Ryegrass varieties in relation to dairy cattle performance

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1 New Zealand Journal of Agricultural Research ISSN: (Print) (Online) Journal homepage: Ryegrass varieties in relation to dairy cattle performance G.F. Wilson & R.M. Dolby To cite this article: G.F. Wilson & R.M. Dolby (1969) Ryegrass varieties in relation to dairy cattle performance, New Zealand Journal of Agricultural Research, 12:3, , DOI: / To link to this article: Published online: 05 Jan Submit your article to this journal Article views: 101 View related articles Citing articles: 5 View citing articles Full Terms & Conditions of access and use can be found at

2 489 RYEGRASS VARIETIES IN RELATION TO DAIRY CATTLE PERFORMANCE IV. Milk production from cows grazing ryegrass pastures at two stages of growth and receiving two levels of nitrogen fertiliser By G. F. WILSON* AND R. M. DOLBYt (Received 14 March 1969) ABSTRACT The effects of cows grazing short and long pastures of 'Grasslands Ruanui' perennial ryegrass on the yield and composition of the milk were compared in two experiments. The cows grazing short pasture produced significantly more milk in both experiments than those grazing long pasture. The butterfat percentage in the milk from the two groups did not differ, and the solids-not-fat percentage was depressed by the short pasture in the first experiment and by the long pasture in the second. The depression in the solids-not-fat percentage caused by the short pasture in experiment 1 may have been associated with the chemical composition of the pasture, but the depression caused by the long pasture was probably associated with a lowered intake of digestible energy. The effect on milk yield and composition of cows grazing Ruanui ryegrass pastures which had received high and low levels of nitrogen fertiliser was also examined. The milk yields of cows grazing pasture which had received high levels of nitrogen fertiliser were similar to those of cows grazing low-nitrogen pastures, but the milk contained significantly lower percentages of solids-not-fat and protein. The pastures which had received high levels of nitrogen fertilisers contained higher levels of nitrogen and ether extract and lower levels of soluble carbohydrate and nitrogen-free extract. INTRODUCTION In a previous experiment (Wilson and McDowall 1966) 'Grasslands Ruanui' perennial ryegrass was found to be of lower nutritive value for milk production than two other ryegrass varieties grazed at similar heights. Subsequent results (Wilson 1966) suggested that the voluntary intake of the cows grazing the three ryegrasses probably differed, and that small differences in the digestibility of the grasses may have also contributed to the observed production differences. As part of the production differences between the ryegrass may have been associated with the grazing of Ruanui ryegrass at an above-optimum height, it was of interest to extend the previous results by comparing the production obtained from groups of cows grazing Ruanui ryegrass at two heights. Two such short-term experiments (experiments 1 and 2) in consecutive springs are described. * Massey University, Palmerston North. "t New Zealand Dairy Research Institute, P.O. Box 1204, Palmerston North. N.Z. Jl agric. Res. (1969), 12:

3 490 Ryegrass varieties and dairy cattle performance. IV TABLE I-Details of Experiments Experiment Pastures Treatments Description Date pasture closed (NI4hS04 applied/ac Experimental dates Short Ruanui ryegrass 6-10 in. long; some seeding 27 Oct. 18 Aug. (1 cwt) 14 Sept. (1 cwt) 27 Oct. (1 cwt) Pre experimental period (mixed pasture) Experimental period (short v. long Ruanui ryegrass) Animals Number of cows used Breed of cows Long Ruanui ryegrass 8-12 in. long; considerable seeding 24 Sept. 14 Aug. (l cwt) 14 Sept. (l cwt) 25 Oct.-IS Nov. 15 Nov.-8 Dec. Five pairs of monozygous twins 3 pairs Jersey, 1 pair Jersey x Friesian, 1 pair Jersey X Ayrshire Experiment 2 Pastures Treatments Description Date pasture closed (NI4hS04 applied/ac Experimental dates Short Ruanui ryegrass 6-10 in. long; some seeding 26 Oct. 7 Aug. (l cwt) 20 Sept. (1 cwt) 23 Oct. (1.5 cwt) Pre-experimental period (mixed pasture) Experimental period (short y. long Ruanui ryegrass) Animals Number of cows used Breed of cows Long Ruanui ryegrass in. long; very heavy seeding 28 Sept. 7 Aug. (1.5 cwt) 20 Sept. (1.5 cwt) 27 Oct-12 Nov. 12 Nov.-30 Noy. Seven pairs of monozygous twins 5 pairs Jersey, 1 pair Jersey X Friesian, 1 pair Jersey X Ayrshire Experiment 3 Pasture Treatments Description Date pastures closed 2 cwt (NI4hS04 appliedjac Experimental dates High N Ruanui ryegrass 8-12 in. long; some seeding 25 Oct. 15 Aug., 15 Sept., 18 Oct., 29 Oct. Pre-experimental period (mixed pasture) Experimental period (high y. low nitrogen applications) Animals Number of cows used Breed of cows Low N Ruanui ryegrass 8-12 in. long; some seeding 15 Oct. 20 Sept., 15 Oct., Eight pairs of monozygous twins 6 pairs Jersey, 1 pair Friesian, 1 pair Jersey X Ayrshire 25 Oct.-1O Nov. IO Nov-24 Nov.

4 G. F. WILSON AND R. M. DoLBY 491 These comparisons revealed differences in milk yield and in squdsnot-fat (SNF) percentage in the milk from the cows grazing the two types of ryegrass. In view of the fact that the short and long growth differed considerably in nitrogen content, a further experiment (experiment 3) compared the milk productions from two groups of cows grazing Ruanui ryegrass pastures differing in nitrogen content but at similar stages of growth. These pastures were obtained by the application of two different levels of nitrogen fertiliser. In addition to the main groups of cows two pairs of lactating twins with rumen fistulae were included in experiments 2 and 3 to measure between-treatment differences in some of the end products of rumen fermentation. Animals and design of experiments EXPERIMENT AL A number of pairs of monozygous twins were used in the three experiments (see Table 1). All cows used in an experiment were grazed together for a preliminary period on typical dairy farm mixed pasture. Twin pair mates were then separated and allocated at random to the treatment groups. The treatment period during which the cows grazed pure swards of Ruanui ryegrass was either 2 or 3 weeks. The objective of management was to ensure that throughout each experiment cows in the different groups were offered sufficient pasture to ensure maximum voluntary intakes. After the experimental periods all cows were again grazed together on mixed pasture. The cows used were of various breeds (see Table 1) and included approximately 20% of first calvers in each experiment. All animals had calved in July or August and the twin pairs selected for use Were very similar in initial milk yield and milk composition. Pastures Five paddocks containing pure swards of Ruanui ryegrass were used for the three experiments which were undertaken during the spring in three separate years. The swards had been established for a number of years and had been maintained with regular dressings of sulphate of ammonia and annual dressings of superphosphate. For experiments 1 and 2 two paddocks were used for obtaining "long" pasture and the remaining three for "short" pasture. For experiment 3 two paddocks were used for each treatment. Fertiliser rates and application dates and the dates at which paddocks were closed are given in Table 1 for the first paddocks to be used in each experiment. Where more than one paddock was used the fertiliser rates were similar within treatments, but applications were at approximately weekly intervals. Pastures were topped just before closing to provide a sward of reasonably uniform height. The mixed pasture used during the preliminary periods consisted of various combinations of Ariki, Ruanui, and Manawa ryegrasses, white clover, cocksfoot, and prairie grass.

5 492 Ryegrass varieties and dairy cattle performance. IV TARLE 2-Chemical Analysis of the Ruanui Ryegrass on a Dry Matter Basis (standard error of means) Experiment I I Experiment 2 I Experiment 3 Short Long Short Long High N Low N No. of samples Crude protein (N X 6.25) 21.9(0.57) 13.0(0.31 ) 18.0(0.07) 15.5( 1.80) 20.1 (1.25) 16.4(0.30) Crude fibre 23.9(1.8) 24.7(2.1) 23.3 (1.I) 28.2( 1.04) 21.1 (0.98) 22.5 (0.86) Ether extract 5.4(0.51 ) 3.8(0.07) 3.3(0.26) 2.5 (1.28) 4.9(0.12) 4.5 (0.27) Ash 10.3(0.30) 7.6(0.34) 9.0(0.1 I) 7.1 (0.78) 8.1 (0.16) 7.7(0.11) Nitrogen-free extract 38.5(2.7) 50. 9( 1.8) 46.4(0.37) 46.7 (2.5) 45.8(0.08) 48.9(0.11) Soluble carbohydrate (0.71) 13.9(0.57) 12.2(0.50) 13.9(0.91 ) Dry matter content 18.1 (0.32) 20.4(0.22) 19.7 (0.55) 24.8(0.75) 20.0(0.20) 21.6(0.21) Sampling and analytical methods Herbage-Large samples from each of the paddocks of Ruanui ryegrass used in the experiments were freeze-dried immediately and later analysed for crude protein, crude fibre, and ether extract by standard methods (A.O.A.c. 1965). The soluble carbohydrate content of the pasture was determined using the method of Bailey (1964). Milk-Milk yields ';Vere measured at all milkings, and 2-day composite samples were taken from individual cows once each week in experiment 1 and twice each week in experiments 2 and 3 for analysis. The total solids content was estimated by the gravimetric method. the fat content by the Gerber method. and the SNF by difference. Total nitrogen was determined by the Kjeldahl method (protein = N X 6.38). Rumen liquor--two pairs of fistulated twins were divided between the two treatments in experiments 2 and 3. Samples of rumen liquor were taken from the middle of the rumen (Davey 1965) on two consecutive days during the second week of each experiment. The first sample each day was obtained before the morning grazing period, and three further samples were taken at 2 hr intervals. Concentrations and proportions of volatile fatty acids. ammonia concentrations, and ph for each sample were determined as described by Wilson and Dolby (1967). Statistical analyses-the milk yield and composition data were analysed by covariance analysis. Tests of significance were made between the adjusted treatment means using the values obtained from individual

6 G. F. WILSON AND R. M. DOLBY 493 COWS during the preliminary period as the independent variables. The significance of the differences between treatment means for the characteristics of rumen liquor was obtained in analyses of variance using the mean data for individual cows (mean of 4 sampling times) and testing treatment effects against the between-cow within-treatment mean square. Chemical composition of pastures RESULTS Analyses of the pasture samples are given in Table 2. Although it was intended that experiment 2 should replicate experiment 1, the pastures used in experiment 2 were longer and more mature than those used originally. In both experiments the long (and more mature) pasture was lower than the short in crude protein, ether extract, and ash content, and higher in crude fibre content, but the extent of the difference between treatments differed in the two experiments. The difference in the crude protein content between treatments in experiment 2 was smaller (25% compared with 8.9%) and that for crude fibre larger (4.9% compared with 0.8%) than the corresponding differences in experiment 1. In experiment 3 the high nitrogen (HN) and low nitrogen (LN) pastures were broadly similar in chemical composition to the short and long pasture respectively in experiment 1. Milk yield and composition State of growth-the mean data for milk yield and composition in experiments 1 and 2 are given in Table 3 and Fig. 1. In experiment 1 the cows grazing the short pasture produced more milk (P < 0.01) which was -slightly higher in butterfat percentage and very much lower in SNF percentage (P < 0.01). The difference between the adjusted treatment means for SNF percentage was In experiment 2 the cows in both groups produced considerably less milk after the change to pure Ruanui ryegrass feeding (Fig. 1). The cows grazing the short pasture produced more milk (P < 0.01) than those grazing long pasture. The butterfat percentage in the milk from the cows grazing the short pasture was slightly higher, and the SNF (P < 0.05) and protein (P < 0.01) percentages were also higher for this group. Nitrogen level-the milk yield of the cows grazing HN ryegrass was higher than that of the LN group in experiment 3 (Table 4 and Fig. 1). The butterfat percentage in the milk of the HN group was slightly lower, and the SNF and protein percentages significantly lower (P < 0.01) than the corresponding values for the milk from the cows grazing LN ryegrass. Fat, SNF, and protein yields from the two groups did not differ significantly. Rumen fermentation-the mean ph, volatile fatty acid concentrations, and ammonia concentrations in the rumen liquor samples from

7 494 Ryegrass varieties and dairy cattle performance. IV TABLE 3-Effect of Ruanui at Two Stages of Growth on Milk Yield Composition : Adjusted Mean Values for the Experimental Period and Experiment 1 15/11-8/12/64 Short Long S.E. of Significance growth growth means of difference Milk yield (lb/cow/day) P<O.OI Fat percentage N.S. Fat yield (lb/cow/day) P<0.05 SNF percentage P<O.OI SNF yield (lb/cow/day) N.S. Experiment 2 12/11-30/11/65 Milk yield (lb/cow/day) P<O.OI Fat percentage N.S. Fat yield (lb/cow/day) P<O.OI SNF percentage D3 P<0.05 SNF yield (lb/cow/day) P<O.OI Protein percentage P<O.OI Protein yield (lb/cow/day) P<O.OI TABLE 4-Effect of Two Levels of Nitrogenous Fertiliser Applied to Ruanui Ryegrass on Milk Yield and Composition : Adjusted Mean Values for Experimental Period (10/11-12/11/66) Experiment 3 High N Low N S.E. of Significance means of difference Milk yield (Ib/cow/day) N.S. Fat percentage N.S. Fat yield (lb/cow/day) N.S. SNF percentage P<O.OI SNF yield (Ib/cow/day) N.S. Protein percentage D3 P<O.OI Protein yield (lb/cow/day) N.S.

8 G. F. WILSON AND R. M. DoLBY 495 the four fistulated cows which grazed the two grasses in experiments 2 and 3 are given in Table 5. In experiment 2 the rumen fluids from the two cows grazing short pasture were of lower ph (P < 0.01) and contained higher concentrations of ammonia (P < 0.10) and volatile fatty acids (P < 0.05) than the corresponding mean value from their twin-pair mates grazing long pasture. The mean molar proportions of acetic, propionic, and butyric acids in the rumen liquor from individual cows were all fairly similar. The rumen fluids from the two cows grazing HN grass were of higher ph (P < 0.01) and contained much higher concentrations of ammonia (P < 0.01) than the corresponding values from the cows grazing LN grass. There were only small differences between treatments for total volatile fatty acid concentrations and molar proportions of individual fatty acids in the rumen liquors; but there were higher proportions of propionic acid (P < 0.05) and lower proportions of acetic acid (P < 0.10) in the rumen fluid from the cows grazing HN ryegrass than from those grazing LN ryegrass. 30 a J ~ 24 :s 22 l: ~ ~ ~ -C>--1) ~ \ ~~ ~~ ~~ i::-. ~ ---- EXPT.. 1 ~~ ~ ~ ~ -V EXPT. 2 EXPT. 3 Fig. I-Average milk yield and composition from groups of cows grazing long (open circle) and short (solid circle) Ruanui ryegrass in experiments 1 and 2, and high (solid circle) and low (open circle) Ruanui ryegrass in experiment 3. The first two samples in each experiment were obtained during grazing of a mixed pasture sward in the preliminary periods.

9 496 Ryegrass varieties and dairy cattle performance. IV TABLE 5-Chemical Determinations Made on the Rumen Liquor from Two Pairs of TWins Grazing Short and Long Ryegrass (Expt. 2) and HN and LN Ryegrass (Expt. 3) Experiment 2 Treatment Cow NH;l cone. mg/1oom] ph Total VFA conc. mmjloo ml Molar proportions of VFA Acetic I Propionic I Butyric Long' Short Long Short Treatment differences significant at: 10% level S>L 5% level 1% level S>L Experiment 3 High N Low N High N Low N Treatment differences significant at: 10% level 5% level 1% level HN>LN HN>LN LN>HN HN>LN Stage of growth DISCUSSION The cows grazing the short pasture in experiment 1 produced more milk than those on the long pasture. The milk yield differences obtained between ryegrass varieties in previous experiments (Wilson and McDowall 1966) might therefore have been smaller if the Ruanui ryegrass had been grazed at a shorter stage of growth than the other two varieties. The outstanding feature of experiment 1 was the significantly (P < 0.01) lower SNF percentage in the milk from the cows grazing

10 G. F. WILSON AND R. M. DOLBY 497 the short Ruanui ryegrass. Changes in SNF percentage of the order obtained in this experiment (0.30) have previously been obtained only after reductions in the feeding level of cows (Riddet, Campbell, McDowall, and Cox 1942) or by using feeds containing very low concentrations of protein (Rowland 1946). Although the change from mixed pasture to Ruanui ryegrass did involve a reduction in the plane of nutrition, as indicated by the change in milk yield (Fig. 1), the fact that the cows grazing short ryegrass produced significantly (P < 0.01) more milk than those grazing the long pasture indicated that an additional factor other than feeding level was responsible for the low SNF percentage obtained. This factor was presumably related to the chemical composition of the short Ruanui ryegrass. Of the characteristics measured, the contents of crude protein and ether extract were higher in the short ryegrass, and the level of nitrogen-free extract was considerably lower than the corresponding values for the long ryegrass. In experiment 2 the relative milk yields for treatments were in the same order as for experiment 1, but the depres.sion in milk yields was much greater after the change to pure ryegrass feeding. The short pasture did not result in a lower SNF percentage, but the long ryegrass resulted in a marked reduction. The pastures in experiment 2 were longer and more mature than those in experiment 1. Thi s was reflected in the lower content of crude protein in both ryegrasses and the much higher level of crude fibre in the long ryegrass in experiment 2. The long ryegrass would be expected to be of low digestibility (high crude fibre) and also to lead to lower levels of intake (Blaxter, Wainman, and Wilson 1961), both of which could be responsible for the rapid depre.ssion in milk yield and the low SNF percentage. The short pasture in the two experiments, which resulted in different changes in SNF percentage, differed in chemical composition. These differences included higher levels of crude protein and ether extract and a lower level of nitrogen-free extract in the short pasture in experiment 1. The finding of a lower concentration of volatile fatty acids in the rumen liquor of the two cows grazing long ryegrass in experiment 2, compared with the values from the twin-pair mates grazing short ryegrass, agrees with the suggestion that the depression in milk yield and SNF percentage in this experiment was due to a reduced level of feeding. The differences in ammonia concentrations between treatments would be expected because of the different nitrogen contents of the two ryegrasses, but probable intake differences between treatments may also have contributed. Nitrogen levels In experiment 3 the two levels of nitrogen application provided pastures which were broadly similar to those used in experiment I, except that they did not differ in height or maturity when they were grazed. The milk yield of the cows grazing the HN ryegrass was higher than that of the cows grazing the LN ryegrass, but the SNF percentage was lower, which was partly accounted for by a lower content of protein.

11 498 Ryegrass varieties and dairy cattle performance. IV The higher levels of ammonia in the rumen liquor of the fistulated cows grazing HN ryegrass compared with the values for their twin mates grazing LN ryegrass were probably mainly due to the relative nitrogen contents of the two feeds. In this experiment the intakes of the cows on the two treatments were probably similar, as milk yields of both groups were similar and the concentrations of volatile fatty acids in the rumen liquor of the fistulated cows were much the same in each group. Application of nitrogenous fertilisers in spring makes the composition of the pasture more like that of autumn pastures, which are characteristically high in nitrogen and low in soluble carbohydrates (Waite 1958; Thomson and Terry 1965; Corbett, Langlands, McDonald, and Pullar 1966). Considerable attention has been paid to comparing the nutritive value of autumn and spring pastures. Corbett et al. (1966) demonstrated that autumn growth had a lower net energy value and suggested that this appeared to be related to the relatively high ratio 9f acetic to propionic acids found in the rumens of the animals grazing this pasture. Bryant and Ulyatt (1965) also found higher ratios of acetic to propionic acids in the rumen liquor of sheep grazing HN pasture compared with LN pasture in the spring. In the present experiment, however, the soluble carbohydrate levels did not differ by aro much as might have been expected, and the proportions of individual volatile fatty acids in the rumen liquors of the fistulated cows were not markedly different. The.slightly lower ratio of acetic to propionic acid in the rumen liquor of the cows grazing HN ryegrass would, from infusion experiments (Wilson, Davey, and Dolby 1967), be expected to give higher, rather than lower, protein contents in milk. Unifying hypothesis for the low SNF percentage The high nitrogen pastures in these experiments have stimulated milk production (relative to the other treatment), and in spite of a fall in SNF and protein' percentages in experiments 1 and 3, the yields of these products have been as high if not higher for these groups of cows. The change in milk composition is hence of most interest, and the results from experiments 1 and 3 indicate that the SNF percentage in milk may be lowered by a factor other than a reduced plane of feeding and under conditions where protein levels in the ration would be expected to be well above requirements. It is suggested that, notwithstanding the high content of nitrogen in the pasture, the low SNF percentages may have been due to a "physiological deficiency" of milk protein precursors. This could occur if protein were used extensively as a source of energy where there was (a) a high demand to maintain milk yield at peak of lactation levels; (b) some degree of underfeeding; (c) large losses of nitrogen in the urine because of exces.sive ammonia production. It has been suggested by many authors (Corbett and Boyne 1958; Johns 1962) that very high protein levels in pasture may lead to excessive protein catabolism, and that this is not only wasteful but may be harmful and affect animal performance adversely; but the current work provides the first experimental evidence to support this contention.

12 G. F. WILSON AND R. M. DoLBY 499 Acknowledgments The authors are indebted to Messrs A. K. McDowell and E. R. Elley (Dairy Research Institute), L. Bristol, J. A. Raven, and N. A. Thomson (Massey University) for technical assistance, and to Dr J. C. Hawke, Prof. D. S. Flux, and Prof. I. L Campbell for advice and discussion. REFERENCES A.O.A.C. 1965: "Official Methods of Analysis of the Association of Official Agricultural Chemists" 10th ed. pp George Banta, Menasha, Wisconsin, 957 pp. BAILEY, R. W. 1964: N.Z. II agric. Res. 7: 496. BLAXTER, K. L.; WAINMAN, F. W.; WILSON, R. S. 1961: Anim. Prod. 3: 51. BRYANT, A. M.; ULYATT, M. I. 1965: N.Z. II agric. Res. 8: 109. CoRBETT, J. L.; BOYNE, A. W. 1958: I. agric. Sa. 51: 95. CoRBETT, J. L.; LANGLANDS, J. P.; McDoNALD, L; PULLAR, J. D. 1966: Anim. Prod. 8: 13. DAVEY, A. W. F. 1965: Proc. N.Z. Soc. Anim. Prod. 25: 106. JOHNS, A. T. 1962: Proc. N.Z. Soc. Anim. Prod. 22: 88. RIDDET, W.; CAMPBELL, I. L.; McDowALL, F. H.; Cox, G. A. 1942: N.Z. II Sci. Technol. 23: 80. ROWLAND, S. J. 1946: Dairy Ind. 11: 656. THOMSON, D. J.; TERRY, R. A. 1965: Proc. Nut. Soc. 24: XXV. WAITE, R. 1958: I. Sci. Fd Agric. 9: 39. WILSON, G. F. 1966: N.Z. II agric. Res. 9: WILSON, G. F.; DAVEY, A. W. F.; DoLBY, R. M. 1967: Ibid. 10: 215. WILSON, G. F.; DoLBY, R. M. 1967: Ibid. 10: 415. WILSON, G. F.; McDowALL, F. H. 1966: Ibid. 9: 1042.