Milk production from irrigated nitrogen fertilized pangola grass.

Abstract

MILK PRODUCTION FROM IRRIGATED NITROGEN FERTILIZED PANGOLA GRASS G.D. CHOPPING*, H.D. DEAN*, R. SIBBICK*, P.N. THURBON*, and MRS. J. STOKOE** The project compared milk production and composition of Jersey and Friesian cows grazing irrigated pangola grass fertilized with 672 kg N/ha~ annum. Friesians were stocked at 5.9 and 7.9 cows/ha, and Jerseys at 7.9 and 9.9 cows/ha. A supplement of 3.6 kg/head/day of molasses/urea/M.A.P. (97:2:1) was also evaluated. High levels of production per unit area were achieved. Supplemented Friesians at the high stocking rate averaged 25626 kg milk and 863 kg fat/ ha, Corresponding values for the comparable Jersey group were 21348 kg milk and 954 kg fat/ha, For both breeds increasing the stocking rate reduced per cow production and generally, though not always, increased per hectare production, Per hectare production of the highly stocked Friesian group exceeded that of the lower stocked oup by an average of 6,s for 763 milk (21551 kg s 230013 kg g 2.8$ for fat r ke; v 784 kg) and 6.6 for S.N.F. (17'71 kgx 1893 kg o For Jerseys, corresponding increases were 9.6 for milk (17921 kg x 19668 kg 3.9 for fat (830 kgs862 kg) and S,C$ for S.N.F. (1529 kgp 1651 Molasses supplement was very effective in raising milk productfollo On average Friesians gave 0.67 kg milk per kg of molasses fed. For Jerseys the figure was 0.39 kg milk per kg of molasses. Supplement feeding also generally increased lactation length and the S.N.F. $ of milk, The project has demonstrated that dairyi- can be successfully undeze takenunder true tropical conditions. I. INTRODUCTION Swain (1971) claimed it was doubtful whether a viable dairying industry could be maintained in the tropics if it had to rely on legume grass pastures. Basically this was because of low output per cow ani per hectare. A graz;ing system based on nitrogen fertilization should be capable of far higher output per hectare because it should support higher cow numbers per unit area. This project was undertaken to examine the effect on per hectare production of breed, stockiag rate and supplementation at a high level of grass fertilization in a tropical environment0 With the increasing use of nitrogen fertilizer on dairy pastures in Queensland this question has major relevance. II, MATERIALS AND METHODS A 2 x 2 x 2 factorial design was used to examine the effect onmilk production of:- breed (Friesianp Jersey; 16 animals (foti oups of four) ha of each breed were involved); stocking rate (5.9 x 7.9 cows r for Friesians, ODd 7.9 v 9.9 cows/ha for Jerseys); and supplement (nils 3*6 . kg/head/day of a mo1asses:urea:M.A.P. mixture (fl:2:1 - in year 3 urea replaced biure t isonitrogenously), - ---~ ~- *Department of Primary Industries, Ayr Research Station, AXR, weensland. **Griffiths University, BRISBANE9 Queen&a& 481 (a) Pasture mawement The pasture was irrigated Digitaria decumbens* A two paddock system per group of four cows was used, each addock being gra!zed for three weeks and rested for three weeks. Nitrogen P672 kg/ha/am as ammonium nitrate in yesrs 1 and 2 and urea in year 3) was applied in equal applications every six weeks during the pasture rest phase0 Phosphate (43 kg/ha) and potassium(62kg/ha) were applied as a single dressing every August. An electric fear:@ shifted daily was used to ration pasture from autumn to late spring0 (b) Animal management Initially within each breed cows were randomly allocated to one of four stocking rate x supplement treatments approxitely six weeks prior to the mea33 calving date. In subsequent years one cow in each group was replaced by a heifer when the cow to be replaced completed her lactation. For I4 days following calving each cow was yard fed on Medicago sativa hay and molasses to determine initial milk yield under a fixed nutriG system. This data was used for a covariance correction to minimise variation due to initial yield differences, Apartfromthis14 day period the cows were maintained year round on the same pasture area. Daily milk yield, weekly fat and S.N.F. percentages and monthly iive. weights were recorded* Cows were dried off when the weekly milk yield declined to 23 kg. Rectal temperatures of the cows were taken weekly at an afternoon milking over the period December, 190 to March, l'~lo III. RESULTS Each years results were analysed separately by covariance analysis using milk production over lactation days 5 to 14 on a standard ration as a covariate to correct for inherent differences in production. Corrected treatment effects on per cow and per hectare milk, fat and total s&ids production are shown in Table 1, Actual milk composition data (not covariance corrected) is also given in Table 1, - 482 Milk production in the first lactation averaged 16.9 above the second lactation and 39.18 above the third lactation. Friesians and Jerseys averaged 3272 kg milk and 114 kg fat, and 2130 kg milk and 96 kg fat per lactation respectively. For both breeds increasing the stocking rate reduced per cxw production and generally increased per hectare reduction, For'Friesians, increasing the stocking rate (5.9 to 7.9 cows P reduced ha) average per hectare production in the first lactation but increased production in lactations two and three. The average increase in per hectare production due to increased stocking rate was 6.s for milk (28551 kgx 23003 ), 2,s for fat (763 kg v 784 kg) and 6.6 for S.NA (WV kg s: For Jerseys corresponding increases were 9.s for milk (17927 kg x 19668 kg), 3.s for fat (830 kg v 862 kg) and 8.6 for S&F, (1529 kg 1 1893 kg 7l 1651 kg). - Molasses raised milk yield by an average of 0467 kg milk/kg molasses with Friesians and 0.39 kg milk/kg molasses with Jerseys0 In addition, supplement feeding generally increased lactation length and the S,N.F. 5 of milk. Milk casein percentages were low especially over summer when mesian milk averaged 2.1& and Jersey milk 2.6@& Weekly variations in mean rectal temperature for each breed are show-n in Fig..1 for the period December, 1970 to March, 1 9710 The mean tesnpeature for both groups over much of this period was outside what is regarded as a normal range (Hungerford 1967), Friesians-showed more obvious signs of heat stress than did Jerseys. Fig. 1. Variations in rectal temperature (OC) of Friesians and Jerseys at one afternoon milking weekly over period December 19'70 to March 1971 483 IV. DISC USSION Payne (1.963) suggested it should be possible on 'good humid tropical pastures' to maintain five dairy cows/ha each producing at least 2'720 kg of milk annually; This target of 13600 kg milk/ha has beengreatly surpassed in this experiment. . Furthermore, consistent results in the second and third lactations would indicate that the system used was reasonably stable0 The higher production levels recorded in the first lactations were caused by two factors. Firstly only mature animals were used in the first lactation while in the second and third lactations one heifer/group was used0 Secondly, animals commenced the first lactation in better codition than they commenced subsequent lactations. Ephemeral fever was a problem in the third year, especially with Jerseys. This had the effect of nullifying the effect of supplement with this group in that year and is the major cause of the differenr:e between breeds in milk response to supplement, Rectal temperature data during summer indicated that heat stress was at a level where substantial effects on milk production and composition . could be expected (Bianca 1965). Milk protein is a sensitive indicator of heat stress (Donnegan pers. comma) and low summer casein percentages recorded for both Jersey ati Friesian are consistent with this and go a way to explaining the problem of low S.N.F. content of milk, However, low S.N.F.'percentages were recorded year round and it is probable that the low energy concentration of tropical species combined with relatively low intakes of pasture dry matter (c.f. temperate species) are largely responsible. Heat stress in summer would aggrevate the problem further by reducing intake, The above would indicate good responses could be expected both in milk production and S.N.F. 5 to energy supplementation even in those periods of the year when feed is available in excess (e.go summer). Results from this trial are consistent with this, It would seem that the tropics by exploiting the high levels of dry matter that can be produced under their clirktic conditions axxi utilizing a cheap energy source such as molasses can rival temperate regions in milk production per unit of land even though individual cow yields are not high0 v, RE3EREEJcEs BIAEA, W, (1965). Journal of dairy Researchz:291. HIJXXRFORD, T.G, (196'7)o 'Diseases of Livestockn 6th ed* (Angus and Robertson: Sydney). PAYBE, W&A. (1963). Proceedixs of world Concress of animal Production Rome 3205. . SWAIN* F.C: (t971)o Tropical Grasslands 5&269 484