J. Anim. Sci. 2002. 80:2809-2816
© 2002 American Society of Animal Science
Genetic and nutritional effects on swine excreta
A. W. Crocker and
O. W. Robison1
* Department of Animal Science, North Carolina State University, Raleigh 27695-7621
Correspondence:
phone: (919) 515-4015; fax: (919) 515-7780; E-mail:
ow_robison{at}ncsu.edu.
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Abstract
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The objective of this study was to investigate genetic and nutritional effects on swine excreta. Two studies were used. Study I was a 3 x 2 x 2 factorial design with three genetic groups, two diets, and two sexes. Genetic groups were a maternal line (WL), paternal line (BL) and their F1 progeny. Corn-soybean meal diets with either 18 or 14% CP, differing only by substitution of soybean meal for corn, were used in both studies. Study II was a 2 x 2 factorial design with two genetic groups and two diets. High testosterone (D2) and low testosterone (D1) Duroc lines were used. Solid and liquid wastes were collected for 3 d. A total of 108 pens in Study I and 50 pens in Study II were sampled twice. Total excreta were measured and samples collected for chemical analysis of N, NH3N, P, Ca, Cu, K, Zn, and Fe. Measures were adjusted for pig weight and feed disappearance. Maternal-line pigs excreted significantly less P, Ca, Cu, Zn, and Fe than F1 or BL pigs and numerically smaller quantities of all nutrients than BL pigs. In study II, differences were found between lines of the same breed. Line D2 pigs had greater output of P, Ca, and Cu (P < 0.05) than D1 pigs and numerically larger quantities of all other nutrients except NH3N and Fe. Pigs fed 14% CP excreted less N, NH3N, and K (P < 0.01) in both studies and excreted significantly less P in Study I. Pigs on a 14% CP diet excreted numerically smaller amounts of all nutrients in both studies except Ca in Study II. In Study I, gilts excreted smaller (P < 0.05) amounts of all nutrients than barrows. Genetic, nutritional, and gender differences influenced waste output.
Key Words: Excreta • Genetics • Nutrition • Pigs
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Introduction
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Intensive swine production may create nutrient buildup. Regulations on amount of waste that may be applied to land may place limits on disposal of manure as a fertilizer. Primary nutrients of concern are N and P. Therefore, methods of reducing amount of nutrients in swine excreta would be beneficial.
Several methods for reducing nutrient output of animals have been studied. Wiener (1979) reviewed effects of copper metabolism in sheep. He found that genetic groups of sheep vary in plasma copper levels. Thus, genetic differences in utilization exist, and it may be hypothesized that genetic differences influence amount and composition of excreta.
Others have studied nutritional effects on excreta. Kerr and Easter (1995) reviewed 28 experiments and concluded that for every 1% reduction in crude protein in swine diets, N excretion is decreased by 8%. Thus, reducing crude protein can significantly reduce N excretion.
This study was designed to investigate genetic, sex, and dietary effects on swine excreta.
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Material and Methods
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Study I consisted of three replicates in a 3 x 2 x 2 factorial design, with three genetic groups, two diets, and two sexes. Genetic groups were a maternal line (WL), paternal line (BL), and maternal x paternal cross (F1). Group WL was a Landrace x Large White composite selected for 10 generations for number born alive. The BL was a Hampshire x Duroc composite selected for 10 generations for decreased backfat thickness and days to 105 kg (D105). The F1 is characteristic of pigs used in commercial productions. A total of 12 WL, 12 BL, and 12 F1 pens were used in each replicate with eight pigs per pen. Both barrows and gilts were used and animals were penned by sex, genetic group, and diet.
Study II consisted of a 2 x 2 factorial design with two genetic groups and two diets; two trials were run in this study. Two lines of Duroc pigs were used. Lines were selected for low testosterone levels (D1) or high testosterone levels (D2). Lines were selected for 10 generations and then maintained by random selection for five generations. Following 10 generations of selection, lines differed three-fold in testosterone production (Robison et al., 1994). A total of 24 D1 and 26 D2 pens were used.
Dietary treatments were the same in both studies. Diets were corn-soybean meal rations formulated to either 18 or 14% CP. Diets differed only in substitution of soybean meal for corn, and met all requirements suggested by the Nutrient Requirements of Swine (NRC, 1998) (Table 1
). Pigs were randomly assigned to diets and remained on that diet throughout growing and finishing.
Procedures were similar for both studies. Pigs were grouped with eight pigs per pen and nine pens assigned each week. The second trial in Study II included only three pigs per pen. Collection phase included total fecal and urinary output over 3 d. A second collection of 3 d was done on each pen of pigs 4 wk after the first collection. Two observations per pen allowed measurements to be taken at different weights and stages of growth and development. Pigs weighed approximately 75 kg at first collection.
Pigs were provided ad libtum access to feed. Feed was weighed into the feeder, and residual feed was weighed when pigs were removed. Feed disappearance was considered the difference between initial and residual feed. Pigs were weighed when removed from pens. Average daily gain was measured between replicate measuring period. Days to 105 kg (D105) were calculated, and backfat was measured by metal ruler at approximately 105 kg.
Pigs were placed in collection pens for 3 d. Pens were equipped to separate solid and liquid waste. Each pen had an iron mesh floor that allowed both fecal material and urine to pass through. Next, a wire mesh caught the fecal waste and allowed urine and waste water to pass through to be collected in a bottom pan.
Feces and urine samples were taken at random locations throughout the pen, after pigs were removed. Total fecal material and total liquid were measured. Fecal samples were placed in plastic bags and put on ice until taken to the lab. Urine samples were collected in bottles and placed on ice.
Fecal and urine samples were analyzed by the NC Department of Agriculture Laboratory for N, NH3N, P, Ca, Cu, K, Zn, and iron (Fe).
Data were analyzed using pens as an experimental unit, following general linear model procedures of SAS (SAS Inst. Inc., Cary, NC). A model including genetic groups, diet, sex, replicate, sex by genetic group, sex by diet, and diet by genetic group was assumed. Feed disappearance and total weight of pigs in a pen were included as covariates.
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Results and Discussion
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Results are reported using both total pig weight within a pen and feed disappearance as covariates. While significant, they did not materially influence genetic group or diet comparisons. Backfat had no significant effect on any measure. Interactions and replicate effects were not significant and thus are not reported.
Genetic Effects
Swine excreta differed among genetic groups in these studies (Table 2). Pigs from the F1 group excreted greater amounts of Ca (P < 0.01) than the BL and WL groups, and excreted greater amounts (P < 0.01) of P than WL. Excreta from WL pigs contained less (P < 0.01) P, Ca, Cu, Zn, and Fe than that from F1 and BL pigs, and numerically less of all elements than BL.
The conclusion is that genetics may influence amount of nutrients excreted. Line WL pigs excreted lower amounts of all nutrients (except NH3N), than BL or F1 pigs. This may be related to slower growth of WL pigs. Line WL pigs had significantly more days to 105 kg (Table 3). Total output and D105 were negatively correlated (-0.23). Thus, more D105 resulted in lower amounts of minerals and total output per day. Line WL pigs may consume less feed resulting in slower growth and less feed disappearance (Table 3). This effect may be due to changes in hormone levels, especially estrogen, caused by selection for larger litter size. This lower consumption may be why WL pigs excreted lower amounts of nutrients and had less total waste per day.
Differences between BL and WL or F1 pigs also may be due to selection for increased growth and decreased backfat in BL, which may have resulted in greater amounts of minerals being excreted due to increased tissue turnover. The F1 cross was intermediate to BL and WL in excretion of minerals except for P, Ca, and NH3N. For P, Ca, and NH3N, F1 animals excreted amounts more similar to BL pigs. This may have resulted from dominant gene action. Pigs in the F1 group had more backfat and faster growth rate than BL pigs. The 3-d difference in D105 between F1 and BL pigs was significant. Thus, F1 pigs may more efficiently use nutrients, which may help lower total amount of urine and feces excreted. Differences in excreta between F1 and BL groups also could be contributed to genetic differences not associated with growth (Table 2
). Despite slower growth of WL, lifetime outputs of P, K, Zn, Fe, and Cu were lower than for BL or F1 pigs (P < 0.05).
There appear to be genetic differences for swine excreta. Thus, genetic selection may be an effective method for altering nutrient utilization and output. Line WL had more D105 than BL and F1, with no difference between the D1 and D2 lines. More D105 for line WL may mean additional cost for producers. Benefits of decreasing D105 vs lowering amounts of nutrients in manure would depend on specific operation and production situations. These decisions will likely be considered in future swine production plans.
In Study II, a difference was found between two Duroc lines (Table 4). High-testosterone pigs had significantly greater (P < 0.05) output of P, Ca, Cu, and K, and numerically larger amounts of all nutrients except NH3N and Fe than D1 pigs (P > 0.05). Further, D2 pigs excreted greater (P > 0.05) amounts of all minerals except NH3N and Fe.
Differences in mineral excretion between D1 and D2 pigs may be a correlated response to divergent selection for testosterone. Perhaps selection for high testosterone in D2 caused an increased turnover in tissue due to hormonal effects resulting in more excreta output. Contrasts between lines for D105 and feed disappearance were not significant (Table 5); therefore differences between lines in excreta output appear to be more basic than growth rate or feed disappearance.
These results are similar to evidence reported by Wiener (1979), who indicated that genetic groups of sheep differ in plasma Cu levels and probably other minerals. Wiener (1979) suggested that this difference could be due to genetic variation among genetic groups.
Differences also were observed among lines for daily nutrient concentration per kg of pig weight (Table 6). There was only a slight difference between BL and F1 with F1 being higher (P < 0.01) for Ca. Line WL excreted the lowest concentrations of all nutrients especially (P < 0.01) P, Ca, Zn, and Cu (Table 6). Reduced excretion in WL may be explained in part by slower growth rate or better efficiency.
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Table 6. Daily output of nutrients, feces, and urine per kilogram of pig weight by genetic group, adjusted for feed disappearance
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Duroc lines showed small differences in nutrient concentrations excreted per kg of pig weight (Table 7). Line D1 had the lowest concentration for all minerals, except Fe, being significantly lower (P < 0.05) in P, Cu, Ca, and K. Lower output could be due to the lower testosterone levels and/or better utilization of nutrients by D1.
Concentration levels and total output per day per kilogram of pig weight allow for calculation of nutrient levels expected to be excreted depending on weight of pigs in an operation. This could be used to help determine amounts of specific nutrients to be checked to allow land application. However, diet, sex, and genetic group must be considered as well.
Diet Effect
There was a significant difference between 18 and 14% CP diets in both studies. Pigs on the 14% CP diet excreted lower (P < 0.01) amounts of N, NH3N, and K than those on 18% CP diet in both studies (Tables 8 and 9), and had significantly lower output of P in Study I. Pigs on a 14% CP diet excreted a smaller amount of all nutrients in both studies with the exception of Ca in Study II. Pigs fed 14% CP performed similarly to those fed 18% CP (Tables 10 and 11).
Changing from 18% CP to 14% CP had a significant effect on amount of nutrients excreted, but did not significantly change growth. The 14% CP diet decreased P, Zn, Fe, and Cu levels between 5 and 10% compared to the 18% CP diet. Reducing CP by 4% lowered N output by 31% (Study I) and 40% (Study II). Other studies show similar results from reducing CP levels. Jongbloed and Lenis (1992) suggest that lowering CP for growing-finishing pigs by 2% will reduce N excretion by approximately 20%. Kerr and Easter (1995) reviewed 28 experiments and concluded that each 1% unit reduction of dietary crude protein combined with crystalline AA supplementation could reduce N losses by 8%. Thus, changing CP in a diet will alter N excretion. Decreasing CP will lower N levels in waste for land application and may help to reduce odors by reducing ammonia.
Also, reducing dietary crude protein to 14% lowered P excretion by 10% (Study I) and 17% (Study II). These reductions would allow more manure to be used in land application while meeting regulations.
Reduction in dietary crude protein had its main effects on output of N, P, and K. Reducing crude protein did not effect output of other nutrients, but allowed reduction of nutrients of primary concern. There were no significant (P > 0.10) effects on performance when decreasing CP, but significant declines in specific nutrient output were evident. However, differences in P and K levels among diets could be due to greater amounts of those two nutrients in soybean meal. Reducing dietary CP may result in a reduction in N and P excretion without adversely affecting growth. Thus, solving some of the problems associated with manure treatment and disposal.
Differences existed between dietary treatments for daily output of nutrients per kilogram of pig weight. In both Study I and Study II, pigs on an 18% CP diet excreted higher (P < 0.01) amounts of N, K, and P (Tables 12 and 13). These differences may be caused by the small differences observed in growth rate between treatments or excess levels of these nutrients in the 18% CP diet. Total urine output per kilogram of pig weight was significantly different between dietary treatments (P < 0.01). Greater urine output may be due to excretion of excessive levels of nutrients in the 18% CP diet. Reducing CP may allow a better balance of AA or may result in a diet closer to the requirements for the genetic groups studied.
Sex Effect
Significant differences in excretion of some nutrients were found between sexes in Study I. Barrow excreta contained greater amounts (P < 0.01) of N, P, Ca, and Cu and greater amounts of NH3N, Zn, and Fe (P < 0.05) than gilt excreta (Table 14). Gilts took 8 d longer to reach 105 kg (P < 0.01), had less backfat (P < 0.01), and numerically lower feed disappearance (Table 15).
Gilts had less (P < 0.05) nutrient excretion by approximately 12 to 20% for all nutrients. This reduction could be due to slower growth of gilts or better nutrient utilization.
Daily output of nutrients per kilogram of weight (Table 16) by gilts was significantly less for all nutrients (P < 0.01). Faster growth of barrows results in greater turnover of nutrients, thus higher amounts of all nutrients per kilogram of pig weight are excreted.
Farms that house only one sex may have different amounts of nutrients in manure. Farms with different sex ratios may require different land application rates.
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Summary and Conclusions
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Line WL animals excreted significantly less P, Ca, Cu, Zn, and Fe than BL or F1 pigs. Excreta from F1 pigs contained greater amounts of (P < 0.05) Ca than excreta from WL or BL pigs. In Study II, differences between two Duroc lines for excreta may be due to selection for testosterone levels. Line D2 excreted greater amounts of all nutrients being significantly higher in Cu, K, Ca, and P.
Reducing CP from 18 to 14% decreased N excretion by 31 (Study I) and 40% (Study II), and daily urine output per pig by 32 (Study I) and 28% (Study II). Thus, reducing CP may reduce output of nutrients and urine. Reducing dietary CP did not affect performance in either study.
Gilts had significantly less nutrient output (12 to 20%) than barrows. Barrows grew faster and had more backfat, which may have resulted in higher nutrient excretions. While gilts may have better efficiency in nutrient retention than barrows.
Genetic effects on nutrient excretion and total excreta output were present in these studies. Selection could be used as a tool to alter utilization or requirements of nutrients. Lowering CP decreased excreta output, but did not affect performance. Future research is needed to examine effects of genetic differences on excreta output. In addition, further research is needed to identify diets that minimize nutrient excretion and maximize performance. Excreta output can be lowered to meet regulations and could be done through genetic selection and/or dietary changes.
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Implications
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Genetic differences may exist for nutrient excretion. Reducing percentage crude protein in diets results in reduced urine and nitrogen output. Gilts also excrete lower levels of all nutrients than barrows. These data provide a basis for estimating quantity and quality of urine and fecal output for pigs of a specific genetic group, diet, and/or sex.
Received for publication June 25, 2001.
Accepted for publication July 2, 2002.
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Literature Cited
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Jongbloed, A. W., and N. P. Lenis. 1992. Alteration of nutrition as means to reduce environmental pollution by pigs. Livest. Prod. Sci. 31:75–94.
Kerr, B. J., and R. A. Easter. 1995. Effect of feeding reduced protein, amino acid-supplemented diets on nitrogen and energy balance in grower pigs. J. Anim. Sci. 73:3000–3008.[Abstract]
NRC. 1998. Nutrient Requirements of Swine. National Academy Press, Washington, DC.
Robison, O. W., D. Lubritz, and B. Johnson. 1994. Realized heritability estimates in boars divergently selected for testosterone levels. J. Anim. Breed. Genet. 111:35–42.
Wiener, G. 1979. Review of genetic aspects of mineral metabolism with particular reference to copper in sheep. Livest. Prod. Sci. 6:223–232.
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Abstract
Introduction
