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Effects of sire line, sire, and sex on plasma urea nitrogen, body weight, and backfat thickness in offspring of Duroc and Landrace boars^1,2

USDA-ARS, US Meat Animal Research Center, Clay Center, NE 68933

	Abstract

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In pork production, the efficiency of dietary protein (AA) use is low, resulting in urinary excretion of large quantities of nitrogen as urea. Use of AA and formation of urea are under enzymatic regulation, suggesting genetic regulation. The current study examined the effects of sire line, sire, and sex on growth characteristics and plasma urea nitrogen (PUN) concentrations in the offspring of 11 Duroc sires and 11 Landrace sires bred to Yorkshire-Landrace dams. Plasma samples were obtained at approximately 107 (age class = 107 d), 128 (age class = 128 d), and 149 (age class = 149 d) d of age from 511 boars, gilts, and barrows group-penned and fed standard finishing diets. Body weight and backfat (BF, mean of 3 measurements) were recorded at the time of blood sample collection. Sex, age class, and their interaction influenced (P < 0.01) BW, BF, and PUN. Predicted traits (i.e., ADG, BW at 21 wk, average daily change in BF, BF at 21 wk, and the mean of 3 PUN measures) were generated. Means (±SD) were: ADG, 888 ± 204 g; BW at 21 wk, 94.2 ± 12.5 kg; average daily change in BF, 0.083 ± 0.052 mm; BF at 21 wk, 13.8 ± 3.0 mm; and the mean of 3 PUN measures, 16.2 ± 4.4 mg/dL. Predicted weight traits were influenced (P < 0.05) by sire line, and sex influenced (P < 0.01) all predicted traits. Heritability estimates for PUN at 107, 128, and 149 d of age were 0.35 ± 0.15, 0.21 ± 0.13, and 0.16 ± 0.12, respectively. Phenotypic correlations of PUN with growth and fat traits were low. Genetic correlations of PUN measured at 107 d with growth and fat traits were low. However, genetic correlations of PUN measured at 128 or 149 d with growth and fat traits ranged from 0.81 to 0.95. Determination of PUN, as herein, may be of sufficient precision to allow its use in a selection protocol. Selection of pigs with superior growth performance and low PUN may result in a greater efficiency of dietary nitrogen use and a reduced negative environmental impact.

Key Words: genetic influence • growth • plasma urea nitrogen

	INTRODUCTION

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Among the problems facing the swine industry are inefficient use of inputs, particularly dietary AA, which account for approximately 25% of feed costs, and management and disposal of manure. Contributing to inefficiency of AA use are dietary recommendations for AA that have been developed for populations and diets that are formulated to ensure only a few individuals are fed below their individual requirements. Amino acids fed in excess of requirements for tissue repair and accretion are transaminated or deaminated or both, and the nitrogen moiety is converted to urea in the liver (Salway, 1994). Urea is excreted in urine. Urinary excretion and circulating concentrations of urea have been measured in evaluation of AA requirements of swine under different physiological conditions. Coma et al. (1995) used plasma urea nitrogen concentrations (PUN) to monitor dietary AA adequacy in growing gilts and found PUN values have potential as an indicator of efficiency of lean tissue growth. Additionally, the response in PUN to diet is influenced by initial PUN, that is, PUN while pigs were fed a common diet, indicating individuality in PUN and possibly a genetic influence. Chen et al. (1999) determined optimal dietary concentrations of CP, source of AA, as evaluated by rate and efficiency of BW gain. In addition, PUN was positively correlated with dietary CP. Feeding CP or AA in excess results in high PUN, which is excreted in the urine and subsequently converted to ammonia, a volatile environmental pollutant. Thus, problems of manure management are inextricably associated with inefficient use of dietary nitrogen.

The objective was to evaluate the relationship between PUN and performance traits and the effect of sire line or breed and sex. An additional objective was to determine the influence of additive genetic variation on PUN and performance traits and ultimately evaluate the potential efficacy of PUN as a quantitative trait.

	MATERIALS AND METHODS

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All animal procedures were reviewed and approved by the US Meat Animal Research Center Animal Care and Use Committee.

Animals used were from initial crosses in production of a swine resource population developed to provide for identification of QTL for production traits. Dams were a broad sample from a Yorkshire x maternal Landrace composite population. Sires were 11 unrelated Duroc boars and 11 unrelated high-lean terminal Landrace boars obtained from commercial AI companies. Boars used were selected to be representative of the breeds.

Boars, barrows, and gilts (n = 511) from 2 farrowing groups were selected for sampling for the current study. Average birth dates were May 14 (SD = 6.7) and July 17 (SD = 5.9). Distribution of pigs within sires and sexes is presented in Table 1. Throughout the study, pigs were housed in group pens in an enclosed growing/ finishing facility, segregated by sex (10 to 15 pigs per pen, depending on size of the pen; minimum of 0.95 m² allocated for each pig). Feed consisted of ground corn-soybean meal, 3-phase, growing-finishing diets that met or exceeded recommendations (NRC, 1998) and was provided ad libitum in self-feeders. Diet composition and the 3-phase growing-finishing regimen are presented in Table 2.

Plasma samples were analyzed for urea nitrogen using a Technicon Autoanalyzer (Marsh et al., 1965). On the day of or the day after blood sample collection, BW and average backfat thickness (AvBF) were recorded. Backfat was measured ultrasonically (Lean-Meater, Renco Corp., Minneapolis, MN) 5 to 8 cm lateral to the midline at the first rib, last rib, and last lumbar vertebrae, and these 3 measures were averaged to obtain AvBF. Average daily gain and average daily change in backfat thickness (ADCBF), which are accretive measures and were estimated while the animals were in the finishing facility, were determined by within-pig linear regression using the 3 recorded BW and AvBF measures. Parameters of the linear regression equations were used to predict BW (BW21wk) and AvBF (BF21wk) at 21 wk of age for each pig. The 3 determinations of PUN, a circulating moiety, were averaged to obtain average or mean plasma urea nitrogen (mPUN).

Temporal and predicted performance variables and PUN data were examined utilizing the Mixed model procedures of SAS (SAS Inst. Inc., Cary, NC). Mixed model analyses of temporal data are presented in Table 3. The model used for temporal traits included sire line, sex, age class, and all interactions among them, and farrowing season nested within age class, as fixed effects. Sire and litter, both nested within age class, were included as random effects. Mixed model analyses of predicted traits are presented in Table 4. The model for predicted traits was the same as for temporal traits, except age class and its interactions were not included, and no effects were nested within age class. The Kenward-Roger method was used to compute the denominator df.

	RESULTS

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Farrowing season, sex, and interaction of sex and age class influenced (P < 0.01) BW, AvBF, and PUN (Table 3). Least-squares means for the main effects significant (P < 0.05) in the analyses are presented in Table 5. Body weights were greatest in boars and barrows and least in gilts. Average backfat was greatest in barrows and least in boars. Plasma urea nitrogen concentrations were greatest in barrows or gilts (depending on age) and least in boars. Pigs sired by Duroc boars had greater BW. All temporal measures increased with age class.

The estimated heritability of PUN (Table 6) varied considerably by age class, decreasing from 0.35 at 107 d to 0.16 at 149 d. However, the litter variance, as a proportion of phenotypic variance (Table 7), increased from 0.09 at 107 d to 0.16 at 149 d. This may be due to sampling error in partitioning of variance between the additive genetic and litter components of variance. The total proportion of variance that accounted for additive genetic and litter effects decreased with age but less dramatically than heritability.

Environmental (Table 6) and phenotypic (Table 7) correlations among PUN traits or among growth and backfat traits were generally moderate in magnitude and positive in direction. However, environmental and phenotypic correlations between these 2 groups of traits were generally of low magnitude. Correlations among litter effects (Table 7) tended to follow the same general pattern but were somewhat erratic and had much greater SE.

	DISCUSSION

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In this group of pigs, sire within line and interaction of sex and age class influenced temporal measurements of BW, AvBF, and PUN. The influence of sire within line on BW and AvBF was expected. Body weight and AvBF are known to be genetically determined quantitative or additive traits and have been capitalized by quantitative methods. A primary question in this study was whether PUN is genetically determined and whether it may be an exploitable quantitative trait. The heritability estimates for PUN ranged from 0.16 to 0.35, and thus PUN appears to be a candidate for exploitation as a quantitative trait.

The premise of this work is that PUN may be an easily measured index or phenotypic marker of efficiency of AA use for maintenance and accretion of lean tissue applicable in selection programs. Plasma urea nitrogen concentrations, as well as urinary excretion of urea, have been measured to estimate AA requirements (Brown and Cline, 1974; Coma et al., 1995; Chen et al., 1995). In normal, healthy animals, circulating urea concentrations are primarily determined by ammonia availability resulting from transamination and deamination of AA and hepatic production of urea via the Kerbs-Henseleit ornithine or urea cycle in the liver (Salway, 1994). The availability of ammonia for urea synthesis in animals such as growing-finishing pigs is determined by the AA content of the diet relative to AA requirements for protein accretion. If AA are consumed in excess, relative to potential for protein accretion or dietary energy, or in unbalanced proportions, the AA that cannot be used in protein synthesis undergo transamination and deamination. In the Krebs-Henseleit ornithine or urea cycle, the amino moiety is removed and converted to ammonia, and the carbon skeleton is ultimately used for energy or synthesis of nonnitrogenous substances such as glucose, glycogen, or fatty acids. The ammonia, which is toxic, is converted to urea, primarily in the liver, and ultimately excreted via the kidneys. Feeding a diet high in CP results in greater activity of hepatic urea cycle enzymes (Rosebrough et al., 1983), and increasing AA requirement for protein synthesis decreases the activity of those enzymes (Bush et al., 2002). In contemporary swine production systems, diets are formulated to achieve the optimal balance of AA based on the best knowledge of AA requirements of growing-finishing pigs within economic constraints imposed by feed ingredient prices (NRC, 1998). Consequently, the most probable cause of high PUN in swine is consumption of a diet that provides AA in excess of the requirement to meet the potential for protein accretion. An individual may consume excess AA because the AA content of the diet is in excess of that individual’s AA requirements, the AA content of the diet is improperly formulated for that individual, or that individual may consume excess quantities of the diet through hyperphagia (overconsumption of both energy and AA).

Efficiency of dietary nitrogen retention is low in pigs; very little of the consumed AA are incorporated into body protein. Analysis of data presented by Reeds et al. (1980) indicated that over a growing-finishing period of 30 to 97 kg, 23% of the ingested nitrogen is retained. A portion of this inefficiency is due to indigestibility of AA. True ileal digestibilities of essential AA range from 78 to 93% (NRC, 1998). This is the proportion of ingested AA that have disappeared when the digesta reaches the terminal ileum. Amino acids disappear from the gastrointestinal tract due to metabolism within the gastrointestinal tract or absorption through the wall of the small intestine and entry into the circulation. Amino acids that enter the circulatory system of the pig can be incorporated into body tissue, enzymes, protein hormones, and other regulatory moieties. Amino acids that are not incorporated into proteins are catabolized, and the amino groups are ultimately incorporated into urea. The circulating quantities of this urea, arising from digested and absorbed AA that are not used for synthesis of body proteins, was measured as PUN herein and is primarily excreted in the urine.

An objective of pork production is efficient production of marketable lean product. Protein is a major component of marketable lean product. Rate and efficiency of protein accretion are determinants of rate and efficiency of marketable lean product accretion (Leymaster and Jenkins, 1985). In pork production, accretion of lean product can be approximated from live BW gains, particularly if a measure of fatness (e.g., ultrasonically measured backfat thickness) is included. Estimates of marketable product can be obtained from trimmed lean cuts in pigs. Actual measurement of lean or protein accretion is much more difficult. Measurement of whole body protein accretion requires slaughter of the animal as does acquisition of trimmed lean cuts data. As for the components of protein accretion, measurements of protein synthesis and degradation are expensive and difficult. Efficiency of dietary nitrogen retention (nitrogen balance) can be measured; however, it is labor intensive. Ideally, efficiency of dietary AA use for accretion of body proteins would be estimated from measurement of AA intake, or better AA absorption from the small intestine, and measurement of protein accretion.

Quantification of protein accretion, synthesis, and degradation, and nitrogen balance cannot be accomplished within the physical and fiscal limitations of most research laboratories on a sufficient number of individuals to be of use in determination of genetic parameters. Herein, we estimated genetic parameters for the traits measured, including mPUN, using data from 511 individuals. Estimates of the heritability of PUN ranged from 0.16 to 0.35, indicating it may be an exploitable quantitative trait that has potential in the identification of animals with superior efficiency of AA use for accretion of marketable product.

Herein, we report genotype and sex influences on PUN in swine. There are environmental influences on PUN in swine, particularly nitrogen intake (Chen et al., 1995). In pigs that are growing, the relationship between dietary nitrogen intake and PUN is positive, even in young pigs fed a diet extremely low in dietary protein (Pond et al., 1992). Time in relation to meal consumption influences PUN and urea excretion (Reeds and Fuller, 1983; Cai et al., 1994; Whang and Easter, 2000). Ideally, blood samples for measurement of PUN would be collected at a fixed time in relation to consumption of a standardized diet and meal size. However, Cai et al. (1994) report relatively stable PUN measured at 2-h intervals throughout the day in pigs with continuous free access to feed. If one needs to measure the parameters in a production setting on a large number of animals, it may not be feasible to standardize meal time, meal size, and time of blood sample collection; and the results of Cai et al. (1994) indicate it may not be necessary. Herein, blood samples were collected from animals in a common environment, including diet, which was available ad libitum. Time of blood sample collection in relation to feed consumption was not controlled.

Although it may not be necessary to be concerned about time of blood sampling relative to meal consumption in pigs with free access to feed, it may be important to consider the AA content of the diet the pigs are consuming. Examination of the results of Chen et al. (1995) yields evidence that relationship between nitrogen consumption and PUN values in gilts is cubic. Incremental changes in PUN due to increasing nitrogen consumption are least at low dietary CP, 10 to 13%, and high dietary CP, 19 to 25%. Plasma urea nitrogen concentrations are most responsive to changes in dietary nitrogen intake at CP levels near the recommended levels, between 13 and 19%. Genetic potential for protein accretion influenced the relationship between nitrogen intake and PUN values; however, the cubic relationship was preserved in both genetic lines examined. Subsequently, Chen et al. (1999) reported the effect of sex and dietary CP on PUN. The previously observed cubic relationship between dietary CP and PUN was seen in gilts, but the relationship was linear in barrows. These results reported by Chen et al. (1995, 1999) indicate that the pigs fed a diet formulated to approximately meet their requirement for AA (i.e., as per NRC recommendations) should segregate into more and less efficient utilizers of dietary AA based on PUN values.

Selection against high PUN, which would be selection for efficient use of dietary AA based upon the premise of the current study, should result in reduced nitrogen excretion, nitrogen concentration in manure, and ammonia entry into the atmosphere. The genetic correlations of PUN128 with BF21wk (0.87) and BW21wk (0.94) are strong and positive, suggesting that selection for lower PUN would have a favorable effect on fatness but an unfavorable effect on BW. The genetic correlations of PUN with rates of change in these traits were also high. The moderate to high phenotypic correlations between PUN and predicted adipose traits are expected. The urea in plasma arises from deamination of AA that are not used for body protein synthesis. The carbohydrate backbone of the deaminated AA is used for energy or synthesis of substances such as glucose, glycogen, or fatty acids that contribute to adipose accretion.

Ideally, selection against high PUN would result in pigs that have more desirable production traits (e.g., rates of BW and backfat gain, yield of marketable pork, and efficiency of feed use for production of marketable pork). However, reduced PUN and urea excretion alone may justify selection against high PUN. Improved use of dietary AA, and reduction in urea excretion and subsequent environmental impacts and costs associated with mitigation of excessive nitrogen in manure, may justify the selection efforts.

If PUN is an exploitable quantitative trait, then its use in selection of breeding animals may yield improvements in efficiency of dietary AA use and environmental impact. The overall mean PUN128 was 12.7 ± 5.4 mg/ dL (mean ± SD) in boars, 16.6 ± 5.8 mg/dL in gilts, and 16.4 ± 6.4 mg/dL in barrows. If selection within boars and gilts was practiced to achieve 1 SD, the average selection differential would be 5.11 mg/dL. The genetic gain in reducing mPUN would be 1.1 mg/dL assuming heritability of 0.21. Assuming the castration effect would remain the same (+29%), mPUN in barrows would be about 15 mg/dL or 91% of the parental generation. These assumption-laden calculations suggest that genetic progress in reducing mPUN, and thus urinary excretion of urea, is possible.

	IMPLICATIONS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
Plasma urea nitrogen is influenced by sire line, sire, and sex and is heritable. Plasma urea may be an exploitable quantitative or additive trait that can be capitalized to improve efficiency of dietary protein use in, and reduce negative impacts of, pork production.

	Footnotes

 
¹ The authors acknowledge the secretarial assistance of J. Byrkit, the technical assistance of P. Nuss, the entire MARC swine crew for husbandry of the animals and assistance with blood collection, and J. Joe Ford for assistance with blood collection.

² Mention of a trade name or manufacturer does not constitute a guarantee or warranty of the product by the USDA or an endorsement over products not mentioned.

³ Corresponding author: klindt{at}email.marc.usda.gov

Received for publication December 9, 2004. Accepted for publication January 18, 2006.

	LITERATURE CITED

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Boldman, K. G., L. A. Kriese, L. D. Van Vleck, C. P. Van Tassell, and S. D. Kachman. 1995. A Manual for Use of MTDFREML. USDA, ARS, Clay Center, NE.

Brown, J. A., and T. R. Cline. 1974. Urea excretion in the pig: An indicator of protein quality and amino acid requirements. J. Nutr. 104:542–551.[Abstract/Free Full Text]

Bush, J. A., G. Wu, A. Suryawan, H. V. Nguyen, and T. A. Davis. 2002. Somatotropin-induced amino-acid conservation in pigs involves differential regulation of liver and gut urea cycle enzyme activity. J. Nutr. 132:59–67.[Abstract/Free Full Text]

Cai, Y., D. R. Zimmerman, and R. C. Ewan. 1994. Diurnal variation in concentrations of plasma urea nitrogen and amino acids in pigs given free access to feed or fed twice daily. J. Nutr. 124:1088–1093.[Abstract/Free Full Text]

Chen, H.-Y., A. J. Lewis, P. S. Miller, and J. T. Yen. 1999. The effect of excess protein on growth performance and metabolism of finishing barrows and gilts. J. Anim. Sci. 77:3238–3247.[Abstract/Free Full Text]

Chen, H.-Y., P. S. Miller, A. J. Lewis, C. K. Wolverton, and W. W. Stroup. 1995. Changes in plasma urea concentration can be used to determine protein requirements of two populations of pigs with different protein accretion rates. J. Anim. Sci. 73:2631–2639.[Abstract]

Coma, J., D. R. Zimmerman, and D. Carrion. 1995. Relationship of rate of lean tissue growth and other factors to concentration of urea in plasma of pigs. J. Anim. Sci. 73:3649–3656.[Abstract]

Leymaster, K. A., and T. G. Jenkins. 1985. Characterization of accretion rates of growth constituents in male Suffolk sheep. J. Anim. Sci. 61:430–435.[Abstract/Free Full Text]

Marsh, W. H., B. Fingerhut, and H. Miller. 1965. Automated and manual direct methods for the determination of blood urea. Clin. Chem. 11:624–627.[Abstract]

NRC. 1998. Nutrient Requirements of Swine. 10th rev. ed. Natl. Acad. Press, Washington, DC.

Pond, W. G., K. J. Ellis, and P. Schoknecht. 1992. Response of blood serum constituents to production of and recovery from a kwashiorkor-like syndrome in the young pig. Proc. Soc. Exp. Biol. Med. 200:555–561.[Abstract]

Reeds, P. J., A. Cadenhead, M. F. Fuller, G. E. Lobley, and J. D. McDonald. 1980. Protein turnover in growing pigs. Effects of age and food intake. Br. J. Nutr. 43:445–455.

Reeds, P. J., and W. F. Fuller. 1983. Nutrient intake and protein turnover. Proc. Nutr. Soc. 42:463–471.[Medline]

Rosebrough, R. W., N. C. Steele, and J. P. McMurtry. 1983. Effect of protein level and supplemental lysine on growth and urea cycle enzyme activity in the pig. Growth 47:348–360.[Medline]

Salway, J. G. 1994. Pages 40–41 in Metabolism at a Glance. Blackwell Sci. Ltd., Osney Mead, Oxford, UK.

Whang, K. Y., and R. A. Easter. 2000. Blood urea nitrogen as an index of feed efficiency and lean growth potential in growing-finishing swine. Asian-Aust. J. Anim. Sci. 13:811–816.

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