80% of the growth of the foetus occurs in the last six weeks. Ewes therefore have to pick up weight to prevent them using their reserves for the growth of the foetus. Ewes cannot take in sufficient energy for milk production daily and they need to build up sufficient fat reserves during this period.
The following are guidelines for minimum weight gain during the last 6 weeks of pregnancy:
- Single ewes: 5 to 7 Kg
- Twin ewes: 8 to 10 Kg
- Triplet ewes: 10 to 15 Kg (they can gain as much as 24 kg!)
Towards the end of gestation, the growth of the uterus with the foetus(ses) can cause the rumen to lose as much as 70% of its original volume. Ewes therefore struggle to digest roughage and all rumen functions are reduced. Concentrate feeding is now required. Green feed, for example oats, can contain as much as 80 to 90% moisture and is therefore not suitable for feeding ewes in late pregnancy.
Normal veld grasses in the winter has very low nutritional value and cannot supply the nutritional requirements of the ewes. These grasses are also poorly digestible and considering the reduced rumen capacity ewes are unable to 5 meet their requirements for maintenance, growth of the foetus, wool production and building of reserves. Karoobushes can supply most of the ewe’s nutrients but will probably lack energy.
Urea can only be converted to protein if the rumen microorganisms are functioning properly. It requires a slightly acid environment, minerals such as phosphate and trace elements and adequate carbohydrates in the form of starches and sugars. Urea can make the rumen very alkaline. My experience is that heavily pregnant ewes cannot convert urea to protein.
I recommend that ewes only receive natural protein in the last 6 weeks of pregnancy. All other sheep should not receive more than one third of their crude protein requirement from urea. Ketosis (twin lamb disease) in late pregnancy is common in ewes that are fat and carry multiples.
The cause is an energy deficiency that forces ewes to utilise their fat reserves to maintain their blood sugar levels. Fat is broken down partially and the substances that remain unused causes changes in the liver and supresses the brain.
A calcium deficiency occurs together with ketosis especially if the rumen pH is alkaline. Calcium is more soluble in an acid medium and the ewe cannot absorb sufficient calcium. Urea aggravates this problem. Lime should therefore be supplied together with the concentrates to prevent ketosis.
The following basic lick could be used:
- 1 % CLC Lime or Dicalcium phosphate or P12 lick 50% Maize meal,
- Other grain or Hominy chop (good quality)
- 12% Seed oil cake meal or HPC 36 urea free 19% Milled lucern or Voermol
- Super 18 18% Salt (50 Kg sea salt plus 1 Kg Epsom salts)
I am often requested to assist with lambs that are stuck in the birth canal with swollen heads in ewes running on green feed. Farmers often blame good nutrition.
Lambs do not grow in their heads alone!
The real problem is that green feed lacks energy and also has too little calcium and magnesium for the normal birth process. The lamb is pushed into the birth canal but no further when the ewe runs out of energy.
The blood drainage from the head is blocked while the arteries keep on pumping. The head starts swelling and becomes too big to be expelled by the ewe. The problem is always solved by supplementing ewes with chocolate grain or energy licks. I have never seen green feed as the cause of lambs getting too big.
In the next article, focus will be paid on post pregnancy.
By Dr Johan A. van Rooyen M.Med. Vet. Specialist Veterinarian
Steynsburg Animal Hospital