This article was downloaded by: [MTT Agrifood Research Finland] On: 3 February 2010 Access details: Access Details: [subscription number 907653358] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Acta Agriculturae Scandinavica, Section A - Animal Science Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713690045 The effect of concentrate level and concentrate composition on the performance of growing dairy heifers reared and finished for beef production A. Huuskonen a ; P. Lamminen ab ; E. Joki-Tokola a a MTT Agrifood Research Finland, Animal Production Research, Ruukki, Finland b School of Renewable Natural Resources, Oulu University of Applied Sciences, Oulu, Finland Online publication date: 29 January 2010 To cite this Article Huuskonen, A., Lamminen, P. and Joki-Tokola, E.(2009) 'The effect of concentrate level and concentrate composition on the performance of growing dairy heifers reared and finished for beef production', Acta Agriculturae Scandinavica, Section A - Animal Science, 59: 4, 220 229 To link to this Article: DOI: 10.1080/09064700903431533 URL: http://dx.doi.org/10.1080/09064700903431533 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Acta Agriculturae Scand Section A, 2009; 59: 220229 ORIGINAL ARTICLE The effect of concentrate level and concentrate composition on the performance of growing dairy heifers reared and finished for beef production A. HUUSKONEN 1, P. LAMMINEN 1,2 & E. JOKI-TOKOLA 1 Downloaded By: [MTT Agrifood Research Finland] At: 10:29 3 February 2010 1 MTT Agrifood Research Finland, Animal Production Research, Ruukki, Finland, and 2 School of Renewable Natural Resources, Oulu University of Applied Sciences, Oulu, Finland Abstract The objectives of the study with growing dairy heifers were to determine the effects on animal performance of (1) concentrate level and (2) the concentrate composition in the grass silage-based diet. Animals (30 heifers) were randomly assigned to three feeding treatments: (1) low level (1.75 kg dry matter (DM)/d) of rolled barley (LB); (2) low level (1.75 kg DM/d) of commercial pelleted concentrate (LC); and (3) medium level (3.5 kg DM/d) of commercial pelleted concentrate (MC). All animals were also offered grass silage and hay. The commercial concentrate contained more crude protein than barley grain (135 g/kg DM vs. 205 g/kg DM). The data were analysed using analysis of variance and differences between the treatments were tested by orthogonal contrasts: LC vs. MC and LB vs. LC. The growth of the heifers increased and carcass conformation improved with increasing concentrate level. Commercial concentrate did not improve animal performance compared with barley grain. Keywords: Beef production, carcass characteristics, concentrate feeding, dairy heifers, feed intake, gain. Introduction Dairy heifers are mainly raised for replacement but also for slaughter. For example, in 2007, 10% of Finnish beef originated from heifers, including both dairy and beef breeds (Information Centre of the Ministry of Agriculture and Forestry [ICMAF], 2008). The supply of domestic beef has decreased in Finland during recent years, giving rise to a clear discrepancy between the demand for and supply of domestic beef. In 2007, for instance, beef production was 87 million kg, whereas the consumption was 99 million kg (ICMAF, 2008). Consequently, heavy carcasses are favoured in the pricing of Finnish slaughterhouses and, therefore, the average carcass weight of heifers has increased from 204 kg in 1996 to 237 kg in 2007 (ICMAF, 2008). Market demand in Finland concerning carcass fat is different from those beef markets where marbled beef is favoured. In Finland, consumers generally favour low-fat products and the Finnish beef industry has stated that optimally two thirds of the carcasses would have a EUROP fat score of 2 and one-third a EUROP fat score of 3 (Tuomas Herva, Atria Ltd., Finland, unpublished data). High-fat carcasses cause a lot of expenditures for the meat industry; lean carcasses are favoured in the pricing and there are penalties for fat carcasses. For these reasons, carcass fat score is an important production parameter affecting the profitability of farms and the entire beef chain. However, in Finland there is a conflict between a need of heavy carcasses and low carcass fat content. In Finland, the feeding of heifers is based on grass silage and grain, typically on barley or/and oats. In general, the growth response to concentrate supplementation is lower with higher digestibility (Drennan & Keane, 1987) or higher intake/restricted fermentation (Agnew & Carson, 2000) grass silage. However, to our knowledge, there exist no studies on feeding experiments on the performance of dairy heifers reared and finished for beef production with a carcass weight over 200 kg. Nowadays, many beef Correspondence: A. Huuskonen, MTT Agrifood Research Finland, Animal Production Research, FI-92400 Ruukki, Finland. Tel: 358 17 264 4800. Fax: 358 17 264 4851. E-mail: arto.huuskonen@mtt.fi (Received 12 February 2009; revised 19 August 2009; accepted 21 October 2009) ISSN 0906-4702 print/issn 1651-1972 online # 2009 Taylor & Francis DOI: 10.1080/09064700903431533
producers in Finland supplement grass silage-based rations with commercial concentrates of high protein concentration rather than straight grain. However, the price of these concentrates is very high compared with those of grain or forages. In addition, feeding protein-rich concentrates increased the P excretion to the environment, because the P content of protein supplements is generally high relative to that of grass silage and cereals (Huuskonen, 2009a). Huuskonen et al. (2007a, 2008) reported with dairy bulls that rapeseed meal (RSM) supplementation did not affect animal performance on total mixed ration (TMR) feeding, when RSM was used as a protein supplement to increase ration crude protein (CP) concentration. In addition, Huuskonen (2009a) concluded that there is no reason to use protein supplement for finishing dairy bulls when they are fed high or medium digestibility, well-preserved grass silage and barley grain. However, relative to dairy bulls, much less research has been carried out on the feeding of dairy heifers reared and finished for beef production. Now it is of interest to obtain more information concerning animal performance when finishing dairy heifers are slaughtered above 220 kg carcass weight. Whether there is enough protein in the grass silage-grain-based diet to support high growth of dairy heifers without protein-rich concentrates is an important question for Finnish beef producers. The objectives of the present study with growing dairy heifers slaughtered at 230 kg carcass weight were to determine the effects on animal performance of (1) concentrate level in the diet and (2) the concentrate composition, including protein concentration, in the grass silage-based diet. Because lean carcasses are favoured in Finland, a special aim was to study the effects of concentrate level and concentrate composition on carcass fat content of heifers. Materials and methods Animals, housing and experimental design The feeding experiment, started in March 2004 and ended in September 2005, was conducted in the experimental barn of North Ostrobothnia Research Station of MTT Agrifood Research Finland, Ruukki, 64844?N, 25815?E. The experiment included 30 Finnish Ayrshire heifers. All animals were purchased from local dairy farms when they were 4593.1 kg (mean9sd) kg live weight (LW) and 1492.5 days old, on average. Before the beginning of the feeding experiment the calves received milk replacer, grass silage, hay and a commercial pelleted calf starter during the preweaning and weaning periods, from Performance of dairy heifers reared for beef production 221 0.5 to 3.0 months of age. The feeding experiment started after weaning when the animals were three months old. At the beginning of the experiment the animals were divided into 10 blocks of three animals by LW. One randomly selected animal in each block was assigned to each treatment. Age was not taken into account in the grouping because of the small variation in age. All animals were offered grass silage and hay with one of the following concentrate supplements: (1) low level of rolled barley (LB); (2) low level of commercial pelleted concentrate (LC); and (3) medium level of commercial pelleted concentrate (MC). The low and medium target concentrate levels were 1.75 and 3.5 kg dry matter (DM) per head per day, respectively. The commercial pelleted concentrate supplied by Raisio Nutrition Ltd., (P.O. Box 101, FI-21201 Raisio, Finland) included (g/kg DM) barley (180), oats (130), wheat bran (110), RSM (95), rapeseed cake (80), molassed sugar-beet pulp (80), malted sprouted barley (55), wheat (50), wheat syrup (50), wheat feed meal (46), soybean meal (40), distilled solubles (40), vegetable oil (2) and minerals and vitamins (42). All animals received hay ad libitum. Grass silage was offered 3 kg DM per head per day from three to nine months of age and 4 kg DM per head per day from nine months to slaughter. Grass silage allowances were carried out according to feeding programmes of Raisio Nutrition Ltd. The commercial pelleted concentrate included also vitamins and minerals, but the LB group received also mineral and vitamin supplementation. The grass silage used was direct-cut primary growth from a timothy (Phleum pratense) and meadow fescue (Festuca pratensis) sward and ensiled in bunker silos with a formic acid-based additive, AIV-2 Plus: 760 g formic acid/kg and 55 g ammoniumformate/kg; supplied by Kemira Ltd., P.O. Box 171, FI-90101 Oulu, Finland, applied at a rate of 5 L/tonne of fresh grass. In the first experimental period, from three to six months of age, the animals were housed on peat bedding in six pens, 3.03.5 m; five calves in each, providing 2.1 m 2 per calf. Then there were five animals/pen and two pens/treatment. In the second experimental period, from six month to slaughter, the heifers were placed in an insulated barn in adjacent tie stalls. The width of the stalls was 7090 cm for the first four months and 113 cm until the end of the experiment. The heifers were tied with a collar around the neck and with a chain of 50 cm, which was attached to a horizontal bar 4055 cm above the floor. The floor surface was solid concrete under the forelegs and metal grids under the hind legs. No bedding was used on the floor. The heifers had free access to water from an open water bowl throughout
222 A. Huuskonen et al. the experiment. Feed was offered three times a day, at 8:00 a.m., 12:00 a.m. and 6:00 p.m. Refused feed was collected and measured daily at 7:00 a.m. Feed analyses Silage, hay and concentrate samples were analysed for DM, determined at 1058C for 20 h, at the beginning of the experiment and thereafter twice a week. Silage DM was corrected for the loss of volatiles. Silage sub-samples for chemical analyses were taken twice a week and stored at 208C. Thawed samples were pooled over periods of four weeks and analysed for DM, ash, CP, neutral detergent fibre (NDF), crude fat, silage fermentation quality (ph, water-soluble carbohydrates (WSC), lactic and formic acids, volatile fatty acids, soluble and ammonia N content of total N) and digestible organic matter (DOM) in DM (D value). Concentrate and hay sub-samples were collected weekly, pooled over periods of eight weeks and analysed for DM, ash, CP, NDF and crude fat. Hay samples were analysed also for D value. The analyses of DM, ash, CP, NDF and crude fat were made as described by Huuskonen et al. (2007a, 2007b). The silage was analysed for fermentation quality by electrometric titration as described by Moisio and Heikonen (1989). The silage and hay samples were analysed for D value by the method described by Nousiainen et al. (2003). The D value results were calculated using correction equations to convert pepsincellulase solubility values into in vivo digestibility based on a data set comprising Finnish in vivo digestibility trials (Huhtanen et al., 2006). Diet digestibility was determined in all animals when the heifers were 320925 kg LW. Feed and faecal samples were collected twice a day, at 7:00 a.m. and 3:00 p.m. during the collection period (5 d) and stored frozen prior to analyses. The samples were analysed for DM, ash, CP and NDF as described above. Diet digestibility was determined using acid-insoluble ash (AIA) as an internal marker (Van Keulen & Young, 1977). The metabolisable energy (ME) contents of the feeds were calculated according to Finnish feed tables (MTT, 2006). The ME value of the silage and hay was calculated as 0.16D value (MAFF, 1981). The ME values of the concentrates were calculated as described by Huuskonen et al. (2008). The digestibility coefficients of concentrates were taken from Finnish feed tables (MTT, 2006). The supply of amino acids absorbed from the small intestine (AAT) and protein balance in the rumen (PBV) were calculated according to the Finnish feed tables (MTT, 2006). Live weight (LW) and carcass measurements LW of the heifers was measured every four weeks. The target carcass weight in the experiment was 230 kg, and the heifers were selected for slaughter based on LW and an assumed dressing proportion. The live weight gain (LWG) was calculated as the difference between the means of initial and final weights. After slaughter in a commercial meat plant, carcasses were weighed hot. Cold carcass weight was estimated as 0.98 of hot carcass weight. Dressing proportions were calculated from the ratio of cold carcass weight to final LW. Carcass conformation and carcass fat score were determined according to the EUROP classification (Commission of the European Communities, 1982). Statistical methods The results are shown as least squares means, because the records on the three excluded animals were not replaced. In the first experimental period, from three to six months of age, pen, a group of five calves, were used as an experimental unit and thus the mean values for each pen were calculated. Therefore it was not possible to use the random effect of block when the results of the first experimental period were tested statistically. There were two experimental units per treatment, in total 10 heifers for each feeding. Feed and energy intake data were analysed using one-way analysis of variance and the following statistical model (1): Y ik mb i o ik (1) where i1, 2, 3 (concentrate feeding), k1, 2 (two groups per concentrate feeding). Y ik is the dependent variable of the kth group in the ith concentrate feeding, m is the general mean and b i the effect of the ith concentrate feeding. Furthermore, o ik is the residual error. The remaining response variables in the first experimental period were measured individually and analysed using the following statistical model (2): Y ijk mb i u j(i) o ijk (2) where i1, 2, 3 (concentrate feeding), j1, 2 (two groups of five heifers per feeding). Y ijk is the observation from the kth animal in the ith concentrate feeding and the jth group in concentrate feeding, m is the general mean and b i is the effect of the ith concentrate feeding. Furthermore, k j(i) is the effect of group and it was used as an error term when concentrate feedings were compared using orthogonal contrasts. Finally, o ijk is the residual error. All statistical analyses in the first experimental
Performance of dairy heifers reared for beef production 223 Downloaded By: [MTT Agrifood Research Finland] At: 10:29 3 February 2010 period were performed using the SAS GLM procedure (SAS Institute Inc., Cary, NC, USA). During the second experimental period, from six months to slaughter, animal was used as an experimental unit. The data were subjected to analysis of variance using the SAS MIXED model procedure. The model (3) used was Y ijk ma j b i e ijk (3) where m is the overall mean, a j is the random effect of block (j1,...,10), e ijk is the random error term and b i is the fixed effect of concentrate feeding. Differences between the concentrate feedings were tested by making two orthogonal contrasts: LB vs. LC and LC vs. MC. The first contrast described the effects of concentrate composition and the second contrast the effects of concentrate level. The effect of concentrate level on the performance was a mixed effect of increasing both the energy and protein supply in the ration. Results Feeds The calculated ME value of barley was 6% higher than that of commercial concentrate, but commercial concentrate contained 52% more CP and 53% more crude fat than barley grain (Table I). The AAT content of commercial concentrate was 8% higher and the NDF content 3% lower compared with barley. The grass silage used was of good nutritional Table I. Chemical composition and feeding values of concentrates, hay and grass silage. quality as indicated by the D value as well as the AAT and CP contents. The fermentation characteristics of the silage were also good as indicated by the ph value and the low concentration of ammonia N and total acids (Table I). The silage used was restricted fermented with high residual WSC concentration and low lactic acid concentration. Effects of concentrate level (LC vs. MC) Three animals were excluded from the study due to pneumonia. There was no reason to suppose that the diets had caused these problems. Otherwise, there were no diseases and no veterinary treatments were given. During the first experimental period, from three to six months of age, the average concentrate proportions of LB, LC and MC diets were 530, 480 and 730 g/kg DM, respectively. The total dry matter intake (DMI) of heifers did not differ between LC and MC treatments. However, the ME intake (MEI) of LC heifers was lower than that of MC heifers (PB 0.05) (Table II). Also the AAT (PB0.05) intake of LC animals was lower than that of MC animals, but there were no treatment differences in CP or PBV intakes. Although there was no significant difference in LWG during the first experimental period, there was a tendency for LWG of MC heifers to be higher than that of LC heifers (P0.099). There was no difference in feed conversion rate (MJ/kg LWG) during the first experimental period between LC and MC feedings (Table II). Silage Hay Barley Commercial concentrate N a 16 8 8 8 Dry matter (DM) (g/kg feed) 252 830 875 888 Organic matter (g/kg DM) 923 956 971 920 Crude protein (g/kg DM) 164 62 135 205 Neutral detergent fibre (g/kg DM) 504 675 257 249 Crude fat (g/kg DM) 49 21 34 52 D value (g/kg DM) b 681 589 ND c ND Metabolisable energy (MJ/kg DM) 10.9 8.8 13.0 12.3 AAT (g/kg DM) d 85 74 106 115 PBV (g/kg DM) e 19 63 38 25 Fermentation quality of silage ph 3.9 Volatile fatty acids (g/kg DM) 15 Lacticformic acid (g/kg DM) 60 Water-soluble carbohydrates (g/kg DM) 62 In total N, g/kg N Ammonia N 50 Soluble N 453 a Silage, one sample per feeding period (four weeks); hay and concentrates, one sample per two feeding periods. b Digestible organic matter in DM. c Not determined. d Amino acids absorbed from small intestine. e Protein balance in the rumen.
224 A. Huuskonen et al. Table II. Daily feed intakes, live weight gains (LWG) and feed conversions of heifers during the first experimental period (from three to six months of age). Concentrate feeding a P-value LB LC MC SEM b C1 c C2 c Downloaded By: [MTT Agrifood Research Finland] At: 10:29 3 February 2010 Animals 9 10 8 Duration (d) 56 56 56 Dry matter intake (kg DM/d) Silage 1.44 1.89 1.04 0.107 0.059 0.011 Hay 0.03 0.02 0.03 0.008 0.538 0.466 Concentrate 1.67 1.75 2.94 0.073 0.472 0.001 Total 3.14 3.66 4.01 0.122 0.055 0.140 Metabolisable energy intake (MJ/d) 36.1 40.3 46.6 1.32 0.110 0.044 Crude protein intake (g/d) 503 722 804 24.1 0.008 0.097 AAT intake (g/d) d 294 354 423 11.2 0.032 0.022 PBV intake (g/d) e 12 143 127 7.9 0.001 0.252 Live weight gain (LWG) (g/d) 679 734 920 55.6 0.532 0.099 Feed conversion (MJ/kg LWG) 54.2 59.4 51.5 5.12 0.520 0.353 a LB, low level of rolled barley; LC, low level of commercial pelleted concentrate; MC, medium level of commercial pelleted concentrate. Low and medium target concentrate levels were 1.75 and 3.5 kg DM per head per day, respectively. b Standard error of mean. c Differences between concentrate feedings were tested by making two orthogonal contrasts: C1LB vs. LC and C2LC vs. MC. d Amino acids absorbed from small intestine. e Protein balance in the rumen. Table III. Performance and slaughter data of heifers during the second experimental period (from six months of age to slaughter). Concentrate feeding a P-value LB LC MC SEM b C1 c C2 c Animals 9 10 8 Duration (d) 386 355 327 Dry matter intake (kg DM/d) Silage 3.97 4.04 3.59 0.073 0.488 B0.001 Hay 0.29 0.35 0.10 0.033 0.138 B0.001 Concentrate 1.74 1.74 3.44 0.024 0.978 B0.001 Total 6.00 6.13 7.13 0.090 0.275 B0.001 Metabolisable energy intake (MJ/d) 68.8 68.8 82.5 0.10 0.995 B0.001 Crude protein intake (g/d) 907 1043 1305 14.5 B0.001 B0.001 AAT intake (g/d) d 547 572 710 8.0 0.021 B0.001 PBV intake (g/d) e 11 96 149 2.9 B0.001 B0.001 Apparent digestibility Organic matter 0.769 0.739 0.748 0.0081 0.009 0.429 Crude protein 0.752 0.739 0.749 0.0086 0.267 0.388 Neutral detergent fibre 0.706 0.667 0.621 0.0131 0.028 0.017 Live weight gain (LWG) (g/d) 875 901 1065 28.3 0.487 B0.001 Feed conversion (MJ/kg LWG) 78.9 76.6 77.7 1.94 0.358 0.672 Slaughter data Carcass weight (kg) 232 225 236 2.7 0.064 0.006 Dressing proportion (g/kg) 502 501 492 5.0 0.844 0.200 EUROP conformation f 3.44 3.00 3.76 0.148 0.027 0.001 EUROP fat classification g 3.56 3.31 3.41 0.245 0.437 0.769 a LB, low level of rolled barley; LC, low level of commercial pelleted concentrate; MC, medium level of commercial pelleted concentrate. Low and medium target concentrate levels were 1.75 and 3.5 kg DM per head per day, respectively. b Standard error of mean. c Differences between concentrate feedings were tested by making two orthogonal contrasts: C1LB vs. LC and C2LC vs. MC. d AAT, Amino acids absorbed from small intestine. e Protein balance in the rumen. f Conformation: (1, poorest; 15, excellent). g Fat cover (1, leanest; 5, fattest).
Live weight (kg) 500 450 400 350 300 250 200 150 100 50 0 75 135 195 255 315 375 435 495 Age of heifers (d) LB LC MC Figure 1. Live weights of growing dairy heifers fed different concentrate feedings. LB, low level of rolled barley; LC, low level of commercial pelleted concentrate; LM, medium level of commercial pelleted concentrate. Low and medium target concentrate levels were 1.75 and 3.5 kg dry matter per head per day, respectively. During the second experimental period, from six months of age to slaughter, the average concentrate proportions of LB, LC and MC diets were 290, 280 and 480 g/kg DM, respectively. The total DMI increased 16% and MEI 20% with increasing concentrate level (PB0.001; Table III). Also CP, AAT and PBV intakes of animals increased with increasing concentrate level (P B0.001). LWG of MC heifers was 18% higher than that of LC heifers during the second experimental period (P0.001), and improved gain of MC heifers also emerges from the LW curves of the animals (Figure 1). During the second experimental period there was no difference in feed conversion rate between LC and MC feedings (Table III). According to diet digestibility determinations, concentrate level had no effect on diet apparent CP or organic matter digestibility (OMD). However, the apparent digestibility of NDF (NDFD) decreased with increasing concentrate level. The average (all treatments) carcass weight of animals was 231 kg and very close to the preplanned. Carcass weight of LC heifers was slightly (6%) lower than that of MC heifers (P B0.01). Concentrate level did not affect the dressing proportion or carcass fat classification but carcass conformation improved with increasing concentrate level (PB0.001; Table III). Effects of concentrate composition (LB vs. LC) During the first experimental period there was no significant difference in DMI but, there was a tendency for silage DMI and total DMI of LC heifers to be higher than those of LB heifers (P 0.059 and 0.055, respectively). There was no Performance of dairy heifers reared for beef production 225 significant difference in MEI but CP (PB0.01), AAT (PB0.05) and PBV (PB0.001) intakes of LC heifers were higher than those of LB heifers. Concentrate composition did not affect the LWG or feed conversion rate of heifers during the first experimental period (Table II). The LW curves of the LB and LC heifers were very similar throughout the whole feeding experiment (Figure 1). During the second experimental period, concentrate composition had no effect on total DMI or MEI (Table III). However, CP (P B0.001), AAT (PB0.05) and PBV (0.001) intakes of LC heifers were higher than those of LB heifers. Concentrate composition did not affect the LWG or feed conversion rate of heifers during the second experimental period. Diet apparent OMD and NDFD with LB diets were higher than those with LC diets (PB0.01 and PB0.05, respectively) but concentrate composition had no effect on diet apparent CP digestibility. There were no differences in carcass weight, dressing proportion or carcass fat classification between LB and LC treatments (Table III). However, carcass conformation score of LB heifers was 15% better than that of LC heifers (PB0.05). Discussion Effects of concentrate level All animals received hay ad libitum, but grass silage was offered according to the feeding programme of Raisio Nutrition Ltd. From three to six months of age the pre-planned silage allowance, 3 kg DM/head/d, seemed to comply with appetite but in the last phase the 4 kg DM allowance seemed to be below appetite. Therefore, LB and LC heifers tried to compensate the restricted silage allowances by increasing the intake of hay. In general, if cattle are fed high-energy rations that are palatable, low in fill and readily digested, intake is regulated to meet the energy demands of the animal, unless the diet is fermented too rapidly and digestive disorders occur (Forbes, 2007). It is suggested that, when the energy content of the diet decreases, usually with increasing NDF content, the animal can increase its DMI until rumen fill (Forbes, 2007). However, in the present study, the heifers could not fully compensate the restricted silage allowance by increasing hay intake, because it was obvious that rumen fill was a limiting factor. Therefore, increasing concentrate level led to increasing DM and energy intake. This is in agreement with many studies in which increasing the level of supplementary concentrates in the diet of growing cattle reduced roughage intake but increased total DMI (e.g. Drennan & Keane, 1987; Dawson et al., 2002; Caplis et al., 2005).
226 A. Huuskonen et al. Substitution rates for the first and second experimental periods were 0.71 and 0.26 kg silage DM/kg concentrate DM, respectively. This implies that the effect of increasing concentrate level on the intake of silage DM is more pronounced at an early than at a later age. In general, the magnitude of the decrease in silage intake is usually greater with silage of higher digestibility (Drennan & Keane, 1987; Steen, 1998). For diets containing low to moderate levels of concentrate, B0.47 of dietary DMI, substitution rates range from 0.29 to 0.64 kg silage DM/ kg concentrate DM with high-digestibility grass silage (Patterson et al., 2000; Dawson et al., 2002; Caplis et al., 2005). Contrary to earlier results by Steen et al. (2002) and Keady et al. (2007), the diet apparent OMD did not increase with increasing concentrate proportion in the diet. In general, substitution of silage with cereal grain-based concentrates improved the digestibility, because the digestibility of cereals is usually higher than that of silage (Huuskonen, 2009a). However, in the present study, the NDFD decreased clearly with increasing concentrate level in the diet and therefore OMD did not increase with increasing concentrate level. This indicates that the improved LWG with increasing concentrate level was not due to improved diet digestibility. The reduction in diet apparent fibre digestibility due to increased concentrate proportion has been well documented in growing cattle (e.g. Steen et al., 2002; Keady & Kilpatrick, 2006) and is an effect of ph and changes in rumen fermentation pattern (e.g. Hoover, 1986) but also an effect of feeding level and increased passage rate of NDF (Dijkstra et al., 2005). Increasing concentrate level led to improved LWG which was probably due to increasing DM and energy intake. The response in LWG to concentrate supplementation was 156, 96 and 104 g LWG/kg DM additional concentrate, for the first and second experimental periods and an average for both periods, respectively. Consistently, Drennan and Keane (1987), feeding grass silage with an in vitro DM digestibility (DMD) of 725 g/kg to steers, reported a linear increase in carcass gain of 52 g per kg concentrate DM fed within the range of 2.910.9 kg/head/d. Caplis et al. (2005), feeding grass silage with an in vitro DMD of 758 g/kg, obtained a curvilinear increase in the LWG of steers (decreasing from 130 to 13 g LW/kg additional concentrate DM) with increasing concentrate level (08.72 kg/head/d). Steen (1998) calculated that the response in carcass growth rate to concentrate supplementation within the range of 29 kg/d was curvilinear (decreasing from 93 to 4 g carcass/kg additional concentrate) and linear (58 g carcass/kg additional concentrate) for high (733 g DOM/kg DM) and medium (625 g DOM/kg DM) digestibility silage, respectively. The explanation for improvement of carcass conformation with increasing concentrate level is not clear. The higher energy intake may partly explain the increased conformation score. For example, Caplis et al. (2005) reported that carcass conformation of finishing steers increased with increasing concentrate level and energy intake. However, in our previous study with growing dairy bulls, carcass conformation was not significantly affected by the concentrate level (Huuskonen et al., 2007a). Concentrate level did not affect the carcass fat classification. However, the average fat classification score, 3.43, was quite high, which was probably due to high carcass weights of heifers. For cattle finished on grass silage and concentrates, Steen and Kilpatrick (2000) concluded that reducing slaughter weights is likely to be a more effective strategy to control carcass fat content than reducing energy intake either by diet restriction or concentrate proportion. Effect of concentrate composition Diet apparent OMD and NDFD with LB diets were higher than those with LC diets which were possibly due to differences in sources of both carbohydrates and protein between these two diets. Except grain, the commercial pelleted concentrate included also different by-product fractions, e.g. wheat bran and wheat feed meal. Although commercial concentrate did not include more cell wall fractions than did barley grain, the NDFD of these by-product fractions is generally lower compared with the NDFD of barley grain (MTT, 2006). In addition, it is possible that the decreasing OMD and NDFD with LC diet was partly due to the fat content of commercial concentrate which was slightly higher than that of barley grain, 52 g/kg DM vs. 34 g/kg DM. Fat-based concentrates are inferior to starch or fibre-based concentrates as supplements to grass silage which is attributed to a lower OMD for the former (e.g. Moloney, 1996). Fat supplementation, even at quite low levels, 4050 g/kg DM, has been shown to depress fibre digestion (e.g. Ikwuegbu & Sutton, 1982). However, disruptions in ruminal fibre digestion with added fat have been observed mostly with sheep or steers fed at or slightly above maintenance intakes (Ikwuegbu & Sutton, 1982; Jenkins & Palmquist, 1984). DMI has a great effect on ruminal digestion of OM and passage of microbial protein to the duodenum and may thus override many of the negative effects of fat supplementation (Merchen et al., 1997). The DMI of heifers reared for beef production is clearly lower than that of highproducing dairy cows. It is therefore possible that the
fibre digestion may have been affected in the present trial when the fat content of diet increased in LC diet compared with LB diet. However, differences in diet apparent OMD and NDFD did not lead to differences in the intake or gain parameters between LB and LC diets. There was a tendency for silage DMI and total DMI of LC heifers to be higher than those of LB heifers during the first experimental period, but there were no differences during the second period. Also in earlier experiments with growing dairy bulls reported by Huhtanen et al. (1989) and Aronen (1990) positive effects of increasing concentrate protein concentration were restricted only to the early phase of the growth period. Similarly, calculations by Titgemeyer and Löest (2001) showed that while amino acids were a limiting factor in lighter weight calves offered grass silage, energy availability was a limiting factor with heavier steers. CP, AAT and PBV intakes of LC heifers were higher than those of LB heifers during both experimental periods, because commercial concentrate contained more protein than barley grain. Concentrate composition had no effect on MEI and there was no difference in LWG or feed conversion between LB and LC treatments. This result is in agreement with our earlier studies in which protein supplementation, generally RSM, did not affect animal performance of growing dairy bulls (Huuskonen et al. 2007a, 2008; Huuskonen, 2009b). However, the effect of concentrate protein concentration on LWG of growing cattle has been rather inconsistent in various feeding experiments. In general, the greatest responses have been measured with young cattle (Steen, 1992) and often the positive effect of increasing protein concentration on intake and LWG was restricted only to the early phase of the growth period, i.e. LW below 300 kg (e.g. Huhtanen et al., 1989). Responses to protein supplementation are also largely related to differences in the quality of the grass silage used. According to the literature, increasing concentrate protein composition may have a positive effect on the daily growth rate when the gain without protein supplementation is low, which may be the case with low digestibility (Steen, 1988) or extensively fermented (Jaakkola et al. 1990) or poorly preserved (Hussein & Jordan, 1991) silage. The responses to protein supplementation seem to be related also to the level of concentrate supplement. Growing cattle fed grass silage alone respond to protein supplementation with ruminally undegraded protein with relatively large improvements in LWG (Titgemeyer & Löest, 2001). The rate of protein synthesis in rumen improved with moderate addition of barley-based concentrate to a silage diet Performance of dairy heifers reared for beef production 227 and, for example, Hagemeister et al. (1980) reported a tendency towards lower protein synthesis with rations containing very low, 020%, or high, 70 100%, proportions of concentrate. According to Aronen (1992) medium level of concentrates together with well-preserved grass silage may sustain efficient microbial protein production. In the present study, the D value of the silage was high, 681 g/kg DM, and so was the CP concentration, 164 g/kg DM. The fermentation quality of the silage was good, and the silage was restrictively fermented with high residual WSC concentration and low lactic acid concentration. In addition, as all the treatments included at least 28% concentrates, the microbial protein synthesis can be assumed to have been adequate for fairly good growth of dairy heifers also with LB diet. Carcass conformation score of LB heifers was better than that of LC heifers, but the explanation of this effect is not clear. In general, there were no effects of concentrate carbohydrate (Huhtanen et al., 1989; Root & Huhtanen, 1998) or protein (Huuskonen et al., 2007a, 2008) composition on the carcass conformation score or carcass fat score of growing cattle offered grass silage-based diets. However, Berge et al. (1993) reported that steers given protein supplementation have leaner carcasses than steers which were not given protein supplementation. On the contrary, Steen (1996) reported that there was a tendency for steers given concentrates containing soyabean meal to produce fatter carcasses than those given barley alone. In conclusion, the LWG of the heifers increased and carcass conformation improved with increasing concentrate level. Concentrate level did not affect the carcass fat classification. The average carcass fat classification score was quite high, which was due to high carcass weights of heifers. 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