation, Mismothering, Exposure (SME)
2. Dystocia → neurological issues from lack of oxygen, haemorrhage, odema or congestion from trauma
3. Predation → puncture wounds, soft tissue or extensive carcass damage

What are minor causes of lambing losses?

* Death in utero → lethal congenital malformations)
* Prematurity → smaller lamb liveweights
* Infectious diseases → campylobacter or toxoplasmosis
* Trauma other than dystocia → stood on by ewe
* Trace element deficiencies (I, Se and Cu)

Describe the main epidemiological features and diagnostic methods of the following condition: starvation/ mismothering complex.

Check the following:

* Breathed or not → aeration in lungs?
* Presence of milk clot in abomasum → suckling
* Presence of white scattered substance in intestinal lymphatics → digested milk
* Brown adipose tissue (BAT) reserves
* Brain and/or spinal cord lesions → dystocia
* Yellow subcutaneous oedema of extremities → hypothermia

Describe infections that can cause perinatal lamb loss?

1. Navel Infection

Poor hygiene → peritonitis or septicaemia or focal infections


2. Weakly Lambs

Starved or infected by Campylobacteria or Toxoplasma


3. Watery Mouth

Ingestion of faecal matter looking for udder → E. coli endotoxaemia

What trace element in foetuses must be derived from maternal sources?

Iodine is essential for thyroid hormone production → necessary for CNS development and foetal growth, and thermoregulation after birth

**Subclinical**

* Decreased metabolic rate
* Impaired brain development, reduced lung development, impaired suckling behaviour
* Weak lambs and kids, very susceptible to cold stress

**Iodine Deficiency**

* Small woolless lambs which are weak and susceptible to coldstress
* Usually also high incidence of still births
* Goitre → enlarged thyroid → may cause dystocia
* Goats more susceptible than sheep

You dissect and weigh a lamb’s thyroid glands after a PM. What does the weight of the thyroid gland indicate?

Lamb thyroid > 0.4 g/kg BW → subclinical iodine deficiency

Lamb thyroid > 0.8 g/kg BW → goitre

Describe a simple post-mortem technique that your client could perform to determine whether a dead lamb:


1. Was born alive of still-born
2. Managed to get up is feet and walk
3. Died before or after all its reserves of energy were exhausted

1. Evidence of breath → aeration in lungs or presence of congenital defects
2. Presence of eponychium on hooves
3. Analyse the BAT (soft gelatinous pink/red if metabolised)