The effect of the digestible undegradable protein
concentration of concentrates and protein source
offered to ewes in late pregnancy on colostrum
production and lamb performance
L.E.R. Dawson
a,*, A.F. Carson
a,b, D.J. Kilpatrick
a,baAgricultural Research Institute of Northern Ireland, Hillsborough, Co. Down BT26 6DR, UK
bThe Department of Agriculture for Northern Ireland, Queen's University of Belfast, Belfast, UK
Received 4 March 1999; received in revised form 26 July 1999; accepted 4 August 1999
Abstract
An experiment was carried out to determine the effect of level of digestible undegradable protein (DUP) concentration and source of protein offered to ewes in late pregnancy on subsequent colostrum production and lamb performance. Ninety-one twin-bearing ewes of mixed breeds were offered grass silage and one of six concentrate treatments for a period of 6 weeks prior to lambing. The concentrates were formulated to provide increasing levels of DUP from approximately 13±65 g DUP/kg DM. The DUP was supplied in the form of xylose-treated soyabean (soypass) or fishmeal. Silage was offered at a constant rate of approximately 0.5 kg dry matter per day. Protein source and DUP concentration of the concentrate had no significant effect (P> 0.05) on ewe blood composition, colostrum yield and quality, lamb birth weight and lamb live weight gain from birth to weaning. The results of this study indicate that, for ewes with a mean condition score of 2.6 at 6 weeks prior to lambing and offered well fermented silage, protein source i.e., soypass versus fishmeal or level of DUP in the concentrate have no significant effect on ewe performance, in terms of colostrum production or lamb birth weight.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Protein; Ewes; Pregnancy; Colostrum
1. Introduction
Eighty percent of foetal growth occurs in the last 2 months of pregnancy leading to a significant increase in nutrient requirements (Robinson, 1990). McNeill et al. (1997),
Animal Feed Science and Technology 82 (1999) 21±36
*Corresponding auhtor. Tel.:44-1846-682-484; fax:44-4846-689-594
observed that in the ewe, in late pregnancy mammary gland growth had priority over growth of carcass tissues, a fact also noted by Robinson et al. (1978). The carcass tissues also act as a supply of protein such that in a situation where protein requirement exceeds supply, protein is mobilized from carcass tissues to satisfy the requirements of the mammary gland and uterine organs. Protein nutrition in late pregnancy can influence the net flux of amino acids to and from the carcass tissues (McNeill et al., 1997) which can ultimately influence mammary gland and uterine tissue growth.
The fact that protein and energy intake in late pregnancy are intrinsically linked has been recognised for some years (Robinson, 1990). When ME intakes are reduced there is a concomitant reduction in the synthesis of microbial protein and thus, a lower contribution of microbial protein to the protein needs of the ewe (Robinson, 1983). To correct this deficit, supplementation with low degradability protein is required. In view of this, fishmeal which is relatively undegradable in the rumen and hence provides a large supply of undegradable protein (DUP) to the small intestine has been considered to be an important component of ewe diets in late pregnancy (de B Hovell and érskov, 1989). However, concerns have been raised recently over adverse effects of industrial fishing on fish stocks (House of Lords, 1996) and the use of animal protein in ruminant diets (GAFTA, 1997). Therefore, there is a need to investigate the effects of replacing fishmeal with vegetable protein sources on ewe and lamb performance.
Lambs are born hypoimmunocompetent (Brambell, 1970), with a small store of energy, and rely on colostrum to supply maternal immunoglobulins and energy. Colostrum production is, therefore, extremely important. Mellor and Murray (1985), observed that underfeeding ewes energy and protein in late pregnancy reduced the total yield of colostrum produced during the first 18 h after birth by decreasing the prenatal accumulation of colostrum and its subsequent rates of secretion. O'Doherty and Crosby (1997) noted that increasing the crude protein content of diets deficient in energy increased colostrum yield. These authors also found that improving ewe protein nutrition pre-lambing increased the lamb's efficiency to absorb colostral IgG during the first 24 h of life.
The objectives of the current experiment were to compare the effect of protein source (fishmeal versus a protected vegetable protein source) and level of digestible undegradable protein (DUP) concentration in the diet of ewes in late pregnancy on lamb output, colostrum production, and IgG concentration of the colostrum.
2. Materials and methods
2.1. Animals
Ninety-one mature twin bearing ewes of mixed breeds (Greyface, Texel X Greyface and Rouge X Greyface), were allocated to six treatments at 7 weeks prior to the predicted mean lambing date. Mean liveweight and condition score 6 weeks prior to lambing were 76 and 2.6 kg, respectively. All the ewes were oestrus synchronized the previous September and mated with either Texel or Rouge de l'Ouest rams. All the ewes were housed 8 weeks prior to lambing. Sixty of the ewes were housed individually in slatted
pens to facilitate the measurement of individual intakes. The remaining 31 ewes were housed in groups of 4 in slatted pens and given food at the same level as the individually penned animals.
2.2. Dietary treatments and feeding
The ewes were offered grass silage at a constant rate of 0.5 kg DM/day. The silage was produced by harvesting the primary growth of a perennial ryegrass sward. An additive, formic acid was applied at 3 l/t. The grass was unwilted and harvested using a precision chop forage harvester.
Six dietary treatments were examined. These consisted of six isonitrogenous supplements containing barley and varying proportions of soypass (xylose treated soyabean meal), fishmeal and urea. Prior to the start of the experiment, the in situ rumen nitrogen degradability characteristics of the dietary components i.e., silage, barley, soypass and fishmeal components were determined. Full details of this procedure are given in Section 2.4. Nitrogen degradability characteristics are presented in Table 1. From these results, the amount of undegradable protein (UDP) and digestible undegradable protein (DUP) supplied by each of the dietary components was calculated according to the equations of AFRC (1990). The calculations of Robinson (1983) indicate that for a twin bearing ewe, offered a diet containing 10.5 MJ ME/kg DM requirement for additional UDP at the end of pregnancy, is approximately 24 g/day. On the basis of this information, treatments 1±5 were then designed to provide a range of levels of UDP, through increasing the proportion of soypass in the supplement and reducing the proportion of urea. Full details of the quantities and composition of barley, soypass, urea and fishmeal offered per day for each of the supplements are presented in Tables 2 and 3. The supplements were offered to the ewes from 6 weeks pre-lambing to lambing.
2.3. Experimental design
The dietary treatments were balanced for ewe live weight, condition score and age. There were 13 replicates per treatment for treatments one to five. Treatment six had twice the number of replicates as the other treatments (n26). The treatments were applied for a period of 6 weeks (i.e. 6 weeks pre-lambing to lambing).
Table 1
In situ nitrogen degradability characteristics of silage, barley, soypass and fishmeal components of the diets offered
Dietary component Degradability characteristic
a b c P(0.05) P(0.08)
Barley 51.2 46.0 0.131 0.84 0.80
Soypass 10.2 81.8 0.026 0.39 0.31
Fishmeal 46.2 55.2 0.002 0.47 0.47
Silage 62.6 28.2 0.055 0.77 0.74
2.4. Measurements
In situ rumen degradabilities of the silage, barley, soypass and fishmeal components of the diets were determined in three Friesian cows fitted with permanent ruminal cannulae. They were offered grass silage ad libitum plus 2 kg concentrates once daily. The rate of N disappearance was determined using the in sacco method as described by Mehrez and érskov (1977) with three bags per silage or concentrate for each withdrawal time. Nitrogen disappearance was calculated using the following equation:
Pab 1ÿeÿct
Wherea,bandcare constants (érskov and McDonald, 1979),Pis the amount degraded at timet,athe rapidly degradable fraction,bthe potentially degradable fraction andcis the fractional rate at which the fraction described by b is degraded. The effective degradability was calculated at two outflow rates as recommended by Agricultural Research Council (1984) i.e., 0.05/h (P(0.05)) and 0.08/h (P(0.08)).
The concentrates were incubated for 0, 3, 8, 12, 15, 24 and 48 h, and the silage was incubated for 0, 3, 8, 12, 24, 48 and 72 h.
Silage, concentrate and total dry matter (DM) intakes were recorded daily over the course of the experiment. Samples of silage were analysed for toluene DM, crude protein, volatile fatty acids, pH, lactic acid, ammonia, gross energy (GE), buffering capacity and ash. A sample of concentrates offered was analysed for nitrogen, GE and ash.
Ewe live weights and condition scores were measured at 6, 4, and 2 weeks pre-lambing, at pre-lambing, 6 weeks post-lambing and at weaning. A blood sample was taken from the jugular vein of each ewe prior to feeding at 6, 4 and 2 weeks pre-lambing and Table 2
Quantities (g DM/day) of concentrate diets offered, DUP, UDP and ERDP (g/day) supplied by the concentrates Treatment Barley Soypass Urea Fishmeal UDP supply
(g/day)a
aCalculated from the equations of AFRC (1990) and degradability information provided in Table 1.
Table 3
Composition (g/kg DM unless otherwise stated) of barley, soypass, urea and fishmeal in treatments 1±6
Parameter Barley Soypass Urea Fishmeal
Oven dry matter 871.7 854.6 990.7 917.2
Crude protein 108.9 517.6 2825.7 695.0
Gross energy (MJ/kg DM) 18.5 19.9 ± 19.7
Ash 24.7 66.4 ± 200.1
analysed for b-hydroxybutyrate, non esterified fatty acids, urea, total protein, albumin and globulin.
Availability of colostrum was determined by milking the ewes completely at 1, 10 and 18 h after parturition. Prior to each milking the ewes were injected intramuscularly with 10 i.u. of oxytocin (Oxytocin-S; Intervet Laboratories, Cambridge, England) and both quarters hand milked after 3 min (Doney et al., 1979). Samples taken at each time interval were analysed for total nitrogen, ash, dry matter and IgG concentration.
Lambs were weighed immediately after birth and then at two weekly intervals until weaning. Lambing difficulty was assessed on a five-point scale, where zero equated to unassisted lambing and five equated to a caeserean section. Following milking of the ewes, colostrum was fed to the lambs at a rate of 20±50 ml/kg lamb birth weight. Where insufficient colostrum was available substitute colostrum was fed. Approximately 5 ml of a blood sample was taken from each lamb by jugular venipuncture before colostrum was fed and 24 h later. The samples were subjected to zinc sulphate turbidity (ZST) analysis (McEwan et al., 1970).
The digestibility of each of the diets fed was determined in vivo using four castrated male sheep per diet treatment according to the method described by Steen (1986). Urine was also collected and analysed for creatinine and purine derivative (uric acid, xanthine, hypoxanthine and allantoin) concentrations.
2.5. Chemical analysis
2.5.1. Feeds and excreta
Chemical analysis of silage, concentrates, faeces, urine and dacron bag samples were undertaken according to the methods described by Pippard et al. (1995). Concentration of purine derivatives were determined according to the method described by Keady et al. (1988).
2.5.2. Blood
Total protein concentration of blood was determined on a clinical chemical analyser (Hitachi) using Boehringer Mannheim (Boehringer Mannheim GmbH, Mannheim, Germany) kits. Albumen concentrations were measured on a clinical chemical analyser (Hitachi) using a Randox (Randox Laboratories Ltd, Crumlin, Co. Antrim, UK) kit. Globulin concentrations were calculated by the subtraction of albumen from total protein concentrations.b-hydroxybutyrate concentrations were determined on a clinical chemical analyser (Hitachi) according to the method of McMurray et al. (1984). NEFA concentrations were determined on a clinical chemical analyser using WaKo (Wakop Chemicals GmbH, Neuss, Germany) kits.
2.5.3. Colostrum
The IgG concentration was measured by the method of Fahey and McKelvey (1965), using single radial immunodiffusion (RID) kits (The Binding Site, Birmingham, UK). Total N concentration was determined by Kjeldahl analysis as described by Ling (1963). Dry matter concentration was determined by drying the colostrum at 1008C for 48 h. Ash was subsequently determined by drying the sample in a furnace at 6008C for 24 h.
2.6. Statistical analysis
Due to the unbalanced nature of the experimental design, silage intake, ewe weights, lamb weights, blood analysis, colostrum analysis etc. were analysed using REML (Restricted Maximum Likelihood) analysis.
3. Results
The silage offered was well preserved as indicated by chemical composition (Table 4). Crude protein intakes were similar across all treatments and there were small, but significant (P< 0.001) differences in ME intake between treatments. Total DUP intake (silage plus concentrates) increased linearly (P< 0.001) from treatment T1 to T5. Ewe live weight change from 6 weeks pre-lambing to lambing and from lambing to 6 weeks post-lambing was not signficantly (P> 0.05) affected by DUP content of the concentrate or protein source (Table 5).
Total protein, albumin, globulin, betahydroxybutyrate, urea and non-esterified fatty acids concentrations were not significantly (P> 0.05) affected by DUP content of the concentrates or protein source (Table 6).
Lamb birth weight was not significantly (P> 0.05) affected by DUP content of the concentrate or protein source offered to the ewes. Lambs born from ewes receiving the different treatments had similar live weight gains from birth to weaning irrespective of treatment (P> 0.05). Protein source and DUP content of the concentrate had no significant effect on lamb serum IgG concentration of lambs blood before and after receiving colostrum (P> 0.05) (Table 7).
Colostrum yield, component concentration (g/l) and component yields (g) were not significantly (P> 0.05) affected by protein source or DUP content of the concentrate, although there was a slight tendency (P0.29) for total colostrum yield to increase with increasing DUP content of the concentrate (Table 8).
Protein source had an effect on allantoin output in the urine (mmol/day) (P0.06) and microbial protein supply (g/day) (P0.08). The animals offered fishmeal tended to have
Table 4
Chemical composition of silage as fed
Parameter Component
Alcohol corrected toluene dry matter (g/kg fresh) 224.58
pH 3.7
Crude protein (g/kg DM) 123.8
Ammonia (g/kg TN) 97
Lactic acid (g/kg DM) 79.1
n-butryic acid (g/kg DM) 0.7
Ash (g/kg DM) 73.9
GE (MJ/kg DM) 20.0
DOMDa 709
aDigestible organic matter in the dry matter (D-value).
Table 5
Effect of DUP content of the concentrate and protein source on DM, CP, DUP and ME intake and ewe liveweight change
Treatment Sem Significance
Silage 555 556 554 555 558 550 0.007 NS NS NS NS
Concentrate 519 515 511 507 501 507 ± ± ± ± ±
Total 1075 1071 1064 1062 1058 1056 0.007 * * NS NS
CP intake (g/day)
Silage 69 69 68 69 69 68 0.8 NS NS NS NS
Concentrate 97.2 98.3 97.2 96.8 96.4 98.0 ± ± ± ± ±
Total 166 167 166 166 165 166 0.84 NS NS NS NS
DUP intake (g/day)
Silage 9.93 9.95 9.89 9.93 9.97 9.83 0.085 NS NS NS NS
Concentrate 6.50 12.72 19.01 24.41 32.58 21.97 ± ± ± ± ±
6 weeks pre-lambing to lambing 4.6 5.2 5.2 5.9 6.7 6.2 1.73 NS NS NS NS
Table 6
Effect of DUP content of the concentrate and protein source on mean ewe blood composition pre-lambing
Blood metabolite Treatment Sem Significance
T1 T2 T3 T4 T5 T6 T1±T6 Linear
(T1±T5)
Quadratic (T1±T5)
Protein source
Total protein (g/l) 66.5 68.4 65.0 66.4 67.8 66.9 1.48 NS NS NS NS
Albumin (g/l) 28.8 29.3 29.1 28.0 28.8 28.8 0.57 NS NS NS NS
Globulin (g/l) 37.7 39.1 35.9 38.4 39.1 38.1 1.48 NS NS NS NS
Betahydroxybutyrate (mmol/l) 0.55 0.60 0.57 0.67 0.54 0.64 0.059 NS NS NS NS
Urea (mmol/l) 5.13 5.42 5.13 4.66 7.20 5.11 1.357 NS NS NS NS
Non-esterified fatty acids (m Eq/l) 0.28 0.35 0.23 0.29 0.26 0.28 0.048 NS NS NS NS
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Table 7
Effect of DUP content of the concentrate and protein source on lambing difficulty, lamb birth weight, lamb liveweight gains birth to weaning and immunological status of the lambs before and after receiving colostrum
Treatment Sem Significance
T1 T2 T3 T4 T5 T6 T1±T6 Linear
(T1±T5)
Quadratic (T1±T5)
Protein source
Birth weight (kg) 4.3 4.4 4.2 4.0 4.4 4.4 0.21 NS NS NS NS
Liveweight gain-birth to weaning (g/day) 204 207 236 227 219 226 10.6 NS NS NS NS Lamb serum IgG (g/l)
Before receiving colostrum 2.2 2.9 ±0.5 2.3 0.5 1.5 1.94 NS NS NS NS
After receiving colostrum 28.2 23.9 21.1 26.8 ± 20.6 3.78 NS ± ± ±
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Table 8
Effect of DUP content of the concentrate and protein source on colostrum yield and composition
Treatment Sem Significance
T1 T2 T3 T4 T5 T6 T1±T6 Linear
(T1±T5)
Quadratic (T1±T5)
Protein source
Total colostrum yield (l) 928 955 1208 1171 1151 1256 171.8 NS NS NS NS
Composition (g/l)
Crude protein 199 191 169 202 152 171 24.4 NS NS NS NS
Ash 11.0 10.8 10.1 10.2 10.4 10.5 0.56 NS NS NS NS
Total solids 353 332 319 326 337 301 19.5 NS NS NS NS
IgG (g/l) 88.7 85.7 70.6 83.6 79.6 75.7 5.103 NS NS NS NS
Component yields (g)
Crude protein 177 149 283 242 165 205 48.6 NS NS NS NS
Ash 9.3 10.4 14.0 11.3 11.3 13.1 2.09 NS NS NS NS
Total solids 279 310 423 316 352 375 54.9 NS NS NS NS
IgG 69.6 73.5 101.4 68.8 85.7 91.6 14.24 NS NS NS NS
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Table 9
Purine deriviative and creatinine excretion and microbial protein supply for diets offered
Treatment Sem Significance
T1 T2 T3 T4 T5 T6 T1±T6 Linear
(T1±T5)
Quadratic (T1±T5)
Protein source Purine derivative concentration (mmol/day)
Allantoin 17.4 21.4 19.6 19.3 19.8 24.4 1.99 NS NS NS P0.06
Hypoxanthine 0.57 0.78 0.64 0.45 0.46 0.69 0.179 NS NS NS NS
Uric acid 0.90 0.85 0.77 0.84 0.65 0.60 0.132 NS NS NS NS
Xanthine 0.75 0.62 0.70 0.46 0.71 0.50 0.162 NS NS NS NS
Microbial proteinasupply (g/day) 106 128 118 114 117 142 11.5 NS NS NS P0.08
aMicrobial protein supply estimated from the excretion of purine derivatives using the equations of Chen et al. (1992).
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higher concentrations of allantoin in the urine than the animals offered soypass and estimated microbial protein supply was greater in the animals offered fishmeal than in those offered soypass (Table 9).
4. Discussion
Feeding strategies for late pregnancy that recognise the need for diets to supply increasing amounts of DUP as the deficit between ME requirements and ME intake increases are now accepted in practice (Robinson, 1990). Therefore, the response to increasing DUP supply obtained in the current study will be influenced by the ME intake of the ewes. AFRC (1990) and Robinson (1983), provide recommendations for ME requirements at various stages of pregnancy. These are given in Table 10. Total ME supplied by each of the treatments is given in Table 11 for comparison. It should be noted that in the current study a flat rate system of feeding was adopted so that ME intake
Table 10
Estimated energy (ME) and protein (MP and UDP) requirements at various intervals until lambing Weeks pre-lambing
6 4 2 0
Energy requirements
ME requirements (MJ/day) AFRC (1990)a 12.6 14.4 17.0 20.2 Robinson (1983)b 13.0 13.9 14.9 15.8
Protein requirements
UDP requirements (g/day) Robinson (1983)b 22.7 33.6 44.5 55.0
MP requirements (g/day) AFRC (1990)a 100 109 122 137 aRequirements predicted for a 80 kg twin-bearing ewe offered a diet containing 11 MJ/kg DM.
bRequirements predicted for a 78 kg twin-bearing ewe, total lamb birthweight 8.6 kg and ME concentration
of the diet 13.6 MJ/kg DM.
Table 11
Estimated energy (ME) and protein (MP and UDP) supply from silage plus concentrate diets Treatment
T1 T2 T3 T4 T5 T6
Energy supply
ME intake (MJ/day)a 14.4 14.2 14.4 14.7 14.8 14.5
Protein supply
UDP supply (g/day)b 24.0 30.2 36.3 42.6 49.8 39.1
MP supply (g/day)c 126 155 150 153 162 177
aTaken from Table 3, total ME intake.
bEstimated from the equations of AFRC (1990). Results refer to total UDP supplied from silage plus
concentrate diets.
cEstimated from the equations of AFRC (1990) and from microbial protein supply (Table 7). Results refer to
total MP supplied from silage plus concentrate diets.
remained constant over the last 6 weeks of pregnancy. On the basis of the recommended requirements, the diets offered in the current study provided 1.15 (AFRC, 1990) and 1.12 (Robinson, 1983), of requirements at 6 weeks prior to lambing and 0.72 (AFRC, 1990) and 0.92 (Robinson, 1983) at lambing i.e., there was a transition from a positive to a negative energy balance over the period.
Robinson (1983), recommended, that provided ewes are consuming adequate amounts of energy to meet their needs in late pregnancy, then diets containing 10 g CP/MJ ME would supply their protein needs up to about 3 weeks before lambing. After this period the rapid increase in the needs of the foetuses together with the growth of the udder and production of colostrum cause an extremely rapid increase in protein needs to around twice that supplied by the basal diet containing 10 g CP/MJ ME. Robinson (1983), provided estimates of protein requirements at various intervals until lambing, in terms of UDP, while AFRC (1990) estimated requirements in terms of metabolizable protein (MP). Recommended values are given in Table 10. Corresponding protein supply from the diet (i.e. silage plus concentrate), in terms of UDP and MP is given in Table 11. MP supply was calculated using the estimates of microbial protein supply of the diets as given in Table 7 and the equations of AFRC (1990). Values obtained for UDP supply were slightly higher than the DUP intakes given in Table 3. These results indicate that there was a deficit between UDP supply and UDP requirements at lambing, the deficit being greater with treatments T1±T3. However, treatments T2±T6 satisfied MP requirements throughout pregnancy while treatment T1 was sufficient until the last 2 weeks of pregnancy.
Calculations based on the data of Robinson (1983), indicate that all the treatments failed to supply sufficient protein (in terms of UDP) to meet the needs of the ewes in late pregnancy. However, in terms of MP (AFRC, 1990), only treatment T1 failed to satisfy the requirements in the last few weeks of pregnancy. In addition, according to the recommendations of AFRC (1990), ewes offered all the treatments would have been in an energy deficient state in the last 2 weeks of pregnancy. In view of this, the lack of an effect of protein source or increasing the DUP concentration of the diet (i.e. comparing treatment T1 with T5) on any of the measured parameters is surprising. The lack of response to protein source or DUP supply may reflect the fact that the ewes were in good condition at the start of the experiment (mean condition score 2.6) and offered well fermented, good quality silage. Various other parameters measured in this study would also support these results. For example, lamb birth weight has often been used as an indicator of whether ME supply to ewes in late pregnancy meets the ME requirements. In the current study lamb birth weight was not significantly different between treatments and averaged approximately 4.3 kg. This was within the normal range for healthy lambs of these breeds (O'Doherty and Crosby, 1998). Caution however, should be used when using lamb birth weight to indicate nutritional status. For example, in a study by O'Doherty and Crosby (1998), the ME intake of ewes in late pregnancy ranged from less than 0.5 to 0.8 of their requirements. However, lamb birth weight was within the expected range for the breed concerned and there was no relationship between lamb birth weight and ME intake. O'Doherty and Crosby (1998) surmised that the effect of energy supply on lamb birth weight is small due to the low efficiency of dietary energy use for conceptus growth. Circulating levels ofb-hydroxybutryate are also indicators of nutritional status. Russel (1984), stated that b-hydroxbutyrate concentrations greater than 0.8 mmol/l indicate
energy deficiency. In the current study the meanb-hydroxybutryate concentration over the 6 weeks prior to lambing was below this level. Two weeks prior to lambing, b -hydroxybutyrate concentration of ewes offered Treatment 4 was 0.85, but at all other intervals is was less than the `critical' level quoted above. This result would indicate that the ewes in the current study were not suffering from energy deficiency. However, in the study by O'Doherty and Crosby (1997), where ME intakes were as low as 10 MJ/ewe/day during the last 3 weeks of pregnancy, theb-hydroxybutyrate concentrations were within the generally accepted limits leading the authors to question the effectiveness of b -hydroxybutyrate as a sensitive index for energy status.
Despite the fact that treatment T1 failed to supply sufficient protein (MP and UDP) to satisfy requirements in late pregnancy, ewe performance, in terms of lamb output and milk production was not adversely affected and there was no response to increasing the DUP concentration of the diet. This may be explained by the fact that pregnant ruminants appear to be able to adapt their metabolism so that when dietary protein is limiting, foetal requirements can be met. For example, Bell (1995), noted that maternal undernutrition had little effect on foetal uptake of amino acids in late-pregnant ewes, due to the fact that the active placental transport of most amino acids is largely independent of changes in maternal blood concentration. Also, increased hepatic protein synthesis has also been observed in preparturient dairy cows despite unchanged or declining protein intake (Bell, 1995). McNeill et al. (1994), observed that ewes fed a low protein diet during late pregnancy had decreased tissue protein stores and muscle weight indicating a substantial capacity for mobilization of amino acids. Coffey et al. (1989) indicated that pregnancy per se enhanced protein absorption in the small intestine.
5. Conclusions
The results of the current study indicate that for ewes in good condition (condition score 2.6) at 6 weeks prior to lambing and offered well fermented silage, little benefit is to be obtained in terms of ewe performance, from supplementing with a protein source or increasing the DUP concentration of the diet. This occurred despite the fact that, on the basis of both AFRC (1990) and Robinson (1983), the diets were deficient in energy and in some cases protein. In studies by O'Doherty and Crosby (1997, 1998), in which responses to protein supplementation occurred, supplementation of the basal silage diet with a protein source increased ME intake as well as CP intake. Also the basal diets had much lower ME intakes than the basal diet in the current study. Greater responses to protein supplementa-tion may, therefore, have been obtained in the current study if the ewes had been in a more energy deficient state. It also appears that in situations where, nutrient requirement exceeds supply, the ewe can adapt her metabolism so that foetal requirements will be met.
Acknowledgements
The authors wish to thank the staff of the sheep unit and Mr M. Porter and the laboratory staff for their assistance. Thanks are also due to the staff of the Veterinary Sciences Division for carrying out all the blood analysis.
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