Adrián Pichardo, Miguel Cervantes-Ramírez, Manuel Cuca, José L. Figueroa, Alfonso B. Araiza,

 Noemí Torrentera and Maximiliano Cervantes

Adrián Pichardo González. Agricultural Engineer, Universidad Autónoma de Chapingo, México. M.Sc. in Animal Production, Colegio de Postgraduados, México. Nutrition Specialist, ALPURA, México.

Miguel Cervantes-Ramírez. Zoothecnical Engineer. Ph.D in Ruminal Nutrition, University of Kentucky, USA. Professor, Instituto de Ciencias Agrícolas, Universidad Autónoma de Baja California, Mexicali, Baja California, México (ICA-UABC). Address: Lago Reindeer # 933, Jardines del Lago, Mexicali, B.C., México. e-mail: Miguel_Cervantes@uabc.mx

Manuel Cuca García. Agricultural Engineer. Ph.D. in Animal Nutrition, University of Wisconsin, USA. Professor, Colegio de Postgraduados, Montecillos, México.

José L. Figueroa Velasco. Agricultural Engineer. Ph.D. in Animal Nutrition, University of Nebraska, USA. Researcher, Colegio de Postgraduados, Montecillos, México.

Alfonso B. Araiza Piña. Agricultural Engineer, Universidad de Sonora, México. M.Sc. in Animal Production Sciences, ICA-UABC.

Noemí Torrentera Olivera. Food Engineer and Master in Meat Sciences, Universidad Autónoma Metropolitana, México. Researcher, ICA-UABC).

Summary

Four experiments involving 136 crossbred (Landrace-Hampshire-Duroc) pigs were conducted to determine the order of the first three limiting amino acids (LAA) in wheat for growing and finishing pigs. Treatments consisted in additions of lysine, threonine and/or methionine to adjusted basal and control diets. In Exp. 1, lysine increased daily gain (ADG), intake of feed (FI), lysine (LI), threonine (TI) and methionine (MI), and improved feed conversion (F/G). Additional threonine increased ADG and TI, and improved F/G. Methionine increased MI, but did not affect ADG or F/G. In Exp. 2, threonine increased ADG and TI, and improved F/G. Inclusion of methionine tended to decrease ADG and depressed F/G. Pigs fed lysine-threonine added and control diets showed no differences in ADG, FI or F/G, although control fed pigs had higher TI and MI. In Exp. 3, threonine alone did not affect ADG or F/G, but combined with methionine increased ADG and improved FG. There were no differences in ADG and F/G between control or lysine-threonine added diets. In Exp. 4, threonine tended to increase ADG and improved F/G while methionine reduced ADG. Addition of threonine plus methionine increased ADG, but did not affect FI or F/G. These data indicate that, in wheat, lysine and threonine are the first and second LAA for growing and finishing pigs. Methionine alone does not limit growth in pigs fed wheat-based diets, but appears to enhance the threonine response in finishing pigs. Lysine and threonine can replace soybean meal in wheat-based diets for growing-finishing pigs.

Resumen

Se realizaron cuatro experimentos con 136 cerdos cruzados (Landrace-Hampshire-Duroc) para determinar el orden de los tres primeros aminoácidos limitantes (AAL) en trigo para cerdos en crecimiento y finalización. Los tratamientos consistieron en adiciones de lisina, treonina y/o metionina a dietas base y en una dieta testigo. En el Exp. 1, lisina incrementó la ganancia diaria de peso (GDP), consumo de alimento (CDA), lisina (CDL), treonina (CDT) y metionina (CDM), y mejoró la conversión alimenticia (C/G). La adición de treonina incrementó GDP y CDT, y mejoró C/G. Metionina incrementó el CDM, pero no afectó GDP o C/G. En el Exp. 2, treonina incrementó GDP y CDT, e incrementó C/G. La inclusión de metionina tendió a reducir GDP y a deprimir C/G. No hubo diferencias en GDP, CDA o C/G entre los cerdos bajo dieta base con lisina y treonina o dieta testigo; aunque los testigos tuvieron mayor CDT y CDM. En el Exp. 3, treonina sola no afectó GDP o C/G, pero combinada con metionina incrementó GDP y mejoró C/G. No hubo diferencias en GDP y C/G entre las dietas testigo y la adicionada con lisina y treonina. En el Exp. 4, treonina tendió a incrementar GDP y a mejorar C/G, mientras que metionina redujo GDP. La adición de treonina y metionina incrementó GDP, pero no afectó CDA ni C/G. Estos datos indican que, en trigo, lisina y treonina son el primero y segundo AAL para cerdos en crecimiento y finalización. Metionina sola no limita el crecimiento de cerdos en dietas con base trigo, pero parece potenciar la respuesta de treonina en cerdos de finalización. Lisina y treonina pueden sustituir la pasta de soya en dietas con base trigo para cerdos en crecimiento y finalización.

Resumo

Realizaram-se quatro experimentos com 136 porcos cruzados (Landrace-Hampshire-Duroc) para determinar a ordem dos três primeiros aminoácidos limitantes (AAL) no trigo para porcos em crescimento e finalização. Os tratamentos consistiram em adições de lisina, treonina e/ou metionina a dietas base e numa dieta testemunha. No Experimento 1, lisina incrementou a ganância diária de peso (GDP), consumo de alimento (CDA), lisina (CDL), treonina (CDT) e metionina (CDM), e melhorou a conversão alimentícia (C/G). A adição de treonina incrementou a GDP e o CDT, e melhorou a C/G. Metionina incrementou o CDM, mas não afetou a GDP ou a C/G. No Experimento 2, treonina incrementou a GDP e o CDT, e incrementou a C/G. A inclusão de metionina tendeu a reduzir a GDP e a deprimir a C/G. Não houve diferenças na GDP, CDA ou C/G entre os porcos sob dieta base com lisina e treonina ou dieta testemunha; embora as testemunhas tiveram maior CDT e CDM. No Experimento 3, treonina só, não afetou a GDP ou a C/G, mas combinada com metionina, incrementou a GDP e melhorou a C/G. Não houve diferenças na GDP e a C/G entre as dietas testemunha e a adicionada com lisina e treonina. No Experimento 4, treonina tendeu a incrementar a GDP e a melhorar a C/G, enquanto que metionina reduziu a GDP. A adição de treonina e metionina incrementou a GDP, mas não afetou o CDA nem a C/G. Estes dados indicam que, no trigo, lisina e treonina são o primeiro e segundo AAL para porcos em crescimento e finalização. Metionina só, não limita o crescimento dos porcos em dietas baseadas no trigo, mas parece potenciar a resposta de treonina em porcos de finalização. Lisina e treonina podem substituir a massa de soja em dietas baseadas no trigo para porcos em crescimento e finalização.

Re ceived:02/11/2003. Modified: 04/04/2003. Accepted: 04/25/2003

Introduction

The order of the limiting amino acids (LAA) in corn and sorghum is well known (Russell et al., 1983; Tanksley and Knabe, 1984; Cervantes et al., 1997), but very little is known about wheat. Lysine is the LAA in most cereals (Lewis, 2001) but there is scarce information regarding the next LAA in wheat. Based on the AA composition (NRC, 1998), lysine, threonine and methionine appear to be the first LAA in wheat; however, there is no available data to support that assumption. The high availability of crystalline AA in the market, at competitive prices, makes it necessary to identify the first LAA in wheat, in order that feed ingredients could be used more efficiently in diets for swine. The objectives of this study were to determine the order of the first LAA in wheat for growing and finishing pigs, and to evaluate the response of pigs fed low protein, wheat-based diets added with crystalline AA.

Four experiments involving 136 crossbred growing-finishing pigs (Landrace-Hampshire-Duroc) were conducted at the Experimental Swine Unit of the Instituto de Ciencias Agrícolas, Universidad Autónoma de Baja California, Mexico. Sufficient animals were weighed to obtain homogeneous groups of pigs based on age, weight, sex and litter, before starting each experiment. These groups were randomly distributed among the different treatments; no more than one pig from the same litter was allowed to remain in the same treatment, in order to avoid genetic effects. Both the basal and control diets (Table I) were added with a vitamin and mineral premix to meet or exceed their requirements for growing and finishing pigs (NRC, 1998). Single sources of wheat and soybean meal were used. Amino acid analysis of wheat (Table II) was performed at the University of Missouri Experiment Station Chemical Laboratories (Columbia, MO) using ion-exchange chromatography after acid hydrolysis.

Pigs were housed either individually in 0.6 x 1.2m pens (Exp. 1 and Exp. 2, growing trials) or in pairs (one male and one female) in 1.0 x 1.2m pens (Exp. 3 and Exp. 4, finishing trials). Twenty-eight growing pigs, distributed in four treatments, were used in each of Exp. 1 (22.5kg initial weight) and Exp. 2 (24.8kg initial weight); there were 7 replicates per treatment, and each experiment lasted 28d. Forty finishing pigs were used in each of Exp. 3 (54.2kg initial weight) and Exp. 4 (53.7kg initial weight); there were 5 two-pig replicates per treatment, and each experiment lasted 49d. All animals had free access to feed and drinking water all the time, and were weighed on a weekly basis. Feed intake (FI), feed:gain ratio (F/G) and daily intakes of lysine (LI), threonine (TI) and methionine (MI) were also registered weekly. All experiments were conducted according to a randomized complete block design (Steel and Torrie, 1980). The pen was considered as the experimental unit. The data were analyzed using the GLM procedure of SAS (SAS, 1988); mean comparisons were made by non-orthogonal (Exps. 1, 2 and 3) and orthogonal (Exp. 4) contrasts.

This experiment was conducted to determine the order of the first three LAA in wheat for growing pigs. Four treatments consisted of the corresponding basal diet (see Table I); basal diet + 0.38% HCl-L-lysine (L); basal diet + 0.38% L + 0.23% L-threonine (T); and basal diet + 0.38% L + 0.23% T + 0.05% DL-methionine (M). The basal diet (Table I) was formulated with wheat as the only major ingredient, supplemented with vitamins and minerals and corn starch. Crystalline L, T and M were added to the diet to contain 0.75, 0.56 and 0.26%, respectively. The wheat content in all diets remained constant.

Since the growth capacity and protein deposition decreases with the increase in age of the pigs, this experiment was conducted to determine if the order of the first three LAA in wheat was the same for growing as for finishing pigs. Four treatments consisted of the corresponding basal diet containing 0.75% L; the same + 0.14% T; the latter + 0.05% M; and control wheat-soybean meal diet. The basal diet was formulated with wheat as the only major ingredient, and supplemented with 0.38% L. Crystalline L, T and M were added to elevate their content in the diet to 0.75, 0.52 and 0.31%, respectively. The control diet was formulated with wheat and soybean meal (see Table I) to contain 0.75% lysine.

Results from Exp. 3 do not show clearly which are the second and third LAA. Therefore, this experiment was designed to separate the effects of added T and M, and to determine which is the second LAA for finishing pigs. Four treatments consisted of the corresponding basal diet with 0.75% L; the same + 0.14% T; basal diet + 0.75% L + 0.05% M; and basal diet + 0.75% L + 0.14% + 0.05% M. The basal diet was formulated with wheat as the only major ingredient and supplemented with 0.38% crystalline L. The data were analyzed according to the indicated design, with a 2x2 factorial arrangement; the factors were the additions of T and M; also, three orthogonal contrasts were constructed to analyze the effects of single and combined additions of threonine and methionine.

The results of Exp. 1 are presented in Table III. Lysine addition to the basal diet increased (P<0.01) the average daily gain (ADG), FI, LI, TI and MI, and improved (P<0.01) F/G. The ADG increased 64%, while FI, LI, TI and MI increased 42, 218, 41 and 41%, respectively, as compared to pigs fed the basal diet. This response indicates that lysine is the first LAA in wheat for growing pigs, and coincides with the estimation made considering the AA composition values of wheat and the requirements of growing pigs (NRC, 1998). Although lysine was the only crystalline amino acid added in T2, the increase in TI and MI was attributed to the increase in FI. On the other hand, the percentage increment in LI was four times higher than that observed in ADG. Also, the ADG of pigs that received the basal diet added with lysine, was smaller than the expected for pigs weighing between 20 and 50kg (NRC, 1998). This indicated that the basal diet added with lysine was still limiting in one or more of the other essential AA.

Threonine inclusion additionally improved (P<0.01) ADG, F/G and TI, but did not affect (P>0.10) FI, LI and MI. The additional increase in ADG was around 55%, while F/G and TI additionally improved by 34 and 44%, respectively, as compared with pigs fed the basal diet. This response indicates that threonine is the second LAA in wheat for growing pigs. The increase in ADG and TI was similar, which suggested that the performance of pigs fed the wheat diets could still be improved with higher dietary threonine levels. Methionine inclusion increased (P<0.05) MI, but no additional effect (P>0.10) on ADG, FI, LI and TI, or F/G was observed. This response indicates that methionine is not limiting in wheat for growing pigs, and confirms the previous suggestion that only lysine and threonine limit the growth of pigs fed diets containing only wheat as the major feed ingredient.

In Exp. 2 (Table IV), threonine addition to the basal diet increased ADG and TI, and improved (P<0.01) F/G, but did not affect (P>0.10) FI, LI or MI. This result agrees with that obtained in Exp. 1, and confirms that threonine is the second LAA in wheat for growing pigs. The additional inclusion of methionine did not improve performance; in fact, it tended to reduce (P<0.10) ADG and deteriorated (P<0.01) F/G. In a previous study (Cervantes et al., 1997), the inclusion of crystalline methionine to low protein, sorghum-soybean meal diets, negatively affected FI and ADG; therefore the excess of methionine could have affected FI. Although the addition of crystalline methionine in this experiment slightly increased its content in the diet to 0.25%, which is hardly equal to 12.5% above the requirement, Edmonds and Baker (1987) indicated that young pigs are very sensitive to excess methionine. Katz and Baker (1975) found that chicks fed excess methionine decreased plasma threonine concentration and increased threonine oxidation. Because the basal diet was added with sufficient amounts of crystalline lysine, threonine became the first LAA; thus, an increase in the oxidation of threonine as a result of the methionine excess could have even enhanced the limitation of threonine in the wheat-based diet. In this regard, Wahlstrom and Libal (1974) found that as little as 0.2% added methionine reduced the performance of growing-finishing pigs, and this effect was alleviated by the addition of 0.2% threonine. The interactions between these amino acids may be responsible for the depression in performance of pigs caused by supplementing methionine to wheat-based diets.

Results of Exp. 3 are shown in Table V. Although threonine addition to the basal diet increased (P<0.05) TI, it did not affect (P>0.10) ADG, FI, or F/G. The inclusion of methionine in diet added with lysine and threonine increased (P<0.05) ADG and MI, and tended to improve (P<0.10) F/G, in comparison with pigs that received the basal diet. This response suggests that either methionine is the second LAA or that both threonine and methionine are equally limiting in wheat for finishing pigs. Pigs that consumed the basal diet with threonine and methionine had a higher (P<0.05) ADG as compared with those fed the control diet. TI of pigs fed the control diet tended to be lower (P<0.10) than that of pigs fed the diet added with threonine and methionine (13.3 vs. 15.2g/d, respectively), but MI was similar (P>0.10) between both treatments. The LI was similar in all pigs; this was expected because there were no differences in FI and because all diets were formulated to contain the same lysine level.

The results of Exp. 4 (Table VI) show an interaction (P<0.01) between dietary threonine and methionine inclusions, in ADG, FI, LI, TI and MI. The single addition of threonine tended (P<0.10) to increase ADG, increased (P<0.01) TI and improved (P<0.01) F/G. In contrast, the single inclusion of methionine reduced (P<0.01) ADG, FI, LI, and TI, even though MI increased (P<0.01). But, when threonine and methionine were added together to the diet, ADG was higher (P<0.01), as compared with the basal diet. TI and MI were also higher (P<0.01), as expected, in pigs fed the diet added with threonine and methionine. The ADG results of this experiment indicate that threonine is the second LAA in wheat for finishing pigs; also, the F/G ratio shows no additional benefit from adding methionine to the lysine-threonine-supplemented basal diet. The reduction in ADG and feed efficiency of pigs fed the basal diet supplemented only with methionine, resulted from the deficiency of threonine. Thus, methionine does not seem to limit the performance of finishing pigs; although there is a tendency to improve the ADG of finishing pigs when this amino acid is added to the wheat-based, lysine-threonine-supplemented diet.

Based on NRC (1998), the methionine requirement of finishing pigs (50 to 120kg body weight) ranges from 0.13 to 0.16%. On the other hand, Araiza et al., (2002) evaluated the apparent ileal digestibility of amino acids in the same wheat batch used in these experiments. They found that the content of ileal digestible methionine in this wheat was about 0.14%, which is equivalent to 90-108% of the amino acid requirement for these pigs. This indicates that methionine may be limiting in pigs weighing from 50 to 60kg, but it also suggests that there is a surplus of methionine when pigs weigh from 70 to 120kg. This might explain why methionine did not limit the overall growth when pigs weighed from 50 to 105kg.

Lysine appears to be the first LAA in all cereals, while the order of the other AA is different, depending on the grain. In sorghum, lysine and threonine are the first and second LAA for growing pigs (Hansen et al., 1993). Methionine and isoleucine in sorghum seem to jointly limit the growth of pigs (Cervantes et al., 1997), although the response to their inclusion in the diet has not been consistent. On the other hand, in corn, lysine is the first LAA, followed by tryptophan, and threonine and methionine seem to share the third limiting order for growing pigs (Russell et al., 1983). Although there was little information about the second and third LAA in wheat for growing and finishing pigs, data from these experiments show that threonine is the second LAA.

In this study the response to the addition of synthetic AA in pigs fed the wheat-based diet was higher than the response of pigs fed with sorghum based (Hansen et al., 1993; Cervantes et al., 1997) or corn based (Russell et al., 1983) diets. The ADG of pigs fed sorghum-soybean meal diets containing 10.5% CP and added with lysine, threonine, methionine, isoleucine and histidine, is consistently lower than that of pigs consuming sorghum-soybean meal diets with 16.5% CP (Cervantes et al., 1997). Similarly, pigs consuming corn-soybean meal diets with 10% CP, added with lysine, tryptophan, threonine and methionine, did not grow as fast and efficiently as those with high CP diets (Russell et al., 1983). In contrast, the data from Exps. 2 and 3 show that crystalline lysine and threonine can completely replace soybean meal in wheat-based diets without affecting the performance of finishing pigs.

Lysine is the first limiting amino acid in wheat for growing and finishing pigs. Threonine is the second limiting amino acid for growing pigs. Methionine does not limit the weight gain or the feed/gain ratio of growing pigs. But methionine appears to enhance the growth of finishing pigs fed wheat-based diets added with lysine and threonine. Crystalline lysine and threonine in wheat-based diets can completely replace soybean meal without affecting the performance of growing and finishing pigs.

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