Abstract:
Animal Production in Australia THE RESPONSE OF DAILY LIVEWEIGHT GAIN TO DIETARY LYSINE AND LIVE WEIGHT IN GROWING PIGS L.R. GILES*, E. BELINDA DETTMANN* and E.S. BATTERHAM* SUMMARY Response surface functions were developed for average daily liveweight gain (DLG) as a function of dietary lysine percent and live weight. Measurements were made over 10 kg liveweight ranges on a total of 128 pigs of both sexes fed two feed levels (ad libitum and restricted) from 20 to 80 kg live weight. The dietary lysine percent which produced maximum DLG varied with live weight for each feed level and sex. Ad libitum-fed males had a maximum DLG response to at least 1.00% lysine between 20-40 kg live weight declining to 0.79% at 70-80 kg. Ad libitumfed females had a maximum DLG response at 0.88 % lysine up to 40 kg live weight which declined to less than 0.56% by 80 kg. However, restrictively-fed males and females responded to at least 1.00% lysine up to 50 kg and thereafter the maximum response for both sexes declined to 0.82% lysine by 70-80 kg. INTRODUCTION There is limited information on the lysine and energy requirements of growing pigs under Australian conditions and much reliance is placed on overseas estimates. Lysine requirements derived in Western Europe (Agricultural Research Council (ARC) 1967; Cole 1980) are higher than those of the National Research Council (NRC) (1979). These differences may reflect the lower feed levels and the greater emphasis-on carcass quality in Western Europe. They may also reflect in part an over-estimation of requirements as a result of inefficient utilization of the synthetic lysine used to determine lysine responses under restricted feeding conditions (Batterham and Murison 1981). The objective of this study was to determine the daily liveweight gain (DLG) of growing pigs in response to graded levels of synthetic lysine when fed either restricted or ad Zibitm energy intakes under conditions that ensured full utilization of added synthetic amino acids. The effect of reducing the level of dietary crude protein and lysine by 20 % after 50 kg live weight (ARC 1967) was also investigated. A response surface approach was developed for DLG as a function of dietary lysine and live weight. MATERIALS AND METHODS A 4x2~2~2 factorial experiment, involving 128 Large White pigs was conducted to determine the effect of lysine level (0.7, 0.8, 0.9 and l-O%, air dry basis) energy intake (restricted or ad Zibitm), sex (entire males or females) and a 20% reduction in lysine levels (0.56, 0.64, 0.72 and 0.80%) during the later growth phase (SO-85 kg). The basal diet of wheat and soyabean meal, adequately fortified with minerals and vitamins, was formulated to contain 17.4% crude protein (N x 6.25), 13.9 MJ digestible energy (DE)/kg and 0.7% lysine. Free lysine was added to this diet to provide the respective treatment levels. Supplements of L-threonine and DL-methionine were added to maintain the pattern of amino acids, relative to lysine, as recommended by Cole (1979). To test the effect of a 20% reduction in amino acid levels during the later growth phase a second series of diets was * N.S.W. Department of Agriculture, Agricultural Research Centre, Wollongbar, N.S.W. 2480. 553 Animal Production in Australia formulated, in a similar manner, to contain 14.4% crude protein, 13.9 MJ DE/kg and lysine content from 0.56 to 0.80%. The diets were allotted to the pigs at 20 kg live weight. The pigs were fed at three hourly intervals to ensure full utilization of the added free amino acids (Batterham and Murison 1981). The restrictively-fed pigs were offered 13.9 MJ DE/day at 20 kg live weight, increasing by 1.39 MJ/d/5 kg liveweight increment, to a maximum of 29.2 MJ/d at 75 kg live weight and thereafter. Live weight was recorded weekly and all pigs were slaughtered at 85 kg live weight. The days on which each pig successively reached weights of 30, 40, 50, 60, 70 and 80 kg were estimated by linear interpolation between adjacent weekly weights. DLG was then calculated for each animal over each 10 kg liveweight range from 20 to 80 kg. Response surface functions were developed for DLG as a function of dietary lysine %, lysine % squared, live weight, square-root of live weight and all two-way interactions for each sex by feed level. The main effects were included in each prediction equation while the interaction terms were chosen to minimise the residual standard deviation. Each DLG function was differentiated with respect to lysine and the differentials were equated to zero. The lysine percent which produced maximum DLG was calculated from each new equation for various live weights. RESULTS Feed intake Ad Zibitwn intake DE/We-75/d) for males and declined to 2.7 M between females and declined from 70-80 kg. increased up to 3.4 M (where M = Maintenance = 0.5 MJ 3.6 M for females between 30-40 kg live weight and then 70-80 kg. Restricted intake was similar for males and 2.4 M between 20-30 kg live weight to 2.2 M between Response curves The prediction equations of DLG chosen for each sex by feed level combination are presented in Table 1. Each of these response surface functions explained a highly significant (P < -01) proportion of the total variation in DLG. DLG response to lysine % was curvilinear and varied with live weight. both sexes, precision of the prediction equations was less (reduced R2 and increased R.s.D.) for ad Zibitwn intakes. For The dietary lysine percentages which produced maximum DLG for each sex by feed level combination at live weights between 20 and 80 kg are presented in Table 2. Maximum DLG response for ad Zibitwn-fed males declined from at least 1.0% lysine at 25 kg to 0.79% at 75 kg. However maximum DLG response for. ad Zibitmfed females declined from 0.88% lysine at 35 kg to less than 0.56%.at 75 kg. Maximum DLG response for restricted intakes was almost identical for both sexes. In this case lysine percent declined from at least 1.0% at 25 kg live weight to 0.82% at 75 kg. 554 Animal Production in Australia TABLE 1 Regression coefficients of average daily liveweight gain (kg/d) as a function of dietary lysine percent and live weight for two feed levels (AL - ad libitum and R- restricted) and sexes (M - male and F - female) TABLE 2 Dietary lysine percent which produced maximum daily liveweight gain for two feed levels (AL - ad Zibitm and R - restricted) and sexes (M - male and F - female) with increasing live weight 555 Animal Production in Australia DISCUSSION In this experiment the dietary lysine percentages which produced maximum DLG were greater than those recommended by the ARC (1967) or the NRC (1979) but were similar to Cole's (1980) estimates. These higher values may reflect the increased emphasis on genetic selection for lean meat deposition which has been practised in western Europe and Australia in recent years. When feed intake was restricted in this experiment the DLG response to dietary lysine was the same for each sex. However under ad Zibitwn feeding, female pigs needed less lysine than males for maximum growth. To take advantage of this difference with fully-fed pigs would require separate diets and penning for each sex. The dietary lysine at maximum DLG declined by approximately 20% as the animals grew from 20 to 80 kg live weight. This result is in line with the ARC (1967) recommendation that grower and finisher pigs be fed different levels of lysine. However the decline was found to be continuous and did not occur arbitrarily at 50 kg live weight as the ARC (1967) recommendations imply. In empirical growth studies it is usually necessary to measure responses to amino acids over wide liveweight ranges because of the variation in liveweight gain over time in individual animals. As a result there has been interest in using alternative techniques that are suitable over narrow liveweight ranges, e.g. urinary nitrogen exc$etion (Fuller et al. 1979) and blood urea levels (Taylor et - al. 1981). However the approach described here allows estimates of maximum lysine response to vary with live weight. In addition this technique has produced estimates of maximum lysine response with small errors and promises to be a useful analytical tool in this area of research. ACKNOWLEDGEMENTS The authors wish to thank Messrs. N.R. Thompson, A.W. Davis, H.M. Essery and E.R. Layton for management of the pigs and skilled technical assistance; and Mrs. L. Wilkins for assistance with the statistical analysis. REFERENCES AGRICULTURAL RESEARCH COUNCIL. (1967). 'The Nutrient Requirements of Farm (Agricultural Research Council: London.) Livestock. No. 3, Pigs', p. 130. BATTERHAM, E.S., and MURISON, R.D. (1981). Br. J. Nutr. 5: 87. COLE, D.J.A. (1979). 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