Abstract:
61 T.E. TRIGG*, C.R. STOCKDALE*, ANN GALLAGHAN* and R. CURRIE* Three acperimnts are described in wuch cows were ottered irrigated pasture and several levels of concentrate. Responses in rmlk and milk solids production at various stages of lactation, and with pasture and concentrates of different quality have been masured. The significance of these data to irrigated dauying in northern Victoria is considered. A third of Victoria's dairy cows are in tne irrigated areas of northern Victoria. Dairyfamirq in these districts is unique with respect to patterns of feed supply and the quality of that feed (Stockdale 1983). This is caused by low water tqxratures, high summr t-ratures, the species present in the pastures and a guaranteed supply of water in summr. Feed production am3 quality in spring and autumn are similar to those of the temperate seasonal rainfall districts; huweverr in summr high temperatures enSure good grab&h of low quality paspaltzdommat pastures. In w3nterr grazing is often on annual pastures based on sub-clover and ryegrasses. Traditionally hay supplements have been oftered at tunes'of feed shortages. Haweverr the generally poor response of dairy cows to hay supplements (King and Stockdale 1981; Stockdale s a. 1981) has resulted in renewed interest in the use ot hxgh energy concentrates as SU@efiWkS for lactating CUWSm Many factors my influence the magnitude of responses of grazing COWS t0 SU~lermenta~ feeds. Of these, quality of tne pasture and suppl&nmt, levels of feeding of pasture and supplement and stage of lactation are the mst important. The following experiments form part of a series of trials designed to quantify responses of cows in tne irrigated areas of northern Victoria to variations in these factors. Three experimnts were conducted at We Animl and Irrigated Pastures &search Institute, ICyabram, in 1982 in which kgh energy concenixates were offered to pasture-fed cows. !I!!he type and duration of each experimnt are given in Table 1 together with tie nmbers 0% cows and their stage of lactation. A description of the productivity of tne cows and same characteristics of the feedstuffs are also given in Table 1 . 4 - the cows wereallocated to eight groups and otfered one of twD levels of wture PIable 2) At each pasture alMwance# each roup of cuws was offered an amunt of pellets ranging fran 0 to ad 9 ibitm. l * Animal and Irrigated Pastures Research Institute, KyabramVic 3620 62 2 - COWS in either early or late lactation were offered 6.5 kgWca&day of good quality pasture &olium perenne/Trifollum repens) and this was supplemented with pellets ranging fr& 0 to ad libitum (Table 3). These cuwswere individually fedbothpastureand pellet- in stalls. . -3- wasalsoa stall-feeding experimnt andtnecaws in tnis experiment were fed 7.0 kgWc&day of good quality pasture or 7.1 kglWccw/day of `poor quality mure @aspdun dilatatmdmimnt) (Table 1). !lChe psture was supplementedwith quantities of p&lets or what ranging frcm 0 to ad libitum (Table 4) l T%E%E 1 D&ails of the yield (kg/c&day) r canposition (%)and live weight (kg) of the cuws used in each exper&k, and of the in vivo digestibility, (IY!!D) Kjeldahl nitmgen content (NJ and neutral detergent fibre (NDF) (% of dq weight) of tne pasture and concmtrates oftered. InExperiment 1, each group of cows was given a fresh strip of pasture once daily, im&iately after the nmmingmilking. Each group was confined to its allocated area and bacKgrazing was prevented. Pellets were bdividually fed to the- immediately ater eachmilking prior to their return to the *We. Feeding of pellets occurred at approximately 08.00 and 16.00 h. 63 In EXperirmmts 2and3,thepastureandconcentrate requiremmts of each ccw were split between Wo feeding times. The first feed comenced at 08.00 h, ixmdiately after the mrnirq milking. AU cuws were offered their pasture first and then concentrates titer the pasture was fmished. The process was repeated after the aternoon rmlking, ccxtmncing at 16.00 Caws being offered ad libm concentrates had continuous access to h &eir concentrates. Effects of treatments on ccws were assessed by regression of covariate adjusted data. Milk yield and wsition for nme days prior to each experiment were used as mariates. Prior to the collection of data three weeks were allowed for tne fed concentrates to adjust to NW diets. The quantity of concentrates was gradually increased until the projected level. of feeding ws achieved. Both during this period,andsubsequently,drenChingwith sodium bicarbmate was used as a curative procedure for acidosis; regular dosing for prophylaxis was not practiced. COWS Milk yield was recorded at each milking, the fat content was measured daily and the protein cmtent once each week. All cows were weighed daily, immediately after the mrning milking. In Experiment 1, pre7 and post-grazing pasture yields were measured with a rising plate meter (Brie and MGwan 1979) using a double sampling procedure. Ihily pasture intake was calculated frum the differences between the estimated yields before and after graZiragm Intakes in Expertits 2 and 3weremasumdfransaqlesof thepasture and concentrates offered and rejected, after drying these at 100�C for 24 h Samples of all feedtuffs in all experinmts were collected daily for the determination of Kjeldahl nitrogen content and neugral detergent fibre Goering and Van Soest 1970). Thee& were drled at 60�C for 72 hm Estimates of the in vivo digestibility of the pastures used in E%perimnts2and 3 were made using wethers and collecting faeces for ten days. Regression analysis relating animal proauctivity to concentrate intake was used In Experiment 1, group data were used while in mperimnts 2and 3, the data frm individual cows were used. l The rrrean pasture allowances were 15.4 and 26.2 k$Wcuw/&y and tne range in pellet intake was the same at both allawances (0 to 6 kslm/C&dayIm Pasture intakes and the post-grazing yields associated with the various cmbinations of wture bllmces and pellet intakes are givin in Table 2. Rates of substitution of pellets for pasture dependedmpastureallawance (Table 2); atthelawpastureallcmance, 64 substitutiOn was evident only men mlets were oftered ad libitum, while at the higher pasture a~owance, substitution was at its greatest at the lowest of pellets on offer and diminished thereafter. 4 TABLE2 Effect of the intakeof feedstuffs (kgM/cow/d@ onthe production of milk products (kg/cow/dayIr milk caqosition (%I and liveweight change (kg) of cuws in late lactation offered two levels of pasture (kgDN/cow/dayL Pasture availability and residual pasture (tU!l/ha) and the substitution rate (kg reduction in pasture intake/kg concentrate eaten) have also been presented. The different pasture allowances significantly ti~uenced fat yield ow; however, while the Wwer allowance tended to reduce rmlk and protein yields, these were not significant. When ad libitum pellets were offered man intake of pellets approached 10 kgM/ccw/day for cows inearly lactationand6kglWcuMday for cows in late lactation (Table 3). Ikvelsofproductionatthese two stages of lactation are also given in Table 3. Milk (r2=41.91; rsd=l.59) and protein (r*=O.88; r&=0.059) yield, aM liveweight change (r*=O.72; r&MS) all increased linearly with'intake of pellets. The marginal returns frm feeding a kg of pellets were 0.9 and 0.7 kg milk for cmm in early and late lactation, respectively. !I!be response in fat yield to feeding extra pellets was significantly curvilinear (r*=O.56; rscM.093~ and maxbum yield again occurred at about 4-SkgM/ccMday of pellets fed regardless of stage of lactation. This was associated with a marked reduction in the fat content of the rmlk among those cows offered ad n . 65 libitum pellets; respectively) l (2.75 and 3.51% for cuws in early arld late lactation, Ma&m intake of approximately 9 and of concentrate feeding contrasting quality are pellets and wheat when offered ad libitum were 6 kgWcuw/day respectively (Table 4). The exfects on the productivity of the cows oftered pasture ot also given in Table 4. m~~4 Effect of concentrate intake (kgU!Ucow/day) ontheproduction of milk products (kg/cm/dayL milk constituents (%I# and liveweight change (kg) of cows fed either qpgrasdwhite clover pasture (7.0 WWcddayl or pspaltrm daunmt pture (7.1 kgDM/cuw/day) l Higher levels of productivity were generally obtained frcm cows offered good quality pasture ccqpred to those oftered poor quality pasture. However, there were interactions associated with tne type ot concentrate fed. Response in milk (r*=0.79; rsd=l.73), fat (r*=O.S& 66 rsMl.085~ and protein (rWl.82; rsd=O.060) yield obtained from both pellets and wheat when u&l to supplmt good quality pasture were similar to those reported for feeding pellets in Esrperimnts land 2. Milk and protein yield responses were linear (marginal returns from feeding a kg of concentrates were 1.0 kg milk and 0.040 kg protein, respectively) Vlxile the response of fat yield to concentzates was curvilinear. Maximum yield again occurred at about 5 kgWcuw/day of concentrates fed. !t!Ms was associated with a depression in fat test at high concentrate intakes (Table 4) although this was not as severe as in Experiment2. Production of milk solids fran cows offered poor quality pasture indicates an interaction of concentrates with pasture quality at hxgh levels of intake (Table 4). Supplementing poor quality pasture with pellets gave the same response in rmlk yield as tnat recorded for good quality pasture. However, use of wheatsup@lemnts resulted in a large reduction in milk yield at high concmtiate intakes (r*=O.88; rsd=l.30), While fat depression was obvious when wheat was the supplment, this was not the case &en pellets supplemnted poor quality pasture(r*=O.77; rsd=O.O77L Although the response to extrapelletswas curvilinear, the best fed ccws had still not achieved peak yield. Production responses from feeding concentrate supplements to grazing dairy cows can readily be masured as imzdiate or carry-over effects on milk yield and/or ccmposition. Iess obvious are responses associated with changes in partitioning of nutrients to or frti body tissue or those involved with substitution of concentrates for pasture. May good reviews describe supplementary feeding concentrates Leaver et & 1968; Broster, St a. production data from pasture-fed c0ws value because tiey are then complicated only to a single set of circumstancesm the qualitative effects of to daxy cows. (eg., Rook l%la,b; 1978) o However, quantit&ive are few and generally of little by substitution effect or refer The wrimentsdescribedinthis paper provide information useful for the nutrition of dairy cows that graze pastures typical to tne irrigation areas of northern Victoria. aWhilemeaningfulchangesinboq -condition could not be estimated and L liveweight change data in bese short-term trials are of doubtful value, the responses in animal products have been determined without the confounding effect of substitution, with the exception Of Experiment le Responses in milk yield to increasing levels of con-bate supplementation at all stages of lactation were within the range of tnose sumarisedbyLeaver&& (1968) and Bryant and Trigg (1982). Maxim-m respotlse to supplementation of milk yield was in early lactation when cows also ate the mstconcentrates. !Lbis difference in response - be attributed to an alteration in energy partitioning to favour increased tissue synthesis, due to an altered acetate : proprlonate ratio with increasing concentrate intake. The effect on partitioning of progressing stage of lactation is also implicated. 67 Regression analysis showed that mximm butterfat production, at all stages of lactation, occured when cows ate approximately 4-5 kg concentrate. Fat dlepression was greatest in the cows fed the highest levels of COnCe.IltIateSe Levels of concentrate intake achieved in ,early lactation were mre than 50% greater than in late lactation, however, the relative mgnitude of the depression was greater in late compamd with early ldctatiOne The literature contains many reports of the dewce of milk fat contt on dietary roughage kg., Kesler and spahr 1964; Broster & . &. 1978) and low total N.D.F. in OUT rations (Table11 suggest that law fibre had a major influence on this result. - Pasture quality did not influence the marginal response of rmlk production to concentrate supplmentation though the difference in total productivity did reflect the contrasting quality of the pasture. The mch gre&ter reductionof milk fat test of the cam offered high levels of concentrates with ryqrass/white clover pasture compared with those offered paspalum reflect the lower levels of dietary m in the former (average NDF: ryegrass diets 24%; Paspalumdiets 32%). The interaction between ptuxe and concentxate quality on mlk fat yield, such that those cows ofzered paspalum plus wheat supplmt produced less butterfat than similar cows oftered paspalum and pellets or ryegrass/white clover based diets, was related at least partially to nitrogen content of the diets. T&al crude protein content in the EG/K diets was 18.4 and 17.0% for cows supplemnted with the hqher level of pellets and wheat respectively. EQuivalent data for paspalum diets was 14.8 and 11.6% suggesting nitrogen was limiting in the latter diet. That other nutrientsmaybe involved cannot be discounted. of interest also is the maximum level of concentrate eaten they were on dffer without restriction; more pehets tnan wheat were eaten, irrespective of psture type. The possibility of a greater buftering capacity of pellets -red to wheat cannot be discounted as pellets contained both mre N.DeFe than wheat plus 20% limestone of unknown buffering rapacity. Tbe variatibns in the levels of substitution measured in Bqerimnt 1 indicate that a number of factors may influence the rate of substitution of comtrates for pasture. Broster and Thomas (19811 have previously outlmed maq factors affecting substitution rate in lactating cattle. These include forage digestibfiity, type andlevelof concmtrate,and&emical canpositionof the forage. Experimntlsuggests thatwithgrazingcawsthe~ti~ Of pasture on offer is also of major iqortance. Umiously, rate of substitution requires further definition particularly in view of tne pasture types that exist in northern Victoria (Stockdale 1983). The effect of increasing level of concentrate supplementation on 68 residual pasture was mt large in this trial wnich is in contrast to tmt' et al. reported by Stockdale (L981). Thismybaveoccurredbecauseof the very poorqualitypastureusedinExperimmt 1. Anysparingeffect on the level of residual pasture can be critical in tunes of pasture shortage. P The major contribution of this work has been to quantify some effects of imcxeasing levels of concentrate supp&mentation on productivity of c0ws fed pture differing in quality or at different stages of lactation. Further quantitative work winmg the etfect of changing levels of con-trate is indicated. In adcliticn, factors affecting the magnitude of substitution effects together with the influence of nutritive value of the supplembent on intake and productivity, are critical to the definition of ccw responses to supplmentatione BKEEEI, W.H. and THOMAS, C. (1981). Recent Advances in Animal Nutrition. Ed. W. Haresign. Butterworths, London. B-8 WeHer SUTTON, J.De and BINES, J.Ae (1978). ReCent Advances in Animal Nutrition Ed. William Haresign and Dyfed LWiSe Buttenmrths, Imdon. BIWNT, AeMe and =GG, T.Ee (1982). In Dairy Production from Pastures EdSe K.L. MMilla and WI Taf~ae EKERN, A.W. (1972). Feeding of High yielding cows. Report147. Rrryal Agriculture College of Norway. EAEtLE, D.F. and m, AeA. (1979) m** Je m* a Fgtm 0 me & 337. GOEWZG, HeKe ad VAN SO-8 PmJe (197O)e Agric. Handbook 379, Um . KESBt, EeMe ad SPAHR, SeL. (1964)o J* u m . 47, lp2. . l KING, KeR. and S!CRKDU, C.R. (1981). mt. J. &p. UC, m &&. 2, 167. LEAVER, J.De, CZNPLIXG, RX. ad H-r W. (1%8)e Dairy Sci. A&t. JQ(71, 355. d, JeAeFe (1961a) w S& A&& . 2& 25. . m, JeA*F* (196lbIo m me B 0 2;L, 303.. . -8 C.R. (1983)e &St* J* me we Anim, I&& 2J, 131. -8 CeR.8 Km, K*R., PAmr 1.F. and RyANI D.T. (1981). I&&. & 148. l . l l l