STUBBLE GRAZING BY SHEEP
T T Treacher (1), S Rihawi (2) and E Owen (3)
(1) Departamento de Produccion Animal, Escuela Superior Tecnica de Ingenieros Agronomos y de Montes, Apartado 3048, 14080 Cordoba, Spain E-mail: pa1treac@uco.es
(2) Pasture, Forage and Livestock Programme, International Centre for Agricultural Research in the Dry Areas, P O Box 5466, Aleppo, Syria
(3) Dept of Agriculture, University of Reading, Reading RG6 2AT, UK E-mail: aasowene@reading.ac.uk
INTRODUCTION
In the Mediterranean Basin and West Asia, livestock production and crop farming have always been integrated. Cereal stubble and straw are important feed resources not only for animals based in the areas where crops are grown but also for the very large numbers of small ruminants that graze steppe pastures and move into crop growing areas after harvest. Degradation of steppe vegetation in the last 40 years has increased the dependence of livestock production on feeds from the cropping zones (eg Boutonnet, 1989).
In many small ruminant systems in the Mediterranean and west Asia, the period in summer when stubbles are available for grazing coincides with mating and early pregnancy. As nutrition before mating and in the first month of pregnancy affects fertility and prolificacy, the stubble grazing period may have an important effect on the performance of flocks during the whole year. The start of stubble grazing often results in an improvement in nutrition and a surge in oestrous activity in breeds that, although not inherently seasonally anoestrus, often have a period of anoestrus in spring, as a result of poor nutrition or low body condition.
In contrast with the enormous number of studies on all aspects of harvested straw, little research has been carried out on grazing of stubbles or on responses to supplementation during stubble grazing. Some work has been done in Morocco (eg Guessous et al. 1989 and Outmani et al. 1991) and in Spain (Valderrabano, 1991 and Cabello et al. 1992). There are more results from Australia (eg Mulholland, 1976), but these are of limited relevance to the Mediterranean and west Asia as both the crop and sheep husbandry are very different.
ESTIMATES OF THE QUANTITY OF STUBBLE
There are wide variations in the amount of dry matter present in stubble before grazing and in the proportions of straw, grain and green material. These result from a great number of factors that occur in the cereal crop before harvest (eg. seed rate, rainfall, irrigation), during harvesting (eg. cutting height, removal of straw for winter feeding) and harvesting and grazing (eg. rain storms).
Under dryland conditions estimates of total stubble mass before grazing vary from 1.20-2.76 t DM/ha for barley and 0.94-1.80 t DM/ha for wheat, with cutting heights of 14-18 cm (Cabello et al. 1992 and Valderrabano, 1991), to 3.5-4.0 t DM/ha for barley and 5.2-5.6 t DM/ha for wheat in Australia, at a cutting height of 45 cm (Mulholland et al., 1976 and Butler, 1981).
STUDIES OF STUBBLE GRAZING IN ICARDA
The programme on barley stubble started in 1991 consisted of:
FIELD STUDY OF STUBBLE GRAZING
Thirty-nine farmers in northern and eastern Syria were interviewed about stubble grazing, to help define management decisions for subsequent experimentation (ICARDA, 1992).
The main results were:
METHOD OF ESTIMATING INTAKE
As rain rarely occurs in Syria before the end of October, alteration in stubble composition during the grazing period is unlikely to occur, except as a result of grazing. It was, therefore, decided to use a quadrat sampling technique to estimate the rate of removal of particular fractions and the intake of nutrients.
Examination of the stubble suggested that the use of a quadrat of the same size as the cutting width of the combine harvester (4.25 m), placed at right angles to the direction of the combine cut, would result in a systematic sampling of the stubble. A comparison of samples cut, using quadrats of 1.0 x 1.0 m (S), which had been used in earlier studies, and 4.25 x 0.47 m (R), showed a large reduction in the coefficient of variation from 23% with S to 9% with R. The means of total biomass were 1.88 +/- 8 (range 1.20-2.81) and 1.22 +/- 20 (1.06-1.54) t/ha for S and R, respectively.
In the subsequent experiments, removal during grazing of head, leaf and stem fractions was estimated by cutting 10 quadrats (5 in experiments 2 and 3) to ground level on days 0, 3, 5, 7, 9, 14, 19, 24 and 29 of each grazing period. The material was separated into head, leaf and stem. Metabolisable energy (ME) intake was calculated from 0.15 x digestible organic matter in the DM (DOMD). Daily intakes of ME and crude protein (CP) were calculated as the difference between successive samplings divided by the number of sheep and days.
EXPERIMENTATION
Three experiments were carried out on barley stubble (var. Arabi Abiad) cut by combine at a height of approximately 10 cm. Mean mass before grazing was 1110, 1215 and 1140 kg DM/ha in experiments 1, 2 and 3, respectively. The proportions of head, leaf and stem before grazing were approximately 0.05, 0.55 and 0.40, with contents of DOMD of 0.86, 0.54 and 0.36 and CP of 103, 41 and 14 g/kg DM, respectively.
Supplements were fed to the individually yoked sheep in the evening. All sheep received adequate mineral supplementation.
EXPERIMENT 1. EFFECT OF STOCKING RATE ON THE INTAKE OF STUBBLE FRACTIONS
OBJECTIVE
To record the pattern of removal of head, leaf and stem from stubble and measure intakes of ME and CP
DESIGN
Stocking rates of 20, 40 and 60 sheep/ha applied in 3 successive periods of 28 days
MATERIAL AND METHODS
RESULTS
There was a clear effect of SR on the removal of the stubble fractions. Heads were removed in the first 6-8 days on a new area of stubble and contributed 4-6%, 6-8% and 12-14% of the total intake in 28 days of DM, ME and CP, respectively (Table 1). Leaf was preferentially selected until the amount of leaf present on the stubble was low. Leaf comprised 68% of the total DM intake at SR 20 and approximately 55% at SRs 40 and 60. Total intakes of ME declined from 2-2.5 times maintenance (M) in days 1-4 to approximately 0.5, 0.25 and 0.13 M in days 23-28 at SRs 20, 40 and 60, respectively. The stubble was almost completely utilised. The wethers maintained weight at SR 20 and made substantial losses at SRs 40 and 60.
Table 1. Experiment 1. Effect of stocking rate on mean daily intakes of stubble DM, ME and CP and initial weight and weight change
Stocking Rate (ewes/ha) 20 40 60 Sign
Mean intake of DM (kg) 1.06 0.79 0.55 ***
Intake of ME (MJ) Mean 8.7 6.0 4.1 ***
- days 1-4 15.2 15.0 11.9 ns
- days 23-28 4.6 1.7 0.7 ***
Intake of CP (g) 43 26 17 ***
Initial weight (kg) 54.8 53.9 55.0 ns
Mean weight change (kg) 0.3 -2.1 -3.2 ***
EXPERIMENT 2. EFFECTS OF STOCKING RATE AND SUPPLEMENTATION ON INTAKE OF STUBBLE FRACTIONS
OBJECTIVES
To assess the effects of stocking rate and supplementation on the pattern of removal of head, leaf and stem, intakes of ME and CP and on the weight changes and the time for the ewes to become pregnant
DESIGN
2 x 3 factorial with:
Stocking rates of 20 and 40 ewes/ha applied in 3 successive periods of 28
days
Supplementation:
MATERIAL AND METHODS
RESULTS
Supplementation with barley significantly reduced the intake of heads until day 13 and of total stubble in days 1-4, but not over the whole 28 day period, as the total intake was higher later in the period. Supplementation with CSM increased the intake of stem, but the effect was only significant when expressed as ME with mean stem ME intakes in 28 days of 2.71, 2.02 and 2,03 MJ/day for CSM, B and none, respectively. Over the whole 28 day period mean intakes of DM, ME and CP were not affected by supplementation (Table 5). In spite of the small differences in nutrient intakes from stubble, supplementation had large and significant effects on liveweight gain. The barley supplement increased weight change from 0.1 to 2.9 kg and from -1.7 to 1.5 at SRs 20 and 40, respectively. The CSM supplement further increased gains to 4.4 and 2.2 kg at SRs 20 and 40.
As in the previous experiment, stocking rate had a significant effect on intakes of DM, ME and CP and on liveweight change. The intakes of nutrients and liveweight changes of the unsupplemented sheep were similar to those in the previous experiment.
Table 2. Experiment 2. Effect of stocking rate and supplementation on mean daily intakes of stubble DM, ME and CP and initial weight, weight change and days to become pregnant
Stocking Rate
(ewes/ha) 20 40 Sign
-------------- -------------- -----------
Supplement CSM B None CSM B None SR Supp
Mean intake
(kg DM) 1.19 1.14 1.09 0.93 0.85 0.82 *** ns
Intake of ME (MJ)
- Mean 10.0 9.2 9.3 6.4 5.9 6.2 *** ns
- days 1-4 16.9 8.9 14.8 11.7 10.1 13.4 * **
(1) = mean of 6 ewes, as 2 ewes failed to become pregnant
Both SR and supplementation affected the mean number of days for the ewes to become pregnant, which was much greater in the unsupplemented ewes at the higher SR.
EXPERIMENT 3. EFFECTS OF STOCKING RATE AND OF LEVEL AND TYPE OF SUPPLEMENT ON THE REMOVAL OF DIFFERENT STUBBLE FRACTIONS
OBJECTIVES
To assess the effects of stocking rate and supplementation on the pattern of removal of head, leaf and stem, intakes of ME and CP and on the weight changes and the time for the ewes to become pregnant
DESIGN
2 x 3 x 2 factorial with two replications:
Stocking rates of 20 and 40 sheep/ha applied in 2 successive periods of 28
days
Supplementation with two diets at two levels of intake:
MATERIAL AND METHODS
RESULTS
Supplementation had significant effects on the intake of stubble in all periods, but, as intake was initially depressed in days 1-6 and subsequently increased by feeding supplements, mean intake over 28 days was not significantly different between treatments. Intake of stem was affected by supplementation, but, in contrast to experiment 2, was higher with the barley supplement. Although supplementation did not significantly affect total intake of stubble DM, ME or CP, it had a large effect on weight change (Table 3). As in the previous experiments, there were significant effects of SR on intake of stubble and liveweight change. The mean number of days for the ewes to become pregnant was affected by both SR and supplementation.
Table 3. Experiment 3. Mean daily intakes of stubble DM, ME and CP and initial weight and weight change
Stocking rate
(ewes/ha) 20 40 Sign
-------------- -------------- -----------
Supplement M(1) B(2) None M(1) B(2) None SR Supp
Mean DM
intake (kg) 1.09 1.16 1.15 0.85 0.92 0.87 *** ns
ME intake (MJ)
Mean 11.1 11.5 10.9 6.8 7.6 7.3 *** ns
- days 1-4 22.3 18.7 17.4 13.6 14.1 16.4 * ns
Initial
weight (kg) 39.9 39.2 38.4 40.6 40.4 40.1 ns ns
Mean wt
change (kg) 7.1 3.8 0.6 3.0 0.6 -1.2 *** ***
Days to get
pregnant 15 29 42 30 45 46 *** ***
(1) = Mean of treatments M320 and M160
(2) = Mean of treatments B300 and B150
CONCLUSIONS
The results of these experiments show that, where there is no rain in the grazing period, the patterns of removal of the different stubble fractions can be described, using frequent sampling with a quadrat the same length as the combine cutting width, which allows systematic sampling of all the material on the stubble.
There were clear patterns in the removal of different fractions from stubble by grazing sheep. Heads were selected first and removed in the first 4 to 8 days of grazing at stocking rates of 20-60 sheep/ha. Intake of stem increased when most of the leaf had been removed. Mean contributions of head, leaf and stem to total DM intake on the unsupplemented treatments in the three experiments were 7, 64 and 29% at SR 20 and 5, 61 and 34% at SR 40.
Supplementation with barley decreased intake of stubble in the first 4 to 6 days on a new area of stubble but, as intake was subsequently higher, total intake of stubble DM in 28 days was not significantly affected. Intake of stem was increased by supplementation with CSM in experiment 2, but not by the supplement with a higher protein content in experiment 3. Supplements, especially those with higher protein contents, had large effects on weight change and reduced the time taken for the ewes to become pregnant. More research is needed to obtain a clear understanding of the effects of different types and levels of supplementation on intake of stubble by sheep and on their performance.
In view of the importance of stubble as a source of feed in small ruminant systems in west Asia, more research is needed on grazing not only of barley, but also of wheat stubble, under dryland farming.
REFERENCES
Boutonnet, J. P. 1989. La speculation ovine en Algerie. INRA Serie Notes et Documents No 90.
Butler, L.G. 1981. Supplementary feeding of Merino wethers grazing weed-free stubble pastures. Australian Journal of Experimental Agriculture and Animal Husbandry. 21, 272-276.
Caballero, R., Rioperez, J., Fernandez, E., Arauzo, M. and Hernaiz, P.J. 1992. Performance of Manchega ewes grazing cereal stubbles and cultivated pastures. Small Ruminant Research. 7, 315-329.
Guessous, F., Luginbuhl, J.-M., Rihani, N. and Pond, K.R. 1991. Influence of supplementation on the performance of gestating ewes grazing wheat stubble pastures. Animal Feed Science and Technology, 35, 95-103.
Guessous, F., Rihani, N., Kabbali, A. and Johnson, W. L. 1989. Improving feeding systems for sheep in a Mediterranean rain-fed cereals/livestock area of Morocco. Journal of Animal Science. 67, 3080-3086.
ICARDA 1992. Pasture, Forage and Livestock Program Annual Report for 1990/1991. Survey of methods of feeding barley straw and of grazing stubble in Syria. pp 149-153.
Mulholland, J.G., Coombe, J.B., Freer, M. and McManus, W.R. 1976. An evaluation of cereal stubbles for sheep production. Australian Journal of Agricultural Research, 27, 881-893.
Outmani, A., Luginbuhl, J.-P., Guessous, F. and Johnson, W.L. 1991. Utilization of wheat stubble pastures by gestating sheep. Small Ruminant Research. 4, 257-267.
Valderrabano, J. 1991. Utilizacion de las rastrojeras de cereal por el ganado ovino. 31 Reunion cientifica de la SEEP. Murcia 1991. pp 368-372.