Mating, Pregnancy & Lactation Nutrition: Comprehensive Study Notes

Mating Nutrition, Puberty & Conception

Reproduction = cornerstone of efficiency in all grazing livestock; economic & ethical obligation to optimise.
Key performance indicators (KPIs)
- Ovulation rate (OR)
- Conception rate (CR)
- Post-partum anoestrus interval (PPAI)
Primary drivers affecting OR/CR/PPAI
- Attainment of puberty
- Breed/genetic fecundity (e.g. Boroola, Inverdale genes)
- Age/physiological maturity
- Live-weight (LW)
- Body-condition score (BCS)
- Disease status / health
- Acute nutritional plane ("flushing")
Ethical considerations
- Balancing maximal reproduction with animal welfare & longevity
- Avoiding excessive metabolic load, dystocia, or under-nutrition

LW facilitates but is not the sole trigger – interaction with relative maturity & body fat–derived adipocytokines.
Practical target LW = species specific; sheep ≈ \text{65 kg} for optimal reproductive success.

Kenyon et al. (2004):
- \text{OR} increases \approx 2\% per extra 1\,\text{kg LW} at mating.
- Little advantage above BCS 2 (5-point scale).
LW > 90\,\text{kg} in hinds reduces between-year variation in CR.
LW, BCS & fat reserves are inter-linked; insufficient reserves compromise reproduction.

WET = previous fawning status
EXP = experienced sire
CHS = back-up stag present
SHIFT = number of paddock shifts
SUR = % of time near roads/buildings (stress proxy)
AVMIT = mean minimum temperature
STOCK = mob re-compositions
→ Each alters behavioural stress, oestrous detection & ultimately CR.

Rising plane of nutrition immediately (< 7 d) pre-mating overrides static LW.
Protein supply, not energy per se, is the dominant component of the flushing response.

Determinants
- Maternal nutrition (early & mid-gestation critical)
- Disease
- Birth weight (BW)
- Brown adipose tissue (BAT) & neonatal thermoregulation
Multiples incur higher loss rates; scanning-to-day-120 feeding pivotal.

Deer gestation length decreases when dams are underfed (Scott 2008; Asher 2005).
Late-gestation protein needs escalate across species; shortage shortens gestation & lowers BW.

Similarities

Protein requirement surges in late gestation.
Protein restriction → ↓ BW, impaired muscle, altered glucose-insulin axis.
Both low-protein (LP) & high-protein (HP) weaken offspring immunity.
Differences
Pigs: highly sensitive to LP early/mid gestation (≈6\% CP).
Dairy cows: demand RP ratio optimisation; critical mid gestation 15.7\% CP.
Sheep/goats: placental vascular adaptation; over-feeding early ↑ adiposity.

BW drives BAT reserves ➔ neonatal heat production ➔ survival.
Russel et al. (1977): effect of metabolizable energy (ME) intake on BW
• Singles – 14.3\,\text{MJME d}^{-1} ⇒ 5.99\,\text{kg} BW
• Twins – 16.3\,\text{MJME d}^{-1} ⇒ 4.65\,\text{kg} BW
• Intake <8.1 MJME ⇒ dramatic BW decline.
Cotyledon number governs nutrient transfer:
- Sheep/cattle/pigs/goats: 75\text{–}125 cotyledon “burrs”/uterus.
- Deer: 4\text{–}6.
- Rhind (1980): 20\% ↓ cotyledons/foetus ⇒ 11\% ↓ foetal weight.
Arginine supplementation (Erichsen 2024)
- ↑ placental weight & gene expression (AA transport) in female foetuses; negligible in males.

Corner-Thomas (2015): BCS at lambing had less impact on lactation than feed allocation P141–L79 (800–1700 kg DM).
Sheep that lose LW during lactation wean heavier lamb weight (Scobie 2016) – elasticity trade-off.
Geenty & Sykes (1986): Efficiency of lactation declines with adipose mobilisation; lean tissue mobilisation exceptions.

Pasture alone insufficient for high-output ewe:
• LW ↓ up to 20\,\text{kg}
• BCS ↓ up to 1.5 units.
Mobilisation hierarchy: adipose > skeletal muscle (lean mass preserved).
LW change during lactation predicts the following year’s reproductive performance (Scobie 2016).

Total ME needs = Maintenance + Production:
\text{ME}_{\text{maint}} = 0.5 \times W^{0.75} \; (\text{MJ d}^{-1})
Pasture quality central – normally energy limiting; protein becomes limiting for OR and rapid growth.
Shortfalls can be temporary but must be replenished before the next mating.

Milk → primary nutrient for lamb; ewe draws on body reserves plus diet.
Both protein & energy requirements rise with growth, but \frac{\text{Protein}}{\text{Energy}} requirement of the lamb declines.
Typical nutritive values
• Milk: \approx10\,\text{g MP MJME}^{-1}
• Spring pasture: \approx7\,\text{g MP MJME}^{-1}
Risk: As milk yield falls, lamb may experience protein deficit even when energy is adequate.

Decision hinges on lamb’s capacity to harvest sufficient MP from herbage.
Early weaning → growth check; model the balance:
- Microbial protein synthesis ≈ 11\,\text{g MCP MJ FME}^{-1} where \text{FME}=0.9\times ME.
- UDP flow: 0.1 of CP, 80\% true protein, 65\% digestible.
- Milk MP: 43\,\text{g kg}^{-1}; ME density 4.14\,\text{MJ kg}^{-1}.
- Efficiency of ME for tissue gain: k_g = 0.0435\times (\text{MJME kgDM}^{-1}).

Inputs

Plane of nutrition in the fortnight pre-mating (protein-rich flush) offers high ROI.
Ensure LW targets (species-specific) and avoid excessive BCS (>3) wastage.
Feed multiples above maintenance from scanning to d120 gestation.
Monitor BCS monthly; replace any lactation-induced deficit by next mating.
Consider strategic AA supplementation (e.g. arginine) to enhance placental function, especially in ewe lambs.
Weaning decisions should be data-driven—calculate MP:ME balance rather than fixed dates.
Always weigh welfare & ethical obligations against production targets—avoid pushing animals beyond physiological capacity.