Determining the threonine requirement of the high-producing lactating sow. D.R. Cooper, J.F. Patience, R.T. Zijlstra and M.

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1 66 Determining the threonine requirement of the high-producing lactating sow D.R. Cooper, J.F. Patience, R.T. Zijlstra and M. Rademacher Introduction There are two steps in the design of a feeding strategy. The first is to set reproductive targets including the amount of maternal weight gain for sows of differing parities and the number of piglets a sow should nurse during lactation. The second step is to set nutrient requirements to meet these specified targets. Models have been developed for sow nutrient requirements in gestation (Whittemore and Morgan, 1990; Whittemore, 1998). These models attempt to partition nutrient requirements into three components (maintenance, growth of the conceptus and reproductive tissue and conceptus growth). These models have lead to the development of the factorial approach to defining nutrient requirements in gestating sows. Improved production practices are needed to better suit the capabilities of new high producing genotypes to ensure that their genetic potential is being realised. In particular, nutrient requirements of sows need to be re-defined. Failure to meet the amino acid requirements of the sow in lactation can lead to decreased milk production and litter weaning weights (King et al., 1993), and increased reproductive performance (King and Williams, 1984). Threonine is often the second limiting amino acid in most practical swine diets; however, limited research has been done on the threonine requirement of the sow in lactation. Overall, both gestation and lactation phases within a sow s reproductive life need to be properly managed. By optimising energy intake in gestation and meeting nutrient requirements for sows in lactation, overall reproductive performance will be maximised. Objectives 1. To evaluate two levels of amino acids in gestation on sow productivity. 2. To evaluate the factorial approach to defining energy requirements in pregnant sows. 3. To determine the threonine requirement of the high-producing sow in lactation. Materials and methods At mating, 419 PIC sows were assigned randomly within parities 1, 2 and 3+ to a gestation diet containing either 0.44 (low lysine) or 0.55% (high lysine) total lysine and 3100 kcal DE/ kg; other indispensable amino acids were adjusted to lysine based on ideal protein ratios. Daily feed allowance in gestation was determined using the maintenance requirement proposed by Close et al. (1985) of 110 kcal DE/kg BW 0.75, the target weight gains proposed by Verstegen and den Hartog (1989) and the energy required for protein and lipid gain reported by Pettigrew and Yang (1997). Feed allowances were calculated using BW at mating and the target BW gains set for each parity. Lactation diets were formulated to contain 0.80 or 1.06% total lysine with threonine set at 37.5% of lysine and added at increments of 0.05% to maximum total threonine levels of 0.65 and 0.70% for the 0.80 and 1/06% lysine diets, respectively (Table 1 and 2). One positive control diet at each lysine level, containing barley, wheat and soybean meal, as well as synthetic L-valine, was fed to determine if performance on the semisynthetic diets was equivalent to sows fed a more commercially typical formulation. Sow BW was measured at days 1, and weaning in lactation. Average daily feed intake was measured for periods of d 0-7, 8-11, 12-15, and 20-weaning. Litter size was adjusted to a minimum of 11 piglets within 48 hours after farrowing and the litters were weighed at birth, days 7, 11, 15, 19 and weaning. Blood

2 67 was collected on days 10 and 18 of lactation for plasma urea nitrogen analysis. Weaning to estrus interval and subsequent litter size were recorded. Results Gestation Sows gained 49.6 ± 0.5 kg in gestation and 4.8 ± 0.6 kg in lactation. Sows farrowed 12.0 ± 0.1 piglets and 11.2 ± 0.1 live born piglets per litter. Gestation lysine level did not affect gestation body weight gain, regardless of parity (P > 0.10). Gestation BW gain was affected by parity (P < 0.05) as sows of parity 1 and 2 were actually fed to gain more weight than sows of parity 3 and higher (P < 0.05; Figure 1). Gestation weight gain was correlated negatively with lactation weight changes (P < 0.05). A treatment x parity interaction for backfat was found in lactation (P < 0.05), parity 2 sows on the HL gestation diet lost more backfat in lactation than parity 2 sows on the LL gestation diet. The total number of pigs born and the pigs born alive per litter were not affected by gestation lysine level (P > 0.10), but were affected by parity with parity 1 sows farrowing fewer piglets (P < 0.05). Gestation weight gain and the number and weight of piglets born and born alive were correlated positively (r = 0.41, 0.40, 0.51, 0.51 for piglets born per litter, piglets born alive per litter, total weight of the litter and total weight of the piglets born alive, respectively; P < 0.05). Every kg BW gain in gestation corresponded to an extra 0.14 piglets born and 0.04 piglets born alive. This resulted in 50 g additional litter weight at birth. Sows gained an average of 10.6 kg above the target total gestation BW gain. It was clear that this model over-predicted DE allowance for sows in gestation, therefore, performance data for the sows was entered into the NRC (1998) model. The actual number of piglets farrowed was put into the NRC (1998) model; a component not entered into the original model that was used. Comparisons between the predicted BW gain and the actual BW gain were then made. The deviation between the predicted and actual BW gains was then organized by parity, BW at breeding, total number of piglets born and the total weight of the litter born (Figures 1 and 2). The deviations between predicted and actual gains (NRC prediction Actual BW gains) decreased with increased parity and initial BW at breeding until the 5 th parity and a BW range of kg, where it then increased. NRC (1998) obtained the closest estimate of BW gain in gestation for sows with litters larger than 11 piglets and litters weighing between kg at birth. Lactation Sow ADFI exceeded expectation, averaging 6.9, 7.4 and 7.2 kg/d for parity 1, 2 and 3+ sows, respectively. Sows gained an average of 4.8 kg in lactation and body weight gain was maximized at 0.54% total threonine (quadratic; P <.05; Figure 3). Plasma urea nitrogen levels were minimized at 0.54% total threonine (quadratic; P <.05; Figure 4). Average piglet weight at weaning (5.6, 6.2 and 5.8 kg for parity 1, 2 and 3+, respectively) and litter weight gain (2.49, 2.53 and 2.44 kg/d for parity 1, 2 and 3+, respectively) were maximized at 0.53% total threonine (Figure 5). The subsequent total piglets born (mean = 12.3) and the subsequent born alive (mean = 11.3) were not affected by threonine treatment (P >.10). No difference in ADFI, BW changes and litter growth were found between the experimental and positive control diets (P > 0.10). The lack of differences in performance indicates that high levels of synthetic amino acids in the lactation diets did not restrict performance. Discussion Feeding sows to meet and not exceed nutrient requirements will lead to increased efficiency and sustainability, as well as lower costs. This study demonstrated that total lysine intakes greater than 10.6 g Tlys/d (8.3 g Dlys/d) did not improve sow productivity, indicating that the NRC (1988) recommended lysine requirements met to needs of these sows for maximum productivity.

3 68 This study also demonstrated the complexity of predicting daily energy allowances for sows in gestation. Predicting daily DE allowances that will maximise sow and litter performance is possible with sows between parity 3 and 5. Too much variation existed in younger and older parity sows to predict sow performance with any accuracy; therefore, there is still a need for more research in this area. The size and weight of the litter at farrowing is important in determining the BW gain of the sow in gestation. Therefore, using the actual litter size and sow BW within a sow herd is desirable when using the factorial approach to determine daily feed allowance. To minimise sow body tissue breakdown, the threonine requirement was found to be 37, 40 and 39 g total threonine/d (29, 31 and 30 g Dthr/d) for parity 1, 2 and 3+ sows, respectively. To maximise litter growth, the threonine requirement was found to be 37, 39 and 38 g Tthr/d (28, 30 and 30 g Dthr/d) for parity 1, 2 and 3+ sows, respectively. The maintenance requirement for threonine in the sow is 41 mg Tthr/kg BW 0.75 (Pettigrew, 1993). The threonine requirement for litter growth in this study was 14.3 g Tthr/kg litter growth. Using these requirements for maintenance and litter growth, pork producers can calculate the threonine requirement of lactating sows on their farms. References Close, W.H., J. Noblet and R.P. Heavens 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: King, R.H. and I.H. Williams The effect of nutrition on the reproductive performance of first-litter sows. 1. Feeding level during lactation, and between weaning and mating. Anim. Prod. 38: King, R.H., M.S. Toner, H. Dove, C.S. Atwood, and W.G. Brown The response of first-litter sows to dietary protein level during lactation. J. Anim. Sci. 71: Pettigrew, J. E Amino acid nutrition of gestating and lactating sow. Biokyowa Technical Review - 5. Nutri-Quest Inc. St. Louis, MO. p 11. Pettigrew, J.E. and H. Yang Protein nutrition of gestating sows. J. Anim. Sci. 75: Verstegen, M.W.A. and L.A. den Hartog Nutrition of sows in relation to environment. Pig News Info. 10: Whittemore, C.T Energy and protein requirements for maintenance, growth and reproduction. In: The Science and Practice of Pig Production. Blackwell Science, Cambridge. pp Whittemore, C.T. and C.A. Morgan Model components for the determination of energy and protein requirements for breeding sows. Livest. Prod. Sci. 26:1-39.

4 69 Table 1. Ingredient composition of basal lactation diets. Ingredient 80% lysine,.30% threonine b 1.06% lysine,.40% threonine c.80% lysine positive control 1.06% lysine positive control Wheat Hulless barley Soybean meal (44% CP) Corn starch Beet pulp Oat hulls Canola oil Vitamin premix d Mineral premix e Dicalcium phosphate Limestone Salt Choline chloride Sodium bicarbonate Potassium carbonate lysine-hcl L-valine L-leucine L-isoleucine L-phenylalanine L-histidine DL-methionine L-tryptophan deb (meq/kg) a based on total calculated lysine and threonine values b Threonine was added at.05% increments to the following six diets to a total of.65% in the last diet at the expense of corn starch. c Threonine was added at.05% increments in the following seven diets to a total of.70% in the last diet at the expense of corn starch. d Provided the following per kg of diet: vitamin A, 82,500 IU; vitamin D 3, 825 IU; vitamin E, 40 IU; menadione, 4 mg; thiamine, 1 mg; riboflavin, 5 mg; d-pantothenic acid, 15 mg; niacin, 35 mg; vitamin B 12,.025 mg; d-biotin,.2 mg; folic acid, 2 mg. e Provided the following per kg of premix: zinc, 100 mg; iron, 80 mg; manganese, 25 mg; copper, 50 mg; iodine,.5 mg; selenium,.1 mg.

5 70 Table 2. Nutrient composition of lactation diets, as fed basis Nutrient.80% lysine,.30% threonine a 1.06% lysine,.80% lysine.40% threonine a positive control a 1.06% lysine positive control a Calculated analyses DE Mcal/kg CP, % Lysine Total, % Apparent digestible, % Threonine Total, % Apparent digestible, % Methionine Total, % Apparent digestible, % Tryptophan Total, % Apparent digestible, % Ca, % Total P, % Nutrients, analysed DE (Mcal/kg) CP, % Lysine Total, % Apparent digestible, % Threonine Total, % Apparent digestible, % Methionine Total, % Apparent digestible, % a based on total calculated lysine and threonine values.

6 71 BW change, kg Parity Figure 1: Deviation between predicted and actual BW gain by parity NRC predicted-actual BW change No. piglets born Figure 2: Deviation between predicted and actual BW gain by number of piglets born Sow BW gain (kg) Threonine Level (%) PUN (mmol/l) Threonine Level (%) Figure 3. Effect of dietary total threonine level (%) on sow BW changes in lactation (kg). Figure 4. Effect of dietary total threonine level (%) on plasma urea nitrogen levels (mmol/l) in lactation Total litter gain (kg) Threonine Level (%) Figure 3. Effect of dietary total threonine level (%) on total litter gain (kg) in lactation.