Supplementation of Graded Levels of Desmodium Intortum Hay to Sheep Feeding on Maize Stover Harvested at Three Stages of Maturity 1
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Animal Feed Science and Technology 85 (2000) 239±257 Supplementation of graded levels of Desmodium intortum hay to sheep feeding on maize stover harvested at three stages of maturity 1. Feed intake, digestibility and body weight change Adugna Toleraa,b,*, Frik Sundstùlc,1 aDepartment of Animal Production and Rangeland Management, Awassa College of Agriculture, P.O. Box 222, Awassa, Ethiopia bDepartment of Animal Science, Agricultural University of Norway, P.O. Box 5025, N-1432 Aas, Norway cAgricultural University of Norway, Noragric, P.O. Box 5001, N-1432 Aas, Norway Received 16 April 1999; received in revised form 15 February 2000; accepted 3 March 2000 Abstract Feed intake, digestibility and body weight change of lambs fed basal diets of maize stover harvested at three stages of maturity and supplemented with graded levels (0, 150, 300 and 450 g per head per day) of desmodium (Desmodium intortum cv. Greenleaf) hay were studied. The maize stovers were harvested at 30, 22 and 12% grain moisture content which were designated as stages I, II and III, respectively. The crude protein (CP) content of the stovers showed a decreasing trend whereas the ®bre contents showed an increase from stages I to III. The desmodium hay had higher CP, phenolic compounds, calcium, sulphur and manganese contents and lower ®bre (neutral and acid detergent ®bres, cellulose and hemicellulose) contents than the stovers. Maize stover, total dry matter (DM) and organic matter (OM) intake showed a decreasing trend (p>0.05) with increasing stage of maturity of the stover. The CP intake was signi®cantly higher (p<0.05) in sheep fed maize stover harvested at stage I than at stages II and III. Total DM, OM and CP intake increased whereas maize stover DM intake showed a signi®cant decrease (p<0.05) with increasing level of supplementation. Desmodium hay constituted about 28, 47 and 66% of the total DM intake and, on average, there was a substitution of about 12, 21 and 37% of the stover by the desmodium hay at 150, 300 and 450 g of supplementation, respectively. Dry matter, OM and neutral detergent ®bre (NDF) digestibilities showed a decreasing trend (p>0.05) with increasing stage of maturity. Crude protein digestibility and the intakes of digestible * Corresponding author. Tel.: 251-6-200221; fax: 251-6-200072. E-mail address: [email protected] (A. Tolera) 1 Present address: SACCAR, Private Bag 00108, Gaborone, Botswana. 0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0377-8401(00)00135-8 240 A. Tolera, F. Sundstùl / Animal Feed Science and Technology 85 (2000) 239±257 OM and metabolizable energy (ME) were signi®cantly higher (p<0.05) in sheep feeding on maize stover harvested at stage I than stage III and showed a general declining trend with increasing stage of maturity of the stover. Supplementation resulted in improved digestibility of the diet. There was a signi®cant increase (p<0.05) in CP digestibility, digestible OM intake, digestible organic matter in the DM (DOMD), ME concentration of the diet and ME intake with increasing level of supplementation. The body weight gain showed a signi®cant increase (p<0.05) with increasing level of supplementation whereas all sheep without supplement lost body weight. The weight loss increased with increasing stage of maturity of the stover. Considering DM intake and digestibility, 300 g of desmodium hay appears to be an optimum level of supplementation, under similar conditions to the current study. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Maize stover; Stage of maturity; Desmodium intortum; Feed intake; Substitution rate; Digestibility; Body weight gain 1. Introduction Maize produces the largest proportion of crop residues in the world compared to other crops (Kossila, 1984; Chaudhry, 1998). The quantity and quality of maize stover is very variable depending upon variety, agro-climatic conditions and management factors (Harika et al., 1995). Stage of maturity of the crop at the time of harvest is one of the management factors in¯uencing the nutritive value of crop residues and much work on this subject has been undertaken (Fleischer et al., 1989; Irlebeck et al., 1993; Harika and Sharma, 1994; Tolera et al., 1998). Based on ®eld, in sacco degradability and laboratory studies, Tolera et al. (1998) showed that early harvesting of maize after attaining its physiological maturity, followed by immediate sun drying of the grain and the stover improved quality of the stover without adversely affecting grain yield and quality. However, the voluntary feed intake and the ef®ciency of extraction of nutrients from the feed during digestion are the most important determinants of nutritive value of a feed. Low digestibility of poor quality roughages results from their failure to provide rumen micro-organisms with all nutrient requirements. Nitrogen (N) de®ciency is the most important limiting factor in these feeds. When the N content of the diet is less than 1.2%, rumen function may be impaired, feed intake reduced and animal performance markedly reduced (Conrad and Hibbs, 1968). Fibrous crop residues, therefore, require appropriate supplementation as they cannot sustain effective animal production or even maintenance when they are fed alone. Conventional concentrate supplements are costly and in short supply in developing countries (Anderson, 1987). Thus, supplementation with leguminous forages, that can be grown on the farm, appears to be a more feasible alternative to improve the feeding value of cereal straws and stovers in most developing countries (Devendra, 1985; Mosi and Butterworth, 1985a; Yilala, 1989). In general, legumes can contribute to better utilization of cereal crop residues. They are rich in protein (both fermentable and by-pass protein depending upon the level of tannin content) and other nutrients such as minerals. The amount of forage legumes needed to provide effective supplementation could vary with the quality of the basal diet and the quality of the supplement at the production level envisaged. In the present study, feed intake, digestibility and body weight gain of lambs feeding on basal diets of maize stover A. Tolera, F. Sundstùl / Animal Feed Science and Technology 85 (2000) 239±257 241 harvested at different stages of maturity and supplemented with graded levels of desmodium (Desmodium intortum cv. Greenleaf, commonly known as Greenleaf desmodium) hay were studied. This trial will aid in assessing the potential improvements that could be achieved through management of maize stover harvesting stages and forage legume supplementation. 2. Materials and methods 2.1. Animals and management Seventy two intact male lambs of the local sheep from southern Ethiopia, with average initial live weight of 18Æ1.5 kg, were used in the experiment. The lambs were purchased from local markets, about 70±95 km northwest of the experimental site at Awassa. Before the commencement of the experiment, the lambs were accustomed to the experimental feed for about 1 month and they were drenched against internal parasites and sprayed against external parasites at the same time. 2.2. Feeds used in the experiments Feeds used in the experiment were maize stover, harvested at three stages of maturity, as a basal diet and Desmodium intortum hay as a supplement at four levels (0, 150, 300 and 450 g per head per day on as fed basis which, on average, constituted 0, 16, 30 and 46%, respectively, of total feed offered). The maize stovers were harvested at 30, 22 and 12% grain moisture content which were designated as stages I, II and III, respectively. The maize stovers harvested during the ®rst and second stage were sun-dried in the ®eld to decrease the stem moisture content for safe storage. There was heavy rain during the ®rst and second harvests which could impact negative effects on the quality of the stover. The desmodium was harvested by hand, using a sickle, at late ¯owering stage and sun dried into hay on canvas to minimize leaf loss. The maize stover was chopped before the start of the experiment and thoroughly mixed in order to obtain a uniform material. The desmodium hay was similarly treated. Both feeds were then fed separately. 2.3. Growth experiment During the growth experiment, which lasted for 63 days, the lambs were assigned to 12 treatments of six animals each in a factorial arrangement (three maturity stages of maize stoverÂfour levels of desmodium hay supplementation). They were housed and fed in individual pens provided with feed troughs. The chopped desmodium hay was divided into two portions and offered as the ®rst feed in the morning at 08:00 and at 15:00 hours in the after noon. The maize stover was offered separately ad libitum at 150% of the previous day's intake (50% refusal rate). Clean water was freely available all the time. Awash mineral lick was provided free choice at the beginning of the experiment. However, when some animals showed a tendency of consuming excess amount of the mineral due to its molasses content (5%) and loose nature, the mineral offer was ®xed at 242 A. Tolera, F. Sundstùl / Animal Feed Science and Technology 85 (2000) 239±257 6 g per head per day to avoid possible risk of copper toxicity as the mineral lick was high (1974 mg/kg) in copper content. Amounts of maize stover and desmodium hay offered and refused were monitored and the values used to calculate intake levels. Substitution rates were calculated as the ratio of the difference in the intake of maize stover between the unsupplemented and supplemented diets to the intake of the supplement. The lambs were weighed every 2 weeks to monitor their body weight change. Although the experiment was initially designed for 76 days of data collection, it was terminated after 63 days due to declining feed intake and progressive loss of body condition of sheep feeding on the unsupplemented stover.