The Role of Concentrate Supplementation
Grazed grass is currently the cheapest feed source available for beef cattle in Ireland, with an estimated cost of £38/tonne digestible dry matter. Corresponding digestible dry matter (DM) costs for silage and purchased concentrates are £98 and £155/t respectively. The intake of grass, or its contribution to total intake, needs to be increased if the cost of animal carcass gain is to be reduced. This can be achieved by producing a high yield of grass and utilising it efficiently throughout a long grazing season, while maintaining high levels of animal performance. Critical to this strategy is maintaining good animal performance at grass in the autumn. Acceptable liveweight gains are generally achieved on commercial farms until mid-summer.
However, animal performance is often poor later in the season. Grass growth varies widely throughout the year and as grass growth declines in the autumn, herd demand often exceeds feed supply. The shortage of feed can be corrected by appropriate and judicious supplementation. Figure 1 shows a typical grass growth curve and a feed demand curve for a drystock farm stocked at 2 L.U./ha. Furthermore autumn grass has a lower dry matter digestibility (DMD) than grass in spring. Also, at similar DMD values, autumn grass has a lower feeding value, and lower intake characteristics, in comparison with grass available in early and mid-season. The nutritional value of autumn grass may thus be insufficient to support satisfactory levels of animal liveweight gain, thereby necessitating the need for supplementary feeding.
Beef farmers must no longer consider themselves as producers of live or carcass weight but as providers of a quality food product if they are to sell beef onto the high value markets of the world. Scientific evidence is available (Larick et al., 1987) from some countries to show that beef produced from feedlot cattle can be more tender and have better flavour than pasture-finished beef. This information is used to gain a marketing advantage by countries such as Australia and the United States where feedlot finishing is the norm. If Irish beef is to gain a share of the quality consumer market then its strengths must be identified and sold.
The presence of certain polyunsaturated fatty acids (PUFA) in the human diet has been shown to be beneficial. Decreasing the ratio of n-6 (primarily linoleic acid) to n-3 (primarily linolineic acid) PUFA has been shown to reduce the incidence of cardiovascular disease (Wood and Enser, 1997). Despite a hydrogenation effect in the rumen, some dietary unsaturated fatty acids bypass the rumen intact for absorption and deposition in body fat (Wood and Enser, 1997). Ruminant tissue fat of concentrate-fed animals has been shown to contain a higher ratio of n-6 to n-3 fatty acids than grass-fed animals. A number of experiments have been conducted at Grange Research Centre, in collaboration with the National Food Centre, to quantify the animal production and meat quality responses of supplementing autumn grazed grass with concentrates.
Economics of Meal Feeding
The economics of meal feeding at pasture depend upon the animal production response and the relative price of animal product and concentrates. The break-even animal production responses in terms of kg beef carcass/kg concentrate consumed are shown in Table 1. If concentrates cost £130/tonne and beef is worth 170p/kg carcass, then it is economical to feed up to 13 kg concentrate to produce each additional kg carcass.
|Table 1: Break-even responses to meal feeding at pasture|
|Concentrate price (£/tonne)|
|(p/kg carcass)||kg concentrate / kg beef carcass for break-even|
Exp 1: Concentrate Level and Gross Allowance
A previous study carried out during the autumn of 1995 and 1996 at Grange (Drennan et al., 1997), compared feeding 3.5kg of a barley or pulp based ration per head per day to 17 month old continental cross heifers. They achieved an 11:1 carcass response the first year and a 36:1 response the next year. During the first year, heifers were stocked at 4/ha compared with 2.5/ha in the second year. There was no effect of the concentrate type on animal performance. The results of this study would indicate that the carcass response to concentrate supplementation was dependent on grass supply.
In 1996 an experiment was carried out to quantify the relationship between grass supply and concentrate supplementation level on animal performance. The trial lasted 100 days (23 August to 1 December) and 110 continental crossbred steers were used. Three herbage allowances and three concentrate levels were compared. A group was also offered concentrates ad-libitum.
The daily herbage allowances offered were 6, 12 and 18kg DM/head, equivalent to 1, 2 and 3% of bodyweight respectively, while the daily supplementation levels were 0, 2.5 and 5kg (2.5kg twice per day) of concentrates. The concentrate pellet comprised of barley (0.29), unmolassed beet pulp (0.29), maize gluten (0.29), soya bean meal (0.07), molasses (beet) (0.03) and min./vits. (0.03) and was fed individually to all animals. The swards used were re-growths following a series of silage harvests. Kill-out proportion, carcass weight, carcass and liveweight gains are shown in Table 2.
Table 2: The effect of daily herbage allowance (% liveweight) and concentrate level (kg/day) on liveweight and carcass gain, kill-out proportion, carcass conformation and fat score and internal fat weight.
|Herbage allowance (% liveweight)||1%||2%|
|Concentrate level (kg/day)||0||2.5||5||0||2.5||5|
|Grass DM intake (kg)||5.29||5.40||5.23||9.28||7.98||7.34|
|Final liveweight (kg)||583||620||654||619||643||669|
|Liveweight gain (kg/day)||0.14||0.54||0.94||0.53||0.78||1.06|
|Carcass weight (kg)||304||332||352||323||348||361|
|Carcass gain (kg/day)||0.088||0.393||0.617||0.290||0.551||0.695|
|Kill-out rate (g/kg)||522||537||538||521||541||540|
|Carcass conformation 1||2.27||2.73||3.18||2.64||3.09||2.91|
|Fat score 2||3.73||3.79||3.79||3.85||4.15||3.91|
|Internal fat (kg)||5.05||7.35||8.82||6.79||7.57||8.92|
|Internal fat / carcass (g/kg)||17||22||25||21||22||25|
Table 2 (cont.): The effect of daily herbage allowance (% liveweight) and concentrate level (kg/day) on liveweight and carcass gain, kill-out proportion, carcass conformation and fat score and internal fat weight.
|Herbage allowance (% liveweight)||3%||Ad-lib.||S.E.M.|
|Concentrate level (kg/day)||0||2.5||5||conc.|
|Grass DM intake (kg)||12.95||9.41||9.27||0.586|
|Final liveweight (kg)||641||668||676||703||14.1|
|Liveweight gain (kg/day)||0.75||1.05||1.14||1.43||0.09|
|Carcass weight (kg)||330||355||363||371||8.4|
|Carcass gain (kg/day)||0.360||0.631||0.727||0.809||0.0344|
|Kill-out rate (g/kg)||515||532||538||528||5.3|
|Internal fat (kg)||7.93||9.19||10.25||10.69||0.746|
|Internal fat / carcass (g/kg)||24||26||28||29||0.1|
Liveweight gain in the absence of concentrates was 0.75 kg/head/day at the high herbage supply. Increased live and carcass weight gains were associated with increased grass supply, however, the response to additional grass supply diminished when concentrates were provided. At current prices (carcass = 170p/kg and concentrates = £130/tonne) there was an economical response to the first 2.5kg of concentrate at all grass supplies and to the second 2.5kg of concentrate at the lowest grass supply. The carcass production responses to concentrate level at the different grass supplies are shown in Table 3. At all grass allowances concentrate supplementation improved carcass conformation score (Table 2). However increased grass supply improved conformation only in the absence of concentrates.
Table 3.Carcass response (kg concentrate/kg carcass)
|Herbage allowance||Concentrate level (kg/day)|
|(kg DM/hd/day)||0 to 2.5||2.5 to 5||0 to 5|
To determine the impact of supplementing autumn grass with concentrates on meat quality, the right hand side M. Longissmus dorsi (LD) was excised, post slaughter, from all animals used in Experiment 1. Intra-muscular fat content was determined in all samples. Fat was extracted from 1 g of the LD muscle and the fatty acids were quantified and expressed as g/100 g fatty acid methyl esters (FAME).
Fourteen days post-slaughter, steaks were taken from 6 treatments, shown in Table 4. Warner Bratzler Shear Force (WBSF) which is a mechanical measurement of meat tenderness was measured and a sensory analysis was performed on cooked samples by a group of trained taste panellists. The 6 treatments were selected to give a range of pre-slaughter diets varying from all grass to all concentrates.
Table 4. The effect of daily herbage allowance and concentrate level on intra-muscular fat, fatty acids, WBSF and sensory analysis
|Herbage allowance (% liveweight)||1%||2%|
|Concentrate level (kg/day)||0||2.5||5||0||2.5||5|
|Intra-muscular fat (g/100g muscle)||2.85||2.82||2.32||2.20||2.54||2.77|
|Saturated fatty acids(g/kg fat)||552||574||522||574||522||581|
|Monounsaturated fatty acids (g/kg fat)||468||452||498||454||489||445|
|Polyunsaturated fatty acids (PUFA) (g/kg fat)||32||28||29||27||36||26|
|Polyunsaturated : Saturated ratio||0.06||0.05||0.06||0.05||0.07||0.05|
|n-6 PUFA (g/kg FAME1)||19||14||18||15||19||13|
|n-3 PUFA (g/kg FAME)||10.1||5.6||6.9||8.0||11.2||6.9|
|n-6 : n-3 PUFA ratio||1.9||2.5||2.6||1.9||1.7||1.9|
|Warner Bratzer shear force (kg)||4.34||3.98||4.08|
Table 4 cont. The effect of daily herbage allowance and concentrate level on intra-muscular fat, fatty acids, WBSF and sensory analysis
|Herbage allowance (% liveweight)||3%||Ad.lib||S.E.M.|
|Concentrate level (kg/day)||0||2.5||5||conc.|
|Intra-muscular fat (g/100g muscle)||2.32||2.37||2.90||4.42||0.14|
|Saturated fatty acids(g/kg fat)||517||522||581||507||4.8|
|Monounsaturated fatty acids (g/kg fat)||501||495||496||512||4.8|
|Polyunsaturated fatty acids (PUFA) (g/kg fat)||29||32||25||30||1.6|
|Polyunsaturated : Saturated ratio||0.06||0.06||0.05||0.06||0.003|
|n-6 PUFA (g/kg FAME1)||16||18||16||23||0.8|
|n-3 PUFA (g/kg FAME)||8.2||9.3||6.6||4.4||0.81|
|n-6 : n-3 PUFA ratio||2.0||1.9||2.4||5.2||0.60|
|Warner Bratzer shear force (kg)||4.79||4.16||3.85||0.279|
There was no effect of supplementing grass with concentrates on intra-muscular fat concentration or the concentrations of saturated, mono-unsaturated or PUFA. However the animals offered concentrates ad-libitum produced meat with a higher concentrations of intra-muscular fat and n-6 PUFA and lower concentration of n-3 PUFA. There was no effect of pre-slaughter diet on tenderness as measured by WBSF or on any of the qualities assessed by the taste panellists.
Thus, it has been shown (at Grange) that autumn grass in plentiful supply can maintain a daily liveweight gain of 0.75 kg /day but grass wastage is very high. In practice, at normal stocking rates, such a supply of grass will generally not be available after August. Supplementation of cattle at pasture with concentrates, even at the high grass allowance, will improve carcass gain and carcass conformation. The economical level of supplementation was shown to be 2.5kg/head/day at the high grass supply and 5.0kg of concentrates where grass was scarce (6kg DM/hd/day).
Animals offered concentrate supplemented autumn grass produced meat of similar consumer acceptability as that of animals offered concentrates ad-libitum. However, animals offered concentrates and grass produced an intramuscular fatty acid profile that was more beneficial to human health than that of animals offered concentrates ad-libitum.
Exp 2: Concentrate Carbohydrate Source and Herbage Allowance
Studies with dairy cows (Meijs, 1986) have shown higher grass intakes when grazing animals were supplemented with concentrates based on digestible fibre rather than starch. It has been demonstrated that high inputs of quickly fermentable substrates such as soluble sugars or rapidly fermentable starch can increase the concentrations of volatile fatty acids and lactate in the rumen thereby causing a marked decrease in pH. This can reduce cellulolytic activity by rumen microbes, resulting in a lower rate of forage fibre digestion and an increase in non-fermented residue, which in turn can restrict feed intake. Furthermore, autumn grass has the potential disadvantage of relatively low levels of water-soluble carbohydrates and high levels of rapidly degradable protein.
The objective of this study was to determine the effects of supplementing cattle grazing autumn grass with concentrates formulated using different carbohydrate types on grass intake and animal performance where grass supply was considered to be either adequate or limiting.
Eighty-four continental crossbred steers (494kg mean starting liveweight) were assigned to seven treatments in a two (herbage allowances) by three (concentrate types) factorial design, plus a positive control of concentrates offered ad-libitum. The daily herbage allowances were 5.5 and 11.0 kg DM/head, approximating to 1 and 2 % of bodyweight, respectively. Five kg of concentrates were offered individually to each animal daily, in two equal feeds. Three concentrate rations were formulated to be iso-energetic and iso-nitrogenous, but to differ in carbohydrate source (Table 5). Six rumen fistulated steers were simultaneously used to estimate the effect of diet on rumen fermentation and kinetics. The grazing experiment took place between August 22 and November 19.
Table 5. Ingredient formulation (g/kg) of the concentrates.
|Unmolassed beet pulp||0||419||852|
Concentrate type did not effect rumen fluid pH (Fig. 2).
Increasing concentrate starch content at the expense of digestible fibre increased liveweight gain but not estimated carcass gain, reflecting the poorer kill-out rate of the cattle on the barley-based diets. Animals offered the high herbage allowance had a carcass gain not significantly different from the ad-libitum concentrate group, which consumed 12.5kg concentrate/day. Increasing the herbage allowance increased grass intake and carcass gain. There was no interaction between the effects of concentrate type and herbage allowance on carcass gain. Cattle fed on the concentrate of higher starch content produced carcasses with lower fat scores and lower proportion of internal fat than those fed the more fibrous concentrate (Table 6).
|Herbage allowance||Conc. type||Grass intake (kg/DM/day)||Carcass gain (kg/day)||Fat score||Internal fat1 (g/kg)|
Table 6. The effects of grass allowance and concentrate type on herbage intake, liveweight gain, carcass gain, carcass fat score and internal fat.
Thus, there was no effect of concentrate type on carcass gain (kg) per day.
- Autumn grass offered at 3% of bodyweight is capable of supporting moderate levels of liveweight gain (0.75 kg/day). However, grass utilisation is very poor (50-60%) at this allowance.
- At a grass allowance of 3% of bodyweight, supplementing with 0.5 kg of concentrate per 100kg liveweight gave a response of 1 kg of carcass per 10-12 kg of concentrate fed. If carcass weight is worth £1.70 per kg, then concentrates offered at this rate will be economical if they can be fed for less than £160 per tonne. Where grass intake is limited by supply, feeding up to 1 kg of concentrate per 100kg liveweight can be justified economically.
- Supplementing autumn grass with concentrates increased carcass conformation by 0.5 conformation units.
- There were no effects on eating quality of any of the diets varying from all grass to ad-libitum concentrates. However, in comparison to the ad-libitum concentrate group, including a proportion of grass in the diet yielded a fatty acid profile that was more beneficial to human health.
- When concentrates were formulated to similar estimated net energy and nitrogen content the form of carbohydrate in the concentrates did not significantly affect the carcass gain of cattle grazing autumn grass.
- In the study reported here, concentrates of lower starch content tended to increase internal fat but did not significantly affect fat scores.
- Drennan, M.J., Moloney, A.P., O’Riordan, E.G. and McGee, M. 1997. Effects of supplementary concentrates on performance of finishing heifers at pasture in autumn. Irish Journal of Agricultural and Food Research, 36,1: 123
- Larick, D.K., Hedrick. H.B., Bailey, M.E., Williams, J.E., Hancock, D.L., Garner, G.B. and Morrow, M.E.1987. Flavour constituents as influenced by forage- and grain-feeding. Journal of Food Science, 52, (2): 245
- Meijs, J.A.C. 1986. Concentrate supplementation of grazing dairy cows. 2. Effect of concentrate composition on herbage intake and milk production. Grass and Forage Science 41: 229-235.
- Wood, J.D. and Enser, M. 1997. Factors influencing fatty acids in meat and the role of anti-oxidants in improving meat quality. British Journal of Nutrition 78 (1): S49
The studies outlined above were undertaken as part of a Ph.D. degree programme. The author acknowledges the support and assistance he received from his colleagues at Grange and U.C.D. Financial assistance was received from the Agricultural Trust, R&H Hall, Waterford Foods, Golden Vale Foods plc., Lakelands Dairies Co.-Op., Dairygold Co.-Op., N.C.F. Co.-Op. and the European Union Structural Funds (EAGGF).
- Padraig Frenchis a graduate of Agricultural Science from University College Dublin. He is currently completing his Ph.D. Thesis at Grange Research Centre.