USING UREA IN RATIONS OF DROUGHT FED CASHMERE DOES
FIRST PUBLISHED JUNE 1989
AUTHOR: B.A. McGregor, Goat Specialist, Animal Research Institue, Department of Agriculture and Rural Affairs, Werribee, Victoria 3030
Cashmere and feral does may need to be fed supplements during major droughts or during long dry summers. During droughts, the quality of pasture, forage and browse declines.
It is quite common for the nitrogen content of drought pastures (usually referred to as crude protein) to drop to levels below 1 % (~ 6% crude protein). In these circumstances lactating does will have insufficient nitrogen in their feed to successfully rear kids and they will suffer large losses in liveweight. It is therefore important to develop strategies which will minimise the effects of drought on breeding does but at a reasonable cost.
The research work described in this Goat Note is, in principle, applicable to a range of low quality rations. The low quality diet used in this example is oats with a low nitrogen content. Producers who wish to undertake such a feeding program are advised to obtain further advice from their local Department of Agriculture.
Whole oat grain is a commonly used supplementary feed for domestic livestock in south eastern Australia, particularly during drought. However, in south eastern Australia, oats characteristically have a low nitrogen content (1.28 - 1.44%, equivalent to 7-9% crude protein). In periods of drought, nitrogen content of dry pastures can be very low. It has been shown that ewes fed oats supplemented with urea compared to ewes fed oats alone ate significantly more oats, grew more wool and had heavier lambs which grew significantly faster. The additional benefits observed by supplementing oats with protein pellets or lucerne chaff were not of practical or economic importance.
The question arises as to whether lactating does fed low nitrogen oats during drought would respond to supplements or urea in the same way as ewes or whether the additional nitrogen should be provided in the form of roughage. This is important because, during drought in Australia, good quality lucerne of pasture hay is either unavailable or prohibitively expensive whereas urea remains available and relatively cheap.
Urea is a naturally occurring product of metabolism in goats and other ruminants. Urea is a source of nitrogen used for protein syntheses in the digestive tract. Approximately 70% of the nitrogen eaten daily passes into the blood plasma urea pool. Some urea then passes back into the rumen and satisfies the nitrogen requirement of rumen micro-organisms which are digesting herbage. Some urea is excreted from via the kidney. Urea is also recycled through the rumen via saliva.
Urea is commonly included in commercially prepared goat feed sold in Australia and is only toxic when fed in excessive amounts or when rapidly introduced to the diet.
In the experiment described below the intake, growth and lactation of domesticated Australian feral does fed oats supplemented with either urea or lucerne chaff was recorded together with the growth of their Angora cross kids.
MATERIALS AND METHODS - ANIMALS AND DIETS
The does used in this experiment came from the Animal Research Institute's flock which was established in 1976 from feral goats captured in north western Victoria.
Does were grazed on annual pastures and mated with an Angora buck. The does were from 3.5 to 6.5 years old and had a mean bodyweight of 45.7 kg one day after kidding. The rations were based on oats of 1.38% nitrogen (dry matter basis). Diet OU was comprised of 97.1 % oats, 1.4% urea and 1.5% mineral supplements, giving a ration with 1.98% nitrogen. Diet OL was 69% oats, 29.5% lucerne chaff and 1.5% mineral supplements (lucerne chaff being 2.70% nitrogen giving the complete ration a concentration of 1.78% nitrogen. Composition of the mineral supplement was 66.7% CaCO3, 16.7% NaCL, 13.3% K2SO4 and 3.3% microminerals and vitamins.
The urea was dissolved in water and sprayed onto the oats as the oats were being mixed on a horizontal paddle mixer. The method of dissolving urea is to place the urea into a small drum and add the equivalent weight of hot water (i.e. for each 1 kg of urea add 1 litre of water). Place the drum in a hot bath and continually stir the mixture.
Urea requires a lot of energy to dissolve so if the mixture is made up without added heat the urea may not dissolve. The urea solution should be applied immediately to the grain. Concrete mixers can be used for mixing the oats and urea.
Does were housed from approximately 2 weeks before kidding to 4 weeks after. Food intake was measured daily.
Results of food intake are presented as the dry matter intake (DMI) that is the weight of food without the water (Table 1). OL-fed does ate 1.7kg DM per day and their kids grew faster than OU fed does, primarily because the intake of OU fed does was 30% less.
TABLE 1: Food intake and growth rates of Australian feral goats and their Angora cross kids, fed oats and lucerne chaff (OL) or oats and urea (OU) diets and milk production of does rearing twins.
This difference in feed intake and kid growth is clearly reflected in the mean milk production of twin rearing does when measured at 3 weeks after kidding. In addition, the OU fed does lost more liveweight during the first 4 weeks after kidding, probably due to their reduced intakes.
The results indicated a large variation in the production response of does given OU compared to those offered OL. It was apparent that some does did not consume enough of diet OU after kidding to maintain a high level of milk production. Does which did consume reasonable levels of OU (1.9kg day) reached levels of production close to that achieved by supplementing with lucerne chaff. To reduce the variation in OU-fed animals it may be necessary to provide a longer introductory period (6 weeks) and this is likely to happen in a prolonged drought.
There was no evidence of urea toxicity even though some groups consumed 29g/goat/day of urea. Overall, OU-fed does consumed on average more oats than OL-fed does (1.27 kg day compared to 1.18 kg day) because the addition of lucerne resulted in an 18% substitution of oats.
The growth rate of the kids born to the does given OU was high enough to provide satisfactory weaning weights under drought feeding conditions in Australia. It is important to test oats for nitrogen content during drought feeding periods. If the nitrogen content is low adding urea is probably the cheapest form of nitrogen compared to purchasing expensive lucerne or protein supplements.
Cutting Mulga for drought feed.
© 1989 ACGA