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ANIMAL PRODUCTION |
,2
* Food Animal Health and Management Center and
and
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201
Abstract
Two trials were conducted to determine the effects of weaning age on pig performance in a multisite production system. The second trial also evaluated the effects of modifying the nursery feeding program according to weaning age. In Trial 1 (2,272 pigs), treatments included weaning litters at 12, 15, 18, or 21 d of age. In Trial 2 (3,456 pigs), litters were weaned at 15, 16, 18, 19, 21, or 22 d of age and categorized into three treatments (15.5, 18.5, or 21.5 d of age). In Trial 2, pigs in each age group were fed one of two nursery feeding programs. Nursery feeding programs varied in both diet formulation and in the quantity of diets fed containing increased levels of whey and spray-dried animal plasma. Each trial was conducted as a randomized complete block design with four blocks of nursery and finishing sites. All weaning-age treatments were weaned from a 7,300-sow farm on the same day into the same nursery. Each block remained intact as pigs moved from nursery to finishing site. Increasing weaning age (12, 15, 18, or 21 d in Trials 1; and 15.5, 18.5, or 21.5 d in Trial 2) increased (linear, P < 0.001) ADG (299, 368, 409, 474 ± 7 g/d; 435, 482, 525 ± 13 g/d) and tended to decrease (linear, P < 0.09) mortality (5.25, 2.82, 2.11, 0.54 ± 0.76%; 2.17, 1.56, 1.30 ± 0.36%) in the initial 42 d after weaning. Finishing ADG (722, 728, 736, 768 ± 11 g/d; 783, 790, 805 ± 11 g/d) also improved (linear, P < 0.01) with increasing weaning age. Overall, increasing weaning age increased (linear, P < 0.001) wean-to-finish ADG (580, 616, 637, 687 ± 8 g/d; 676, 697, 722 ± 6 g/d), weight sold per pig weaned (94.1, 100.5, 104.4, 113.1 ± 1.3 kg; 107.6, 111.6, 116.2 ± 1.1 kg), and decreased (linear, P < 0.03) mortality rate (9.4, 7.9, 6.8, 3.6 ± 0.95%; 3.9, 3.4, 2.5 ± 0.5 %). Altering the nursery feeding program did not affect wean-to-finish growth performance. In this multisite production system, increasing weaning age from 12 to 21.5 d of age increased weight sold per pig weaned by 1.80 ± 0.12 kg for each day increase in weaning age. These studies suggest increasing weaning age up to 21.5 d can be an effective management strategy to improve wean-to-finish growth performance in multisite pig production.
Key Words: Growth Performance • Swine • Weaning Age
Introduction
Multisite swine production has become a widely applied strategy in commercial pig production. Multisite production has evolved through the implementation of an age segregated production technology called segregated early weaning (SEW). Segregated early weaning involves removing weaned pigs from the sow herd and rearing them separately from other age groups of pigs (Harris, 2000
). In addition to segregation, it has been suggested that decreasing weaning age decreases the transfer of growth-depressing pathogens to offspring (Harris, 2000). Applying the concepts of SEW and multisite production has improved pig performance in herds with low or high levels of endemic pathogens present (Dritz et al., 1996a; Fangman et al., 1996, and Patience et al., 2000). Although the concepts of segregation and all-in, all-out management (i.e., depopulating and cleaning of facilities between groups of pigs) seem to be essential for improvements in performance, the importance of younger weaning age is less clear. Published research has not been conducted to determine the incremental effects of weaning age on wean-to-finish performance within a commercially applied multisite swine production scheme. Therefore, the objective of our first trial was to quantify the effects of weaning age on pig performance within a multisite production system. A second trial was completed to evaluate the effects of weaning age and nursery feeding program on pig performance. The second trial served to determine whether growth performance responses due to weaning age were affected by altering the nursery feeding program.
Materials and Methods
Animals and Procedures
Two trials were conducted with pigs in a multisite production system containing a 7,300-sow farm weaning pigs into geographically distinct nursery and finishing sites. The nursery and finishing sites only receive pigs from this single-sow farm and are depopulated, cleaned, and disinfected before another group of pigs are placed in the site. In Trial 1, treatments included weaning litters of pigs at 12, 15, 18, or 21 d of age, with all pigs fed a common nursery feeding program formulated to exceed nutrient requirements provided by NRC (1998; Table 1). Trial 1 was conducted in a randomized complete block design with four wean age treatments (12, 15, 18 or 21 d of age) in four blocks. In Trial 2, litters were weaned at 15, 16, 18, 19, 21, or 22 d of age resulting in three categorized wean age treatments of 15.5, 18.5, and 21.5 d. Pigs within each wean age treatment were fed a nursery feeding program that was classified as either more or less complex. The nursery feeding program classifications were based on the amount of lactose and spray-dried plasma protein in the diet and the quantity fed per pig (Table 2). All diets were formulated to exceed nutrient requirements provided by NRC (1998). The two nursery feeding program classifications and three wean age treatments were arranged in a 2 x 3 factorial with four randomized complete blocks.
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).
Using the individual 42-d postweaning weight and gender information, pigs (1,920 and 3,000 total pigs in Trials 1 and 2, respectively) were individually reallotted within treatment group and block to the finishing phase of the evaluation. Reallotting was required due to different pen sizes in the nursery and finisher sites. As described for the nursery allotment, finishing pens were allotted such that each pen was a replicate of the population of feeder pigs being weighed out of the nursery at d 42 after weaning specific for each treatment and block. In Trial 1 (96 total pens), each finishing block had six randomly assigned pens per weaning age treatment. In Trial 2 (120 total pens), each block had five randomly assigned pens per wean age by nursery feeding program combination. All pigs were fed the same feeding program throughout finishing. Diet specifications and feeding program are outlined in Tables 1
and 2. Finishing feed allocations were designed to exceed nutrient requirements provided by NRC (1998) for all treatments. However, feed delivery data was not collected on a pen basis during the finishing period. In Trial 1, pigs (20 pigs per pen; 10 barrows and 10 gilts) were placed in 2.29 x 6.71-m finishing pens. In Trial 2, pigs (25 pigs per pen; 13 gilts and 12 barrows) were placed in 2.90 x 6.71-m finisher pens. Finishing pens had partially slatted concrete flooring (2/3 solid, 1/3 slatted), and the curtain-sided buildings were naturally ventilated. Each pen had two nipple waterers and a feeder with four feeding spaces. Pens were weighed off-test on d 156 (Trial 1) and d 153 (Trial 2) postweaning with individual weights being recorded.
Growth Performance Calculations and Statistical Analysis
Data from the nursery and finishing phases were used to determine wean-to-finish performance. The nursery allotment weight and nursery mortality data for each treatment and block was applied to each finishing pen placed in that same treatment and block. Transferring the within treatment and block nursery allotment weight and nursery mortality data allowed for the measurement and analysis of wean-to-finish growth performance.
In these analyses, weight and days lost due to mortality were not accounted for in ADG calculations. This allowed for measurement of the effect the imposed treatments (Trial 1 = weaning age, Trial 2 = weaning age and nursery feeding program) had on ADG realized by the production system on a per-pig-placed (or pig space) basis. Similarly, weight sold per pig weaned was calculated to determine the effect of treatment on total weight sold in a fixed number of days postweaning. Expressing weight sold on a per-pig-weaned basis allowed wean-to-finish performance to be quantified in a manner that directly relates to the value of the weaned pig. As a more traditional measure of biological growth not influenced by mortality, weight per day of age was calculated at the end of the nursery and finishing phases, and average pig gain per day after weaning was calculated in the wean-to-finish analysis. Additionally, the effect of treatment on weight variation was evaluated using the individual pig weights to determine the coefficient of variation for each nursery and finishing pen.
Analysis of variance was used to analyze growth performance data as a complete randomized block design using the PROC MIXED procedures of SAS. In both trials, the statistical model included the fixed effect of weaning age, and block as the random component. Linear and quadratic contrasts were used to determine the effects of increasing weaning age. In Trial 2, the model also included the fixed effect of nursery feeding program (less or more complex), and the interactive effect of weaning age x nursery feeding program.
Because of the similarities in the current trials, the lack of significant nursery feeding program effects on wean-to-finish growth performance in Trial 2, and the linear nature of the primary response criteria, data from both trials were pooled for additional modeling. Data from these two trials were fitted using a single mixed model with weaning age as the fixed effect, and trial and block as random components. This enabled a collective estimate of the rate of change (slope) in wean-to-finish performance observed for each day change in weaning age. Pen was the experimental unit in all data analyses.
Results
Nursery Performance
In Trial 1, allotment weight increased (linear, P < 0.001, Table 3) with increasing weaning age. Furthermore, the variation in allotment weight (i.e., as measured by determining the coefficient of variation for each pen) was decreased as weaning age increased (quadratic, P < 0.001). Allotment weight variation was most noticeably increased in the pigs to be weaned at 12 d of age, with variation being similar in pigs weaned at 15, 18, or 21 d of age. Nursery ADG, ADFI, mortality rate, d 42 after weaning weight, and d 42 postweaning weight per day of age improved (linear, P < 0.001) as weaning age increased from 12 to 21 d. Feed efficiency (quadratic, P < 0.03) and variation in d 42 postweaning weight (quadratic, P < 0.01) also improved as weaning age increased. Feed efficiency and d 42 after weaning weight variation were poorer in the 12-d wean pigs, with feed efficiency and weight variation among older weaning ages being similar. However, step-wise improvements in d 42 postweaning weight variation were observed as weaning age increased.
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0.26) during the nursery phase (Table 4). Allotment weight increased (quadratic, P < 0.001; Table 4) with increasing weaning age. Nursery ADG, ADFI, d 42 postweaning weight, and d 42 postweaning weight per day of age improved (linear, P < 0.001) as weaning age increased from 15.5 to 21.5 d. Weight variation at the end of the nursery phase improved (linear, P < 0.003) and mortality rate tended to decrease (P < 0.09) as weaning age increased. Contrary to Trial 1, feed efficiency was poorer (linear, P < 0.001) as weaning age increased. The decrease in mortality observed with increasing weaning age in Trial 2 did not overcome the expected decreasing feed efficiency with increasing body weight. Altering the nursery feeding program did not affect (P 0.29) growth rate, feed efficiency, or mortality. However, pigs fed the more complex nursery feeding program tended (P < 0.06) to have decreased variation in weight at d 42 after weaning.
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) as weaning age was increased from 12 to 21 d. However, there were no differences (P 0.19) in finishing mortality.
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0.14) on finishing growth performance. Finishing ADG, off-test weight, and off-test weight per day of age improved (linear, P < 0.003, Table 6) as weaning age increased from 15.5 to 21.5 d. Contrary to Trial 1, the decreased variation in d 42 postweaning weight observed with increasing weaning age did not translate into decreased variation at slaughter. There were no treatment differences (P 0.20) in finishing mortality.
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and 8), and wean-to-finish mortality (linear, P < 0.03) improved as weaning age increased from 12 to 21 d or 15.5 to 21.5 d in Trials 1 and 2, respectively. Nursery feeding program did not affect (P 0.27) wean-to-finish growth performance in Trial 2.
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). The estimated slopes for several primary response criteria are illustrated in Table 9. These modeled slopes are intended to provide a reference that succinctly illustrates the rate of linear improvement in growth performance observed in these studies as weaning age increased. Understanding these slopes (rate of improvement on a per day increase in weaning age basis) enables the implications of altering weaning age within a production system to be readily modeled.
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Previous studies have illustrated positive effects of SEW production systems in which weanling pigs are removed from the sow farm of origin and reared in environments isolated from other age groups of pigs (Dritz et al., 1996a; Fangman et al., 1996; Patience et al., 2000). This management practice is also referred to as isowean production, age-segregated rearing, and segregated disease control (Harris, 2000). Multisite pig production systems have become commonplace due to the positive effects on postweaning growth performance. The improvements in growth performance in SEW are due to reduced pathogen or antigenic exposure to the growing pig (Harris and Alexander, 1999; Harris, 2000). Additionally, the site segregation and all-in, all-out management (i.e., facilities depopulated, cleaned, and disinfected between groups of pigs) accompanying this technology decreases the opportunities for pathogens to be continuously passed between groups of growing pigs. Reducing weaning age and segregated production have been shown to be a means of rearing pigs free of specific pathogens that are present in the sow farm of origin (Alexander, 1980; Harris, 1988; Alexander and Harris, 1999). However, limited research has been conducted to independently determine the effects weaning age without being confounded by site segregation (Dritz et al., 1996b; Fangman et al., 1996). On commercial farms, weaning age is generally an outcome determined secondarily from the number of sows farrowing each week, lactation space available, and how efficiently the lactation space available is being used. Furthermore, weaned pigs within commercial production systems are commonly considered to be of equal value and are assumed to have similar postweaning performance potential, as long as minimum quality standards are met. The performance differences observed in our studies strongly suggest that weaning age has a significant impact on the economic value of a weaned pig.
The effects of incrementally increasing or decreasing weaning age on postweaning performance in a commercially applied SEW production scheme, given a uniform health status and environment, have not been previously reported. The extensive individual pig allotment procedures described were implemented to make certain that each nursery and finishing pen replicated the actual weight distribution within each treatment. Replicating the weight distribution within each pen ensured that each pen was a similar and representative sample of the treatment populations being evaluated. We feel the extensive allotment procedures used, and numbers of population replications achieved, were the critical components in our effort to estimate the effects of weaning age on wean-to-finish performance in this multisite production system.
In these studies, wean-to-finish growth performance and productivity (as measured by ADG, mortality, off-test weight per day of age, and weight sold per pig weaned) improved as weaning age increased from 12 to 21 and 15.5 to 21.5 d of age. These improvements in growth and mortality largely occurred in the initial 42 d after weaning, with some further improvements in growth in finishing. The improvements in postweaning ADG and ADFI with increased weaning age are similar to those reported by Dritz et al. (1996b) and Fangman et al. (1996). However, the improvement in weight per day of age at slaughter was not observed when 9- and 19-d weaned pigs were segregated at weaning and raised in a common off-site location (Dritz et al., 1996b). Hohenshell et al. (2000) weaned pigs at 10 or 30 d of age into a common environment in a behaviorally focused study and did not find weight per day of age differences between treatments at slaughter. The differences between the Dritz et al. (1996b) and the Hohenshell et al. (2000) studies and the current trials may be due to differences in age range evaluated (Hohenshell et al., 2000), health status, group or pen size, or growing environment. The Dritz et al. (1996b) and Hohenshell et al. (2000) studies were completed in facilities with not greater than five pigs per pen, whereas the Fangman et al. (1996) study was completed in commercial facilities with 28 pigs per pen, more similar to the current studies.
The linear improvements in wean-to-finish growth and productivity observed with increasing wean age in the current trials is likely a function of both weight and physiological maturity at weaning. Weaning weight has been shown to improve wean-to-finish growth rate (Mahan and Lepine, 1991; Mahan et al., 1996; Wolter and Ellis, 2001); however, weaning weight is directly confounded within weaning age in this study. Therefore, it is not appropriate to translate the weaning age effects directly back to weaning weight in the current studies. Wolter et al. (2002) found that increasing weaning weight by means of a supplemental milk replacer during lactation had no effect on ADG from weaning at 21 d to 14 kg, or from weaning to 110 kg. However, Wolter et al. (2002) did observe a reduction in days from birth to 110 kg in pigs supplemented with milk throughout the 21-d suckling period. Translating weaning age performance improvements back to an incremental increase in weaning weight basis is only appropriate when the improved weaning weights are due to an increased weaning age. The effect of weaning age on weaning weight (0.257 ± 0.003 kg increase in weaning weight per day increase in weaning age) was similar in Trials 1 and 2.
It should be recognized that the improvements in wean-to-finish growth performance observed in these studies might vary between different multisite production systems due to differences in health status, environment, or genotype. These studies suggest the magnitude of growth rate improvement observed with increasing wean age is rather predictable within a given multisite production system. However, the magnitude of the mortality improvement likely depends on baseline mortality rates, as well as pig-flow, site, or other system-specific challenges.
There were no weaning age x nursery feeding program interactions on growth performance in Trial 2. Additionally, altering the nursery feeding program did not affect wean-to-finish growth performance. A trend toward reducing variation in d 42 postweaning weight was the only performance measure affected by altering the nursery feeding program. Increasing diet complexity has been shown to increase wean-to-finish performance in pigs (Mahan, 1998) when increasing diet complexity was defined as increasing the inclusion rates of whey and specialty proteins. The differences in nursery feeding programs fed in Trial 2 may not have been large enough to create detectable differences in mean growth performance. Other research has found that increasing diet complexity increased growth performance in the initial postweaning period (weaning to 7.0 kg), with no detectable improvements through slaughter (Dritz et al., 1996b). Therefore, these data and the numerical reductions in variation indicate that diet complexity is most important for the transition to eating feed after weaning. However, once pigs start consuming feed, the importance rapidly declines. Finally, the observations in Trial 2 are consistent with other research indicating that weight at weaning has more influence on postweaning growth than altering postweaning feeding regimens (Mahan et al., 1991, 1998; Wolter and Ellis, 2001).
Implications
Increasing weaning age from 12 to 21.5 d improved wean-to-finish growth performance in a multisite swine production system. Linear improvements in growth and mortality rate largely occurred in the initial 42 d postweaning period, with some ongoing growth improvements in finishing. These studies suggest increasing weaning age up to 21.5 d can be an effective production strategy to improve wean-to-finish growth performance in a multisite pig production.
Footnotes
1 Contribution No. 03-412-J from the Kansas Agric. Exp. Stn., Manhattan 66506. 
2 Correspondence and current address: 301 Alexander Ave., Suite B, Ames, IA 50010 (phone: 515-663-9296; fax: 515-663-9297; e-mail: rmain{at}murphyfarms.com).
Received for publication August 7, 2003. Accepted for publication February 4, 2004.
Literature Cited
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