Model components for the determination of energy and protein requirements for breeding sows: a review

Livestock Production Science, 26 ( 1990 ) 1-37

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Elsevier Science Publishers B.V., Amsterdam

Model components for the determination of energy and protein requirements for breeding sows: a review C.T. Whittemore and C.A. Morgan

Edinburgh School of Agriculture, West Mains Road, Edinburgh EH9 3JG (Gt. Britain) (Accepted for publication 19 January 1990)

ABSTRACT Whittemore, C.T. and Morgan, C.A., 1990. Model components for the determination of energy and protein requirements for breeding sows: a review. Livest. Prod. Sci., 26: 1-37. Factorial and empirical data from recent work at various research centres provide a quantitative information resource from which nutrient response models may be constructed. Given an initial protein mass (Pt) of some 16.6 kg, breeding sows require subsequently to accumulate protein at rates of around 11.1, 7.8, 4.5 and 2.4 kg per parity. A lipid mass of some 1.5 times the protein mass is consistent with satisfactory reproductive performance, while reproductive efficacy is threatened if the mass of lipid in the breeding sow falls below the mass of protein. Energy requirements for maternal protein and lipid gains appear to be 50 MJ ME kg-~, while amino acid requirements may be modelled from knowledge of ileal digestibility and the efficiency of utilisation post-absorption. Maintenance requirements for energy are probably in the region of 2.51 PIT M MJ ME daily, while maintenance protein requirements may be estimated as 0.004 Pt. The energy and protein needs have to be added for the gravid uterus, the developing mammary tissues and, especially, lactation; the latter being a function of both potential supply and realised litter demand. The interval between weaning and oestrus is closely related to fatness, particularly in primiparous sows; weaning to oestrus interval (days) =29.3-2.03 P2+0.0433 P22, where P2 is the (ram) fat depth 65 mm from the mid-line at the position of the last rib. Changes in P2 fat depth during pregnancy may be estimated as 0.036 total pregnancy food intake- 9.3, while change in P2 fat depth during lactation may be estimated as 0.037 total (28 day) lactation feed intake-0.497 number of piglets sucking-0.265 P2 fat depth at partur i t i o n - 0.283. Litter size and individual piglet birth weight is weakly, but positively, related to maternal live weight. Overall, optimum levels of dietary nutrient supply can be estimated, and the consequences of failure to provide for requirement predicted with regard to both the breeding sow herself and to her productivity. Keywords: energy; lactation; models; protein; sow nutrition.

INTRODUCTION The breeding sow must achieve reproductive

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patency, conceive, bear the

© 1990 - - Elsevier Science Publishers B.V.

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C.T. WHITTEMORE ET AL.

products of conception to term and lactate. Additionally she must maintain her body tissues and body activities, and grow in size toward natural maturity. Recommendations for the level and composition of food allowances for pigs are best founded on the dynamics of animal response to nutrients rather than on rigid chosen values purporting to elicit optimum performance in all circumstances (Agricultural Research Council (ARC), 1967). The recognition that optimum animal performance requires a flexible approach to nutrient need has led to the definition of pig response to nutrient inputs (Standing Committee on Agriculture (SCA), 1987 ). One of the most effective means of defining nutrient response is through simulation models, and these have been constructed with some degree of success (Whittemore and Fawcett, 1974, 1976; ARC, 1981; Whittemore, 1983) for growing pigs of 20-120 kg liveweight (W). Second generations have emanated from Black et al. (1986), Moughan et al. (1987), Moughan (1989) and others; Black et al. (1986) in particular having also presented some novel elements of a simulation model for the breeding sow. The shortcomings of the ARC ( 1981 ) review, with respect to its attempt to lay down recommendations as to the nutrient needs of breeding sows have been well recognised, and a report from a consequential working party (Technical Committee on Responses to Nutrients (TCORN)) on this topic is awaited. Recently the body of information concerning the nutrition of the breeding sow has been considerably enhanced by Black and Williams and their colleagues in Australia (Black et al., 1986), by the Shinfield group in the U.K. (Mullan and Close, 1989a, b), and by the data collected by Yang and Eastham since 1985 in Edinburgh (Eastham et al., 1988; Yang et al., 1989). The National Research Council (NRC, 1988 ) approach to the nutrition of the sow has been rather disappointing, while the pursuit of a simultaneous model for sow feeding by Williams et al. ( 1985 ), Black et al. ( 1986 ) and SCA (1987) has remained largely unconsummated. Dourmad (1987) produced a detailed model for the energy and protein requirements of the pregnant sow, and Nobler et al. (1988) have outlined a model of energy requirements in lactation. Workers at Edinburgh have long been concerned with the science of response prediction modelling, but its application to the breeding sow has thus far been elusive. It is possible to model nutrient requirements either mechanistically (deductively) or empirically. Given the nature of biological science, most working simulation models are mixed. This review will not present finished models but rather will attempt numerical values, equations, algorithms and hypotheses for the construction of mixed mechanistic and empirical models. Firstly the factorial components of a model of energy and protein requirements will be considered under the subject areas of growth to maturity, maintenance, pregnancy and lactation. Then information yielding equations for a model derived from empirical responses from field trials will be reviewed.

MODELSENERGYANDPROTEINFORSOWS GROWTH TO MATURITY

Derivation of the requirements of a growing sow for energy and protein requires knowledge of the pattern of accretion of body protein and lipid. Growth concepts for animals slaughtered at less than 50% of mature size are inadequate descriptors for the growth of breeding sows whose rate of potential protein retention (Pt) approaches zero at maturity. Studying protein growth of pigs between 20 and 200 kg live weight Whittemore et al. (1988a) concluded the Gompertz function to be a useful means of describing both early growth and growth to maturity A × e-e-astt-t*)

where: A is weight at maturity; Bg is the growth rate parameter; the point of inflection occurs at t* days; and (A × Bg)/e is the maximum growth rate. Since time of maturity is a more intransigent character than tissue growth rate (Emmans and Fisher, 1986), animals with greater rates of protein deposition have a greater mature protein weight (Pt); Whittemore (1983) mooted Pt = 300 PL and with estimates for the value P~ in current stocks of improved hybrids in the region of 150 g day-1, p~ will be around 45 kg, as reported by Yang et al. ( 1989 ). Comparison of the data collected by Yang et al. ( 1989 ) for breeding animals with that of Whittemore et al. (1988a), using serially slaughtered ad libitum fed growing pigs over the uninterrupted growth period 20-200 kg W, shows that the breeding animals had a reduced growth rate from first conception to parity 4 (280 kg W). Values for body protein (Pt, kg) for the adequately fed sows (fed in pregnancy to achieve 20 mm P2 (depth of backfat plus skin taken 65 mm from the midline at the position of the last rib) prepartum, and ad libitum in lactation) calculated from the data of Yang et al. (1989) are presented in Fig. 1. With an initial value for Pt at first conception of 16.6 kg, respective gains from conception to conception over the first four parities are I 1. l, 7.8, 4.6 and 2.4 kg. If protein weight is static during lactation, these gains would be achieved during the pregnancy phase. It is evident that the rate for protein retention (Pr) measured for these sows can only be regarded as observed performances under the duress of the reproductive cycle, and not as any indication of what may have been a preferred pig growth target, but it was clear from the results of the study that it was not detrimental. The relationship between post-pubertal protein growth and reproduction in the sow remains obscure. King (1987) forwards the hypothesis that postweaning anoestrus is related to the absolute (estimated) body protein mass at weaning. Weaning to oestrus interval ( d a y s ) = 8 2 - 3 . 6 Pt. However, the effect of protein was not dissociated from the influence of body weight which appeared equally as influential. Besides, critical protein mass for rebreeding

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C.T. WHITTEMORE ET AL.

6( WEIGHT OF 5C LIPID (Ct) AND PROTEIN(Pt) IN 4C BODY (kg) 3C Pt = 4 5. e20

1C

I

0

I

I

I

I

I

100 200 300 400 500 600 DAY FROM FIRST CONCEPTION (t)

Fig. l. Increasein maternalbody protein and maternal body lipid from the time of first conception. The point of inflection (t*) was coincidentwith conception (t*= - 1), indicatingconception to be the point at which the daily rate of growth beganto diminish. at 18 kg at the beginning of Parity 2 seems to be so low as to be a useful indicator only of grave physiological distress in sows. From the data of Whittemore and Yang (1989), where total body lipid is Lt, the (protein + lipid) free weight of the body of the live sow ( W - (Pt + Lt) ) can be computed as W - ( P t + L t ) =8.21

P t °'7s9

This expression allows estimation of all non-protein and non-lipid body components as a function of protein mass. These components include water, body carbohydrate, ash, and gut and bladder fill. The assumption that protein gain is about 23% of combined protein plus water gain (Shields and Mahan, 1983) is consistent with this calculation. Mature lipid mass and its rate of attainment under nutritionally unlimiting conditions may be approached in a similar manner to that for protein (Emmans and Whittemore, 1989 ). However, growth to mature lipid mass is likely to represent an outer boundary to fat growth which is far distant from the normal operational ranges for fatness in sows under the vicissitudes of bearing and suckling young. But although it is impossible to quantify in a mechanistic way the causal relationships between body fatness and the reproductive processes, it is quite evident that lipid plays a central role in mammalian reproduction (Kirkwood, 1985 ). Dyck ( 1988 ) notes that puberty is reached by only half commercial gilts at 200 days of age depending upon nutrition, environment and genotype. Grossly

MODELS ENERGY AND PROTEIN FOR SOWS

excessive or inadequate levels of fat will delay puberty (Duncan and Lodge, 1960; Kirkwood, 1985 ). In general, faster growing females will reach puberty at a younger age, being heavier and fatter (Friend, 1976). Kirkwood and Aherne ( 1985 ) propose the concept of a minimum level of fatness, as well as minimum age and weight, for the onset of puberty but come to no particular conclusion as to what the minimum level might be. Under full feeding, or with earlier genotypes, Lt > 2 Pt seems unremarkable (O'Grady et al., 1975; Tullis, 1982; King et al., 1986 ) but with current genotypes of gilts destined for breeding Lt= 1.2- 1.5 Pt is more usual and consistent with P2 backfat depths of < 15 mm at first mating (Whittemore et al., 1988b; Whittemore and Yang, 1989). Low-level feeding, resulting in excessive lactational weight and fat loss, increases the incidence of anoestrus, extends the weaning to conception interval, reduces ovulation rate and decreases embryo survival (Hardy and Lodge, 1969; King and Williams, 1984; Kirkwood et al., 1987 ). It appears that reproductive efficacy may be threatened if Lt < Pt (Whittemore et al., 1988b; Yang et al., 1989). The lipid content of the adequately fed sows of Yang et al. ( 1989 ) can be estimated from L t - 1.56 P t - 4 . 1 o r L t = 1.1 Pt L°7. Weights of body lipid from first conception are shown in Fig. 1. With an initial value for Lt at first conception of 22.2 kg, conception to conception lipid gains for Parities 1-4 were 16.2, 11.7 7.0 and 3.7 kg Lt, respectively. Gains of Lt were approximately equal to 1.5 Pt. Within parity, pregnancy gains of Lt were greater than this ( 1.6 Pt) to allow for Lt losses in lactation; the ratio of Pt:Lt being 1 : 1.3 at the time of weaning. As ash may be estimated as 0.2 Pt, any gain in Lt of less than 1.2 Pt will have the consequence of the sow becoming progressively thinner over her breeding life. Verstegen et al. ( 1987 ) proposed pregnancy gains of 45 kg, comprising 25 kg maternal body and 20 kg of conception products. The composition of the maternal gain was estimated by Shields et al. ( 1985 ) to be about 25% lipid and 15% protein. Maternal gains of 25 kg during pregnancy are far short of the 50-65 kg and 35-50 kg maternal gains during pregnancy measured for four parities with fat and thin sows, respectively, by Yang et al. (1989). It is self-evident that the target chosen for maternal gains in pregnancy has an important influence on the nutrient requirement that will be estimated. It is equally clear that there are widely differing views expressed in the literature as to what the recommended rate and composition of pregnancy gains should be.

Energy requirements for growth for lipid retention (ELf) and protein retention (Ee,) Prediction of response requires knowledge of the energy content of the diet.

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C.T. WHITTEMORE ET AL.

The most appropriate measure is digestible energy (DE) since this is relatively unaffected by animal factors (Morgan and Whittemore, 1982). Metabolisable energy and, even more so, net energy are functions of the use to which the energy is put and will differ from one animal to another. Estimates of DE can be obtained from knowledge of the ingredient formulation of the diet, or predicted from chemical composition (Morgan et al., 1987). The energy requirements of the pig are most conveniently stated in terms of metabolisable energy (ME) which is calculated from the net energy of a particular function (protein accretion, milk production, etc. ) and the associated efficiency of utilisation of ME (ARC, 1981 ). Conversion of the DE value of a food to the ME it supplies can be calculated simply using a factor of 0.96 (ARC, 1981 ) but this is not sufficiently accurate for modelling purposes. Therefore, in recognition of the effects of oil and fibre on the efficiency of use of DE and the consequences of the cost of protein metabolism, Whittemore (1983) proposed that effective ME of a diet is calculated as ME = E p f - 23.6 Pr + Qd where: Pr is the protein accreted; Epf is the protein-free DE where Epf= 1.1 × D E from lipid+0.5×DE from fibre+ 1.0×DE from carbohydrate- 23.6 × digestible crude protein; and Qd is the energy yielded from protein deaminated (Pm), Qd = 11.5 Pm. The effective ME is then partitioned to meet the needs of maintenance, growth (protein and fat accretion), conceptus gain, milk production and the thermal environment. The efficiency of conversion (kz) of dietary ME to retained body lipid (Lr) for growing pigs is around 0.74, thus ELf = 13.9 Lr+ 39.6 Lr although efficiency might be higher and the total cost lower, therefore, if the diet derives an increased proportion of its energy from dietary fats rather than dietary carbohydrates. During pregnancy, kfmay be increased to 0.80 (Close et al., 1985; Nobler and Etienne, 1987a) for deposition of fatty storage tissues which may subsequently be utilised during the course of lactation. There is less agreement with regard to the efficiency of utilisation (kp) of dietary ME for the retention of protein. ARC ( 1981 ) suggest kp=0.54, thus Epr =20.2 Pr+ 23.6 Pr but this value is rather lower than the 67 MJ ME kg- ~protein deposited suggested by Kielanowski (1972) and those calculated from first principles by Whittemore and Fawcett (1976). The suggestion of Whittemore ( 1983 ) that the energy cost of protein deposition should be calculated from a knowledge of the rate of protein turnover (Px)

MODELS ENERGY AND PROTEIN FOR SOWS

3.6 Px+23.6 Pr is attractive in that, in common with the proposition of Kielanowski (1972), it allows for the energy cost of protein deposition to be an increasing function of body weight (protein mass) of the animal on account of P x = (Pr) / (0.23 ( P ~ - P t ) / P t ) Whereas the ARC ( 1981 ) estimate calculates to 43.9 MJ energy kg- ~protein deposited, the latter function calculates to 52-96 MJ kg- ~ protein deposited for sows of 20-35 kg Pt, respectively; not dissimilar from the 67 MJ suggested by Kielanowski. The energy cost of protein deposition near to maturity has never been measured in sows and the calculation involving protein turnover has the unfortunate consequence that as maturity is approached the cost of the small remaining increments of protein deposition approaches infinity, which is not acceptable. At this point, what is energy cost of protein deposition and what is energy cost of maintenance remains an unresolved conundrum. NRC (1988) propose the energy costs of both maternal protein and maternal fat gains to be 50 MJ ME kg- l, or 20 MJ kg- ~liveweight gain.

Protein requirementsfor growth The concepts of protein metabolism in the model for growing pigs of Whittemore and Fawcett (1976) were developed further by Whittemore ( 1987 ) and supply was described as CPxF×VxDxv where CP is the crude protein content (g kg- ~) of the diet and F is feed intake (kg). The factor V is the protein value or score as compared with the protein needs of the pig calculated according to the method of ARC ( 1981 ). In this assessment of the suitability of dietary protein to meet requirements, the amount of each essential amino acid in the diet protein is compared with that in Ideal Protein, and the amino acid in shortest supply provides the score V. The balance of amino acids in the ARC ( 1981 ) definition of Ideal Protein is similar to that in pig tissue. D is the digestibility of the protein and v is the efficiency of utilisation of digested Ideal Protein in supplying tissue needs. Since the score of the dietary protein is based on the balance of amino acids in pig tissues, ARC ( 1981 ) assumed that digestibility and efficiency of utilisation are the same for all amino acids. The digestibility of amino acids is most accurately measured at the end of the terminal ileum (Di~), since the metabolism of amino acids by bacteria in the hind gut changes the profile of amino acids that appear in the faeces. NRC (1988 ) give some example ileal digestibilities of some amino acids in some feedstuffs. Black et al. (1986) and SCA (1987) used the concept of amino

C.T. WHITTEMOREET AL.

acid availability (digestible, absorbable and utilisable amino acid; Low, 1982); effectively combining Dil and v. Availability was based mainly on Di~ with a correction for individual feed ingredients (SCA, 1987 ). However, owing to the lack of information, the availability of lysine was applied to all amino acids. In the model of Black et al. (1986), the individual available amino acids were compared with the tissue demand; that in shortest supply governing the actual response. It is now clear that Di~ differs for each amino acid (Heartland Lysine, 1988) and therefore the assumptions of ARC ( 1981 ) and the approach of Black et al. (1986) require amendment. At present there is insufficient evidence to quantify the degree of difference among amino acids for the efficiency of utilisation of digestible amino acids, v; but a model of response must take this possibility into account. Whittemore (1983) suggested that v was 0.85-0.95. Stranks et al. (1988) and Beyer et al. (1988) preferred 0.85. The model for protein supply can be written in terms of each of 9 ( + 2) essential amino acids, aa t,) ( i = 1 - 9 ) aa~,~ x F X D i l ( i )

Xv(i)

to give the supply of utilisable aati) (uaa~i)) at tissue level. The supply of uaato is then compared with the amino acid spectrum of product protein (maintenance, body tissue, milk and conceptus) and the identification of the amino acid in shortest supply allows determination of the number of units of final product that can be formed. The proteins in products of conception, pig tissue growth and milk have similar amino acid spectra (ARC, 1981 ) and the following proportions (g kg- ~) are suggested: histidine 25, isoleucine 40, leucine 70, lysine 70, methionine + cystine 40, phenylalanine + tyrosine 70, threonine 45, tryptophan 14, valine 50, total essential amino acids 460. Approximately half of the requirements for methionine +cystine and for phenylalanine+tyrosine should be supplied by methionine and phenylalanine, respectively (Fuller et al., 1987). There are indications that the spectrum of amino acids required to supply maintenance protein is different from that given above; for example, cystine can supply most of the requirement for sulphur amino acids (Fuller et al., 1987 ). More information is needed in this area and at present, since maintenance losses are due to body protein turnover, the spectrum given above can be used and applied to the calculated maintenance requirement for protein. MAINTENANCE

Energy requirementsfor maintenance (ME~ ARC (1981) and NRC (1988) offer 0.439 ME W -°'75 daily for sows in pregnancy and lactation, this being derived from estimates ranging between

MODELS ENERGY AND PROTEIN FOR SOWS

0.371 and 0.556. The review of Verstegen et al. ( 1987 ) discusses the possibility, raised by Close ( 1981 ), of an increasing requirement with advancing pregnancy subsequent to Day 40 of 0.001 MJ W -°-75 increase day- l; but such was not the conclusion of Close ( 1987 ) or Noblet and Etienne ( 1985, 1987a). For growing pigs, ARC ( 1981 ) proposed either 0.458 MJ ME W -°75 or 0.719 MJ ME W -°63, ultimately preferring the latter. Noblet and Etienne ( 1987a, b) determined 0.425 MJ ME W -°75 daily for pregnant sows and 0.456 for lactating sows. The review by Black et al. ( 1986 ) pointed to increasing maintenance needs resultant from increasing milk yield and body protein catabolism; however these factors would be best dealt with under those functions rather than maintenance. Using regression techniques for sows in a commercial production environment, Whittemore and Yang ( 1989 ) determined 0.48 MJ ME W -°75 daily over four parities and including pregnancy, lactation and the weaning to conception interval; this latter value containing also within it any demand there may have been for cold thermogenesis. Close et al. ( 1985 ) determined lower values of 0.411 or 0.422 (depending upon the method of calculation ), while the review of Williams et al. ( 1985 ) concluded a value of 0.430. Beyer et al. (1988) propose 0.41 for pregnant sows, 0.44 for young lactating sows, and 0.47 for ageing lactating sows. Values for MEm forwarded since the ARC review of 1981 appear not to have materially detracted from the veracity of that estimate of 0.44 MJ ME W -°-75 day- ~. The need for the exponent and its biological relevance has been discussed by others. An exponent of unity may be more appropriate for animals of low body fatness (Kielanowski, 1972; Graham et al., 1974 ). Whittemore ( 1983 ) related maintenance to the protein mass (Pt) and derived 1.85 Pt °-78 MJ ME day- ~for growing pigs using the body composition data of Stant et al. ( 1968 ). But although the concept of basing maintenance requirement on protein mass remains valid (Black et al., 1986 ), and is likely to be equally as valid for sows with widely differing body fatness as for growing pigs, the relationship derived for pigs of 20-100 kg may not be suitable for breeding sows. The sows of Whittemore and Yang ( 1989 ), of liveweights ranging from 123 to 280 kg, were found to contain from 17.7 to 43.6 kg protein mass according to the equation, P t = - 2 . 3 1 + 0 . 1 8 6 W - 0 . 2 1 6 P2, where P2 is the depth ( m m ) of backfat plus skin taken 65 m m from the midline at the position of the last rib. The value of 0.44 MJ ME W -°-75 transferred to a base of protein mass calculates to MEre (MJ day- i ) = 2.51 Pt °'648 which, in comparison with the equivalent equation for growing pigs, solves to lower values for MEre at greater weight, and is also in better accord with ARC ( 1981 ) estimates for growing pigs.

Energy requirementsfor cold thermogenesis (E~) Ambient temperatures below critical temperature (Tc) induce cold ther-

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C.T. WHITTEMORE ET AL.

mogenesis. Verstegen et al. (1987), reviewing various sources, suggest for sows housed individually that Tc is around 20°C (some 4 ° higher than for sows in groups). Tc is influenced by heat output which is related to level of feeding. Close (1980) suggests that an increased intake of 0.08 MJ ME W -°-75 day-l above maintenance would decrease Tc by 1 ° C: T c = 2 0 - ( ( M E - MEre)/0.08) where ME and MEre are expressed per W 0'75. For pigs kept singly the energy needs of cold thermogenesis have been suggested as 0.016 MJ ME W-0.75 per °C (Verstegen et al., 1973), while ARC ( 1981 ) propose 0.018. The environmental temperature (T) is modified by the physical environment and adjustments such as those proposed by Black et al. (1986) or Whittemore ( 1983 ) might be appropriate.

Influenceofheat Environmental temperatures above critical temperature will reduce feed intake in growing pigs and sows (NRC, 1987 ). While NRC suggest a reduction of 1.65% per degree above optimal temperature, Close and Mount (1978) indicated 2.5%. Sugahara et al. (1970), Nichols et al. (1980) and Smith et al. (1988) respectively estimated a reduction of 0.0011, 0.0008, and 0.0007 kg feed intake kg- 1 live weight per ° C above lower critical temperature. The deleterious effects of high ambient temperatures on the incidence of anoestrus, length of oestrus, conception rate, weaning to conception interval, embryo survival, and on foetal growth and survival during late pregnancy clearly exist, but quantification is not possible.

Protein requirements for maintenance (IPm) Whittemore and Elsley (1976) use 60 g protein as the daily rate of obligatory loss from tissue turnover of sows and therefore requiring replacement; but no allowance is made for sow body weight. Carr et al. (1977) proposed 0.94 W °75, ARC (1981) 0.45 W, Whittemore et al. (1978) 1.32 W °-75, and Whittemore and Fawcett ( 1976 ) 0.004 Pt, which calculate respectively for a 200 kg sow to 50, 90, 70 and 128 g protein day -~. SCA (1987) use the value of Carr et al. (1977). Whereas a wide range of estimates for IPm is of little significance during lactation, where it is a small proportion of the protein economy, for pregnancy the choice of estimate is crucial to the determination

MODELS ENERGY AND PROTEIN FOR SOWS

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of requirement. Although the requirement for protein maintenance in the sow may be lower than in the growing pig, its dependence upon total protein tissue mass appears to be an equally reasonable assumption. An estimate of 0.003 Pt g protein day- 1 is close to the estimate of ARC ( 1981 ), but Beyer et al. (1988) suggest 0.400 g N W -°-75 day -~ which is 133 g protein for a 200 kg sow, close to the earlier ( 1976 ) estimate of 0.004 Pt. PREGNANCY

Energy and protein requirementsfor pregnancy Changes associated with the products of conception are considered independently of maternal body growth. The requirements for pregnancy are those for the development of the foetus, the foetal fluids, the placenta (including foetal membranes), the uterus and for the initial development of mammary gland tissue in anticipation of lactation. ARC ( 1981 ) assumed a progressive increase in requirements as pregnancy proceeds, based on the data of Pomeroy (1960), Moustgaard (1962), Elsley ( 1971 ) and Kemm (1974), but the equations used were not presented. NRC ( 1988 ) adopted the estimate of energy requirement for growth of conceptus derived by Verstegen et al. ( 1987 ) of 0.8 MJ DE day-1. In the model of Williams et al. ( 1985 ) requirements for pregnancy are confounded with body tissue changes in the sow. Dourmad ( 1987 ) presented a similar but more detailed model in which the pregnancy, mammary and maternal gains were considered separately. Black et al. (1986) revert to the original propositions of Moustgaard (1962), whereas Noblet et al. (1985) presented a detailed analysis of the progressive increase in weight, total energy and protein energy in the foetus, foetal fluids, placenta and uterus of sows given 30 MJ ME day-1 in pregnancy. From these latter equations the energy and protein content of the total gravid uterus can be calculated at progressive stages of pregnancy. This then allows estimation of the daily increments against stage of gestation (time (t), days); giving the following derived equations for estimating daily net requirements for the total gravid uterus Energy MJ day- 1= 0.107e °'°27t Protein g day - ~= 3.606e °'°26t Dourmad (1987) also used the data of Noblet et al. (1985) to produce relationships for the prediction of energy and protein deposition in the uterus. The relationships derived by Beyer et al. (1988) for calculating the energy and protein in the products of conception and empty uterus are also dependent on stage of gestation and number of foetuses, and calculations as de-

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C.T. WHITTEMORE ET AL.

scribed for the relationships of Noblet et al. (1985) gave the following equations for the prediction of daily net requirements:

Energy MJ day- l = 0.027eO.O4t Protein g day- 1= 1.129e °'°37t A comparison of requirements for a sow carrying 12 piglets, as derived from Noblet et al. (1985) and Beyer et al. (1988) is shown in Fig. 2. The requirements predicted by Noblet et al. (1985) and Beyer et al. (1988) show the commonly accepted progressive increase with stage of pregnancy. The weight

2.42.2' 2.01.81.6-

ENERGY DEPOSITED (M J/DAY)

1.41.21.00.80.60,4 ~ 0.2O-

,

50

,

,

,

,

,

i

,

60 70 80 90 100 110 120 t (DAYS)

7060PROTEIN DEPOSITED (G/DAY)

|

5040302010O-

• i

i

i

i

n

u

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60 60 70 80 90 100 110 120 t (DAYS)

Fig. 2. Energy and protein deposited during pregnancyin the products of conception. Circles, Noblet et al. ( 1985); squares, Beyer et al. (1988).

MODELS ENERGY AND PROTEIN FOR SOWS

13

of conceptus at term (total gravid uterus ), the total energy deposited and the total protein deposited are similar for Black et al. (1986), and Noblet et al. (1985), being respectively, 24.12 kg, 85.12 MJ and 2750 g, and 23.99 kg, 83.63 MJ and 2655 g. The relationships of Beyer et al. (1988) predict total energy and protein to be 72.54 MJ and 2311 g. Whereas the equations given above, as derived from the data of Noblet et al. ( 1985 ) and Beyer et al. ( 1988 ), give similar estimates of requirement for protein, those for energy diverge at early and late stages of gestation (Fig. 2 ). The equations derived from Noblet et al. (1985) offer the best means for calculating net energy and protein requirements. The energy deposited in the conceptus can be related to ME requirement by applying the appropriate factor for the efficiency of utilisation of ME for conceptus gain. Close et al. ( 1985 ) found that the efficiency of energy deposition in reproductive tissue was 0.72 but Noblet and Etienne (1987a) reported lower values of 0.4-0.5 for uterine deposition (ku). Alternatively ME requirement could be calculated by applying values for the efficiency of utilisation of ME for protein deposition (kp) and fat deposition (k f). In their model, Williams et al. ( 1985 ) used values of 0.6 and 0.8 for kp and kf, respectively, but these were applied to total (i.e. maternal and conceptus) deposition. Close et al. ( 1985 ) reported values of 0.69 and 0.88 and similar values were obtained by Noblet and Etienne (1987a) at 0.58-0.67 and 0.80-0.90, respectively. Beyer et al. (1988) found that the efficiency of utilisation of energy overall was 0.69. It is not clear whether the efficiency of utilisation of energy for protein and lipid gain in the products of conception is different from that of maternal gain of these tissues. The data of Close et al. (1985 ) suggest that these are similar but the ku of Nobler and Etienne (1987a) falls below that expected from kp and kf. Requirements for ME and protein for maintenance of the conceptus can be calculated using the relationships 0.44 MJ ME W -°-75 and 0.004 Pt, respectively. The amino acid spectra for maintenance of the conceptus and for the development of the products of conception were discussed earlier and the requirements, expressed as ideal protein, should be included in the total tissue protein requirement. Towards the end of pregnancy, the requirement for nutrients for the developing mammary tissue becomes increasingly important. Noblet et al. ( 1985 ) presented equations which describe the weight and composition of this tissue in relation to the stage of gestation and ME intake. Following the same procedure as described for the total gravid uterus, the following relationships were derived for the estimation of daily net requirements: Energy MJ day -1 =0.115e ° ' ° 1 6 t Protein g day- ~= 0.038e °°59t

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C.T. WHITTEMORE ET AL.

The relationships of Beyer et al. ( 1988 ) for mammary tissue development predict the presence of much higher energy and protein levels at term than those o f N o b l e t et al. ( 1985); 82.9 MJ and 1109 g as compared with 47.6 MJ and 547 g, respectively. Transformation to derive net daily requirements for energy and protein gives the following equations: Energy MJ d a y - ~-- - 1.7586 + 0.0251 t Protein g day -~

= - 2 6 . 5 5 + 0 . 3 7 9 0 t Pregnancy 1 -- - 5 3 . 3 4 + 0 . 7 6 1 4 t Pregnancy 2 = - 56.48 + 0 . 8 0 5 8 t Pregnancy 3-8

and a comparison of these with those o f Noblet et al. ( 1985 ) is shown in Fig.

1.0.

0.8ENERGY DEPOSITED 0.6(M J/DAY) 0.4-

0.2O-

5~ (~0

70

80

90 100 110 120

t (DAYS) 3530-

PROTEIN DEPOSITED (G/DAY)

20-

10-

| O-

i

so

6o

i

i

70

80

90

loo 11o 12o

t (DAYS) Fig. 3. Energy and protein deposited during pregnancy in the maternal mammary gland. Circles, Nobler et al. ( 1985 ); squares, Beyer et al. ( 1 9 8 8 ) .

MODELS ENERGY AND PROTEIN FOR SOWS

15

3. The predictions according to Beyer et al. ( 1988 ) are linear whereas those of Noblet et al. ( 1985 ) show a progressive increase in requirement with stage of gestation. As with the products of conception, the equations derived from Noblet et al. (1985) are taken to give the best means for the calculation of daily requirements. Whereas the protein requirement can be added to the pool of tissue protein requirement, that for energy poses the problem of the necessity for a value of the efficiency of conversion of dietary ME to mammary tissue energy. The value of 0.72 for the efficiency of energy deposition in reproductive tissue reported by Close et al. ( 1985 ) is reasonable. The foetus, placenta and fluids are lost at parturition, and there is a flush of nitrogen in the urine in early lactation associated with uterine regression (Hovell et al., 1977 ). Mammary tissue regression, which takes place at weaning, may result in a further loss of nitrogen in the urine (Hovell et al., 1977; Whittemore and Yang, 1989 ). LACTATION

Lactation yield depends upon litter size, lactation number and time postpartum (Elsley, 1971 ). The average milk yield found by Elsley for multiparous sows over an 8-week lactation was 7.25 kg day-i. For a litter of nine piglets the suggested average yield was 7 kg, rising by approximately 0.5 kg milk yield day- t for each piglet in the litter over nine. As litter size increased, intake per piglet diminished. Elsley's data set is presented and used by ARC ( 1981 ) and NRC ( 1988 ), and provides the basis for the calculations of Black et al. ( 1986 ). Black et al. ( 1986 ) present an adjusted curve for lactating sows of similar form to that used for dairy cows to describe potential yield; the peak for this curve is little greater than 7 kg which is consistent with the original data source. Actual yield is calculated by use of the equation, 1.81 + 0.58 litter size. Black et al. (1986) also invoke the simple expectation that the primiparous lactation is 0.78 of subsequent lactations. This is likely to be consequential upon both maternal potential and litter size, which are smaller for primiparous sows. It is generally accepted that the size of the sucking litter will increase by one piglet between Parity 1 and Parity 2, and by a further half a piglet between Parity 2 and Parity 3, after which time litter size is fairly constant until diminution sets in for parity numbers above seven; for example, see Brooks (1970) and data from Australian pig units quoted by Black et al. ( 1986 ). Average sow yield expectations of 6-7 kg, with peak yields of 7-8 kg, which appear to be the norm for ARC ( 1981 ), NRC ( 1988 ) and SCA ( 1987 ), do not accord with individual yields measured by Whittemore ( 1967 ) of 50-100 g per suckling, nor with measurements reported by Whittemore and Fraser (1974) of 425 g per litter per suckling; both estimates being more consistent with yields of 9-10 kg. The Elsley (1971) data set, and all subse-

16

C.T. WHITTEMORE ET AL.

quent manipulations of it, was obtained from a limited population of animals some 20 years ago and is not in accord either with likely efficiencies of conversion of milk to piglet body weight, or any longer with the practically observed performances of piglets in larger, more vigorous litters sucking modem hybrid sows of greater body weight. For example, sows having weaned at 21 days of age a litter of 12 piglets of 6 kg average weight would be estimated to have yielded 8.8 kg daily by Black et al. (1986), 8.6 kg according to the original data set of Elsley, but l0 kg according to the data of Noblet and Etienne (1987b). Beyer et al. ( 1988 ) allow for daily yields for litters of 12 of up to 10 kg, and Noblet et al. (1988) predicted even higher values. ARC (1981 ) and NRC (1988) both fail to account adequately for the dynamic relationships between maternal synthetic supply potential and litter growth demand potential. Lactation demand is a function of growth potential of the piglets in the suckling litter. Thus Noblet et al. ( 1988 ) presented equations for the prediction of milk energy output which depended on the rate of growth and number of piglets in the litter: Milk energy (MJ day -I )=20.59×litter gain (kg day-1 ) _ number of piglets X 0.38. Daily piglet gain (kg) for fully healthy and vigorous piglets can be given by Bg × W x l n ( A / W ) where: Bg is a variable depending upon the inherent ability to grow; A is the mature body weight; and W is Axe-e-~,,--) where t is the day of piglet age and t*, the point of maximum growth rate, is In ( - In ( W o / A ) )/Bg where Wo is the weight at birth (Whittemore et al., 1988a). Wo can be taken as 1.2 kg and A as 300 kg. Given Bg, resultant values for t*, W and daily gain may be calculated. Pigs of faster or slower growth rates can be ascribed greater or lesser values of Bg. Potential piglet daily live weight gains are shown in Table 1. Piglets of 6.1 kg liveweight at 21 days of age were found by Whittemore et al. ( 1981 ) to grow over the subsequent week at a rate in excess of 350 g daily liveweight gain, and when slaughtered to comprise 674 g water, 153 g lipid and 148 g protein kg- 1 empty body weight. ARC ( 1967 ) derived, from various sources, piglet liveweights (kg) and daily liveweight gains (kg) for (creep-fed) sucking pigs at Days 0, 7, 14, 21, 28, 35 and 42 post-partum of; 1.4 and 0.16, 2.5 and 0.24, 4.2 and 0.26, 6.0 and 0.27, 7.9 and 0.29, 9.9 and 0.31, and 12.1 and 0.35, respectively. Some recent data from I. Kyriazakis (unpublished data, 1987 ) is shown in Fig. 4. Energy intake calculations from the same source suggest, for litters of l0 piglets, (with the energy value of milk taken to be 5.4 MJ ME kg- ~ and no support to growth from creep-feed until

MODELSENERGYANDPROTEINFORSOWS

17

TABLE 1 Potential piglet daily liveweight gain for various values of Bg, and potential daily milk supply from the sow for various values of a. Derived from equations in the text Days post-partum 0

7

14

21

28

Potential piglet liveweight (kg) Bg=0.0143 1.2 2.0 Bg=0.0165 1.2 2.2

3.3 3.7

5.0 6.0

7.4 9.3

Potential piglet weight gain day- ~ (kg) Bg=0.0143 0.10 0.15 Bg=0.0165 0.11 0.18

0.21 0.27

0.29 0.39

0.39 0.53

Potential milk supply day -~ (kg) a= 18 3.5 6.7 a=24 4.6 8.9

8.4 11.3

8.7 11.6

8.1 10.8

35

42

10.6 13.5

14.5 19.0

0.51 0.69

0.63 0.86

7.1 9.5

6.1 8.2

10 00 AVERAGE 8 WEIGHT OF SUCKING 6 PIGLET (KG)

4 O00 I

7

I

I

14 21 AGE (DAY)

I

28

Fig. 4. Growth of piglets in a litter of eight without access to creep and without symptoms of illhealth (I. Kyriazakis, unpublished data, 1987). D a y 21 ) milk yields (kg) o f 5.8, 7.4, 9.2 and 10.7 at Days 0, 7, 14 and 21, respectively. To meet the estimates for daily piglet growth derived from the equations given a b o v e and shown in Table 1, the energy cost o f piglet gain including maintenance can be a s s u m e d to be around 22 M J ME k g - 1 and the energy value o f milk is 5.4 M J M E k g - l ; thus the daily lactation d e m a n d is: daily piglet gain × n u m b e r o f piglets in the litter (n) × 4 The use o f this conversion factor is well supported by Noblet and Etienne ( 1 9 8 7 b ) using the before and after weighing technique to estimate yield

18

C.T. W H I T T E M O R E E T AL.

(which probably slightly underestimates the amount sucked) who show that 3.7 g of milk result in 1 g of piglet liveweight gain. The energy value of piglet gain, and the energy required from milk to support it, is greater between birth and 14 days of age than subsequently. At birth the piglet will contain about 1.5% lipid and 12.0% protein. Between 14 and 21 days of age the respective contents will have become about 15% lipid and 15% protein (Whittemore et al., 1978; Mullah et al., 1989 ); the approximate 1 : 1 ratio pertaining until weaning (Whittemore et al., 1978). Lactation supply will accord to a lactation curve describing the outer boundaries of potential milk production. The lactation curve for a sow, as yield at day t, can be expressed as

axe-ktxu where a is a variable depending upon sow genotype, k = 0.025, and U ~ e - e(G-B~t)

where G is 0.5, and B~= 0.1 (Oldham and Emmans, 1988 ). The parameter G describes the initial state of the degree of maturity of the mammary system at parturition, and BI is the rate at which the relative growth rate of the mammary gland decreases with size. Potential rates of milk supply are shown in Table 1. Figure 5 shows supply curves for a = 24 and a = 18, together with demand curves for litters of n = 12 and n = 8 when Bg = 0.0143. The equations for milk supply confirm that sows will yield only small amounts of milk sub-

16~-

n=12 / /

14

/

MILK SUPPLY 12 AND DEMAND (kg 1(3

/

n:8 / /

/

/

/

/

/

/

/

/

PER

DAY)

8 6 ~

a

=24 a=18

///

4 2

I 0

I 7

1 14

I 21

I 28

I 35

I 42

DAY OF LACTATION Fig. 5. Supply of milk from the sow (solid line ) and demand for milk by the litter (broken line ). The two values for a describe different potentials for yield, while n is the litter size. For equations see text.

MODELS ENERGY AND PROTEIN FOR SOWS

19

sequent to Day 70 post-partum; the time at which natural weaning usually occurs (Kerr et al., 1988 ). The yield observed will be that described by the lower of the two possible boundaries shown in Fig. 5, and it is the yield observed which will control actual piglet growth on the one hand, and the requirement for nutrients by the sow on the other.

Energy and protein requirernentsfor lactation The rate of synthesis of energy and protein for milk can be calculated from the daily yield and the composition of the milk. Sows milk contains 53-73 g protein, 46-52 g lactose, 73-88 g fat, 7.7-10.9 g ash, and 5.4 MJ gross energy kg-l (Elsley, 1971 ). There is some compositional change through lactation but to take it into account would be to ascribe to the calculation of requirement a level of sophistication which is not warranted owing to inaccuracies elsewhere within the system. Dietary ME is converted to milk energy with an efficiency (kl) of 0.65-0.75 (0.70) (ARC, 1981; Burlacu et al., 1983; Verstegen et al., 1985; Noblet and Etienne, 1987b; Beyer et al., 1988), this value being a conjoint consequence of the efficiencies of energy use for protein, fat and carbohydrate in milk. A value of 0.70 for k~ results in 7.7 MJ ME being required for the formation of 1 kg of milk inclusive of the energy retained in milk. Requirements for amino acids to supply milk protein are added to the pool of tissue protein requirement. The balance of the amino acids was described earlier. In the event of a nutritional shortfall in relation to the needs for milk synthesis there will be catabolism of body fat and body protein, both for the provision of work energy and the supply of precursors for milk constituents. In the simple case of marginal under-supply of diet nutrients maternal catabolism of lipid and protein will supply milk synthetic needs pro rata. However, if the under-supply becomes progressively greater then the sow will become less willing to supply the whole of the demand and the rate of milk synthesis will fall (Whittemore et al., 1988b). The quantification of this phenomenon, and the rules for the partitioning of body loss between tissue protein and tissue lipid, await mechanistic description. However, it is possible to approximate some rates and limits to loss from feeding trials, although there can be little doubt that these will depend upon the perceived size of the available body lipid and protein reserves. The review of King (1987) identifies daily losses in lactation in excess of 1 kg W and 0.3 mm P2; which may be estimated as around 0.73 kg lipid and 0.15 kg protein daily. The first litter sows of Mullan(1987), fed generously in pregnancy and scarcely in lactation, lost 1.5 kg W and 0.28 mm P2 backfat daily during a 30-day lactation suggesting daily losses in the order of 0.72 kg lipid and 0.22 kg protein. Subsequently Mullan and Williams (1988b) measured lactational body tissue losses for sows in good condition given low lev-

20

C.T. WH1TTEMORE ET AL.

els of feed in lactation to be 0.85 kg of lipid and 0.16 kg of protein daily. Beyer et al. ( 1988 ) suggest liveweight loss during lactation to comprise 0.60 kg of lipid and 0.06 kg of protein kg -~. Eastham et al. ( 1988 ) found changes in maternal liveweight and P2 to be a linear consequence of reduction in lactation feed intake, reaching averages of - 1.1 kg W and - 0 . 3 2 m m P2 daily over a 28-day lactation for sows fed the lowest level (2 kg daily), which is approximately equivalent to 0.7 kg lipid daily. Milk yields can be calculated to have been 5.4 kg daily on the lowest feeding level and 7.3 kg daily on the highest level (6.5 kg feed day - l ) where respective changes were + 0.5 kg W and - 0 . l 0 m m P2. The sows of Whittemore et al. (1988b) were full fed in lactation (6 kg) but received different pregnancy feeding rates and were consequently of different body size and condition at farrowing. At parity five sows in poor body condition gained 0.63 kg W daily during the course of a 32-day lactation and lost only 0.041 m m P2, while sows in better condition gained only 0.094 kg W daily but lost 0.063 m m P2. Average calculated yields were 5.5 kg and 7.3 kg day -I. The sows of Yang et al. (1989), in good body condition but with low lactation feed intakes, lost 1.6 kg W and 0.20 m m P2 daily over a 28-day lactation while sustaining average daily milk yields in excess of 8 kg. These losses were equivalent to 0.62 kg lipid and 0.25 kg protein daily. Noblet and Etienne (1987b) measured daily weight losses in sows fed low and high energy diets in lactation as I. 1 kg and 0.65 kg, respectively. The lower rate of loss was determined to be 0.274 kg lipid and 0.075 kg protein daily, while the additional loss at the higher rate was determined to be primarily lipid (0.738 kg lipid and 0.075 kg protein daily). Milk yield was unaffected by treatment. Mullan et al. ( 1989 ) calculated sows of 160 kg suckling 10 piglets and consuming 68 MJ ME dayduring lactation would lose daily an average of 0.16 kg lean, 0.32 kg lipid and 0.50 kg W. Mullah and Close (1989a), offering primiparous sows with litters of 12 pigs either 66.5 MJ ME and 931 g CP day -~ or 33.7 MJ ME and 483 g CP day- l, found the output of energy and CP in milk to be similar in the first 2 weeks of lactation (56.6 MJ ME and 463 g CP day -~ or 57.5 MJ ME and 471 CP day- ~) but to differ in the third week ( 55.6 and 454 or 43.5 and 356 ). Maternal body tissue losses over the lactation were in the order of 8.7 or 29.8 MJ ME day- ~ and 50 or 134 g CP day- 1 for the two levels of feeding. Lipid losses were estimated as 191 or 620 g day- i. Thus within recent experiments daily rates of lipid and protein losses have reached levels as high as 0.85 and 0.25 kg day- 1, respectively. Ratios of losses seem normally to range between 2.5 lipid: l protein and l0 lipid: 1 protein, depending upon the relative availability of fatty tissue stores. In the absence of readily available body energy and protein stores, it appears that lactation yield can be curtailed readily down to levels at least as low as 5 kg daily, but where there are adequate body stores high rates of catabolism can be sustained and lactation yield maintained. Also, as stated previously, lactating

MODELS ENERGY AND PROTEIN FOR SOWS

21

sows appear unwilling to mobilise fat stores when P2 backfat depth falls below 10 mm and when the lipid:protein ratio in the whole body falls below l:l. Lipid released from body tissue for the purposes of milk synthesis is converted with an efficiency of 0.85-0.9 (ARC, 1981; Noblet and Etienne, 1987b; Beyer et al., 1988 ). Through deamination, the efficiency of conversion of body protein energy to metabolisable energy is about 0.5 (Breirem and Homb, 1972; Schulz, 1975 ). Assuming the amino acid spectrum of body protein to be close to ideal for milk protein synthesis, a conversion efficiency (v) of 0.85 may be taken (Beyer et al., 1988).

Lactation feed intake The major determinant of appetite in animals is nutrient need; lactating sows have greater appetites than pregnant ones, as do those suckling larger litters or those with lower levels of available nutrients stored in the body. Appetite is also influenced by environmental temperature (as described earlier), the bulk density of the food, and animal health. O'Grady et al. ( 1985 ) suggest lactation feed intake may increase by 0.2 kg per suckling piglet day -1. Voluntary feed intake is always lower for primiparous sows, and in the first week of lactation (for example, Young and King, 1987 ). The ad libitum fed gilts ofYang et al. ( 1989 ) ate 5.2 kg daily whilst the multiparous sows ate 5.7 kg. The primiparous gilts of Young and King (1987) consumed 3.3 kg daily during lactation, whilst the multiparous sows consumed 4.8 kg daily. About 80% of all the primiparous sows of Lynch ( 1988 ) ate 3-5 kg in lactation (mean 4.2 kg), while about 80% of all multiparous sows ate 4-6 kg (mean 5.2 kg). Absolute ad libitum feed levels recorded with normal sows on conventional medium-high density cereal/soya/fishmeal based diets may vary between 2 kg and 8 kg daily (see Lodge, 1962; Cox et al., 1983; King et al., 1984; Danielsen and Nielsen, 1984; Young and King, 1987 ). Mullah and Williams (1988a) found gilts of 171 kg W and 32 mm P2 at farrowing, and of 126 kg W and 20 mm P2 at farrowing, to have average voluntary feed intakes during lactation of 3.4 and 4.9 kg, respectively. The negative relationship between feed intake in pregnancy and feed intake in lactation has been well recognised since the work of Salmon-Legagneur and Rerat ( 1962 ), and is commonly found in contemporary studies. For the sows of Yang et al. ( 1989 ) the following relationships were derived food intake in 28-day lactation = 240-0.20 food intake in pregnancy food intake in 28-day lactation=212-3.61 P2 (ram) backfat depth at parturition. The latter coefficient gives a rate of reduction identical to that found by Mullan and Williams (1988a).

22

C.T. WH1TTEMORE ET AL.

Litter size An increase in the rate of pregnancy feeding at the beginning, middle or end of gestation will not increase litter size (Elsley, 1973; Henry and Etienne, 1978; Den Hartog and van Kempen, 1980; Hillyer and Phillips, 1980; ARC, 1981; Whittemore et al., 1984) but will marginally increase piglet birth weight. Hovell et al. (1977) found primiparous pregnancy feed intakes of 19.5, 25.8 and 32.1 MJ ME day -~ to result in litter sizes of 9, 9 and 8.6 (NS), but individual piglet birth weights of 1.08, 1.10 and 1.29 kg (P<0.05). Elsley and Shirlaw (1976) from a review of the literature had suggested that a 1 kg increase in daily pregnancy feed intake would result in approximately a 200 g increase in individual piglet birth weight. Mullan and Williams (1988a) feeding 2.7, 2.0 or 1.5 kg daily in pregnancy measured piglet birth weights of 1.47, 1.40 and 1.27 kg. Hardy and Lodge (1969) did, however, demonstrate that lactation feeding could positively influence the number of ova shed at subsequent oestrus. There was a 0.1 change in the number of ova shed for every kg sow maternal liveweight change between parturition and oestrus (the mean number of ova shed was 15.1, and the pre-natal mortality was 40%). O'Grady (1988) has also suggested that subsequent litter size can be reduced by 0.3 piglets for each kg reduction in lactation feed intake. Baidoo et al. (1986), feeding either 6 kg or 3 kg daily to multiparous lactating sows, found no effect on ovulation rate ( 17.3 or 17.1 ) but conception rate fell from 91% to 76%, the number of embryos at Day 25 of pregnancy fell from 13.9 to 12.6 (embryo survival 80% vs. 74%), while the weaning to oestrus interval was extended from 5.6 to 9.1 days. The sows lost respectively, 3.6 or 6.8 mm P2 backfat, and 13.7 or 26.5 kg liveweight during the 28-day lactation. Using multiparous sows, again fed 6 kg or 3 kg daily in lactation, Kirkwood et al. (1987) found the sows lost 2.6 vs. 7.3 mm P2 and 17.7 vs. 41.0 kg liveweight over a 35-day lactation, and to show 0 vs. 15% incidence of anoestrus, 4.3 vs. 5.9 days interval between weaning and mating, 83 vs. 68% embryo survival and 90 vs. 69% pregnancy rate.

Interval between weaning and conception The weaning to oestrus interval is frequently longer in primiparous than multiparous sows; as can be seen in the typical data of Young and King ( 1987 ) which shows the average intervals after Parities 1, 2 and 3 to be 22.0, 11.3 and 8.4 days. Low feed intake in lactation will lengthen the weaning to oestrus interval especially in primiparous sows but also in multiparous sows. The subject has been reviewed by King ( 1987 ), who suggests a critical lactation energy level

MODELS ENERGY AND PROTEIN FOR SOWS

23

of 45 MJ DE day -~. Above this critical level protein shortage in lactation is likely to be responsible for post-weaning anoestrus; a critical level of 700 g crude protein daily being suggested. Thus excessive weight loss and excessive fat loss will be conducive to an extended weaning to mating interval. Both the absolute levels and the rates of reduction of level of protein and lipid reserves are implicated by King in his review. King ( 1987 ) gives the following regression equations for primiparous sows weaning to oestrus interval (days) = 28.1 - 0.28 (MJ DE d a y - 1 in lactation ) weaning to oestrus interval (days) = 32.5 - 0.032 (g CP d a y - l in lactation ) weaning to oestrus interval (days) = 3 8 . 6 - 0.63 (kg body lipid at weaning) weaning to oestrus interval (days) = 81.5 - 3.58 (kg body protein at weaning ) weaning to oestrus interval (days) = 7.3 + 0.39 (kg liveweight loss in lactation ) weaning to oestrus interval (days) = 9.4 + 0.59 (kg body lipid loss in lactation) weaning to oestrus interval ( d a y s ) = 9 . 6 + 3 . 4 4 (kg body protein loss in lactation ) Mullan and Williams (1988a) showed the weaning to mating interval of primiparous sows to be extended if the gilts suffered both low lactation feeding and inadequate body reserves at the start of lactation (the interval rising from an average of 13 to 23 days). Whereas the effects of low body reserves at farrowing could be offset by subsequent high level lactation feeding, low level lactation feeding was deleterious when stores were either high or low at farrowing (Mullah, 1987 ). Both the rate of sow body weight and of fat loss, and the absolute levels of body weight and body fat, appear to have influenced the weaning to service interval. Mullah and Close (1989b), feeding primiparous sows with litters of 12 pigs either 5.5 or 2.9 kg of feed ( 12.5 MJ DE and 156 g CP kg- 1), found over a 21-day lactation liveweight losses of 8.1 or 34.0 kg, P2 backfat losses of 3.0 or 7.0 mm, respectively, and the mean interval between weaning and oestrus to be either 8.7 or 19.2 days. Reese et al. ( 1984 ), feeding 35 or 70 MJ DE daily during a 28-day lactation, measured 36 or 15 kg of weight loss and 9 or 2 m m P2 fat loss; respective proportions of sows in oestrus by 14-days post-weaning were 42 and 93%. The same authors found embryo survival to relate also to weight and fat losses in lactation; 28 kg and 6 m m being associated with 63% embryo survival, and 7 kg and 1.4 m m being associated with 75% embryo survival. Yang et al. ( 1989 ), for primiparous sows, present: weaning to oestrus interval (days) = 2 6 . 6 - 1.28 P2 ( m m ) fat depth at weaning weaning to oestrus interval (days) = 49.1 - 0.23 liveweight (kg) at weaning weaning to oestrus interval (days) = 25.5 - 0.12 total 28-day lactation feed intake (kg) confirming the propositions within the review of King ( 1987 ) that both body weight and fat changes in lactation have dramatic effects upon the propensity

24

C.T. WHITTEMORE ET AL.

to re-breed after weaning the first litter. In the experiment ofYang et al. ( 1989 ) 1 m m of P2 was equivalent to 3 kg of total body lipid in primiparous sows; using this conversion the propositions of both Yang et al. (1989) and King ( 1987 ) with regard to body fat are similar. While the modern literature (in contrast to earlier work) is clear in its view of the influence of absolute level, and the rate of change of fat and body weight upon weaning to oestrus interval in primiparous sows, there is less data relating to multiparous sows and the position is more equivocal; many workers demonstrating little or no effect. Where there is an effect it is invariably weaker in multiparous than in primiparous sows. However, it is also likely that those females most liable to re-breeding problems will already have been culled from the herd in consequence of primiparous phenomena and will not be present in a multiparous data set. Whittemore et al. (1988b) found for multiparous sows weaning to conception or culling interval (log~o d a y s ) = 1.5-0.004 liveweight (kg) at weaning weaning to conception or culling interval (loglo days) = 1 . 2 - 0.02 P2 ( m m ) fat depth at weaning or, in more simple form weaning to conception or culling interval (days) = 1 4 - 0 . 4 P2 (mm) fat depth at weaning For all parities there is also a negative effect of litter size upon weaning to oestrus interval. The effect of litter size is, presumably, also mediated through influence upon the absolute levels and rate of change of body fat stores and maternal live weight during lactation. Yang et al. (1989) present weaning to oestrus interval ( d a y s ) = 2.7 + 0.56 number of piglets in sucking litter while Knudson et al. (1987) indicated a slightly stronger effect for primiparous sows (weaning to oestrus interval (days) = 2.7 + 0.78 number of piglets in sucking litter). Relationships between days from weaning to oestrus and the body weight and condition of the sow are clearly only effectively demonstrated in the form of linear equations over a limited range of values for the independent variable. Sows are most unlikely to return to oestrus in less than 4 days after weaning, and it would also be erroneous to presume that there are no adverse consequences of over-fatness for re-breeding efficiency. Given the above relationships as measured under experimental conditions, Fig. 6 has been derived as an attempt at a more meaningful description of the relationship between the weaning to oestrus interval and sow body fatness. Level of feeding after weaning has a beneficial influence upon the weaning

MODELS ENERGY AND PROTEIN FOR SOWS

25

25

INTERVAL 20 FROM WEANING TO 15 OESTRUS (DAYS) 10

~MULTIPAROUS I s

I I lO 1; 20 2's 3'0 3's P2 BACKFATDEPTHAT WEANING (ram)

Fig. 6. The relationship between the interval from weaning to oestrus and the depth of backfat on sows at the P2 site.

to mating interval. From Brooks and Cole (1972) the following may be interpolated: Weaning to oestrus interval (days) = 43.4 F-~23 where F (kg) is the daily feed supply post-weaning. EMPIRICAL RESPONSES FROM FIELD TRIALS

Field trial results are rarely presented in a form that allows their generalisation for use as model components. More frequently, results from many trials are accumulated, stacked, and overall regression responses produced (e.g. ARC, 1967; Vanschoubroek and van Spaendonck, 1973; Henry and Etienne, 1978; ARC, 1981; Williams et al., 1985 ). However, the statistical and biological validity of combining experimental results in this way has to be questioned. It may be more informative to pursue the possibility of modelling sow response using data sets which have allowed the construction of effective regression relationships within the confines of a single set of environmental variables. Such data sets are not common but those from Edinburgh (Eastham et al., 1988; Whittemore et al., 1988b; Yang et al., 1989 ) may now offer a realistic approach to empirical response prediction modelling in the breeding sow. Where not otherwise stated, the regressions used below are from Yang et al. (1989).

Assumptions ( 1 ) Sow liveweight at first conception is around 125 kg. (2) P2 backfat depth for sows at first conception is around 15 mm.

26

C.T. WHITTEMORE ET AL.

(3) The genotype used is an improved European hybrid type selected for lean tissue growth rate and prolificacy. (4) A cereal/soya bean meal/fish meal diet of 13.2 MJ DE and 162 g CP kg-1 fresh weight is offered throughout breeding life. Note: if the relationships given below are used with a diet of different DE, then the regression coefficients can be divided by 13.2 to give the appropriate coefficient per MJ DE. (5) Growth to maturity is at a rate conducive to efficiency of food use and of reproduction. Yang et al. ( 1989 ) found this to be in the region of maternal conception to conception liveweight gains of 35, 28, 23 and 18 kg for Parities l, 2, 3 and 4, respectively, although lower values may be possible. (6) The weaning to oestrus interval is influenced by sow body fatness according to the propositions given in Fig. 6: (a) primiparous sows weaning to oestrus interval (days)=29.3-2.03 P2 (mm)+0.0433 P22(mm); (b)]multiparous sows weaning to oestrus interval (days)=19.3-1.27 P22 (mm) +0.0295 P22 (mm). The P2 backfat depth at the time of weaning should therefore be maintained above 13 mm for primiparous sows and above 10 mm for multiparous sows. Weaning to oestrus interval is also influenced by litter size (weaning to oestrus interval (days) = 2.65 + 0.56 number of piglets in sucking litter).

Food requirement in pregnancy to increase maternal fatness and liveweight ( 1 ) Maternal fatness (P2) has to be increased in pregnancy (a) to supply the need for lipid catabolism in the forthcoming lactation and (b) to maintain adequate levels of P2 backfat at the time of weaning. (2) Maternal liveweight has to be increased in pregnancy (a) to supply the need for lipid and protein catabolism in the forthcoming lactation and (b) to allow maternal body tissue growth to maturity. ( 3 ) Change in P2 (mm) backfat depth in pregnancy = - 9.3 + 0.036 total food intake in pregnancy. (4) Change in liveweight (kg) in pregnancy = - 27.2 + 0.215 total food intake in pregnancy. Henry and Etienne (1978 ) derived similar equations based on daily DE intake which, with a dietary DE of 13.2 MJ kg- 1become Net change in liveweight (kg) in pregnancy = - 13.99 + 24.48 daily food intake (primiparous sows) or, = - 23.03 + 22.27 daily food intake (multiparOUS SOWS )

Using these equations, responses in P2 fatness and in maternal live weight to various levels of pregnancy food intake can be predicted. These equations represent efficiencies of conversion and may be taken to apply in circumstances other than the confines of the experiment in which they were measured,

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27

although the efficiency will, of necessity, include costs of environmental variables such as cold thermogenesis. The coefficients suggest 28 kg food to be required for a 1-mm increment of P2 backfat depth and 4.7 kg food for a lkg increment of maternal liveweight gain. The latter efficiency of food use in pregnancy (5 : 1 ) is familiar, while equivalent coefficients for pregnancy food intake of 0.042 (for P2) and 0.182 (for liveweight) were measured by Whittemore et al. (1988b).

Calculation of maternalfatness and liveweight change in 28-day lactation ( 1 ) Change in P2 ( m m ) backfat depth = - 0 . 2 8 3 - 0.265 P2 ( m m ) backfat depth at parturition + 0.037 total lactation food i n t a k e - 0.497 number of piglets sucking. (2) Change in maternal liveweight ( k g ) = - 3 . 8 - 0 . 1 5 0 maternal liveweight at parturition + 0.362 total lactation food i n t a k e - 3.33 number of piglets sucking. ( 3 ) Lactation food intake ( 28 day, kg) = 212 - 3.61 P2 (mm) backfat depth at parturition. (4) Sucking litter size = 6.5 + 0.02 maternal liveweight (kg) at parturition (from Whittemore et al., 1988b ). The first two multiple regression equations examine the gross consequences upon sow fat stores and liveweight of (a) the availability of those stores, (b) the nutrient supply from food, and (c) the lactational demand. Eastham et al. (1988) derived change in P2 (mm day-l ) backfat depth = - 0 . 4 0 + 0.049 daily lactation food intake change in maternal live body weight (kg day -1 ) - - - 1.7+0.343 daily lactation food intake. Equivalent equations of change in P2 (mm day-1 ) backfat depth = -0.41 + 0.056 daily lactation food intake change in maternal live body weight (kg day- l ) = _ 2.1 + 0.30 daily lactation food intake may be calculated from the data of Danielsen and Nielsen (1984). Harker ( 1986 ) presented similar relationships; the following are derived examples: change in P2 (mm day-1 ) backfat depth = - 0 . 4 2 + 0.057 daily lactation food intake change in maternal live body weight (kg day- 1 ) = _ _ 2.86 + 0.441 daily lactation food intake

28

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and for a 28-day lactation the equation of Henry and Etienne ( 1978 ) can be transformed to change in maternal live body weight (kg day -l ) = - 1.47 + 0.23 daily lactation food intake. These four latter data sets serve to confirm the regressions of Yang et al. (1989), but being more simplistic are less'flexible. Equations calculating food intake and litter size are useful indications of the magnitude of the effects, respectively, of fatness and weight at parturition. The constants, however, are likely to be highly environmentally dependent and would be unlikely to be appropriate for general use. Conversion factors could, however, be derived to adjust the constants for factors such as environmental temperature (see earlier), genotype and parity number. Harker (1986) related lactation food intake to change in weight or body fatness in pregnancy, the latter giving the best relationships Parity 1: lactation food intake (kg day-l)=6.87--0.21 P2 (mm) gain in pregnancy Parity 2: lactation food intake (kg day-~)=6.22-0.20 P2 (mm) gain in pregnancy.

Calculation of maternal fatness and live weight change in weaning to conception interval ( 1 ) Change in P2 (mm) backfat depth = 1.96- 0.219 P2 at weaning. (2) Change in maternal liveweight (kg) = 28.4-0.172 maternal liveweight at weaning. These equations are included for completeness; their influence on lifetime response is relatively trivial owing to the shortness of this interval.

Calculation of weight of piglets at birth and their subsequent growth to 28-day weaning Birth weight influences subsequent vigour and survival. The latter, expressed as percentage survival of total pigs born can be interpolated from Hall et al. (1984) as 55 W~3, where Wb is weight at birth (kg). (1) Piglet birth weight (kg)=0.43+0.0053 maternal liveweight (kg) at parturition, or (2) Piglet birth weight (kg) = 0.89 + 0.0015 total pregnancy food intake. If this relationship is expressed in terms of the mean daily intake of DE throughout pregnancy it becomes piglet birth weight (kg) = 0.89 + 0.0131 DE intake (MJ day-l). Vanschoubroek and van Spaendonck (1973) also presented a relationship based on DE intake

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29

piglet birth weight (kg) = 0.902 + 0.0231 DE intake ( MJ day- i ) _ 0.0003 DE intake22 (MJ d a y - 1) and Shearer and Adam ( 1973 ) gave similar relationships Parity 1 birth weight (kg) =0.702+0.0296 DE intake (MJ day -I ) - 0 . 0 0 0 4 DE intake22 (MJ day -z ) Parity 2 birth weight (kg) = 0.969 + 0.0115 DE intake ( MJ day- l ) Parity 3 birth weight (kg) =0.883+0.0122 DE intake (MJ day -1 ). The equations derived by Henry and Etienne ( 1978 ) were: Parity 1 birth weight (kg) = 1.140+0.0036 DE intake (MJ day -z ) other parities birth weight (kg) = 1.012 + 0.0088 DE intake ( MJ day- z) These sources give similar predicted birth weight to those of Yang et al. (1989). (3) Piglet growth rate (g day -z ) = 85+0.54 maternal liveweight (kg) at parturition. In the experiment of Yang et al. (1989) growth rates were disappointing for sucking piglets and this equation should be considered as pertaining to minimum expected response. A more appropriate regression may be adapted from Whittemore et al. (1988); piglet growth rate (kg day- ~) = 0.191 - 0.006 maternal P2 ( m m ) change in lactation - 0.0013 maternal liveweight change (kg) in lactation. Eastham et al. ( 1988 ) found, piglet growth rate to weaning at 28 days (kg per piglet d a y - i ) = 0.107 + 0.0089 daily lactation food intake. Likewise Mullan et al. (1989) present review data which indicate a constant of 0.125 and a regression coefficient of 0.010. In this latter case, while the slope appears firm across data sets the constant ranges from 0.108 to 0.148.

Calculation of protein needs Responses of sows to dietary protein level in pregnancy and lactation have been comprehensively reviewed by the three National Committees (ARC, 1981; SCA, 1987; NRC, 1988). Decisions regarding requirement in pregnancy relate to what, if any, protein need is identified for growth of maternal body in pregnancy, and for the replenishment of maternal stores following lactation depletion. The often quoted 180 g daily CP requirement in pregnancy (ARC, 198 l; originating from Elsley et al., 1966 ), satisfactory for the improved small-sized pigs of that era, now fails to address not only the above, but also the need to achieve adequate fat levels in the improved large-sized European hybrid sow which, during its reproductive life, continues to have a strong impulsion for maternal body growth. The need to achieve positive gains in maternal lipid stores necessitates prior satisfaction of maternal protein gains. Preferential partitioning of nutrients prejudices the deposition of fat in

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C.T. WHITTEMORE ET AL.

the absence of the deposition of protein in a normally growing animal; thus a strategy for positive fatty tissue change should also allow for positive protein tissue change. For lactation, ARC (1981 ) suggest 621-825 g CP daily depending upon litter size. But they also qualify their proposals for protein requirements for sows with the statement that the factorial method of estimating nutrient need is not particularly satisfactory with regard to allowances that may be needed for optimum fertility and regularity of breeding. By using the information on sow body chemical composition of Whittemore and Yang (1989), losses of maternal body protein and lipid in lactation may be calculated for the responses ofYang et al. (1989). Sows given, in their daily dietary allowance during lactation, 67.4 MJ DE and 827 g CP lost 71 g maternal body protein and 361 g maternal body lipid daily, while sows given 38.0 MJ DE and 466 g CP lost 257 g maternal body protein and 686 g maternal body lipid daily. Considerable losses of protein, as well as lipid, therefore occurred when sows were fed only 466 g crude protein daily, whereas losses of maternal body protein from sows fed 827 g crude protein daily were conservative. If it is assumed that catabolised body protein is used approximately twice as efficiently for purposes of milk synthesis as dietary crude protein, then in terms of dietary CP equivalent, the demand for the two treatments was 967 and 980 g CP daily. Although such interpretation of empirical trials must be guarded, it would appear that a lactational requirement in the region of 980 g of crude protein daily would be a reasonable supposition to draw from the data. It is further worth noting that the protein quality used in this experiment was high, the supplementary protein sources to a cereal-based diet being high quality soya bean meal and herring meal. Sows given less than their daily requirement of crude protein during lactation, and catabolising maternal body protein in consequence, will require to make good those losses, in addition to supplying the needs for growth itself, in the course of the next pregnancy. CONCLUSION

Deductive models require a view of growth to maturity, energy and protein metabolism for the processes of growth, maintenance, thermogenesis, pregnancy, and lactation, together with some view of the relationships between nutrition and litter size, and nutrition and weaning to conception interval. Empirical models avoid the need for factorisation and may depend upon regression relationships from field trials. Given the present level of knowledge, neither type of model is likely to provide adequately an estimate of nutritional requirement and a mixed format is more appropriate. Components for models to simulate responses of breeding sows to nutrient

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regime are available and adequate for the construction of a first generation of mixed deductive and empirical models. Nutrient requirements and recommended feeding allowances are best derived by use of such models. REFERENCES Agricultural Research Council, 1967. The Nutrient Requirements of Farm Livestock: No. 3 Pigs. HMSO, London, 278 pp. Agricultural Research Council, 1981. The Nutrient Requirements of Pigs. Commonwealth Agricultural Bureaux, Slough, 307 pp. Baidoo, S.K., Kirkwood, R.N. and Aherne, F.X., 1986. The influence of feeding level during lactation and the following pregnancy on the reproductive performance of sows. 67th Annual Feeders' Day Report, University of Alberta, Edmonton, Alta., pp. 59-61. Beyer, M., Hoffman, L., Schiemann, R., Jentsch, W., Burlacu, G., Iliescu, M., Machajew, E.C., Babinszky, L., Gundel, H., Lassota, L., Walach-Janiak, M and Zeman, L., 1988. Biological basics for the factorial derivation of the energy and protein requirements for pregnant and lactating sows and suckling piglets. Fifth International Symposium on Protein Metabolism and Nutrition. E.A.A.P. Publication No. 35 Wissenschaftliche Zeitschrift der Wilhelm-PieckUniversit~it Rostock, 37: 92-93. Black, J.L., Campbell, R.G., Williams, I.H., James, K.J. and Davies, G.T., 1986. Simulation of energy and amino acid utilisation in the pig. Res. Dev. Agric., 3: 121-145. Brierem, K. and Homb, T., 1972. Energy requirements for growth. In" W. Lenkeit, K. Breirem and E. Crasemann (Editors), Handbuch der Tieren~ihrung. Paul Parey, Hamburg, 2: 547584. Brooks, P.H., 1970. Short term nutritional effects on fecundity of sows and gilts. PhD Thesis, University of Nottingham. Brookes, P.H. and Cole, D.J.A., 1972. Studies in sow reproduction. I. The effect of nutrition between weaning and remating on the reproductive performance of primiparous sows. Anim. Prod., 15: 259-264. Burlacu, G., Iliescu, M. and Cfirfimidh, P., 1983. Efficiency of food utilisation by pregnant and lactating sows. 1. The influence of diets with different concentrations of energy on pregnancy and lactation. Arch. Tierern~ih., 33: 23-45. Cart, J.R., Boorman, K.N. and Cole, D.J.A., 1977. Nitrogen retention in the pig. Br. J. Nutr., 37: 143-155. Close, W.H., 1980. The significance of the environment for energy utilisation in the pig. Proc. Nutr. Soc., 39: 169-175. Close, W.H., 1981. The climatic requirements of the pig. In: J.A. Clark (Editor), Environmental Aspects of Housing for Animal Production. Butterworths, London, pp. 149-166. Close, W.H., 1987. Some conclusions of the AFRC Working Party on the energy requirements of sows and boars. Anim. Prod., 44: 464. Close, W.H. and Mount, L.E., 1978. The effects of plane of nutrition and environmental temperature on the energy metabolism of the growing pig. I. Heat loss and critical temperature. Br. J. Nutr., 40:413-42 I. Close, W.H., Noblet, J. and Heavens, R.P., 1985. Studies on the energy metabolism of the pregnant sow. 2. The partition and utilisation of metabolisable energy intake in pregnant and non-pregnant animals. Br. J. Nutr., 53: 267-279. Cox, N.M., Britt, H.H., Armstrong, W.D. and Alhusen, H.D., 1983. Effect of feeding fat and altering weaning schedule on rebreeding in primiparous sows. J. Anim. Sci., 56:21-29. Danielsen, N.V. and Nielsen, H.E., 1984. The influence of different feeding levels on the performance of lactating sows. Proceedings of the 35th Meeting of the Eu. Ass. An. Pr., The Hague.

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Stant, E.G., Martin, T.G., Judge, M.D. and Harrington, R.B., 1968. Physical separation and chemical analysis of the porcine carcass at 23, 46, 68 and 91 kilograms liveweight. J. Anim. Sci., 27: 636-644. Stranks, M.H., Cooke, B.C., Fairbairn, C.B., Fowler, N.G., Kirby, P.S., McCracken, K.J., Morgan, C.A., Palmer, F.G. and Peers, D.G., 1988. Nutrient allowances for growing pigs. Res. Dev. Agric., 5: 71-88. Sugahura, M., Baker, D.H., Harmon, B.G. and Jensen, A.H., 1970. Effect of ambient temperature on performance and carcass development in young swine. J. Anim. Sci., 31: 59-66. Tullis, J.B., 1982. Protein growth in pigs. PhD Thesis, University of Edinburgh, 183 pp. Vanschoubroek, F. and van Spaendonck, R., 1973. FaktorieUer Aufbau des Energiebedarfs tragende Zuchtsauen. Z. Tierphysiol. Tierernaehr. Futtermittelkd., 31: 1-21. Verstegen, M.W.A., Close, W.H., Start, I.B. and Mount, L.E., 1973. The effects of environmental temperature and plane of nutrition on heat loss, energy retention and deposition of protein and fat in groups of growing pigs. Br. J. Nutr., 30: 21-35. Verstegen, M.W.A., Mesu, J., van Kempen, G.J.M. and Geerse, C., 1985. Energy balances of lactating sows in relation to feeding level and stage of lactation. J. Anim. Sci., 60:731-740. Verstegen, M.W.A., Verhagen, J.M.F. and den Hartog, L.A., 1987. Energy requirements of pigs during pregnancy: a review. Livest. Prod. Sci., 16: 75-89. Whittemore, C.T., 1967. Factors influencing within-litter variation in the performance of sucking pigs. Honours Thesis, University of Newcastle upon Tyne, 109 pp. Whittemore, C.T., 1983. Development of recommended energy and protein allowances for growing pigs. Agric. Syst., 11: 159-186. Whittemore, C.T., 1987. Elements of Pig Science. Longman, Harlow, 181 pp. Whittemore, C.T. and Elsley, F.W.H., 1976. Practical Pig Nutrition. Farming Press, Ipswich, 190 pp. Whittemore, C.T. and Fawcett, R.H., 1974. Model responses of the growing pig to the dietary intake of energy and protein. Anim. Prod., 19:221-231. Whittemore, C.T. and Fawcett, R.H., 1976. Theoretical aspects of a flexible model to simulate protein and lipid growth in pigs. Anim. Prod., 22: 87-96. Whittemore, C.T. and Fraser, D., 1974. The nursing and suckling behaviour of pigs. II. Vocalisation of the sow in relation to suckling behaviour and milk ejection. Br. Vet. J., 130: 346356. Whittemore, C.T. and Yang, H., 1989. Physical and chemical composition of the body of breeding sows with differing body subcutaneous fat depth at parturition, differing nutritional during lactation and differing litter size. Anim. Prod., 48:203-212. Whittemore, C.T., Aumaitre, A. and Williams, I., 1978. Growth of body components in young weaned pigs. J. Agric. Sci., 91: 681-692. Whittemore, C.T., Taylor, H.M., Henderson, R., Wood, J.D. and Brock, D.C., 1981. Chemical and dissected composition changes in weaned piglets. Anim. Prod., 32:203-210. Whittemore, C.T., Taylor, A.G., Hillyer, G.M., Wilson, D. and Stamataris, C., 1984. Influence of body fat stores on reproductive performance of sows. Anim. Prod., 38: 527. Whittemore, C.T., Tullis, J.B. and Emmans, G.C., 1988a. Protein growth in pigs. Anim. Prod., 46: 437-445. Whittemore, C.T., Smith, W.C. and Phillips, P., 1988b. Fatness, live weight and performance responses of sows to food level in pregnancy. Anim. Prod., 47:123-130. Williams, I.H., Close, W.H. and Cole, D.J.A., 1985. Strategies for sow nutrition: predicting the response of pregnant animals to protein and energy intake. In: W. Haresign and D.J.A. Cole (Editors), Recent Advances in Animal Nutrition, Butterworths, London, pp. 133-147. Yang, H., Eastham, P.R., Phillips, P. and Whittemore, C.T., 1989. Reproductive performance,

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body weight and body condition of breeding sows with differing body fatness at parturition, differing nutrition during lactation, and differing litter size. Anim. Prod., 48: 181-201. Young, L.G. and King, G.J., 1987. Gestation energy levels for sows. Ontario Swine Res. Rev., pp. 24-31. RESUME C.T. Whittemore et C.A. Morgan, 1990. Composantes d'un modrle pour la drtermination des besoins 6nergrtiques et azotrs des truies reproductrices: une revue. Livest. Prod. Sci., 26: 137 (en anglais). Les donnres factorielles et empiriques provenant des travaux rrcents rralisrs dans divers contres de recherches fournissent une somme importante d'informations grice auxquelles il est possible de construire des modrles de rrponse aux apports nutritionnels. Partant d'une masse protrique initiale (Pt) de l'ordre de 16,6 kg, les truies reproductrices doivent par la suite accumulet environ 1 l, 1, 7,8, 4,5 et 2,4 kg de protrines/paritr. Une masse lipidique d'environ 1,5 fois la masse protrique est compatible avec des performances de reproduction satisfaisantes, alors que l'efficacit6 de la reproduction est compromise lorsque la masse de lipides de la truie devient infrrieure h la masse protrique. Les besoins 6nergrtiques pour les gains de protrines et de lipides matemels seraient de l'ordre de 50 MJ ME kg-l, alors que les besoins en acides aminrs peuvent ~tre modrlisrs h partir de la connaissance de la digestibilit6 ilrale et de l'efficacit6 de leur utilisation aprrs absorption. Les besoins 6nergrtiques d'entretien sont probablement de l'ordre de 2,51 Pt °'65 MJ EM j o u r - ~, alors que les besoins en protrines pour l'entretien peuvent 6tre estimgs ~ 0,004 Pt. II faut ajouter les besoins en 6nergie et en protrines de l'utrrus gravide, des tissus mammaires en drveloppement et surtout de lactation, ces derniers drpendant ~ la fois du potentiel de production et de la demande effective de la portre. L'intervalle sevrage-oestrus est 6troitement li6/l l'rtat d'engraissement, notamment chez les truies primipares; intervalle sevrage-oestrus (jours) = 2 9 , 3 - 2,03 P2 + 0,0433 P22, oil P2 est l'rpaisseur de lard en mm mesurre/l 65 mm de la ligne mrdiane au niveau de la derni~re cbte. La variation de l'rpaisseur de lard au niveau P2 pendant la gestation peut ~tre estimre h 0,036 ×consommation totale d'aliment en gestation - 9.3 et, pendant la lactation,/l 0,037 × consommation totale (28 j ours) d'aliment en l a c t a t i o n - 0,497 X hombre de porcelets a l l a i t r s - 0,265 × P2/l la p a r t u r i t i o n - 0,283. La taille de la portre et le poids individuel des procelets/l la naissance sont faiblement mais positivement corrrlrs avec le poids vif des truies. De fagon globale, on peut estimer le niveau optimal d'apports nutritionnels et prrdire les consrquences d'un drfaut d'apports par rapport aux besoins sur la truie elle-m~me et sur sa productivitr. KURZFASSUNG Whittemore, C.T. und Morgan, C.A., 1990. Modell-Bestandteile f'tir die Bestimmung des Energie- und Proteinbedarfs von Zuchtsauen: eine Obersicht. Livest. Prod. Sci., 2 6 : 1 - 3 7 (auf englisch). Faktoriell und empirisch ermittelte Daten aus der Arbeit in verschiedenen Forschungszentren stellen eine Quelle f'tir quantitative Information dar, aus der Modelle f'tir Niihrstoff-Wirkungen erstellt werden krnnen. Bei einer anf~inglichen Proteinmasse (Pt) von etwa 16,6 kg miissen Zuchtsauen in der Folge pro Tr~ichtigkeit etwa 11,1, 7,8, 4,5 und 2,4 kg Protein einlagem. Fiir eine gute Reproduktionsleistung mull die Fettmasse etwa das 1,5 fache der Proteinmasse betragen, w~ihrend die Reproduktionsleistung beeintriichtigt wird, sofern die Fettmasse in der Zuchtsau unter die Proteinmasse abf~illt. Der Energiebedarf f'tir maternalen Zuwachs von Protein und Fett liegt bei etwa 5 MJ ME pro kg, w~ihrend der Bedarfan Aminos~iuren modellar-

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tig abgeleitet werden kann aus ilealer Verdaulichkeit und Effizienz der postabsorptiven Verwertung. Der Erhaltungsbedarf ffir Energie liegt etwa in der Gegend von 2,51 Pt °,6~ MJ ME pro Tag, w~ihrend der Erhaltungsbedarf f'tir Protein als 0.004 Pt eingesch~itzt wird. Dazu addiert werden miissen Energie- und Proteinbedarf ftir graviden Uterus, entwickelnde Ges~iugegewebe und ganz besonders Laktation, wobei die letztere eine Funktion sowohl der potentiellen Versorgung als auch des Bedarfes ftir den eingetretenen Wurf ist. Der Abstand Absetzen und Oestrus ist eng korreliert mit dem Verfettungsrad, insbesondere bei Ersttragenden Sauen; Tage zwischen Absetzen und Oestrus = 2 9 , 3 - 2,03 P2 + 0,0433 P22, wobei P2 die Fettdicke (in ram) in H6he der letzten Rippe 65 mm vonder Mittellinie ist. Ver~nderungen in P2 w[ihrend der Tragezeit k6nhen eingescha~tzt werden als 0,036×gesamte Futteraufnahme w~ihrend der Tragezeit-9,3, w~hrend Ver~nderungen in dem Fettdicke P2 w~ihrend der Laktation gesch~itzt werden als 0,037 × Futteraufnahme w~ihrend der gesamten Laktation (28 Tage) - 0,497 X Zahl der saugenden Ferkel-0,265 X P2 Fettdicke w~ihrend der Geburt-0,283. Wurfgr6Be und individuelles Ferkelgewicht sind w6chentlich, aber positiv, korreliert mit dem maternalen Lebendgewicht. Insgesamt kann die optimale H6he der N~ihrstoff-Versorgung mit dem Futter abgesch~itzt wetden, ebenso wie die Konsequenzen eines Verfehlens der Bedarfsdeckung in Bezug auf Zuchtsau und ihre Produktivit~it vorhergesagt werden k6nnen.