Effect of level of substitution of protected fat for molasses or grain on milk production of Friesian cows grazing pangola grass.

Abstract

Animal Production in Australia EFFECT OF LEVEL OF SUBSTITUTION OF PROTECTED FAT FOR MOLASSES OR GRAIN ON THE MILK FAT PRODUCTION OF FRIESIAN COWS GRAZING PANGOLA GRASS D.V. KERR*, G.D. CHOPPING* and R.T. COWAN* SUMMARY Thirty-six Friesian cows grazing nitrogen fertilized and irrigated pangola grass pastures were used to study the effects of substituting either 250 or 500 g fat for part of either a molasses or grain supplement. The fat was contained in a tallow-soybean oil supplement protected from rumen degradation by treatment with formaldehyde. Total supplement intake was 2.75 kg dry matter/cow/day throughout two complete lactations. Increasing the level of fat increased milk fat output from 88 kg/lactation for cows given grain or molasses only to 105 kg/lactation for cows given 500 g fat daily (P < 0.05). The associated levels of milk production were 2401 and 2616 kg/ lactation respectively. INTRODUCTION It has been demonstrated that high levels of milk production per hectare can be produced from irrigated, nitrogen fertilized pangola grass pastures with molasses supplementation (Chopping et al. 1976). However the percentage butterfat in the milk is sometimes low. Low fat percentages also occur in other pasture systems. A survey of supplies to one major south-east Queensland factory showed that for the period July to January 1980-81 an average of 36% of butterfat tests taken were below 3.5%. This experiment was conducted to determine whether the feeding of a high energy, protected fat supplement offers an opportunity to increase the output of milk fat. MATERIALS AND METHODS The experiment was done on Ayr Research Station in North Queensland (altitude 10 m, 19O 37's, 147O 23'E) over the two years 1975 and 1976. Average annual rainfall is 1092 mm. A 2 x 2 x 3 incomplete factorial design was used to study the effects of stocking rate, type of energy supplement and level of inclusion of a formaldehyde treated fat product containing a tallow and soybean oil mixture (Hi-En, Alta Lipids Pty. Ltd.). This product contained 37% fat, of which the fatty acid composition was C 14:o 4.2, Cl8 : o 18.7, Cl8 . . 1 37.7, Cl8 : 2 4.0, Cl8 : 3 2.6 molar % respectively. The treatments included were as indicated below. TABLE 1 Treatments applied * Dept. of Primary Industries, Mutdapilly Research Station, M.S. 825, Ipswich 4305. 429 Animal Production in Australia Thirty-six Friesian cows at various stages of lactation were blofcked into groups of nine on age and date of calving. Within groups animals were allocated at random to treatment, and apart from a short period after calving remained on treatments for two years. For ten days after each calving cows were confined to pens and given lucerne (Medicago sativa) hay ad libitum. This data was subsequently used in an analysis of covariance. Cows grazed two pasture replicates on a three week grazing, three week spelling rotation. Pastures were irrigated pangola grass (Digitaria decumbens) and couch (Cynadon dactylon) mixes and were fertilized with 672 kg N/ha/year in nine equally sized dressings, 40 kg P/ha/year as superphosphate and 60 kg K/ha/year as muriate of potash. An electric fence was used to ration the daily allocation of pasture to cows from autumn to spring. Grain and molasses based supplements were given at 2.75 kg dry matter/cow/ day. Grain was placed in selffeeders in the paddock daily, while molasses was placed in open troughs in the paddock twice each week. Milk yields were recorded daily, butterfat and solids-not-fat on one day each week and liveweights monthly. Cows were dried off when the weekly milk production declined to 23 kg. RESULTS Responses to grain and molasses feeding were similar, and increasing the stocking rate from 7.9 to 8.6 cows per hectare had no significant effect on milk yield (P<O.O5). There were no significant interactions between treatments and only .the main effects of level of fat substitution are presented in Table 2. The protected fat supplement increased the output of milk fat (PCO.05; Table 1). This increase was linear with a partial efficiency of use of dietary fat of 0.11 + 0.01. There were slight, though not significant, increases in output of both milk and solids-not-fat through the inclusion of fat in the dietary supplement. Liveweight change was similar for all groups (Table 2). TABLE 2 Effect of level of fat in diet on performance data over a corrected 301 day lactation * Means with different subscripts differ significantly P < 0.05 DISCUSSION The introduction of a protected fat supplement into the diet of cows increased the yield of milk fat. The increase of 56 g milk fat daily for each 500 g of fat in the supplement is similar to that recorded by Pan et al. (1972) for cows given pasture or lucerne hay as the basal diet, but is less than that for cows in a number of other experiments (Storry et al. 1974). Our estimate of the response may be conservative and we suggest that giving a fat supplement would be a practical means of maintaining the fat content of milk in intensive systems of dairy production utilizing grazed pasture as the main source of feed. 430 Animal Production in Australia The changes that occu*red in the fatty acid composition of milk fat were described by Aston and Chopping (1978). There were slight increases in the proportions of those acids in tallow (C18.0 C18.1 and C18:2) and decreases in .I . 1 those acids which are usually produce 6 as a result of fermentation of pasture in the rumen (C4.0 to C > - These changes are similar to those 14:0'16:0 and '18:3 previously reported (Yang et al. 1978). Giving a supplement of protected fat to cows did not increase milk production in our experiment or in other experiments (Palmquist and Conrad 19781. No differences were recorded in milk yield between molasses and grain feeding, and this result supports the suggestion that these two supplements are equivalent in energy value when given at equivalent dry matter. intakes to grazing cows (Cowan and Davison 1978). With a price paid for milk fat of $3.5O/kg it can be estimated from the response measured in our experiment that up to 35c/kg could be paid for a fat supplement. If quota milk is below legal standards for fat content, the feeding of a protected fat supplement would avoid the farmer incurring penalties. ACKNOWLEDGEMENTS We thank the Staff at Ayr Research Station for their help during this experiment, and Alta Lipids Pty. Ltd. for the provision of the protected fat supplement. REFERENCES ASTON, J.W. and CHOPPING- G-D. (l-9781. Proc. Int. Dairy'Congr. Paris, pp 82-3. 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