Fine-tuning threonine requirement for sows

Tuesday, May 31, 2011

University of Alberta research offers some preliminary conclusions on the requirements for essential amino acids in gestating sows

by JANICE MURPHY

Popular thought on nutrition for sows suggests that producers provide a fixed amount of amino acid intake throughout gestation. This recommendation is based on the assumption that the requirement remains constant throughout gestation.

However, recent information has revealed that the demand for nutrients changes as the sow transitions from recovering maternal lean tissue in early gestation to the growth of fetal and mammary tissue in late gestation.

The daily amino acid intakes published in the National Research Council's Nutrient Requirements of Swine (1998) rely on maintenance and growth data established in the 1970s and '80s. However, information from the Canadian Centre for Swine Improvement in 2007 estimated that genetic selection increased lean yield by 1.5 per cent and litter size by 30 per cent between 1999 and 2006.

A sow's daily requirement for threonine may change to an even greater extent from early to late gestation than the requirement for lysine, generally considered to be the first limiting amino acid for pigs. This is due in part to the increase in maintenance requirements to support growth of sows during pregnancy, which are greater for threonine than lysine. Also, growth of sows in late gestation requires the generation of mucosal membranes, which have higher concentrations of threonine.

Researchers at the University of Alberta recently conducted a study to determine the requirement for threonine in early gestation (day 35 to 53 and 25 to 55 for the first and second experiments, respectively) and late gestation (day 92 to 110 and 81 to 111) using the indicator amino acid oxidation (IAAO) technique with l-[1-13C] phenylalanine as the tracer amino acid.

The IAAO technique is based on the concept that when one indispensable amino acid is insufficient for protein synthesis, then all others, including the indicator amino acid (phenylalanine in this case), will be oxidized.

With increasing intakes of the limiting amino acid (threonine in this case), IAAO will decrease, reflecting increasing incorporation into protein. Once the requirement for the limiting amino acid is met, there will be no further change in the indicator oxidation, allowing researchers to determine the breakpoint, or requirement, for the amino acid of interest.

A total of 14 multiparous sows were used, six in the first experiment and eight in the second experiment. Each sow received each of six diets in random order in both early and late gestation. A basal diet was formulated with corn, cornstarch and sugar (see Table 1) with threonine at 60 per cent of the 1998 NRC recommendation in the first experiment, and 20 and 60 per cent of the 1998 NRC in the second experiment for early and late gestation, respectively.

Synthetic threonine was added to create additional diets with approximately 10 per cent incremental increases in threonine at the expense of cornstarch and sugar. All other essential amino acids were provided at a minimum of 150 per cent (first experiment) and 180 per cent (second experiment) of their respective NRC (1998) requirement.

Sows were placed in respiration chambers for 5.5 hours, during which time expired air and blood were collected every 30 minutes. The phenylalanine tracer was given orally during the last four hours, evenly divided over eight 30-minute meals. Measurements were taken of the 13CO²  enrichment of expired air and plasma-free threonine concentration.

The overall litter size and litter weight were 13.5 and 20.5 kilograms, respectively. Using the IAAO technique, the researchers pegged the threonine requirement of gestating sows at between five and six grams a day in early gestation and 12.3 to 13.6 grams a day in late gestation. They suggested that the greater weight gain in late gestation compared with early gestation likely played a role in the greater requirement for threonine at that stage.

Based on these results, the researchers concluded that feeding a single amount of amino acid throughout gestation results in overfeeding in early gestation and underfeeding in late gestation. The doubling in threonine requirement in the last phase of gestation suggests that phase feeding sows through gestation would be a better strategy in order to more closely match nutrient demands. The requirement for essential amino acids in gestating sows needs to be re-evaluated and addressed in early and late gestation in future swine nutrition publications.

Source: C. L. Levesque, S. Moehn, P. B. Pencharz and R. O. Ball. 2011. The threonine requirement of sows increases in late gestation. J Anim Sci 89:93-102.

Nutrient requirements
Speaking of the NRC Nutrient Requirements of Swine, a committee is currently working on an updated version. Meetings began in January 2010 with the 10-member committee, including Dr. Kees de Lange from the University of Guelph.
Any information the committee is planning to include in the document is confidential until its release, which is expected this fall. However, their mandate is to prepare a report that reviews the scientific literature on the nutrition of swine. The key aspects of the new publication will include:

•    An updated list of energy and nutrient requirements, covering all life phases and types of production. New recommendations, especially for amino acids, will be made with appropriate consideration of the increased potential for lean gain of modern genotypes of swine.
•    New knowledge about energy utilization by swine, including net energy systems and values, will be added.
•    Information about feed ingredients from the biofuels industry and other new ingredients (e.g., novel soybean products) will be included.
•    Requirements for digestible phosphorus and concentrations of digestible phosphorus in feed ingredients will be updated.
•    A review of the effects of feed additives routinely used in swine diets (e.g., antibiotic growth promoters, enzymes, acidifiers and beta-agonists) will be included.
•    Effects of feed processing (e.g., pelleting, extrusion and reduced particle size) on the utilization of feed by different categories of swine will be addressed.
•    Strategies to increase nutrient retention and thus reduce fecal and urinary excretions that could contribute to environmental pollution will be reviewed.
•    The computer model included in the NRC 1998 publication to calculate nutrient requirements of different categories of pigs will be updated.
•    Tables of feed composition will be expanded with relevant new information.
•    Future areas of needed research will be identified.

Further information on this initiative is available on the National Academies of Science website at: http://www8.nationalacademies.org/cp/projectview.aspx?key=49161 BP

Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.