ESTIMATION OF WHITE CLOVER AND GRASS INTAKE IN GRAZING LAMBS - R. Sormunen-Cristian^[47] and P. Nykänen-Kurki^[48]

SUMMARY

Herbage intake by grazing lambs was evaluated on three grass pastures with annual nitrogen rates of 0 (G0), 120 (G120) and 250 (G250) kg ha^-1 and on a white clover-grass pasture without nitrogen fertilization (CG0) by total faecal collection in 1994, by the sward cutting method and by using n-alkanes C₃₂ and C₃₃ in 1995. Accurate estimates of herbage intake in grazing lambs were not obtained by the sward cutting method. Not more than 25 percent of lambs acclimatized well to harnesses and dung bags, and daily herbage dry matter (DM) intake measured by total faecal collection was relevant only on CG0 swards, 84 g (kgW^0.75)^-1. By alkanes C32 and C33 estimated herbage intake averaged 106, 79, 64 and 63 g DM (kgW^0.75)^-1 in CG0, G0, G120 and G250 swards, respectively. An overestimation of white clover intake by alkanes was assumed.

Keywords: herbage intake, markers, lamb, n-alkanes, pasture, Trifolium repens L.

INTRODUCTION

In Finland, only a few grazing trials have been carried out to evaluate intake of grass and even more rarely that of white clover pasture. Determination of herbage intake by grazing ruminants is generally based on a sward cutting method or on total faecal collection (Leaver, 1982). The sward cutting method is dependent on successful sampling. Total feacal collection, regarded as the conventional but expensive and labour consuming method, may alter grazing behaviour (Cordova et al., 1978). Herbage intake can be predicted precisely by the combination of dosed and herbage n-alkanes C₃₂ and C₃₃ as internal markers (Mayes et al., 1986). However, suitability of n-alkanes to estimate the intake of white clover pasture by grazing lambs is not well documented. In this study herbage intake by lambs on white clover-grass and grass only pastures was evaluated by methods of sward cutting, total faecal collection and n-alkanes.

MATERIALS AND METHODS

Herbage intake was studied on three grass pastures (mixture of Phleum pratense L. cv Iki, Lolium perenne L. cv Riikka and Festuca pratensis Huds. cv Kalevi) with annual nitrogen rates of 0 (G0), 120 (G120) and 250 (G250) kg ha^-1 and on white clover (Trifolium repens L. mixture of cvs Sonja and Jögeva 4)-grass pasture without nitrogen fertilization (CG0) in Jokioinen (60°54'N, 23°30'E, 107 m above sea level) as described earlier by Sormunen-Cristian et al. (1996). All experiments were carried out at a stocking rate of 63 lambs ha^-1.

For the first experiment, voluntary intake estimates were derived by measuring faecal output and sward digestibility. Total faecal collection was carried out with 16 male lambs for five days in 1994 (27 July-1 August). Feed and faecal samples were collected daily, pooled by a period of five days and analysed for dry matter (DM) and ash. In vitro organic matter digestibility of feed was determined by the cellulase method. Herbage intake was estimated as: faecal output/1-digestibility (Leaver, 1985).

For the second experiment, herbage intake was estimated by sward cutting techniques with 64 lambs in 1995 (14-19 June). The herbage mass was determined in the beginning and at the end of the grazing period. Herbage accumulation was measured with cages. Intake was calculated by difference of offered herbage and refused one.

For the third experiment, herbage intake was determined by using n-alkanes C₃₂ and C₃₃ in 1995 (26 July-4 August). The experiment involved 16 female lambs which were dosed once a day for 10 days with a capsule containing 120 mg of C₃₂. Feed and feacal samples were collected during the final five days and pooled for a period of five days. Feed samples were analysed for DM, ash, crude protein, neutral detergent fibre and in vitro digestibility and faecal samples for DM and ash. In addition, n-alkanes C₃₂ and C₃₃ of samples were determined as in Mayes et al. (1986). Herbage intake (HI, kg DM day^-1) was estimated using an expression derived from Mayes et al. (1986) as: HI = (D₃₂*F₃₃/F₃₂)/ (H₃₃-((F₃₃/F₃₂)*H₃₂)), where D₃₂ is the daily amount of dosed C₃₂ (120 mg day^-1), F₃₂ and F₃₃ the faecal concentrations (mg kg^-1 DM) of C³² and C³³, respectively, and H³² and H³³ the herbage concentrations (mg kg^-1 DM) of C³² and C³³, respectively.

RESULTS AND DISCUSSION

Pasture white clover content averaged 12, 36 and 32 percent in fresh herbage in the first, second and third experiment, respectively. These contents were adequate to affect also animal performance (Thomson, 1984, Fothergill and Davies, 1993). Due to the sowing method and structure of the sward, sward height for grazing was higher than recommended (5-8 cm) for dense sward under continuous sheep grazing. Except height of 12 cm in G0 of the second experiment, sward height of pastures averaged 21, 21 and 19 cm in the first, second and third experiment, respectively. In the first experiment, herbage on offer averaged in the beginning of the grazing period 2 640, 2 680, 2 850 and 2 030 kg DM ha^-1 in CG0, G0, G120 and G250, respectively. In the second one it averaged 1 380, 705, 1 600 and 1 770 kg DM ha^-1 and in the third one 920, 1 020, 850 and 1 300 kg DM ha^-1, respectively.

Table 1. Yield and quality of white clover/grass and grass pastures and estimated feed intake of lambs measured by n-alkanes C32 and C33 in 1995 (31 July-4 August).

Means of daily intake within row with different letters differ significantly (P< 0.05).

In the first experiment with total faecal collection, not more than 25 percent of lambs acclimatized well to harnesses and dung bags. Therefore, herbage intake could be measured successfully only with four CG0 lambs. Daily herbage DM intake of CG0 lambs weighing 43.5 kg, averaged 1.4 kg lamb^-1 (84 g DM (kgW^0.75)^-1). The result is consistent with the findings of Cordova et al. (1978).

In the second experiment with sward cutting techniques, herbage mass allowance in G0 (2.1 kg DM lamb^-1) was relatively low but still in accordance with nutrient recommendations for lambs. Daily herbage intake in CG0 was unsuccessfully estimated whereas it averaged 97, 93 and 73 g DM (kgW^0.75)^-1 in G0, G120 and G250, respectively. Assessment of herbage intake by sward sampling was applicable in systems with a relatively short grazing period and high grazing pressure (Leaver, 1985). Results of grass intake obtained were reasonable, but the variation between blocks was high, although swards were sampled with great care to avoid error and bias. Jeffery and Holder (re. Cordova, 1978) concluded that the upper boundary for daily intake was about 83 g DM (kgW^0.75) ^-1. Linehan et al. (1952) found sward cutting techniques inaccurate giving 30-40 percent higher estimates for herbage intake than the animal weighing method.

In the third experiment, herbage intake was estimated by C₃₂ and C₃₃ alkanes. It was higher in CG0 swards than in G swards (p<0.05) (Table). Among others, Orr et al. (1990) found higher organic matter intake on white clover/grass than on grass-only sward. The difference was 18 percent by Davies et al. (1991), and even 50 percent higher values for CG0 were assumed to be overestimated (Cordova et al., 1976). Mayes et al. (1986) found prediction of herbage intake by the combination of markers C₃₂ and C₃₃ to be most precise. The alkane method, however, seemed to be better for uniform ryegrass than for the mixed sward (Spörndly, 1996) where preference of white clover may occur by lambs. Curll and Wilkins (1980) found the clover content in the diet 14 percent-unit higher than that of herbage on offer. This may have influenced the n-alkane content of the diet in comparison to the offered herbage and therefore increased the calculated intake.

CONCLUSIONS

Accurate estimate of herbage intake was not obtained by the sward cutting method. Total faecal collection was an exact method, but harnesses and dung bags disturbed grazing of lambs. The alkane method suited well for uniform grass but intake of white clover mixture seemed to be overestimated.

REFERENCES

Cordova, F.J., Wallace, J.D. & Pieper, R.D. 1978. Forage intake by grazing livestock: A review. Journal of Range Management 31: 430-438.

Curll, M.L. & Wilkins, R.J. 1980. The relationship between selective grazing by sheep and the botanical composition of a grass/clover sward. Proceedings of the 8^th General Meeting of the European Grassland Federation, pp. 7.17-7.23.

Davies, D.A., Fothergill, M. & Jones, D. 1991. Assessment of contrasting perennial ryegrass, with and without white clover, under continuous sheep stocking in the uplands. 3. Herbage production, quality and intake. Grass and Forage Science 44: 39-49.

Fothergill, M. & Davies, D.A. 1993. White clover contribution to continuously stocked sheep pastures in association with contrasting perennial ryegrasses. Grass and Forage Science 48: 369-379.

Leaver, J.D. 1985. Herbage intake handbook. British Grassland Society, Hurley 1982. 143 p.

Linehan, P.A., Lowe, J. & Stewart, R.H. 1952. The output of pasture and its measurement. Journal of British Grassland Society 7: 73-97.

Mayes, R.W., Lamb, C.S. & Colgrove, P.M. 1986. The use of dosed and herbage n-alkanes as markers for the determination of herbage intake. Journal of Agricultural Science, Cambridge 107: 161-170.

Orr, R.J., Parsons, A.J., Penning, P.D. & Treacher, T.T. 1990. Sward composition, animal performance and the potential production of grass/white clover swards continuously stocked with sheep. Grass and Forage Science 45: 325-336.

Spörndly, E. 1996. Herbage intake by dairy cows. Dissertation. Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management. Report 236. Uppsala 1996.

Sormunen-Cristian, R., Nykänen-Kurki, P. & Peltola, J. 1996. On white clover-based grazing of lamb pastures. In: Parente, G. et al. (Eds.). Grassland and Land Use Systems. Proceedings of the 16^th General Meeting of the European Grassland Federation, Grado (Gorizia), Italy, 15-19 September 1996. p. 625-628.

Thomson, D.J. 1984. The nutritive value of white clover. In: Forage Legumes. Occasional Symposium of British Grassland Society 16: 78-92.