CASE NOTES

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Drought Feeding and Management

BR Watt

Posted Flock & Herd May 2019

This article was originally published in Proceedings number 67 of the University of Sydney Post-Graduate Committee in Veterinary Science refresher course for Veterinarians: Sheep Production and Preventative Medicine, 1983

I have discussed drought feeding and management under the following headings:

1. Drought planning

2. Starting drought feeding

3. Maintenance feeding
i) What to feed
ii) How much to feed
iii) How often to feed
iv) Confinement or lot feeding
v) Additives
vi) Drought monitoring
vii) Hospital mobs

4. Management of young sheep

5. Joining strategies

6. Post-drought management

7. Drought-related diseases

The feeding of pregnant and lactating ewes has been discussed in these Proceedings by Janet Foot.

1 DROUGHT PLANNING

Crucial decisions must be made as the onset of drought becomes obvious. The most important decision is what to sell (or destroy) and what to keep (or agist or put on the road). The simplest way to make this decision is to estimate the following:

• what each class of stock is worth now;
• what each class of stock is likely to be worth at the end of the drought;
• the value of what each class of stock will produce during the drought;
• how much it will cost per month to feed each class of stock;
• when the drought is likely to break.

The difficult questions are what stock are likely to be worth at the end of the drought and when the drought is likely to break. Guidance as to post-drought stock prices can be sought from the various commodity newsletters. I think it is probably fair enough to estimate that stock will be worth a similar price at the end of the drought as they were in the normal market before there were any indications of drought.

In attempting to estimate when the drought is likely to break meteorological records need to be examined. The probability of effective rain falling in any one month can be calculated. Moule (1949) provided such data for Queensland and Morley (unpublished data) determined that the probability of effective rainfall in Western Victoria was about 0.15 per week from mid-March to May.

Once an estimate of the likely length of the drought has been made the total cost of feeding each class of stock through the drought can be arrived at. The cash or assets on hand at the end of the drought can then be determined for each class of livestock if they were sold or kept through the drought.

However in many situations this simple pre- and post-drought budget may not give a realistic picture of the impact on farm income of selling or retaining stock. In grazing areas where the cropping option is not available, and where replacement sheep will not be purchased for fear of introducing diseases such as footrot, then radical destocking before a drought may have serious implications. This may mean that no cast-for-age ewes will be available for sale in the following year. Wool production will be reduced and less surplus young ewes and wethers will be available for sale as the lamb crop will be depleted and more will be needed for replacements. On such properties a projected whole farm budget over 2-3 years may be worthwhile so that the full implications of selling or keeping stock can be estimated.

When the decision on what to keep has been made a cash flow budget should be prepared. This enables farmers to anticipate their financial requirements well in advance and allows them to make appropriate arrangements with their bank managers. Farmers commented during the 1982 drought that planning well ahead took a considerable amount of stress out of drought management.

STARTING DROUGHT FEEDING

I think sheep should be started on grain well before they really need it. A minimal amount of grain run out in a thin trail trains sheep to seek handfeeding and starts the introductory process. Most farmers judge the rate of increase in grain necessary based on the appearance of the sheep and the amount of feed observed in the pasture. Both estimates are unreliable and a better method is to regularly weigh and condition score a sample of sheep in the mob. Grain feeding can be stepped up only as required. We found that the Victorian Department of Agriculture's recommended program for introducing sheep to wheat worked very well. Minimal problems with grain overload and laminitis occurred (except in weaners). The Departmental recommendations were as follows:

FEEDING DAYS		AMOUNT OF GRAIN PER FEED
		Per head	Per head	Kg per 100 sheep>
1,2	Feed daily	2 oz	50 g	5
3,4	Feed daily	4 oz	100 g	10
5,6	Feed daily	6 oz	150 g	15
7,8	Feed daily	8 oz	200 g	20
9,10	Feed daily	10 oz	250 g	25
11,12,13,14	Feed daily	12 oz	300 g	30
15,17	Feed on alternate days	25 oz	600 g	60
19,21	Feed on alternate days	30 oz	850 g	85
23,26,etc	Feed twice a week or every third day	50 oz	1400 g	140

Victorian Department of Agriculture, AGNOTE Order No. 308/79

If many cases of laminitis or grain overload occur it is recommended that you hold the ration at the current level, or revert to daily feeding, until the problem resolves. Where there is concern about grain feeding, one mob (of wethers for example) can be introduced to grain ahead of the remainder of the flock to see if problems occur.

MAINTENANCE FEEDING

i) What to feed

Feeds should be evaluated on the most likely limiting factor which is usually energy. However the protein requirement of young and lactating sheep, and the fibre requirements of lactating sheep,need to be considered. Evaluation of feeds on an energy basis simply involves dividing the cost per tonne (on farm) by the energy content to arrive at a cost per unit of energy. The energy content of the commonly available drought feeds is listed below:

FEED	ENERGY CONTENT MJ/KG DM
Maize	13.5
Wheat, Sorghum, Barley	13.0
Oats	12.5
Sheep pellets	9-13
Hay	7-9

(Oddy 1978)

Other factors also need to be considered when 2 feeds are of similar price per energy unit. These include:

• risk - wheat, for example, is riskier than oats. Commercial pellets can be risky because of batch changes.
• convenience - pellets in bags are convenient for small farmers without bulk facilities.
• wastage - more hay and small grains tend to be wasted than larger grains or pellets.
• energy density - an energy density of at least 7 MJ/kg is recommended for survival and 9.5 for lactation.
• special requirements - roughage usually becomes much more expensive to feed than grains because of limited supplies and high relative transport costs. However roughage is invaluable for getting young sheep onto grain, for feeding hospital sheep, for feeding during cold or wet weather, and finally for lambing ewes. Every effort should be made to conserve hay for these classes of sheep, rather than feeding it out as part of a maintenance ration for dry sheep. At least 5 kg/head should be set aside for post-drought feeding and lambing.

  ii) How much to feed

  The table below aims to summarise some of the maintenance feeding recommendations for dry adult sheep. All levels have been converted to kgs of wheat/week.

  MAINTENANCE FEEDING REQUIREMENT RECOMMENDATIONS - DRY ADULT SHEEP PER WEEK
  	30 KG	35 KG	40 KG
  Franklin (1946a)		3.16
  Franklin (1946b)		2.36*
  Moule (1949)		1.78*
  Franklin (1952)		2.7
  Briggs et al (1956)	2.52
  Sims and Webb (1957)			2.86
  Jefferies (1957)		2.55 - 2.7
  CSIRO 23 (1958)		2.55
  Vic.DAg. (1972)		2.7
  Bull 33 (1976)	2.67	2.94	3.22
  Oddy (1978)	2.8	3.2	3.5
  Vic.DAg. (1979)		3.0
  NSW DAg. (1982)	2.7	3.0	3.3

  * sheep estimated to weigh 35 kg if weight not stated.

  There is a wide variation between the highest and lowest recommendations for an average 35 kg sheep. In view of the economic implications of both underfeeding and overfeeding it is necessary to attempt clarification. Presented below are results of some prolonged drought feeding trials using all, or almost all, wheat feeding.

  SUMMARY OF SOME TRIALS IN WHICH WHEAT WAS FED FOR PROLONGED PERIODS

  Experiment	Ration wheat Kg/week	Roughage Fed	Weight Maint. (kg)	Duration Maint. Feeding (wks)	Survival Rate %	Survival Rate N	Freq. Feeding (per week)
  Briggs et al 1956	2.52	-	30	23	100	20	1
  Sims and Webb 1957	2.54	+*	40	18	81	100	7
  Franklin 1952	2.52	.28**	33	49	96	24	1
  	2.52	.28**	32	49	58	24	7
  Franklin etal 1955	2.12	-	20	35	85+	~22	1
  	2.12	-	20	35	83+	~22	7

  * small unstated amount of paddock roughage available
  ** wheaten chaff
  + survival rate in those treated with Vitamin A

  Franklin (1952) therefore successfully maintained wethers at 33 kg on the equivalent of 2.7 kg of wheat fed once weekly for almost a year. As can be seen the survival rate of 96% in the weekly fed group was very satisfactory. The findings of Briggs et al (1956) and Sims and Webb (1957) were fairly consistent with those of Franklin. Briggs et al (1956) and Franklin et al (1955) also showed that sheep could be fed on wheat alone for an extended duration as long as calcium and vitamin supplementation was adequate.

  These recommended levels should be used as a guide only. Since it is difficult to know how much grazing sheep get from a pasture, monitoring body weight and condition score is the only real way of deciding what should be fed.

  iii) How often to feed

  Franklin (1952) demonstrated the value of intermittent versus daily feeding. In the first 77 days of a drought feeding trial there was a 7.3% mortality in daily fed wethers compared with 0.7% mortality in twice weekly fed wethers. From days 77 to 344 the latter group was fed weekly and the mortality rate was 11.1% whereas in the daily fed group the mortality rate was 22.9%. This reduced mortality was due to a much more even feed distribution among the intermittently fed group. In the daily fed group the shy feeders and slow eaters could not compete. Wool production is also higher in intermittently fed sheep. The increase may range from 5 - 10% (Franklin 1952) up to 55% (Hill et al 1968).

  Intermittent feeding is also much less time consuming than daily feeding. Most of the farmers whom we work with in Western Victoria fed twice weekly during the recent drought and reported that it worked well.

  One disadvantage of intermittent feeding however is increased grain wastage. This occurs through greater opportunity for kangaroos, mountain ducks, cockatoos, etc. to share the grain. There is also more chance of spoilage by wet weather. Twice weekly as distinct from weekly feeding seems like a good compromise.

  iv. Confinement or lot feeding

  The advantages of confinement feeding are that it reduces soil erosion and pasture degradation and makes feeding, watering and observation easier. It is also sometimes argued that sheep may do better in feedlots because they do not expend energy searching for feed. My opinion is that sheep in paddocks however continue, to find some roughage when the paddock appears almost bare. Therefore sheep in paddocks will do better than lot-fed sheep until paddock feed is totally exhausted. The extra walking of paddock-fed sheep may have little effect on their performance (CSIRO 23, 1958).

  In southern Victoria perennial ryegrass and demeter fescue pastures suffered most from heavy drought grazing. Phalaris-based pastures seem to have recovered well. Therefore on light country, susceptible to erosion, or country with predominantly perennial ryegrass or demeter fescue pastures, confinement feeding is recommended to prevent soil erosion and pasture degradation. On heavy black country with phalaris-based pastures there is less need for confinement feeding. However soil erosion and pasture renovation or re-establishment is costly. Where risks exist it is usually better to feed a little more in a feedlot than to win on feed costs and lose on soil and pastures.

  The construction of feedlots need not be elaborate. One Western District farmer lot fed mobs of 1000 sheep or more on about a hectare per mob. Unstrained ringlock held up by intermittent iron posts was sufficient to restrain these unadventurous, store condition, fine woolled Merinos. No doubt something more sturdy would be required for crossbreds in good condition.

  v) Additives

  a) Calcium

  Calcium deficiency can have serious effects on skeletal and dental development in young sheep. Sheep deprived of adequate calcium from 5-8 months of age can be permanently affected. Hypocalcaemia is most likely to develop in pregnant ewes followed by young sheep (Franklin 1950). The addition of 1½% fine ground limestone is adequate to correct a calcium deficient cereal grain ration.

  Dry adult sheep appear to be able to tolerate a calcium deficient diet for at least 3 months and many adult sheep were fed without calcium supplementation for longer than this with no obvious ill effects.

  b) Vitamin A

  Vitamin A deficiency can cause serious mortality in weaner sheep without affecting dental development, wool growth or body weight. This is however only likely to occur if the lambs have been reared during severe, prolonged droughts (Franklin 1955).

  In lambing ewes Vitamin A deficiency produces severe lamb mortality - with most lambs being stillborn or dying soon after. This however is only likely to occur when ewes lamb in the second year of a drought. Dry mature sheep, even after 2 years of drought, are unlikely to suffer from Vitamin A deficiency (Rural Research 13, 1955). Vitamin A deficiency also causes infertility in rams and 1 million international units of Vitamin A is recommended 6-8 weeks pre-joining if they have been drought affected for more tham 6 months.

  A single drench of 500,000 units of Vitamin A has been shown to provide adequate protection to weaners for at least 6 months (Rural Research 13, 1955).

  c) Vitamin E

  In the most recent drought there were numerous reports of myopathy and sometimes lethargy associated with very low plasma Vitamin E levels. Most outbreaks occurred in young sheep, especially weaners, and in some cases mortality rates of 30-40% were reported. Apparent clinical responses to Vitamin E, and sometimes selenium, administration were observed. However the role of Vitamin E (or selenium), and the treatment,is as yet not fully elucidated. A common recommendation was to drench affected mobs with the equivalent to 1000-1500 i.u. of Vitamin E. We found however that this dosage of Vitamin E had no effect on plasma Vitamin E levels 2 weeks later. We also found that weekly injections of 800 i.u. of Vitamin E had no effect on plasma Vitamin E levels until 2 months after administration commenced. A weekly dose of 1500 i.u. of Vitamin E orally did however substantially raise plasma Vitamin E levels (Watt et al, unpublished).

  d) Roughage

  The trials of Franklin et al (1955) and Briggs et al (1956) have demonstrated that sheep can be maintained for long periods on wheat alone. However occasional cases of lethargy and weight loss on adequate wheat rations came to our notice. These cases may have been associated with sand impaction, Vitamin E deficiency, chronic acidosis, or other subclinical disease. However the provision of a small quantity of roughage often markedly improved the demeanour of some of these sheep.

  e) Salt

  Most cereal grains are deficient in sodium and the addition of ½% salt in the ration of young sheep is sometimes recommended. Sodium deficiency causes decreased feed consumption and decreased efficiency of nutrient utilization (NRC 1975). Franklin (1955) found no benefit from adding 0.5% salt to the diet of weaners on prolonged maintenance wheat rations. However at production levels of feeding the addition of 1.5% salt to the ration can greatly increase live- weight gain (Davis 1978).

  vi) Drought monitoring

  We found the regular weighing and condition scoring of a sample of sheep from a few mobs to be a valuable practice in helping farmers feed sheep during the drought. Many farmers were unable to appreciate large changes in condition in their sheep, especially if the sheep had a reasonable fleece. Changes in gut fill are often interpreted as changes in condition. On several occasions disastrous losses in body weight were arrested by increased feeding, and in a few cases sheep were gaining weight and unnecessary feeding was avoided.

  My approach was to tag 25 randomly selected sheep per mob with individually numbered ear tags. These sheep could be easily drafted out each time and their weight and condition score recorded. The intention was to weigh each group of monitor sheep every 1-2 months. This was not always achieved but sheep were weighed more frequently if they were losing weight and getting into trouble. I aimed to maintain dry sheep in strong store condition, that is about condition score 2-2½.

  Franklin (1955) observed that most deaths occurred in sheep that lost more than 40% of their initial body weight (that being in good store condition). We found that fine woolled Merinos maintained in good shape at 30 kg while Corriedales were maintained at 32-35 kg. However, because of different frame sizes on different properties and in different areas, condition scoring should always be used in conjunction with weighing.

  v) Hospital mobs

  Some of the producers with whom we worked made no special provision for shy feeders and "poor doers" and yet had very low sheep mortality rates during the drought. However I think that if losses start occurring, and especially in young sheep, a hospital paddock should be set aside. Sheep which are "poor doers" can usually be drafted off on a basis of condition scoring. The ideal hospital paddock is reasonably sheltered, with good water. Sheep in the hospital mob should be run at a lower stocking rate and provided hay as well as a maintenance level of grain.

  4. MANAGEMENT OF YOUNG SHEEP

  Many producers are reluctant to take the positive action necessary to successfully raise weaners during a drought. Lambs are often left too long on poorly milking ewes. Therefore by weaning time lambs are weak and do not take readily to drought rations. Further problems occur when weaners are underfed and fed unsuitable feedstuffs. The problem is worst in spring lambs because, at least in southern Australia, autumn born lambs usually have access to some green feed during the winter and hopefully have reached a reasonable liveweight before pasture maturity and senescence occurs. High mortality rates before and just after weaning were not uncommon.

  If the ewes are in poor condition the lambs should be weaned as soon as possible. Lambs can be weaned successfully at 6 weeks of age onto highly palatable, nutritious rations fed ad lib. Mixtures of equal parts lucerne chaff and oats (CSIRO Leaflet series No. 23, 1958) and mixes of barley, wheat or oats,and lupins to provide 17% protein (Hodge et al 1982), have been shown to be satisfactory. The smallest weaners should have priority on any available green feed.

  If ewes are in reasonable condition they can be fed extra supplement with the lambs, or the lambs can be creep fed. If the ewes are fed while the lambs are still at foot, then introducing them to a drought ration after weaning is easier. Even if the ewes are in reasonable condition there is little benefit in keeping the lambs on the ewes beyond 8-10 weeks of age under drought conditions.

  It is probably a good policy to grow weaners as quickly as possible to at least 15 kg on a good quality ration of grain and roughage fed ad lib. Mixes of wheat or oats, lupins and 10-20% hay worked well in the recent drought.

  From about 18 kg and 5-6 months of age weaners can be successfully grown on wheat as was shown by Franklin (1955). We conducted a trial in which we fed badly drought affected 6-month old, 14 kg average,Merino weaners on rations of either wheat (plus ½% salt and 1½% limestone), wheat plus 2% bentonite, wheat plus 20% lupins and 10% hay, and wheat plus lupins, hay and bentonite (Watt et al unpublished). We fed the ration twice weekly in a feedlot at the equivalent of 2.7 kg of wheat with the aim of steadily growing the weaners. We found very little difference in the overall growth rates of the lambs but a higher proportion of lambs lost weight in the wheat only groups. My conclusion was that wheat alone is a satisfactory feed to grow weaners provided provision is made to hospitalise those weaners failing to perform on wheat alone. We provided our hospitalised lambs with ad lib average quality grass hay plus ad lib 80% wheat 20% lupins and they all recovered rapidly.

  I believe that weaners should be steadily grown on wheat from about 15 kg to 20 kg. It was our experience in the recent drought that weaners could be maintained in satisfactory condition with very few deaths at around 20 kg.

  5. JOINING STRATEGIES

  Many sheep producers consider not joining during times of drought. The wisdom of this decision depends on the probability of effective rain 1-2 months before the expected lambing date. In southern Victoria the probability of effective rain by late May is about 0.9 so the decision not to join in this area reflects extreme pessimism. We did however consider it worthwhile delaying joining from November until January or February. An analysis of expected feed costs for lambing at different months, based on rainfall, is presented in these Proceedings in the section on Decision Making (F.H.W.Morley).

  While it pays to allow wethers to slip to condition score 2—2½ to lower maintenance feeding requirements, this strategy may not always be desirable in ewes. It will require about an extra 320 kg of wheat to maintain 100 ewes for 3 months at 35 kg versus 30 kg. However the 100 ewes maintained at 35 kg should produce an extra 10 - 15 lambs marked, based on the expected body weight-ovulation rate relationship as reviewed by Morley (1978). So if the value of 10 - 15 lambs exceeds the cost of 320 kg of wheat (or other feed) then the higher ration should be profitable. Well fed ewes should also have a higher survival rate and will grow a little more wool. The economics of replacing some of the wheat with lupins to stimulate ovulation rate should also be examined, but insufficient data are yet available.

  6. POST-DROUGHT MANAGEMENT

  If the drought-breaking rains are accompanied by cold, windy weather losses can be expected in sheep in poor condition and losing weight. A general recommendation is to increase the ration by 20-30% in times of cold stress (Oddy 1978). Roughage generates more heat and should be fed - although in wet, muddy conditions it is usually not practical to feed grain anyway. Sheep may need to be fed for 3-4 weeks after the rains but should be given access to pasture as soon as possible. Autumn deferment usually has little effect on subsequent pasture composition and increases the risk of diseases such as phalaris poisoning. Graziers should also be alerted to the danger of nitrate poisoning, especially on capeweed.

  7. DROUGHT-RELATED DISEASES

  A common comment made was that stock losses during the drought were lower than usual, and that properly fed stock were healthier than normal. However the drought-related diseases we encountered were:

  1) Enterotoxaemia - outbreaks in unvaccinated weaners, associated with wheat, commercial pellet and lupins handfeeding.

  2) Grain overload and laminitis - generally minimal although some problems seen with weaners suddenly coming onto grain.

  3) Nematodirus infestation - we saw no clinical problems but occasionally picked up moderate (200-300 epg) egg counts of Nematodirus in routine faecal examinations over the summer.

  4) Nutritional myopathy - this was the main clinical disease observed and occurred in weaners and 1*3 y.o. ewes. Overall losses on the farms that we worked on were small, but heavy losses were reported. This problem is discussed previously.

  5) Soil impaction. We saw only a few cases with soil impaction although there were widespread reports of problems. In some cases roughage feeding helped and Rifkin (1983) cited an instance of apparent success drenching affected sheep with 40 ml of warm paraffin.

  6) Hypocalcaemia - On one property small outbreaks of hypocalcaemia in mature, lot-fed, dry sheep were observed. This was despite the addition of 1½% limestone to the ration. After the drought hypocalcaemia was a serious problem, with 5 of the properties with which I work experiencing more than 30 cases in mature pregnant ewes. Most responded to calcium therapy.

  7) Phalaris poisoning - Losses from phalaris poisoning were seen on 4 of the farms that I work on, with 2-24 deaths being reported.

  8) Nitrate poisoning - serious losses were reported, especially on capeweed. One of our clients lost 60 weaners with nitrate poisoning.

  9) Polioencephalomalacia - was expected but no cases were reported.

  REFERENCES

  1. Briggs, P.K., Franklin, M.C., McClymont, G.L. (1956) Maintenance rations for Merino sheep. III The performance of adult Merino wethers fed weekly on all-grain rations of wheat, maize, oats, barley or grain sorgharo. Aust.Vet.J. 32: 299-304
  2. CSIRO Leaflet Series No. 23 (1958) Drought Feeding of Sheep. CSIRO, Melbourne
  3. Davis, C.H. (1978) Production feeding of weaner lambs. Proc. Aust. Soc. Anim. Prod. 12:141.
  4. Department of Agriculture, Victoria (1972) Drought feeding of sheep
  5. Department of Agriculture, Victoria (1979) What to do with sheep in a drought. AGDEX 430/15 Order No. 307/79
  6. Franklin, M.C. (1946a) Experimental observations on the efficiency and economics of rations for drought feeding of sheep. Aust.Vet.J. 22(6): 78-84
  7. Franklin, M.C. (1946b) Some nutritional observations on the drought feeding of sheep. Aust.Vet.J. 22(9): 104-112
  8. Franklin, M.C. (1952) Maintenance rations for Merino sheep. I. A comparative study of daily and weekly feeding on rations containing high proportions of wheat and several proportions of roughage to concentrate. Aust. J. Agric. Res. 168-186
  9. Franklin, M.C., McClymont, G.L., Briggs, P.K. and Campbell, B.L. (1955) Maintenance rations for Merino sheep. II. The performance of weaners fed daily and weekly on rations of wheat and wheaten chaff at maintenace levels and the effect thereon of Vitamin A supplements. Aust. J. Agric. Res. 324-42
  10. Hill, M.K., Watson, M.J. and McClymont, G.L. (1968) Effects of daily or weekly feeding of wheat on wool producton. Proc. Aust. Soc. Anim. Prod. 7: 49-53
  11. Hodge, R.W., Bogdanovic, B.and Makin, A. (1982) The effect on lamb production of adding protein and mineral supplements to whole cereal grains compared to incorporation of the supplements in hammer-milled mixtures or pellets. Aust. Soc. Anim. Prod. 14: 495-498
  12. Jefferies, B.C. (1957) A guide to drought feeding of sheep. J. Dept. Agric. S. Aust. 61:113
  13. Ministry of Agriculture, Fisheries and Food (1976) Energy allowances and feeding systems for ruminants. Tech. Bull. No. 33. (London, HMSO)
  14. Moule, G.R. (1949) Handfeeding sheep in drought time. Queensland Agric. J. 68: 234-238
  15. Morley, F.H.W., White, D.H., Kenney, P.A. and Davis, I.F. (1978) Predicting ovulation rate from liveweight in ewes. Agric. Syst. 3: 27-45
  16. National Research Council, (1975) Nutrients Requirements of Sheep. No. 5 Fifth rev. Edn. National Academy of Sciences, Washington, D.C.
  17. NSW Department of Agriculture, (1982) Production Topics. Drought feeding and management of sheep, 70
  18. Oddy, V.H. (1978) Feed requirements of sheep and cattle during drought using a metabolisable energy system. Dept, of Agric. New South Wales. Agbulletin 3, AGDEX 400/53
  19. Rifkin, G. (1983) Sand impaction. Control and therapy. No. 1597. Univ. Syd. Post-grad. Comm. Vet. Sci.
  20. Rural Research in CSIRO (1955) Vitamin A - its value in the drought feeding of sheep. 13 27-30
  21. Sims, H.J. and Webb, C.G. (1957) Sheep management studies at the Mallee Research Station, Walpeup. J. Agric. Vic. 55: 79-92