Beef production as influenced by stage of maturity of grass for silage and level and type of supplementary concentrates Ilmo Aronen, Vesa Toivonen, EliseKetoja and Jukka Öfversten Aronen, 1., Toivonen, V., Ketoja, E. & Öfversten, J. 1992. Beef production as influenced by stage of maturity of grass for silage and level and type of supple- mentary concentrates. Agric. Sei. Finl. 1: 441-460. (Agric. Res. Centre of Finland, Inst. Animal Production, SF-31600 Jokioinen, Finland and Agric. Res. Centre of Fin- land, Data and Information Services, SF-31600 Jokioinen, Finland.) The aim of this study was to examine the effects ofstage ofmaturity of grass for silage (EC = early cut, LC= late cut), and level (LL =low level, i.e., 1.5 kg dry matter (DM) d l , HL =high level, i.e., 3.0 kg DM d' 1) and type (B =barley, BRSM =barley and heat- moisture treated rapeseed meal) of supplementary concentrates on feed intake, animal performance and diet digestion in Finnish Ayrshire bulls. The study was conducted as a 2 3 factorial experiment with six randomized complete blocks. The average initial and final live weights of the bulls were 123 kg and 494 kg, respectively. The crude protein content ofthe ad libitum fed EC and LC silages, cut at an interval of eight days, was 159 and 131 g kg' 1 DM. However, the difference in the estimated content ofAAT (= amino acids absorbed in the small intestine) between the two silages was small, whereas there was a large difference in PBV (= protein balance in the rumen). The respective values for crude fibre were 278 and 304 g kg' 1 DM. At the beginning of the experiment the voluntary grass silage intake of the EC bulls was higher than that of the LC bulls. Towards the end of the experiment the difference in silage intake between the two stages ofcut disappeared. This change in voluntary grass silage intake was followed by a similar change in the rate of daily live weight gain (LWG): the EC bulls started to grow faster than the LC bulls, but the initial slower LWG of the LC bulls had been compensated by the end of the experiment. The LL bulls had a higher intake of silage than the HL bulls. The substitution rate was 0.63 kg silage DM per concentrateDM, regardless of the stage ofcut. HL feeding resulted in faster LWG. Owing, at least partly, to the improved diet digestibility, inclusion ofrapeseed meal in the diet increased the silage intake throughout the experiment followed by a faster LWG. The positive effect ofrapeseed meal was unaffected by the stage ofmaturity of the grass for silage and the level of concentratesupply. The animals were not able to take full advantage of the high protein content of the EC silage. The inclusion of rapeseed meal in the diet, however, improved the rate of gain and resulted in more efficient feed conversion. Key words: rapeseed meal, protein evaluation, diet digestion, feed intake, substitution rate, live weight gain Introduction Livestock production in Finland is largely based on grass silage feeding. Grass is usually cut at an early stage of maturity to obtain silage of high digestib- ility and high protein content. On the other hand, a delayed cutting will increase the dry matter (DM) yield ha ‘. 441 Agric. Sei. Finl. 1(1992) https://www.c-info.fi/en/info/?token=YKgHMaot3yuN7DEB.gYoJLLf6CaSoCagYfMUpBg.HgLqbTWatloVZpPp4XaH8_0ioOkNKdEnN_Q2PVwHDdjp16l_R8cJW89ZS1ni6nJXA7Lg1ssRIeoY1Z0s4CQTCr9oG8LguE6oLTvehEx6RR8Gbcz9znQB17uLG9umjfxjsgYomiATK7cqiDoyi8Vw9MheBNPJVeA_8ftcvaUBEWynGKtVV2T1XUiLYZVOZmTkHFY_H7-4kHvZ0_Sus6cAMSz2TuIiD-WBQQMDrmy3V4kYFMl_G7dZ7WTBGtlZVN8iv4ke26IXEhpQTGLAmNUQUn-Xigqc_Ag3BWlTdsq-qe8JFmTGCXqUuw-VKFEukYMOsBQJR6P8kLQ In an intensive beef production system, grass silage is always supplemented with concentrates to increase the total nutrients intake and thereby the rate of daily live weight gain (LWG). The supple- mentary concentrates are mainly based on barley grain. Rapeseed meal (RSM) is commonly used as an ingredient in protein concentrates. Inclusion of concentrates in the diet usually decreases the voluntary grass silage intake (Ettala and Lampila 1978, Steen 1984). Nevertheless, in many experiments protein supplementation has been found to increase roughage intake (e.g., Cody et al. 1990, Donaldson et al. 1991). It has been suggested that the stimulating effect involves a cycle of improved efficiency of microbial protein synthesis, increased DM digestibility and thereby increased feed intake (Nocek and Russell 1988). However, in experiments with grass silage, results have been somewhat contradictory. Huhtanen et al. (1985), Steen (1988), Aronen (1990) and Moloney (1991) did not find any change in volun- tary grass silage intake when protein supplements were included in the diet, whileAronen (1991) and Aronen and Vanhatalo (1992) recorded an in- creased grass silage intake with a resultant enhancement in LWG of bulls. The aim of this experiment was to study the voluntary grass silage intake and LWG ofAyrshire bulls in relation to the stage of maturity of grass for silage supplemented with two different levels and types of concentrates. Special attention was paid to possible interactions between the stage of maturity of grass for silage and the type of the supplemen- tary concentrates (i.e., barley or barley together with RSM) to find out whether the effect of RSM depends on the protein and energy content of the grass silage. Similarly, the interaction between the protein supplementation and the level of concen- trate in the diet was ofinterest, because earlier find- ings by Waterhouse et al. (1983) suggested that lower responses to protein supplementation were to be expected for diets with a high concentrate level. In some experiments (Hakkola 1985, Joki- Tokola 1991, Aronen and Vanhatalo 1992), the positive effect of protein supplementation on LWG was sustained throughout the experiment, while in others (Huhtanen et al. 1989, Aronen 1990) the positive effect of RSM on LWG was restricted to the early phase of the growth period (i.e., live weight below 300 kg). Therefore, the manner in which the treatment effects and their possible inter- actions change with the phase of the production experiment was examined in the present study. Furthermore, the apparent digestibility of the diets was determinedat the end of the production experi- ment in order to find out the relationship between diet digestion and feed intake. Material and methods Animals and their feeding Six blocks of eight Finnish Ayrshire bull calves were formed on the basis of live weight (LW). The calves within the blocks were then randomly allott- ed to D factorial treatment combinations. The three factors were: stage of maturity of grass for silage (EC = early cut, LC = late cut), level of concentra- tes (LL = low level, i.e., 1.5 kg DM d l , HL = high level, i.e., 3.0 kg DM d 1) and type of concentrates (B = barley, BRSM =barley and RSM). For BRSM diets, 1.5kg ofbarley was replaced by a mixture of barley and RSM (66:34) to provide 0.5 kg of RSM d l . The average initial live weight of the bulls was 123 kg. Three of the animals were lost during the experiment for reasons not related to the treat- ments. Direct cut grass from a cocksfoot-timothy (Dactylis glomerata - Phleum pratense) sward was ensiled in bunker silos with a formic acid-based additive (AIV II; 80% (w/w) formic acid, 2% or- thophosphoric acid) applied at the rate of 5 If 1 . The silages were fed ad libitum. The EC silages (two silos) were harvested on 5-7 June 1989 (at the beginning of the ear emergence stage of timothy) and on 2-3 August 1990 (one silo), and the LC sil- ages on 14-15 June 1989 (two silos) and on 8-10 August 1990 (one silo). The silages in 1989 were of the first cut and in 1990 of the second cut. N, P and K fertilization per ha was 110 kg, 22 kg and 44 kg 442 Agric. Sei. Fint. 1 (1992) for the first cut and 93 kg, 19 kg and 37 kg for the second cut, respectively. The daily allowance of concentrates was gradu- ally increased from 1.5 kg to 2.0 kg for the LL bulls and from 1.5 kg to 5.5 kg for the HL bulls. The RSM was heat-moisture treated (ÖPEX®Tulisalo 1990). Experimental procedure and analytical methods The experiment was started when the animals had reached an average age of 17 weeks and it lasted for 12 four-week periods. The animals were weighed at the start of the experiment and on the last day of each 28-day period. LWG for each 28-day period was calculated by difference. At the end of the experiment the animals were slaughtered. A description of the slaughter technique is given by Aronen (1990). The individual feed intake was measured daily. The pelleted concentrates were fed twice daily and grass silage once daily. Feed samples were taken at every feeding and pooled for periods oftwo weeks for grass silage and four weeks for concentrates. Proximate feed analyses were carried out conven- tionally. The correction for volatile losses in grass silage was made according to Huida et al. (1986). Fermentation quality of the grass silages was ana- lyzed as describedby Vanhatalo et al. (1992). Apparent in vivo digestibility of the silages in the six bunker silos was determined in four wethers. Table values (Salo et al. 1990)were applied for the digestibility of barley and the values determined in wethers (Vanhatalo et al. unpubl.) were applied for RSM. The digestibility coefficients were used to calculate metabolizable energy (ME) and net energy (NE). ME values were calculated according to MAFF (1975) and the values for NE (in feed units, FU) according to Salo et al. (1990). In order to evaluate protein feeding according to the AAT-PBV system (Hvelplund and Madsen 1990), the protein intake was calculated in terms of AAT (amino acids absorbed in the small intestine) and PBV (protein balance in the rumen). The rate of disappearance of feed N from nylon bags was determined for each feed (six silages and two concentrates) in three adult non-lactating Finnish Ayrshire cows equipped with a rumen cannula and a duodenal t-shaped cannula and fed at mainten- ance with grass silage and barley (70:30 on a DM basis). A description of the incubation techniques for concentrates is given by Aronen (1991) and for grass silages by Vanhatalo et al. (1992). Degradability of crude protein (DEG) was calcu- lated according to orskov and McDonald (1979) using a ramen outflow rate (k) of 8% h 1 for concentrates and 3% h' 1 for silages. A correction for microbial contamination in grass silage samples was made according to Michalet-Doreau and Ould-Bah (1989), and a correction for small par- ticle losses from the bags in concentrates according to Weisbjerg et al. (1990). True digestibility of undegraded feed protein in the intestine was calculated according to Hvelp- lund et al. (1991). For this purpose the intestinal degradation of intact feeds was measured by the mobile bag method using freeze-dried grass silage and air-dry concentrates. A description of the method is given by Vanhatalo et al. (1992). During the last four-week period of the feeding experiment, when the animals had reached an aver- age live weight 0f473 kg, the apparent in vivo digest- ibility of the diets was determined. Acid-insoluble ash (AIA) was used as a natural marker (Van Keu- len and Young 1977). Arrangement of the treat- ments during the digestibility trial was similar to that in the feeding experiment, except that the animals on LL feeding received 2.5 kg d 1 of concentrates and those on HL feeding 5.0 kg d l. The silages were of secondcut and were fed at the level of 90% ofthe ad libitum intake. Feed samples were taken at every feeding and pooled for the experimental period of five days. Faecal grab samples were taken when feed- ing the animals at 07.15 hrs and at 15.30hr5.In addi- tion to proximate feed analyses, faecal and feed samples were analyzed for AIA using 4 N acid according to Van Keulen and Young (1977). Due to palatability problems, one of the 45 bulls was excluded from the calculations. 443 Agric. Sei. Finl. 1 (1992) Statistical methods For each bull, LWG and intake of nutrients was first calculated for 12 consecutive periods. It was found that two adjacent measurements could be combined without loss ofany relevant information. Consequently, six repeated measurements (Period 1 to Period 6) of the same variables were recorded for each experimental unit (bull). Typically, the measurements of an experimental unit over time are dependent on each other and a proper analysis of the measurement data must take into account these dependences. In the present study, a multivariate analysis of variance approach was used, which assumes no knowledge of the dependence structure (covariance structure) of the repeated measurements. This approach is pre- sented, e.g., by Crowder and Hand (1990). In the multivariate approach, the effects of the treatments on all response variables, in this case on all six repeated measures of the same experimental unit, are observed simultaneously. This gives a vec- tor response, and not just one (scalar) response as is the case in the separate univariate (one variable at a time) analysis. Let (i, j, k) identify the combination of different factor levels (e.g., i = early stage ofcut, j = low level of concentrates, k = barley). Further, let the response vector for the bull assigned to the (;, j, &)th treatment combination in the /th block be the following (written as a row vector): y ijkl [ yijkir yijkl2’ yijkl3’ yijkl4 5 yijkls> ijklft] The model used for y’ had the form y’yU = H+a +B.+ Yk + (aD).. + (ay),., + (By)., + (afly)., + 5, + eijkl , where, like theresponse, all the parameters are 6xl vectors, and p is the vector of period means, a is the effect of stage of cut, B is the effect of level of concentrate, y is the effect of type of concentrate, aB, ay, By and aßy are the corresponding interac- tions, 5 is the block effect and e is the vector ofran- dom errors. The components of the vector e are assumed to have a joint multivariate normal distri- bution with mean vector 0 and arbitrary covariance matrix Z (i.e., the model does not include any assumptions concerning the covariance structure of the repeated measurements). In a multivariate analysis of variance, the testing of hypotheses is based on a comparison of matrices (instead of sums of squares). There is, however, no one single correct way of comparing matrices, and various alternative test statistics have been pro- posed for hypothesis testing. The SAS GLM pro- cedure (SAS 1990), by which the analyses were performed in this study, includes the four most common test statistics, namely Wilks’ Lambda, Roy’s Largest Root, Hotelling-Lawley Trace and Pillai’s Trace. All of these tests gave similarresults in our study, although this is not always the case. In the digestibility trial, conducted with growing cattle at the end of the production experiment, the digestibility variables (crude protein, ether extract, crude fibre and nitrogen-free extracts) were highly correlated. This data resembled the repeated meas- ures data above in that there were several correlated measurements recorded for each bull. However, now the measurements included four different variables. Nevertheless, the statistical model on which the analysis was based, was analogous to the one given above. The digestibility of organic mat- ter was studiedby using the corresponding univari- ate model. When interpreting the diet digestibility data, the results of the multivariate tests were examined first. Only if these results were significant, the results of the corresponding univariate analyses were then examined to locate those digestibility variables which seemed to contribute most to the results of the multivariate tests. However, the univariate analyses do not take into account the correlations between the response variables and, therefore, when there are correlations, their results should be interpreted with caution. Results Chemical composition and feed value of the feeds The first-cut silages (harvested in 1989) were fed 444 Agric. Sei. Finl. 1 (1992) during Periods 1 to 4 and the second-cut silages (harvested in 1990) during Periods 5 and 6. The fer- mentation quality of both silages was good (Table 1). No butyric acid was observed. During the first four periods the proportion ofNH3-N and soluble N of total N was greater in the LC silage than in the EC silage, the opposite being true during the last two periods. In relation to the time interval between the har- Table 1.Fermentation quality of the grass silages in the feeding experiment. Early cut Late cut Periods 1 + 2 pH 4.1 ' 4.1' ' In dry matter (DM), g kg’ 1 Lactic acid 42 42 Acetic acid 18 20 Propionic acid 0 1 Sugars 32 33 Ethanol 8 9 In total nitrogen (N), g kg 1 NHj-N 46 56 Soluble N 476 520 Periods 3 + 4 pH 4.0 4.1 In DM, g kg ' Lactic acid 48 52 Acetic acid 16 17 Propionic acid 0 0 Sugars 28 32 Ethanol 10 9 In total N, g kg’ 1 NH 3-N 44 59 Soluble N 541 613 Periods 5 + 6 pH 4,0 4.1 In DM, g kg’ 1 Lactic acid 71 34 Acetic acid 15 13 Propionic acid 0 0 Sugars 36 48 Ethanol 6 9 In total N, g kg 1 NH 3 -N 46 31 Soluble N 505 429 vesting of the EC and LC silages, the crude protein (CP) content decreasedby 0.39 %-units per day and the crude fibre (CF) content increased by 0.35 %- units per day for the silages of the first cut. For the second-cut silages the rate of change was slower. The decrease in CP content and the increase in CF content were 0.29 and 0.25 %-units, respectively (Table 2). The digestible crude protein (DCP) content was higher in the EC silage than in the LC silage (Table 3). When the protein value of the silages was given in terms of AAT the difference was much smaller. Flowever, PBV in the EC silage was substantially larger than PBV in the LC silage. Table 2. Average chemical composition (g kg’ 1 dry matter) of the experimental feeds. Grass silage Barley Mixture of barley and RSM" Early Late cut cut Periods 1 + 2 Dry matter (DM), g kg '223 235 873 874 Ash 68 74 28 40 Crude protein (CP) 160 127 157 223 Ether extract (EE) 50 39 26 38 Crude fibre (CF) 279 312 42 68 N free extracts (NFE) 444 449 747 630 Periods 3 + 4 DM, g kg’ 1 233 252 880 881 Ash 68 72 25 41 CP 160 126 139 218 EE 55 43 24 38 CF 281 307 42 70 NFE 437 453 770 633 Periods 5 + 6 DM, g kg’ 1 239 230 877 874 Ash 91 89 28 43 CP 158 139 150 224 EE 52 43 25 34 CF 281 297 43 71 NFE 418 431 755 629 9 Mixture ofbarley and rapeseed meal (66:34). 445 Agric. Sei. Fin!. 1 (1992) Table 3. Feed values (per kg dry matter) and degradability ofcrude protein (DEG) of the experimental feeds. Grass silage Barley Mixture of barley and RSM" Early Late cut cut Periods I+2 NE, FU 0.83 0.79 1.14 1.09 ME, MJ 11.8 11.2 13.3 13.0 DCP, g 123 89 114 179 AAT, g 65 62 104 126 PBV, g 43 15 -10 26 DEG, % 91 92 72 58 Periods 3 + 4 NE, FU 0.83 0.79 1.15 1.09 ME, MJ 11.6 11.1 13.4 13.0 DCP, g 119 86 102 174 AAT, g 64 62 103 125 PBV, g 45 12 -26 22 DEG, % 91 91 72 58 Periods 5 + 6 NE, FU 0.77 0.75 1.14 1.09 ME, MJ 10.9 10.6 13.3 12.9 DCP, g 114 95 109 179 AAT, g 59 60 103 126 PBV, g 50 27 -16 26 DEG, % 91 88 72 58 Mixture ofbarley and rapeseed meal (66:34). NE, net energy; ME, metabolizable energy; FU, feed units; DCP, digestible crude protein; AAT, amino acids absorbed in the small intestine; PBV, protein balance in the rumen; DEG, degradability ofcrude protein. Feed intake The palatability of the concentrates was good and only occasional refusals were recorded. There was no marked difference in concentrate intake between the EC and LC feeding groups (Figure 1). Neither was there any difference in concentrate intake between the two types ofconcentrates, B and BRSM. However, the daily concentrate intake of the HL bulls was, as intended, almost twice as high as that of the LL bulls. The larger grass silage intake of the EC bulls compared to the LC bulls was apparent at the beginning of the experiment (Table 4, Figure la). However, the difference had vanished by the end of the experiment. This interaction between the stage of maturity of grass for silage and the period was significant (p<0.005). The LL bulls had a higher silage intake than the HL bulls (Table 4, Figure lb). As intended, the change with time in concentrate supply during the feeding experiment was steeper in HL feeding than in LL feeding, which resulted in an interaction in silage intake between the level of concentrate and the period (p<0.001). Inclusion of RSM in the diet tended (p=0.07) to increase the grass silage intake throughout the experiment (Table 4, Figure 1c) but no significant interaction in silage intake between the type of concentrate and the period was observed. Protein and energy supply AAT intake, given in AATf (=AAT of feed origin), AAT m (=AAT of microbial origin) and AAT (=AAT, + AAT , total amount of amino acidsv f m’ absorbed in the small intestine), calculated for the entire experimental period, is given in Table 5. In general, the proportion of AATf of total AAT was small. It varied between 13.2% (late-cut silage supplemented with low level of barley) and 25.6% (late-cut silage supplemented with high level of barley together with RSM). Analogously to the changes in DM intake, the difference in AAT intake between EC and LC feed- ing had disappeared (p<0.005 for stage of cut * period interaction) by the end of the experiment (Table 6). The difference in AAT intake between LL and HL feeding increased (p