The effect of molasses and monensin supplementation of Holstein Friesian cows fed Rhodes grass hay (Chloris gayana cv. Callide)

Abstract

Animal Production in Australia 1998 Vol. 22 THE EFFECT OF MOLASSES AND MONENSIN SUPPLEMENTATION OF HOLSTEIN FRIESIAN COWS FED RHODES GRASS HAY (Chloris gayana cv. Callide) B.C. GRANZINAB, G. McL. DRYDENA and J.E. McCOSKER A B A Dept of Animal Production, The University of Queensland Gatton, Lawes, Qld 4343 Present address: NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar, NSW 2477 The low metabolisable energy content of tropical grasses during autumn necessitates the use of an energy supplement to meet the nutrient requirements of even modest milk production (Cowan et al. 1993). Molasses is often used in tropical and subtropical dairying regions as an energy supplement but there is little information on its effects on the digestibility of tropical grasses. Supplementing forage diets with molasses decreases the rumen proportion of propionate and increases the proportion of butyrate and lactate (Karalazos and Swan 1976). This undesirable change in the rumen fermentation might be avoided by supplementing molasses-rich diets with monensin. Monensin has been shown to increase rumen proportions of propionate and decrease the proportion of acetate (Granzin 1995). The aim of this experiment was to examine the effects of molasses supplementation on the intake and digestion of Rhodes grass hay by lactating cows and the effects of supplementary monensin. In an incomplete 4 x 4 latin square experiment, three rumen fistulated cows in mid lactation were offered rations of 60% Rhodes grass hay, mixed with either 40% of a cereal grain-based concentrate, or 12.5% molasses and 27.5% concentrate, or 25% molasses and 15% concentrate, or 25% molasses and 15% concentrate plus 20 mg monensin/kg diet DM. Experimental periods were 17 days, except for the molasses plus monensin treatment which was 24 days. The results (Table 1) indicate that including molasses in a diet based on Rhodes grass may increase intakes and have no adverse effect on digestibility. Although improved milk production was not demonstrated in this study, perhaps because of the short measurement periods, increased food intake and propionate production should improve milk yield in practice. Monensin may reduce the molar proportion of butyrate in these diets; this should reduce the risk of subclinical ketosis. Table 1. Effects of the inclusion of molasses and monensin on intake, digestibility, milk yield, rumen metabolites and rumen passage rate of hay of cows offered mixed diets based on Rhodes grass No molasses 12.5 % molasses 13.65 9.69 756 794 14.9 ab 124.3 89.1 66.58 b 20.57 a 10.78 25 % molasses 14.02 10.24 784 834 13.7 bc 101.6 87.2 68.41 b 19.82 a 10.93 25% molasses + monensin 12.64 9.05 736 780 12.7 c 92.3 88.1 66.59 20.47 10.32 s.e. Dry matter intake (kg/day) Digestible organic matter intake (kg/day) Dry matter digestibility (g/kg DM) Organic matter digestibility (g/kg DM) Milk yield (kg/day) A Rumen ammonia (mg/L) A Rumen volatile fatty acids (mmol/L) Rumen acetate (molar %) Rumen propionate (molar %) Rumen butyrate (molar %) A ab A 11.35 8.06 756 795 12.4 a 132.5 97.8 67.11 a 18.67 a 11.69 b b 0.646 0.875 40.7 45.1 2.88 5.73 2.34 0.512 0.257 0.165 Linear effect detected between C, T1 and T2 (P<0.10) Means with the same or no superscripts are not significantly different (P>0.10) COWAN, R.T., MOSS, R.J. and KERR, D.V. (1993). Trop. Grassl. 27, 150-161. GRANZIN, B.C. (1995). M. Agr. Sc. Thesis. University of Queensland. KARALAZOS, A. and SWAN, H. (1976). In Feed Energy Sources for Livestock. (Eds H. Swan and D. Lewis) pp. 29-46 (Butterworths and Co.: London). 384