Impact of grazing intensity of sheep on biomass availability, feed intake, feed quality and animal productivity in Inner Mongolian steppe
Zusammenfassung der Projektergebnisse
Summary of results (1st and 2nd project phase; 3-6 pages) 1st project phase (2004-2007) Evaluation of titanium dioxide as an inert marker for estimating faecal excretion in grazing sheep Herbage intake of grazing ruminants is a crucial information for evaluating grazing systems. Since direct measurement of herbage intake is impossible, it is often estimated based on measurement of faecal excretion and digestibility of ingested herbage. The aim was to evaluate the external inert marker titanium dioxide (TiO2) for estimating faecal excretion. Stall feeding and grazing experiments were conducted in Inner Mongolia, to determine faecal recovery of TiO2, time to reach equilibrium of intake and excretion of TiO2 after initial administration, the effects of frequency and time of marker administration and of grab sampling on excretion pattern of TiO2, and to evaluate prediction accuracy of faecal excretion. The overall mean of the recoveries in the different experiments (n = 7) amounted P4 - Impact of grazing intensity on feed intake, feed quality and performance of sheep on the steppe of Inner Mongolia. 105 to 1.04 (SD = 0.05; range = 0.96 – 1.09). However, in the stall feeding experiments, faecal recovery of TiO2 was higher (P < 0.001) in hay diets than in diets with hay and concentrate feed with 1.08 and 0.99, respectively. Furthermore, faecal recovery was higher for sheep at high (5 sheep/ha) than low (2 sheep/ha) stocking rate (1.07 vs. 1.00; P = 0.014). The equilibrium of intake and excretion of TiO2 was reached five days after initial TiO2 administration. Faecal TiO2 concentrations differed between grab samples obtained at three times within a day. The variation in faecal TiO2 concentration was smaller and accuracy of prediction of faecal excretion was higher with twice than once daily TiO2 administration and grab sampling. In conclusion, these experiments show that TiO2 is a reliable marker for estimating faecal excretion in grazing sheep. Fecal crude protein content as an estimate for the digestibility of forage in grazing sheep Regression equations were developed to predict the organic matter (OM) digestibility of forage-based diets from contents of crude protein (CP) and acid detergent soluble CP (ADSCP) in feces, with data (721 observations of nine types of diets) obtained from in vivo digestibility trials (n = 159) with sheep conducted at the Federal Research Centre of Agriculture, Braunschweig, Germany and in Inner Mongolia. Using the non-linear mixed model procedure, the developed regression equation was: OM digestibility = 0.899 – 0.644 × exp (-0.5774 × fecal CP [g/kg OM] / 100). The probability values of estimated parameters of the equation were higher than 0.05, and a random effect of diet was not observed (P = 0.131). The mean prediction error (MPE) as proportion of observed mean was 0.071, indicating that the equation fits the data reasonably well. The equation slightly under-predicts the OM digestibility with a small mean bias of -0.014, representing 0.089 of the total mean square prediction error (MSPE). The difference between estimated and measured OM digestibility was mainly caused by random variation (0.899). This indicates that the developed equation is accurate and can be used to predict the OM digestibility of forage ingested by sheep grazing on heterogeneous pasture. Although inclusion of ADSCP instead of CP in the prediction equation results in a slightly lower under-prediction (mean bias of – 0.011, representing 0.062 of MSPE), the prediction accuracy is not improved. Impact of grazing intensity on herbage intake, composition, and digestibility and on live weight gain of sheep High grazing pressure during the last decades caused severe ecological problems in the steppe of Inner Mongolia. The objective of the study was to determine the effects of grazing P4 - Impact of grazing intensity on feed intake, feed quality and performance of sheep on the steppe of Inner Mongolia. 106 intensity of sheep on herbage mass (HM) and intake, chemical composition and digestibility of herbage, and on live weight gain (LWG). A grazing experiment with six different grazing intensities (1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep/ha) was conducted in the growing season of 2005 in the Xilin River Basin. HM decreased from 1.5 t DM/ha at the lowest grazing intensity to 0.6 t DM/ha at the highest grazing intensity. NDF content of the herbage was high (> 700g/kg DM) and relatively constant, whereas acid detergent lignin (ADL) content increased with grazing intensity and with proceeding grazing season. Digestibility of organic matter ingested (DOM) tended to decrease with grazing intensity as well as intake of organic matter (OMI) and of digestible organic matter (DOMI) per sheep (P = 0.090 and P = 0.065, respectively), whereas LWG per sheep decreased with increasing grazing intensity (P = 0.018). DOM and OMI were negatively related to ADL content. However, herbage intake and LWG per ha increased with grazing intensity (P < 0.001) and reached their maximum at 9 and 7.5 sheep per ha, respectively. This observation confirms the current farmers´ practise of high grazing preasure ignoring long term grassland productivity and ecological problems. Therefore, the studies are continued to provide further information on long term effects. This study could show pronounced effects of grazing intensity on animal and grassland productivity and the suitability of the methods applied to measure intake and digestibility of herbage in a large scale grazing experiment with sheep. Rotational and continuous grazing of sheep The aim of this study was to compare the effects of rotational and continuous grazing on herbage mass (HM), organic matter digestibility (dOM) and intake (OMI), and live weight gain (LWG) of sheep grazing, at a stocking rate of 4.5 sheep/ha during the growing season. In the years 2005 and 2006, four 2-ha plots were used of which two were divided into four 0.5 ha paddocks each for rotational grazing, where sheep were moved each 10 days to the next paddock. The dOM was estimated from fecal crude protein concentration, and OMI by oral administration of titanium dioxide. HM was similar in both grazing systems, and dOM and OMI were higher (P<0.05) at continuous grazing than at rotational grazing, but LWG did not differ probably due to extra energy expenditure for grazing and walking in a larger area. The dOM and OMI decreased (P<0.05) with progress of the growing season, and differed between years. Since precipitation during the growing season in both years was lower than the 30 years average and probably responsible that positive effects of non-grazing periods on herbage regrowth and quality at rotational grazing could not occur, the studies are continued to be able to make a final evaluation of these grazing systems. Moreover, it seems necessary to quantify energy expenditure for physical activity of animals in grazing studies. P4 - Impact of grazing intensity on feed intake, feed quality and performance of sheep on the steppe of Inner Mongolia. 107 2nd project phase (2007-2010) Effect of continuous versus daytime grazing on feed intake and growth of sheep in the steppe of Inner Mongolia In the Inner Mongolian steppe sheep generally graze during daytime and are kept in yards over night. This leads to an interruption of the nutrient return to the grassland and might on a long-term negatively impact grassland productivity. Furthermore, reduced grazing time may limit forage intake and thus performance of sheep. The aim of this study was therefore to evaluate the impact of continuous 24 h-grazing (CG) versus the common daytime-grazing (DG) on herbage mass (HM), feed quality, feed organic matter intake (OMI), and live weight gain (LWG) of sheep. The experiments were carried out in 2005, 2006, and 2007 with two replications per grazing treatment (TR) and year, and measurements were performed in July, August, and September. The external faecal marker titanium dioxide (TiO2) was daily given to the sheep on ten consecutive days each month, and faecal grab samples were obtained from day 6 to 10. Faecal samples were analysed for crude protein concentrations to estimate organic matter digestibility (dOM) and for TiO2 concentrations to estimate total faecal output and hence, OMI. LWG of all sheep as well as HM were determined monthly. HM and herbage quality were not different between TR. However, as season progressed, herbage’s concentration of neutral detergent fibre, acid detergent fibre, and acid detergent lignin increased, while HM and crude protein concentration declined. HM and herbage quality parameters differed between years. DOM did not differ between treatments with 0.577 in CG and 0.572 in DG, but decreased from 0.583 in July to 0.558 in September and was different between years. OMI per sheep and OMI per ha were not influenced by TR and remained fairly constant over the grazing season and study years. Mean LWG of animals was almost identical in CG (101.5 g/d) and DG sheep (101.8 g/d), but LWG per sheep and LWG per ha differed between sampling periods and years. Additional grazing time during night does not increase feed intake or animal productivity. Positive effects of nutrient return to the grassland could not be determined in this study. However, they are not expected, since sheep crowd together in one corner of the plots during darkness, faecal and urinary excretion concentrates on such “hotspots”, and no equal distribution of nutrients over the whole pasture occurs. Considering the risk of animal losses and the importance of sheep manure as fuel, our observations confirm the common practice of penning sheep over night to be an adequate management practice for pastoralists in the Inner Mongolian steppe. P4 - Impact of grazing intensity on feed intake, feed quality and performance of sheep on the steppe of Inner Mongolia. 108 Impact of grazing intensity on herbage composition, feed intake, and performance of sheep The aim of this study was to evaluate the effect of grazing intensity (GI) of sheep on grassland and animal performance and to determine an optimal grassland use, which combines sustainability and agricultural productivity. Grazing experiments were conducted from July until September in 2005, 2006, and 2007 to analyse the effect of six different GI from very light (GI 1), light (GI 2), light-moderate (GI 3), moderate (GI 4), heavy (GI 5), and very heavy (GI 6) on herbage mass (HM), herbage composition as well as on digestibility of ingested organic matter (dOM), organic matter intake (OMI), and live weight gain (LWG) in sheep. Each GI consisted of an adjacent grazing and hay-making plot altering annually and was carried out with two replications. Faeces samples were taken from six sheep per plot. HM decreased with increasing GI from 1006 (GI 1) to 448 kg DM/ha (GI 6). A significant influence of GI on crude protein (CP), neutral detergent fibre (NDF) and acid detergent lignin (ADL) concentrations were observed. Diet dOM, OMI, and metabolizable energy intake (MEI) were not different between GI’s. However, OMI per ha increased with increasing GI from 2.2 kg at lowest to 10.4 kg at highest GI. LWG per sheep was not influenced by GI. Corresponding to the increase of OMI per ha, LWG per ha increased with increasing GI, reaching a maximum of 730 g/d at GI 6 compared to 181 g/d at GI 1. Vegetation period had a negative influence on dOM, OMI, MEI and LWG as well as on HM and CP while NFD, ADF and ADL increased with proceeding vegetation period. Great variability in precipitation between years affected HM and herbage quality parameters as well as dOM, OMI per sheep, and LWG per sheep and per area. The results show that intensive grazing does not reduce growth of individual animals but increases productivity per area and therefore, income for farmers. However, in dry years a lack of HM on offer on heavy grazed pastures requires the purchase of additional forage for animals at the end of the vegetation period or the untimely sale of animals. Long-term negative effects of high GI’s on grassland productivity are likely and therefore, this study is continued to obtain further information on long-term effects of intensive livestock grazing. Behaviour of sheep at different grazing intensities in the steppe This study evaluated the effect of grazing intensity (GI) on behaviour and the distance walked in sheep grazing the Inner Mongolian steppe. Seventy female fat-tailed breed sheep were randomly assigned to one of six GI plots, which were defined by different herbage allowance (HA) classes included very light (GI 1), light (GI 2), light-moderate (GI 3), moderate (GI 4), heavy (GI 5), and very heavy (GI 6) with standing biomass allowances of >12, 6-12, 4.5-6, 3-4.5, 1.5-3, and <1.5 kg dry matter kg-1 LW. The sheep continuously P4 - Impact of grazing intensity on feed intake, feed quality and performance of sheep on the steppe of Inner Mongolia. 109 stocked throughout the grazing season from June till October 2008. Behaviour of two sheep per plot was monitored by direct observation during daylight. Walking distance of sheep at different GI’s was recorded by global positioning system technology. Two main grazing periods of sheep were observed at all GI’s with afternoon grazing being longer than morning grazing. With increasing GI animals spent more time grazing, whereas resting time during daylight decreased. GI had no effect on ruminating time and 12 h-walking distance (12:00 h - 24:00 h). Although HA was low at high GI, sheep succeeded in maintaining their daily organic matter intake (OMI) as GI increased from GI 1 to GI 5, while sheep in GI 6 had lower OMI than that in GI 2 and GI 3. When daylight became shorter with advancing vegetation period, sheep tended to decrease their resting time in order to maintain their grazing time. Therefore, it can be concluded that the strategy taken by sheep to avoid negative effects of increasing GI or shorter daylight on their daily feed intake was to increase or at least maintain their grazing time at the expense of their resting time. Despite a similar feed intake it is likely that performance of sheep at high GI is reduced, since higher energy expenditures for physical activity reduce energy available for growth or production. Growth of sheep as affected by grazing intensity and grazing The definition of an optimum grazing system and grazing intensity (GI) is a crucial need for an economically viable use of the grassland without amplifying its desertification. The objective of this study was to evaluate the effects of different grassland use systems and GI’s on liveweight gain (LWG) of sheep grazing the steppe in order to derive an optimum GI, which considers both, farmers’ interests of a profitable livestock production as well as environmental goals. The 5-year grazing experiment was conducted in June-September of 2005-2009, in which six different GI’s (2, 3, 4, 6, 8, and 11 sheep ha-1) and two different grazing systems were installed. The two systems included an alternating grazing system, where grazing and hay-making alternated annually between the two plots, and a continuous grazing system, where the same plots were used either for hay-making or for grazing each year. Results indicated that grazing system had no or only minor effects on sheep’s LWG. However, significant effects of GI on LWG per sheep and LWG per ha were found. LWG per sheep linearly decreased with increasing of stocking rate, while there were quadratic relationships between stocking rate and LWG per ha. LWG per sheep and per ha differed between years and months. In general, lower LWG per sheep and per ha were associated with low rainfall and decreased from July to September. In view of our earlier data regarding the effect of GI on grassland, parameters of an optimum grazing management system for the Inner Mongolian steppe are derived and concluded that, for the specific management (4- P4 - Impact of grazing intensity on feed intake, feed quality and performance of sheep on the steppe of Inner Mongolia. 110 month continuous grazing by sheep with a LW of 30-35 kg) in the Inner Mongolian steppe studied, the optimum GI should be adapted to the specific rainfall conditions in different years. A grazing scheme that aims for an end-of-season standing biomass at 70 g DM m-2 not only would assure the long-term sustainable utilization of the studied grassland, but also satisfy farmer’s economic interests.
Projektbezogene Publikationen (Auswahl)
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(2007): Effects of forage composition and growing season on methane emission from sheep in the Inner Mongolia steppe of China. Ecological Research, 22, 41-48
Wang, C., Wang, S., Zhou, H., Glindemann, T.
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(2008): Impact of grazing intensity on herbage intake, composition, and digestibility and on live weight gain of sheep on the Inner Mongolian steppe. Livestock Science, 124, 142-147
Glindemann, T., Wang, C., Tas, B.M., Schiborra, A., Gierus, M., Taube, F., Susenbeth, A.
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(2009): Evaluation of titanium dioxide as an inert marker for estimating fecal excretion in grazing sheep. Animal Feed Science and Technology, 152, 286-197
Glindemann, T., Tas, B.M., Wang, C., Alvers, S., Susenbeth, A.
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(2009): Fecal crude protein content as an estimate for the digestibility of forage in grazing sheep. Animal Feed Science and Technology, 149, 199-208
Wang, C.J., Tas, B.M., Glindemann, T., Rave, G., Schmidt, L., Weißbach, F., Susenbeth, A.
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(2009): Rotational and continuous grazing of sheep in the Inner Mongolian steppe of China. Journal of Animal Physiology and Animal Nutrition, 93, 245-252
Wang, C.J., Tas, B.M., Glindemann, T., Müller, K., Schiborra, A., Schönbach, P., Gierus, M., Taube, F., Susenbeth, A.
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(2011): Grazing behavior of sheep at different stocking rates in the Inner Mongolian steppe, China. China Applied Animal Behaviour Science, 129 (1), 36-42
Lijun L., Dickhoefer, U., Müller, K., Wurina, Susenbeth, A.
