BY: BEN ALLOTT
Not only are reduced wastage rates an area of potential productivity gains but also animal wastage has been identified as an animal welfare concern and a reputational risk for the red meat industry in New Zealand.
This article explores some of the key contributing factors that influence the loss of lambs between scanning and tailing.
EWE BODY CONDITION SCORE (BCS)
Ensuring all ewes reach BCS of 3 should be a priority. There are numerous benefits in terms of fertility if ewes reach a BCS of 3 before tupping, and in terms of lamb survival if ewes maintain this condition until lambing.
- Lamb survival decreases by 5% for every half of BCS lost in the four weeks prior to lambing
- Lamb survival decreases by 5% for every half of BCS below 3 at lambing
There are few benefits to increasing BCS above 3 and so to achieve the most efficient use of feed the priority is to lift the BCS of light ewes.
SHEARING
A number of trials show that on average, as long as ewes are well fed in the immediate post-shearing period, lamb birth weights increase by about 0.2-0.4kg and multiple lamb survival increases when ewes are shorn between days 70-110 of pregnancy. Shearing later than this (pre-lamb shearing) reduces any positive effects and importantly increases the risk to the ewe of excessive weight loss and metabolic diseases.
FEEDING EWES IN LATE PREGNANCY
Underfeeding of multiple bearing ewes in the last month of pregnancy is common. The impact of such underfeeding contributes to increased lamb wastage through a number of mechanisms, including:
- The birth of smaller lambs with reduced brown fat (energy) stores. Lambs born at less than 4kg have poor survival outcomes.
- Reduced colostrum volume and quality.
- Poor maternal instinct and impaired lamb bonding = mismothering.
- Decreased lamb vitality and impaired ability to regulate body temperature in cold conditions.
- Increased birthing difficulties.
LATE PREGNANCY STRESS
Sudden changes in feed type and feed quality can result in reduced feed intake and increase the risk of metabolic disease if this occurs very close to lambing.
Time spent off feed for pre-lamb treatments – multiple bearing lambs are very sensitive to the effects of withholding feed.
Timing of pre-lamb treatments – get multiple bearing ewes done first with more time before they are due to lamb, 3-4 weeks out is significantly better than 1-2.
Pre-lamb musters and yarding should be well planned to minimise the disturbance to feed intake. Many ewes are pushed significant distances after pre-lamb treatments to be set stocked. If the walk is going to be a long one break it up over several days and plan for feed along the way, especially important for twins.
GENETICS
Newborn lambs from some breeds, and from some genetic lines within breeds, are more vigorous at birth. Mothering ability of ewes is also influenced by genetics. Sheep Improvement Limited (SIL) does have a lamb survival index where the variation due to genes acting in the lamb (“lamb vigour”) and those acting in the ewe (“mothering ability”) are estimated.
TRACE ELEMENTS/VITAMINS
The important ones here are selenium (Se), iodine and vitamin E.
- Selenium – Severe deficiency can result in premature death of lambs.
- Iodine – Low iodine levels result in lambs that have reduced ability to regulate their body temperature. Lambs born from iodine deficient ewes are less vigorous, slow, and succumb more easily, particularly in adverse weather events.
- Vitamin E – Low vitamin E is similar in effect to low Se levels – it affects heart muscle and results in less vigorous lambs and/or premature death.
DISEASES
The most important ones directly impacting on lamb survival are:
- Toxoplasmosis
- Campylobacteriosis
- Clostridial diseases
- Salmonella brandenburg
All farms should have an animal health plan that includes vaccination against Toxo, Campy, and clostridial disease.
PHYSICAL FACTORS/SHELTER
Some paddocks always have better lamb survival than others. With multiple lambs consistently having higher wastage than singles it is well worth putting multiple bearing ewes into these better paddocks and singles into the others.
Usually, steeper paddocks have a higher death rate in twins because if lambs separate, e.g. one lamb slips down the hill, the ewe has to choose which lamb to mother and the second lamb may be unable to follow. The provision of shelter, particularly low shelter that protects from wind at the lamb’s level, is important, especially during adverse weather events.
Incorporating toi-tois, flaxes, and tussocks into shelterbelts or planting shelterbelts in species with dense low branches (e.g. Leyland cypresses, Western red cedar, and pittosporums) can provide very effective shelter. Old pines and macrocarpas provide relatively poor shelter and in many cases create large bare dirt areas beneath them that result in unhygienic conditions through lambing.
EWE MASTITIS
Recent work published by Kate Griffiths has highlighted this huge area for improvement. Where ewes are not routinely uddered, missed udder disease can result in significant lamb deaths from starvation. On post-mortem of the dead lamb it will be impossible to tell the difference between mis-mothered lambs and starvation due to ewe mastitis. Uddering should be carried out on ewes at least a month after weaning because a significant amount of mastitis can occur after weaning, and milk still in the udder in unweaned ewes makes detection earlier more difficult.
EWE DEATHS
The death of the ewe before, at, or soon after lambing is invariably going to result in the lamb’s death as well. Important contributing causes of ewe deaths to explore further can often be grouped into:
- Metabolic disease – milk fever and sleepy sickness, particularly in multiple bearing ewes that experience a nutritional stressor
- Cast ewes
- Bearings
- Chronic disease e.g. Johne’s
- Aged flocks with insufficient culling policies
WHERE TO START?
- Record your current wastage rates and benchmark these against high performing farmers in your district
- Perform autopsies on dead newborn lambs to identify the key reasons you experience wastage.
- Spend the next year questioning vets and other farmers, and get your discussion group to focus on this topic.
Ben Allott is a North Canterbury veterinarian.
