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Effect of dietary regime and group structure on pig performance and the variation in weight and growth rate from weaning to 20 weeks of age
Livestock Science 136 (2011) 216–224
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Livestock Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / l i v s c i
Effect of dietary regime and group structure on pig performance and the variation in weight and growth rate from weaning to 20 weeks of age E. Magowan a,⁎, M.E.E. Ball a,b, K.J. McCracken b, V.E. Beattie c, R. Bradford e, M.J. Robinson d, M. Scott c, F.J. Gordon d, C.S. Mayne a,b a b c d e
Agri-Food and Biosciences Institute, Large Park, Hillsborough, Co. Down, Northern Ireland BT26 6DR, United Kingdom The Queen's University of Belfast, Newforge Lane, Belfast BT9 5PX, United Kingdom Devenish Nutrition Ltd., 96 Duncrue Street, Belfast BT3 9AR, United Kingdom John Thompson & Sons Ltd., 35–38 York Road, Belfast BT15 3GW, United Kingdom Preferred Capital Management, 96 Duncrue Street, Belfast BT3 9AR, United Kingdom
a r t i c l e
i n f o
Article history: Received 21 June 2010 Received in revised form 13 September 2010 Accepted 16 September 2010 Keywords: Pigs Diet Group structure Performance Variation
a b s t r a c t This study aimed to improve lifetime pig performance and reduce variation in growth rate between pigs using managerial and nutritional practices. The experiment (2 × 2 × 2 factorial) compared uniform and mixed weight grouping (SD of weight in group at weaning 0.7 kg and 1.6 kg respectively), offering pigs a high (12 kg) or low (6 kg) allowance of starter diets post weaning and either a special (DE 14.5 MJ/kg, total lysine 11 g/kg) or normal (DE 13.5 MJ/kg, total lysine 9.5 g/kg) finishing diet. Over six time replicates, 960 pigs (Landrace × Large White) were randomly allocated at weaning (28 ± 2 days of age) into groups of 20 according to weight and sex and these groups were split at 10 weeks of age (transfer to finishing accommodation) into two groups of 10. Finishing diet was offered from 11 weeks of age. The FCR of pigs (wean– 7 weeks of age) was significantly (P b 0.001) improved when a high allowance of starter diets was offered (1.25) compared with a low allowance (1.34). However, between 7 and 10 weeks of age a high allowance of starter diets only improved the FCR of pigs in uniform groups. A special finishing diet improved (Pb 0.05) the ADG of pigs during finish (11–20 weeks of age) (860 g/day) compared with a normal finishing diet (827 g/day). The coefficient of variation (CV) of weight at 10 and 15 weeks of age was significantly lower (both P b 0.001) for pigs in uniform weight groups compared with that of pigs in mixed weight groups. A three-way interaction was observed on the CV of ADG (weaning–20 weeks of age) (Pb 0.05) and FCR (11–20 weeks of age) (Pb 0.01). The lowest CV of ADG (weaning—20 weeks of age) and lowest FCR (11–20 weeks of age) were achieved when uniform grouped pigs were offered a high allowance of starter diets post weaning and a special finishing diet (0.117 and 2.43 respectively) whereas the highest values were observed when mixed weight groups of pigs were offered a low allowance of starter diets post weaning and a normal finishing diet (0.162 and 2.70 respectively). In conclusion, although uniform grouping appears to aid the reduction in slaughter weight variation and improve FCR, its effect is dependent on dietary regime. Overall, from weaning to 20 weeks of age, uniformly grouped pigs offered a high allowance of starter diets post weaning and a special finishing diet had a low CV of ADG and the most efficient FCR. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction ⁎ Corresponding author. Tel.: + 44 28 9268 2484; fax: + 44 28 9268 9594. E-mail address: [email protected] (E. Magowan).
The variation in growth rate between pigs on commercial herds can have major financial implications (King, 1999;
1871-1413/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2010.09.013
E. Magowan et al. / Livestock Science 136 (2011) 216–224
Patience and Beaulieu, 2006). Large variation in growth rate within an herd is related to poor average herd growth rate and decreased profitability (Magowan et al., 2007; Roberts and Deen, 1995). Variability in weight and growth rate is a fact of life from birth, and research suggests that, for the porcine species, the position of the foetus in the uterus has a role to play in birth weight and subsequent growth performance of the pig (Milligan et al., 2001, 2002; Wise and Christenson, 1992). Practices such as fostering, creep feeding and split weaning have been used to reduce variation in the weaning weight of pigs with the ultimate goal of reducing variation in slaughter weight. However, the beneficial effects of these practices as observed at weaning, often disappear during the growing period (Milligan et al., 2002; Lawlor et al., 2002; Mahan, 1993). Attempts have also been made to reduce the variation in weight of pigs at various ages by offering diets varying in nutrient density and offering these diets for different time periods post weaning (Lawlor et al., 2002). Furthermore, grouping pigs in uniform weight groups during the growing and finishing periods has been investigated (O'Connell et al., 2005). Higher density diets improved production performance in the studies reported by Lawlor et al. (2002) and pens were cleared at slaughter more efficiently when pigs were uniformly grouped at the start of the finishing period in the studies reported by O'Connell et al. (2005). However, neither of the aforementioned practices, when carried out separately, significantly influenced the variation in growth rate between pigs. Nyachoti et al. (2004) noted that the three main aspects which affect the voluntary feed intake of pigs and hence growth rate, are genetics, environmental stressors and nutrient density. They suggested that, in commercial practice, these three aspects are impossible to separate and often influence voluntary feed intake at the same time. Therefore, research focussing on the combination of environmental and dietary factors influencing pig growth and feed intake is potentially more commercially beneficial. The aim of the current study was to reduce the variation in growth rate between pigs, and hence variation in weight of pigs at various ages, by grouping pigs in either uniform or mixed weight groups at weaning, and offering these groups of pigs superior or normal dietary regimes during the post weaning and finishing periods.
2. Materials and methods
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2.2. Housing At weaning, pigs were transferred to growing accommodations (0.38 m2/pig) with plastic slatted floors. Temperature was 28 °C on the first day of treatment, and this was reduced by 0.5 °C/day to a minimum of 18 °C. In the growing accommodation, pigs were offered feed via a ‘dry’ multi space feeder (Etra Feeders, Northern Ireland). Two feeders were placed along the front of the pen, 0.5 m apart. At 10 weeks of age, pigs were transferred to finishing accommodations (0.61 m2/pig) with fully slatted concrete flooring, where they remained until slaughter (105 kg). In the finishing accommodation pigs were offered feed via a ‘wet and dry’ single space verba feeder (Verba, Verbakel™, The Netherlands). One feeder was used per pen i.e. per 10 pigs. During the trial, all pigs were offered water from bowl drinkers (10 pigs per drinker). They were exposed to natural lighting through windows and artificial lighting during feeding. 2.3. Experimental design and treatments The experiment was designed as a 2 × 2 × 2 factorial (group structure (uniform vs mixed) × post weaning starter diet allowance (high vs low) × finishing diet (special vs normal)). Pigs in uniform groups all had a similar weight whereas pigs in mixed weight groups spanned the full range of weights which can be observed at weaning. Post weaning starter diet allowance treatments compared the practice of offering post weaned pigs a ‘High’ allowance of starter diets (12 kg/pig) or a ‘low’ allowance (6 kg/pig). The 12 kg included 4 kg of ‘starter 1’ diet followed by 8 kg of ‘starter 2’ diet. The 6 kg included 2 kg of ‘starter 1’ diet followed by 4 kg of ‘starter 2’ diet. In practice, each pen of 20 pigs was allocated 20 times the required allowance. For example, for the 4 kg of starter 1 diet, in the ‘high’ allowance treatment, each pen of 20 pigs was offered 80 kg of starter 1 diet. When pens of pigs finished their allocation of starter diets they were offered a grower diet to 11 weeks of age. The finishing diets differed in energy and lysine content creating a ‘special’ (S) and ‘normal’ (N) finishing diet. All diets were offered ad libitum and their compositions are reported in Table 1. Dietary treatments in the finishing period were balanced across the treatments from the post weaning period, so that carryover effects could be tested. Pigs were on experiment from weaning to 20 weeks of age.
2.1. Pre weaning management
2.4. Post weaning period
Piglets received creep feed (DE 15.8 MJ/kg fresh, CP 200 g/kg fresh, lysine 16 g/kg fresh; Devenish Nutrition Ltd, Belfast) ad libitum from 18 ± 2 days of age. The creep feed was offered on the floor of the heated forward creep area, and was the same as the starter 1 diet used in the trial (Table 1). Pigs were vaccinated for Mycoplasma hyopneumoniae at weaning. At the time of the trial, Porcine Circovirus 2 (PCV2) was identified at high levels in some pigs and it was suspected that Post weaning Multi-systemic Wasting Syndrome (PMWS) was apparent at a low level in finishing pigs within the herd (mortality = 6%). Zinc Oxide and Tylan® (Elanco) were included in all diets.
Over six time periods (replicates) a total of 960 pigs (1/4 Landrace × ¾ Large White) were weaned at 28 ± 2 days of age and randomly allocated into groups of 20 according to their weight and sex (groups were balanced for sex (entire boars and gilts)). Within each replicate, eight groups were formed at weaning. Six represented uniform weight groups while the remaining two represented mixed weight groups. Therefore two groups of light weight pigs (average weight 7.1 kg, SD 0.85 kg), two groups of medium weight pigs (average weight 8.9 kg SD 0.50 kg), two groups of heavy weight pigs (average weight 10.4 kg, SD 0.75 kg) and two groups of mixed weight pigs (i.e. light, medium and heavy pigs grouped together,
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Table 1 The ingredients and composition of the diets used from weaning to finish. Diet
Ingredient (g/kg) Wheat Barley Maize Cooked cereal Soya Rice protein Sugar Whey Molaferm Vegetable oil blend Soya oil Limestone Mono DCP Salt Lysine Methionine Devicare (Mins and vits) Emulsifier Lignosulphate binder Chemical analysis as formulated Dry matter (g/kg) Digestible energy (MJ/kg) Crude protein (g/kg) Oil A (g/kg) Fibre (g/kg) Ash (g/kg) Total lysine (g/kg)
Starter 1
Starter 2
Grower
Normal finisher
Special finisher
✓
✓
700
360 394
500 227
217
188
185
30
20 10
✓ ✓ ✓ ✓
(Toasted)
✓
✓ ✓ ✓ ✓ ✓ ✓ ✓
✓ ✓ ✓ (Toasted) ✓ ✓ ✓
✓
✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
904 15.8 200 9.7 18 65 16
888 15.5 200 8.4 22 55 15
20 11 7.5 1.5 4.6 1.4 5
11.5 6.1 2.8 2.3 0.4 5
20 15 26 8.5 6.5 1.2 4.5 0.4 5
867 14.0 186 32 24 48 12
870 13.5 167 25 34 48 9.5
872 14.5 166 55 30 42 11
⁎The diets were commercially manufactured by Devenish Nutrition Ltd. (Belfast) (Starter diets 1 & 2) and John Thompson and Sons Ltd. (Grower, normal and special finisher). The exact amount of each ingredient cannot therefore be disclosed, however a ‘tick’ represents the presence of the raw material in the diet.
average weight 8.8 kg, SD 1.60 kg) were formed per replicate. Starter diet allowance was then balanced across the groups. 2.5. Finishing period At 10 weeks of age, pigs were transferred to finishing accommodation. At this stage, each group of 20 pigs was split to form two similar groups of 10 pigs (balanced for weight and sex (entire boars and gilts)) and the original assignment of ‘light’, ‘medium’, ‘heavy’ or ‘mixed’ remained with the group. All pigs were offered the grower diet to 11 weeks of age and each pen was then randomly allocated to receive either the ‘special’ or ‘normal’ finishing diet, so that diet was balanced across grouping and starter diet allowance. 2.6. Measurements Pigs were weighed and feed intakes were recorded at wean, 7, 10, 11, 15 and 20 weeks of age. Average daily gain (ADG), average daily feed intake (ADFI), feed conversion ratio (FCR), coefficient of variation for weight and the coefficient of variation for average daily gain were subsequently calculated. On a pen basis, pig performance data (weight, ADG, ADFI and FCR) for the uniform group structure treatment was combined and represented the average of the light, medium and heavy weight uniform groups. Coefficients of variation (CV) were calculated by dividing the standard deviation of the data set by the average of the data set. The coefficient of variation for the uniform groups of pigs was calculated in two ways:
1) individual pig weight and ADG data for the heavy, medium and light pigs in the uniform groups were combined as one data set and therefore represented 60 pigs and the same spread in weights as the mixed weight group, and 2) similar to the performance data, CV per pen was calculated for each uniform group and the three ‘pen’ values were averaged resulting in a low coefficient of variation for the uniform groups. 2.7. Statistical analysis Data were analysed on a pen mean basis by Analysis of Variance (ANOVA) using Genstat version 10.1 statistics package (Genstat 10.1, Lawes Agricultural Trust, Rothamsted Experimental Station). Data were analysed according to the 2 × 2 × 2 design (group structure × starter diet allowance × finishing diet). Values for the uniform groups were the average of the three uniform groups unless otherwise stated. All statistical analyses were conducted at a significance level of 5%. No covariates were applied. 3. Results 3.1. Treatment effects on pig weight There were no significant effects of starter diet allowance, finishing diet or group structure on the weight of pigs at any stage of group (Table 2).
E. Magowan et al. / Livestock Science 136 (2011) 216–224
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Table 2 Effects of starter diet allowance, finishing diet and method of grouping on the weight of pigs between weaning and 20 weeks of age. Group structure
Weight (kg) at: Wean 7 weeks 10 weeks 11 weeks 15 weeks 20 weeks
Starter diet allowance
Finishing diet
Uniform
Mixed
SEM
P
Low
High
SEM
P
Special
Normal
SEM
P
8.8 15.3 29.1 33.2 54.4 86.3
8.8 15.4 29.2 33.3 53.9 85.3
0.21 0.27 0.38 0.41 0.59 0.73
NS NS NS NS NS NS
8.8 15.3 28.9 32.8 53.6 85.5
8.8 15.4 29.3 33.6 54.9 86.7
0.19 0.24 0.34 0.37 0.53 0.65
NS NS NS NS NS NS
8.8 15.3 29.1 33.1 54.3 86.5
8.8 15.4 29.2 33.3 54.2 85.7
0.19 0.24 0.34 0.37 0.53 0.65
NS NS NS NS NS NS
NS: P N 0.05.
3.2. Treatment effects on pig performance The FCR of pigs offered a high allowance of starter diets post weaning was significantly (P b 0.001) improved between wean and 7 weeks of age compared with those offered a low allowance (Table 3). There was an interaction between starter diet allowance and method of grouping on the ADG and FCR of pigs between 7 and 10 weeks of age (P b 0.01 and P b 0.001 respectively) (Table 3). The ADG and FCR of mixed weight groups of pigs was poorer when they were offered a high allowance of starter diets (633 g/day and 1.64) compared with a low allowance (672 g/day and 1.57) which was in contrast to uniformly grouped pens of pigs whose ADG was similar and FCR was improved when they were offered a high allowance (669 g/day and 1.54) compared with a low allowance (647 g/day and 1.62) (Table 3). The ADG of pigs between 11 and 20 weeks of age was significantly (P b 0.05) higher when pigs were offered a special finishing diet (860 g/day) compared with a normal finishing diet (827 g/day) (Table 3). There was a significant interaction (P b 0.01, SEM 26.5) between starter diet allowance and finishing diet on the ADFI of pigs between 11 and 20 weeks of age. When pigs were offered a high allowance of starter diets, their ADFI was similar between 11 and 20 weeks of age whether they were offered a special or normal finishing diet (2042 and 2072 g/day respectively). However, when they were offered a low allowance of starter diets, the ADFI of pigs between 11 and 20 weeks of age was significantly lower (1935 g/day) when they were offered a special compared with a normal finishing diet (2052 g/day). A significant three-way interaction (P b 0.01, SEM 0.039) between method of grouping, starter diet allowance and finishing diet was observed for FCR between 11 and 20 weeks of age (Table 3). When pigs were offered a high allowance of starter diets followed by a special finishing diet, FCR was significantly lower in uniform groups (2.30) than in mixed weight groups of pigs (2.53). In addition when pigs in uniform groups were offered a low allowance of starter diets and a normal finishing diet their FCR was similar (2.45) to that of uniformly grouped pigs offered a low allowance of starter diets followed by a special finishing diet (2.35). However, for pigs in mixed weight groups, the FCR between 11 and 20 weeks of age was similar whether pigs were offered a normal or special finishing diet when they had previously been offered a high allowance of starter diets (2.54 and 2.53 respectively). This is in contrast to when they were offered a low allowance of starter diets, in this case FCR was significantly increased when a normal finishing diet was used
(2.63) compared with a special finishing diet (2.35). Overall the best FCR was observed when uniformly grouped pigs were offered a high allowance of starter diets followed by a special finishing diet whereas the poorest FCR was observed when mixed weight pens of pigs were offered a low allowance of starter diets and a normal finishing diet. Overall between weaning and 20 weeks of age, there were no significant effects on ADG. However, the ADFI of pigs between weaning and 20 weeks of age offered a special finishing diet was significantly lower (P b 0.05, 1817 g/day) compared with those offered a normal finishing diet (1861 g/ day). Furthermore, the ADFI of pigs between weaning and 20 weeks of age in uniform groups was significantly lower (P b 0.001, 1784 g/day) than those in mixed weight groups (1891 g/day). A significant three-way interaction (P b 0.01, SEM 0.031) was observed for FCR between weaning and 20 weeks of age (Table 3). The pattern of the interaction reflected that described above for the interaction on FCR between 11 and 20 weeks of age. 3.3. Treatment effects on the coefficient of variation As expected, the CV of wean weight for pigs in uniform groups was significantly lower (P b 0.001) than that of pigs in mixed weight groups (Table 4). The CV of weight for 10, 11 and 15 weeks was also significantly lower (P b 0.001). Method of grouping had no significant effect (P N 0.05) on the CV of ADG at any stage of growth (Table 4). There was a three-way interaction between starter diet allowance, finishing diet and method of grouping on the CV of 20-week weight (P b 0.01), ADG between 11 and 20 weeks of age (P b 0.05) and ADG between weaning and 20 weeks of age (P b 0.05) (Table 4). Although the CV of 20-week weight of pigs in uniform groups was statistically similar, it was numerically lowest when these pigs were offered a low allowance of starter diets post weaning and a normal finishing diet (0.101), however the same dietary regime when offered to mixed weight groups of pigs resulted in the highest CV of 20 week weight (0.169). In addition, offering the dietary regime which included a low allowance of starter diets post weaning and a special finishing diet resulted in the lowest CV of 20 week weight for mixed weight groups (0.120) but the highest for uniform weight groups (0.139). Overall between wean and 20 weeks of age, the lowest CV of ADG was observed when uniformly grouped pigs were offered a high allowance of starter diets post weaning and a special finishing diet or when mixed weight pigs were offered a high allowance of starter diets post weaning and a normal
220
Table 3 Interactions and effects of starter diet allowance (SD), finishing diet (FD) and group structure (GS) on pig performance between weaning and 20 weeks of age. Mixed
Starter diet allowance
Low
Finishing diet*
N
Average daily gain (g/day) Wean–7 weeks 345 7–10 weeks 665 10–11 weeks 551 11–20 weeks 801 Wean–20 weeks 661 Average daily feed intake (g/day) Wean–7 weeks 417 7–10 weeks 1023 10–11 weeks 1123 11–20 weeks† 2012 Wean–20 weeks 1910 Feed conversion ratio Wean–7 weeks 1.33 7–10 weeks 1.57 10–11 weeks 2.33 ‡ 11–20 weeks 2.63 Wean–20 weeks‡ 2.70
Uniform High S
N
Low S
N
High S
N
S
Interaction
Direct effects of
SD × GS
SD 3
FD
GS
SEM
P
SEM
P
P
SEM
P
314 678 595 858 696
338 632 553 823 682
341 634 527 869 706
319 647 596 862 701
324 646 518 847 680
328 667 621 821 687
327 671 603 864 709
8.2 10.8 24.5 12.5 8.2
NS b0.01 NS NS NS
5.2 6.8 15.5 7.9 5.2
NS NS NS NS NS
NS NS NS b 0.05 NS
5.8 7.6 17.3 8.9 5.8
NS NS NS NS NS
417 1023 1218 1967 1812
413 1026 1119 2053 1874
413 1026 1144 2108 1968
420 1013 1162 2091 1829
420 1013 1095 1903 1754
401 1005 1222 1977 1820
401 1005 1185 1976 1734
9.7 13.3 38.8 29.6 27.8
NS NS NS NS NS
6.1 8.5 24.6 18.8 17.6
NS NS NS NS NS
NS NS NS 0.01 b 0.05
6.8 9.4 27.4 20.9 19.7
NS NS NS NS b 0.001
b0.001 b0.01 NS NS NS
NS NS NS b 0.001 b 0.001
1.33 1.57 2.18 2.38 2.53
1.26 1.64 2.31 2.54 2.66
1.26 1.64 2.51 2.53 2.65
1.35 1.62 2.04 2.45 2.58
1.35 1.62 2.32 2.35 2.52
1.24 1.54 2.02 2.51 2.57
1.24 1.54 2.11 2.30 2.43
0.017 0.014 0.096 0.028 0.022
NS b0.001 NS NS b0.05
0.011 0.010 0.061 0.018 0.014
0.012 0.011 0.068 0.020 0.015
NS NS b 0.05 b 0.001 b 0.001
†
Interaction between starter diet allowance and finishing diet (SD × FD) ADG 11–20, P b 0.01 with SEM 26.5. Interaction between starter diet allowance, finishing diet and method of grouping (SD × FD × GS), FCR 11–20 P b 0.01 with SEM 0.039, FCR wn-20 P b 0.01 with SEM 0.031; NS: P N 0.05; * N: Normal finishing diet, S: Special finishing diet. ‡
3
SEM for effect of SD and FD is the same.
E. Magowan et al. / Livestock Science 136 (2011) 216–224
Group structure
E. Magowan et al. / Livestock Science 136 (2011) 216–224
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Table 4 Interactions and effects of starter diet allowance (SD), finishing diet (FD) and group structure (GS) on the coefficient of variation (CV) for weight and growth rate of pigs between weaning and 20 weeks of age. Group structure:
Mixed
Interactions †
Uniform High
Low
High
SD × FD
Direct effect of ‡
Starter diet allowance:
Low
SD × FD × GS
GS
Finishing diet*:
N
S
N
S
N
S
N
S
SEM
P
SEM
P
SEM
P
CV of: Wean weight 10 wk weight 11 wk weight 15 wk weight 20 wk weight Wean–10 wk ADG 10–11 wk ADG 11–20 wk ADG Wean–20 wk ADG
0.181 0.167 0.166 0.172 0.169c 0.186 0.347 0.145ab 0.162b
0.170 0.169 0.154 0.157 0.120ab 0.204 0.407 0.128ab 0.127ab
0.196 0.172 0.163 0.163 0.142bc 0.207 0.454 0.162ab 0.111a
0.183 0.166 0.147 0.149 0.144bc 0.187 0.375 0.160ab 0.154ab
0.070 0.129 0.112 0.112 0.101a 0.178 0.293 0.115a 0.152ab
0.078 0.134 0.123 0.146 0.139abc 0.179 0.358 0.149ab 0.149ab
0.076 0.128 0.118 0.138 0.130abc 0.174 0.329 0.172b 0.144ab
0.083 0.133 0.112 0.116 0.109ab 0.176 0.322 0.130ab 0.117a
0.0089 0.0099 0.0096 0.0082 0.0084 0.0132 0.0327 0.0106 0.0092
NS NS NS b 0.05 b 0.05 NS NS b 0.01 b 0.05
0.0125 0.0156 0.0152 0.0129 0.0132 0.0208 0.0516 0.0167 0.0145
NS NS NS NS b0.01 NS NS b0.05 b0.05
0.0063 0.0078 0.0076 0.0064 0.0066 0.0104 0.0258 0.0083 0.0073
b 0.001 b 0.001 b 0.001 b 0.001 b 0.05 NS NS NS NS
NS: P N 0.05; * N: Normal finishing diet, S: Special finishing diet. † There were no significant (P N 0.05) interactions between SD and GS or FD and GS. ‡ There were no significant (P N 0.05) direct effects of SD or GS. a, b, c numbers with common superscripts are not significantly different (P>0.05).
finishing diet. However, the highest CV of ADG between wean and 20 weeks of age was observed when pigs were in mixed weight groups and offered a low allowance of starter diets post weaning and a normal finishing diet. The data for uniform groups were combined as if the three uniformly grouped pens of pigs represented one pen, therefore, small, medium and large pigs were represented in one group in the same proportion as present in the mixed weight groups (Fig. 1). When these data were analysed, no three-way interactions were observed and as expected the CV of wean weight was similar for mixed and uniform groups (0.181 and 0.174 respectively). However, the CV of 10 and 20week weight was numerically lower and the CV of 15-week weight was significantly lower (P b 0.05) in uniform groups compared with mixed weight groups (Fig. 1).
7 weeks of age, it is estimated that pigs offered a low allowance of starter diets would have moved onto the grower diet approximately 5 days before they were 7 weeks of age whereas pigs on a high allowance would still have had approximately 3.5 kg/pig of starter 2 diet to consume at 7 weeks of age and would have transferred to grower diet by 8 weeks of age. In agreement with a number of previous workers, the feed conversion ratio of pigs in the current study was significantly improved between weaning and 7 weeks of age when a high allowance of starter diet was offered compared with a low allowance (Lawlor et al., 2002; Dritz et al., 1996; Danielson, 1988; Chiba, 1995). This was mainly due to the high allowance being more nutrient dense than the low allowance. The aforementioned workers also found improvements in growth rate which is in contrast to the findings of this study although it is noted that the differences between ‘high’ and ‘low’ dietary regimes used in the aforementioned literature were more extreme than those used in the current study. A high allowance of starter diets also improved FCR between 7 and 10 weeks of age but only of uniformly grouped pigs. Previous research is contradictory regards the effect of grouping on performance of
4. Discussion The dietary regime during the post weaning period, involved pigs being offered a high or low allowance of starter diets. Using the values of feed intake between wean and
Coefficient of variation for weight
0.17 0.16 NS, SEM 0.0042
0.15 NS, SEM 0.0064
0.14
P<0.05, SEM 0.0065
0.13
NS, SEM 0.0067
0.12 0.11
Mixed Uniform
0.1 4 (wean)
10
15
20
Age (weeks) Fig. 1. The effect of method of grouping when the uniform pigs were considered as one group.
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post weaned pigs. McGlone et al. (1987) found no effect but Bruininx et al. (2001) reported that post weaned pigs in uniform groups had a 3% improved FCR compared with pigs in mixed weight groups. This study suggests that an effect of group structure on FCR is related to the dietary regime used. In agreement with previous research (Azain, 2001; Brumm and Miller, 1996; Henry and Walker 1994), the special finishing diet (high lysine and energy) improved feed efficiency and growth rate during finishing (11 to 20 weeks of age) compared with the normal finishing diet. However, the digestible energy intake per kilogram gain was similar when either the normal (35.0 MJ/kg gain) or special (35.4 MJ/kg gain) diets were offered. This suggests that the main reason for the improved feed efficiency when the special diet was offered was the higher energy density provided by the special diet. In this study it was also found that a special finishing diet lowered feed intake, but only when a low allowance of starter diets had been offered post weaning. This is similar to a result observed by Chiba (1995) who found significant interactions between starter and grower diets on the feed intake of growing pigs. In their study they compared simple starter diets with complex starter diets and high or low lysine/MJ energy grower diets. They suggested that the digestive system of the pigs offered the simple diet was not developed adequately to cope with the high lysine/MJ energy grower diet and therefore feed intake was reduced. However, in the current study the same diets were used and the difference arose from the amount of diet pigs were allocated. The second suggestion put forward by Chiba (1995) for the observed interaction therefore seems more likely in that pigs obtained adequate amounts of amino acids during the grower phase (in this study the finisher phase) in accordance with their degree of muscle tissue development, even though their feed intake was reduced. Group structure had no effect on the ADG or ADFI of pigs during finishing which is in agreement with O'Connell et al. (2005) and Wolter et al. (2002). However, in this study the feed intake of uniformly grouped pigs was lower overall between weaning and 20 weeks of age compared with pigs in mixed weight groups. In addition, O'Connell et al. (2005) and Wolter et al. (2002) found no effect of group structure on FCR. In the current study, a three-way interaction was observed on the FCR of pigs during finishing, again suggesting that the effect of group structure on pig performance is dependent on dietary regime. It was interesting to note that the most efficient FCR and lowest CV of ADG between weaning and 20 weeks of age was achieved when uniformly grouped pigs were offered a high allowance of starter diets post weaning and a special finishing diet whereas the poorest FCR and highest CV of ADG were observed when mixed weight groups of pigs were offered a low allowance of starter diets and a normal finishing diet. It is not possible to comment if these two measurements are linked and if they are, more detailed data regarding individual pig feed intake and FCR would be required to aid explanation. Wolter et al. (2002), O'Quinn et al. (2001) and Tindsley and Lean (1984), using a variety of group sizes and start weights (54 pigs/pen, average 31 kg; 12 pigs/pen, average 34 kg and 4 pigs/pen, average 18 kg respectively) did not find any differences in the variation of slaughter weight when pigs were in either uniform or mixed weight groups at the start of
the grow/finish period. O'Connell et al. (2005) also found that pigs placed in uniform groups at weaning (4 weeks of age) had similar variation in weight at slaughter and variation in growth rate from wean to slaughter compared with pigs grouped in mixed weight groups at weaning. The results of the current study agree with those of O'Connell et al. (2005) observed post weaning, in that CV of weight was lower in uniform groups compared with mixed weight groups at 10 weeks of age. However, they are in contrast with the results observed by O'Connell et al. (2005) during the finishing period and with previous studies as the current study found that CV of weight of uniformly grouped pigs at 15 and even 20 weeks was still lower than that of mixed weight groups. In the current study pigs were in groups of 20 post weaning and split into similar groups of 10 during the finishing period whereas in the study by O'Connell et al. (2005) pigs were in the same group of 10 from weaning to finish. This management difference may have been a key aspect with regards to the variable weight of pigs within the uniform groups remaining low to 20 weeks of age in the current study. In addition, the CV of start (wean) weight differed more between uniform and mixed weight groups in the current study than that in the study by Wolter et al., (2002). In agreement with O'Connell et al. (2005) and Wolter et al. (2002) the CV of ADG was similar whether pigs were in uniform or mixed weight groups. Furthermore, results of this study agree with Hastad et al. (2005) who found no difference in the variation of growth rate of finishing pigs grouped in uniform or mixed weight groups and offered a high energy diet. The present results also agree with Chiba (1995) who found no difference in the variation of growth rate between post weaned pigs when they were offered a range of diets varying in nutrient density. However, this study found a significant interaction between these three factors i.e. post weaning starter diet allowance, finishing diet and group structure on the CV of 20-week weight and the CV of ADG between weaning and 20 weeks of age. The CV of 20 week weigh was, as expected, highest in the mixed weight pens but when these pigs were offered a low allowance of starter diets post weaning and a normal finishing diet, the CV of 20 week weight and CV of ADG (weaning to 20 weeks) was highest of all treatments. On the other hand, when uniform weight groups were offered a high allowance of starter diet post weaning and a special finishing diet, the CV of ADG was low which supported the result of a low CV of 20 week weight. It appears that high variation in growth rate equates to high variation in end weight when pigs are initially placed in mixed weight groups but not when uniformly grouped. Furthermore, dietary regime can exaggerate the effects both positively and negatively. Patterson (1985) noted dramatic changes in feed intake when nutrient density of the diet changed e.g. from ‘high’ to ‘medium’ or vice versa. The higher degree of variable growth rate in the current study probably reflects a high level of variation in feed intake (Nyachoti et al., 2004; Bruininx et al., 2001) which may have been related to the change in nutrient density of the diet e.g. change from high allowance of starter diets to normal finishing diet or low allowance of starter diets to special finishing diet. Although Patterson (1985) found no difference in feed intake when the entire finishing period was considered, in the current study, as has been discussed, the
E. Magowan et al. / Livestock Science 136 (2011) 216–224
finishing diet had a significant effect on feed intake and feed efficiency. Unfortunately the coefficient of variation for feed intake could not be determined since feed intakes were measured on a pen basis. It is therefore difficult to explain the above interaction, but this is clearly an area which should be further investigated to test if the result is repeatable and if so tries to establish reasons for it. In agreement with O'Connell et al. (2005), the coefficient of variation for 20-week weight of pigs in uniform groups was almost twice the CV of wean weight but in the mixed weight groups the CV for 20-week weight was lower than that of wean weight. It is also noted that the CV of ADG between wean and 10 weeks of age was similar for mixed and uniform groups of pigs which suggests that the variation in growth rate within a batch of small, or medium or large pigs is just as much as the variation in growth rate between small, medium and large pigs. This result supports previous suggestions that a degree of weight variation is required for the social dynamics of a group to be formed and if variation in weight is not present when the group is formed, it will develop (Tindsley and Lean, 1984; Payne et al., 1999). When the individual pig data for the uniform groups were pooled the resultant CV values represented the group of 60 pigs from the three uniform groups and were similar at weaning to that of the mixed weight groups. When the data was analysed in this form, no three-way interactions were noted and it was found that uniformly grouped pigs, although starting with a similar CV of weight at weaning had a decreased CV of weight at 10, 15 and 20 weeks of age (Fig. 1) compared with mixed weight groups. In practice this result is more commercially applicable and demonstrates that the uniform grouping of pigs at weaning, with further splitting at 10 weeks of age, should lower the variation in weight of pigs at slaughter. It is estimated that the lower CV found in this study equates to a reduced spread in slaughter weight of 7.5 kg (95% confidence limits minimum to maximum). 5. Conclusions A high allowance of starter diets offered post weaning improved the FCR of pigs post weaning and, in combination with uniform grouping, the early effects on FCR appear to be retained after transfer to the finishing accommodation. A higher energy and lysine finishing diet was found to improve growth rate and FCR although the effects on FCR were dependent on the group structure and the post weaning starter diet allowance. Variation in slaughter weight can be reduced by forming uniform weight groups at weaning when the groups are split at 10 weeks of age. However, variation in slaughter weight and variation in growth rate is affected by dietary regime and effects differ for uniformly and mixed weight groups of pigs. It was interesting to note that the most efficient FCR between weaning and 20 weeks of age corresponded with the lowest variation (CV) in ADG whereas the poorest FCR corresponded with the highest variation (CV) in ADG. Acknowledgements The authors gratefully acknowledge John Thompson and Sons Ltd, Devenish Nutrition Ltd and the Department of
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Agriculture and Rural Development for Northern Ireland for their support. We are also thankful for the technical assistance of Agri-Food and Biosciences Institute staff in the care of the animals and the statistical expertise provided by David Kilpatrick.
References Azain, M.J., 2001. Fat in Swine Nutrition, In: Lewis, A.J., Southern, L.L. (Eds.), Swine Nutrition, 2nd Edition. CRC Press, London, p. 100. Bruininx, E.M., van der Peet-Schwering, C.M., Schrama, J.W., Vereijken, P.F., Vesseur, P.C., Everts, H., den Hartog, L.A., Beynen, A.C., 2001. Individually measured feed intake characteristics and growth performance of grouphoused weanling pigs: effects of sex, initial body weight, and body weight distribution within groups. J. Anim. Sci. 79, 301–308. Brumm, M.C., Miller, P.S., 1996. Response of pigs to space allocation and diets varying in nutrient density. J. Anim. Sci. 74, 2730–2737. Chiba, L.I., 1995. Effects of nutritional history on the subsequent and overall growth performance and carcass traits of pigs. Livest. Prod. Sci. 41, 151–161. Danielson, D.M., 1988. Influence of starter diet complexity on subsequent performance of growing finishing pigs. Nutr. Rep. Int. 38, 129–135. Dritz, S.S., Owen, K.Q., Nelssen, J.L., Goodband, R.D., Tokack, M.D., 1996. Influence of weaning age and nursery diet complexity on growth performance and carcass characteristics and composition of high-health status pigs from weaning to 109 kilograms. J. Anim. Sci. 74, 2975–2984. Hastad, C.W., Tokach, M.D., Dritz, S.S., Goodband, R.D., DeRouchey, J.M., Nelssen, J.L., 2005. Effect of initial sorting and amount of added fat on performance of growing-finishing pigs reared in a commercial facility. Kansas State University Swine Day 2005. : Report of Progress 964. Kansas State University, Kansas, USA, pp. 122–133. Henry, W., Walker, N., 1994. Response of pigs to dietary energy and protein with particular reference to the early finishing period. Ir. J. Agric. Food Res. 33, 149–155. King, R.H., 1999. A Review—Nutritional Constraints to Pig Performance and Pig Variability. In: Cranwell, P.D. (Ed.), Manipulating Pig Production VII. Aust. Pig Sci. Assoc, Werribee, Victoria, Australia, p. 245. Lawlor, P.G., Lynch, P.B., Caffrey, P.J., O'Doherty, J.V., 2002. Effect of pre-and post weaning management on subsequent pig performance to slaughter and carcass quality. Anim. Sci. 75, 245–256. Magowan, E., McCann, M.E.E., Beattie, V.E., McCracken, K.J., Henry, W., Smyth, S., Bradford, R., Gordon, F.J., Mayne, C.S., 2007. Investigation of growth rate variation between commercial pig herds. Animal 1, 1219–1226. Mahan, D.C., 1993. Effect of weight, split-weaning and nursery feeding programs on performance responses of pigs to 105 kilograms body weight and subsequent effects on sow rebreeding interval. J. Anim. Sci. 71, 1991–1995. McGlone, J.J., Stansbury, W.F., Tribble, L.F., 1987. Effects of heat and social stressors and within-pen weight variation on young pig performance and agonistic behaviour. J. Anim. Sci. 65, 456–462. Milligan, B.N., Fraser, D., Kramer, D.L., 2001. Birth weight variation in the domestic pig: effects on offspring survival, weight gain and suckling behaviour. Appl. Anim. Behav. Sci. 73, 179–191. Milligan, B.N., Fraser, D., Kramer, D.L., 2002. Within-litter birth weight variation in the domestic pig and its relation to pre-weaning survival, weight gain, and variation in weaning weights. Livest. Prod. Sci. 76, 181–191. Nyachoti, C.M., Zijlstra, R.T., de Lange, C.F.M., Patience, J.F., 2004. Voluntary feed intake in growing–finishing pigs: a review of the main determining factors and potential approaches for accurate predictions. Can. J. Anim. Sci. 84, 549–566. O'Connell, N.E., Beattie, V.E., Watt, D., 2005. Influence of regrouping strategy on performance, behaviour and carcass parameters in pigs. Livest. Prod. Sci. 97, 107–115. O'Quinn, P.R., Dritz, S.S., Goodband, R.D., Tokach, M.D., Swanson, J.C., Nelssen, J.L., Musser, R.E., 2001. Sorting growing–finishing pigs by weight fails to improve growth performance or reduce variation. Swine Health and Production, 9, 1. Amer. Assoc. Swine Pract., Perry, USA, pp. 11–16. Patience, J.F., Beaulieu, A.D., 2006. Variation in the Finishing Barn. Proceed. : Manitoba Swine Sem., 20. Manitoba Agric. Food Rural Initiatives, Manitoba, Canada, p. 129. Patterson, D.C., 1985. The effect of nutrient density of the diet and of a change in nutrient density on the performance of pigs fed ad libitum for bacon. Anim. Prod. 40, 169–174. Payne, H.G., Mullan, B.P., Trezona, M., Frey, B., 1999. Variation in Pig Production and Performance. In: Cranwell, P.D. (Ed.), Manipulating Pig
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Production VII. Australasian Pig Sci. Assoc., Werribee, Victoria, Australia, pp. 13–26. Roberts, J., Deen, J., 1995. Conformance quality in pig production. Comp. Cont. Educ. Pract. Vet. 17, 1308–1311. Tindsley, W.E.C., Lean, I.J., 1984. Effects of weight range at allocation on production and behaviour in fattening pig groups. Appl. Anim. Behav. Sci. 12, 79–92. Wise, T.H., Christenson, R.K., 1992. Relationship of foetal position within the uterus to foetal weight, placental weight, testosterone, estrogens, and
thymosin beta 4 concentrations at 70 and 104 days of gestation in swine. J. Anim. Sci. 70, 2787–2793. Wolter, B.F., Ellis, M., Curtis, S.E., Parr, E.N., Webel, D.M., 2002. Effects of feeder– trough space and variation in body weight within a pen of pigs on performance in a wean-to-finish production system. J. Anim. Sci. 80, 2241–2246.
Contents lists available at ScienceDirect
Livestock Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / l i v s c i
Effect of dietary regime and group structure on pig performance and the variation in weight and growth rate from weaning to 20 weeks of age E. Magowan a,⁎, M.E.E. Ball a,b, K.J. McCracken b, V.E. Beattie c, R. Bradford e, M.J. Robinson d, M. Scott c, F.J. Gordon d, C.S. Mayne a,b a b c d e
Agri-Food and Biosciences Institute, Large Park, Hillsborough, Co. Down, Northern Ireland BT26 6DR, United Kingdom The Queen's University of Belfast, Newforge Lane, Belfast BT9 5PX, United Kingdom Devenish Nutrition Ltd., 96 Duncrue Street, Belfast BT3 9AR, United Kingdom John Thompson & Sons Ltd., 35–38 York Road, Belfast BT15 3GW, United Kingdom Preferred Capital Management, 96 Duncrue Street, Belfast BT3 9AR, United Kingdom
a r t i c l e
i n f o
Article history: Received 21 June 2010 Received in revised form 13 September 2010 Accepted 16 September 2010 Keywords: Pigs Diet Group structure Performance Variation
a b s t r a c t This study aimed to improve lifetime pig performance and reduce variation in growth rate between pigs using managerial and nutritional practices. The experiment (2 × 2 × 2 factorial) compared uniform and mixed weight grouping (SD of weight in group at weaning 0.7 kg and 1.6 kg respectively), offering pigs a high (12 kg) or low (6 kg) allowance of starter diets post weaning and either a special (DE 14.5 MJ/kg, total lysine 11 g/kg) or normal (DE 13.5 MJ/kg, total lysine 9.5 g/kg) finishing diet. Over six time replicates, 960 pigs (Landrace × Large White) were randomly allocated at weaning (28 ± 2 days of age) into groups of 20 according to weight and sex and these groups were split at 10 weeks of age (transfer to finishing accommodation) into two groups of 10. Finishing diet was offered from 11 weeks of age. The FCR of pigs (wean– 7 weeks of age) was significantly (P b 0.001) improved when a high allowance of starter diets was offered (1.25) compared with a low allowance (1.34). However, between 7 and 10 weeks of age a high allowance of starter diets only improved the FCR of pigs in uniform groups. A special finishing diet improved (Pb 0.05) the ADG of pigs during finish (11–20 weeks of age) (860 g/day) compared with a normal finishing diet (827 g/day). The coefficient of variation (CV) of weight at 10 and 15 weeks of age was significantly lower (both P b 0.001) for pigs in uniform weight groups compared with that of pigs in mixed weight groups. A three-way interaction was observed on the CV of ADG (weaning–20 weeks of age) (Pb 0.05) and FCR (11–20 weeks of age) (Pb 0.01). The lowest CV of ADG (weaning—20 weeks of age) and lowest FCR (11–20 weeks of age) were achieved when uniform grouped pigs were offered a high allowance of starter diets post weaning and a special finishing diet (0.117 and 2.43 respectively) whereas the highest values were observed when mixed weight groups of pigs were offered a low allowance of starter diets post weaning and a normal finishing diet (0.162 and 2.70 respectively). In conclusion, although uniform grouping appears to aid the reduction in slaughter weight variation and improve FCR, its effect is dependent on dietary regime. Overall, from weaning to 20 weeks of age, uniformly grouped pigs offered a high allowance of starter diets post weaning and a special finishing diet had a low CV of ADG and the most efficient FCR. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction ⁎ Corresponding author. Tel.: + 44 28 9268 2484; fax: + 44 28 9268 9594. E-mail address: [email protected] (E. Magowan).
The variation in growth rate between pigs on commercial herds can have major financial implications (King, 1999;
1871-1413/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2010.09.013
E. Magowan et al. / Livestock Science 136 (2011) 216–224
Patience and Beaulieu, 2006). Large variation in growth rate within an herd is related to poor average herd growth rate and decreased profitability (Magowan et al., 2007; Roberts and Deen, 1995). Variability in weight and growth rate is a fact of life from birth, and research suggests that, for the porcine species, the position of the foetus in the uterus has a role to play in birth weight and subsequent growth performance of the pig (Milligan et al., 2001, 2002; Wise and Christenson, 1992). Practices such as fostering, creep feeding and split weaning have been used to reduce variation in the weaning weight of pigs with the ultimate goal of reducing variation in slaughter weight. However, the beneficial effects of these practices as observed at weaning, often disappear during the growing period (Milligan et al., 2002; Lawlor et al., 2002; Mahan, 1993). Attempts have also been made to reduce the variation in weight of pigs at various ages by offering diets varying in nutrient density and offering these diets for different time periods post weaning (Lawlor et al., 2002). Furthermore, grouping pigs in uniform weight groups during the growing and finishing periods has been investigated (O'Connell et al., 2005). Higher density diets improved production performance in the studies reported by Lawlor et al. (2002) and pens were cleared at slaughter more efficiently when pigs were uniformly grouped at the start of the finishing period in the studies reported by O'Connell et al. (2005). However, neither of the aforementioned practices, when carried out separately, significantly influenced the variation in growth rate between pigs. Nyachoti et al. (2004) noted that the three main aspects which affect the voluntary feed intake of pigs and hence growth rate, are genetics, environmental stressors and nutrient density. They suggested that, in commercial practice, these three aspects are impossible to separate and often influence voluntary feed intake at the same time. Therefore, research focussing on the combination of environmental and dietary factors influencing pig growth and feed intake is potentially more commercially beneficial. The aim of the current study was to reduce the variation in growth rate between pigs, and hence variation in weight of pigs at various ages, by grouping pigs in either uniform or mixed weight groups at weaning, and offering these groups of pigs superior or normal dietary regimes during the post weaning and finishing periods.
2. Materials and methods
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2.2. Housing At weaning, pigs were transferred to growing accommodations (0.38 m2/pig) with plastic slatted floors. Temperature was 28 °C on the first day of treatment, and this was reduced by 0.5 °C/day to a minimum of 18 °C. In the growing accommodation, pigs were offered feed via a ‘dry’ multi space feeder (Etra Feeders, Northern Ireland). Two feeders were placed along the front of the pen, 0.5 m apart. At 10 weeks of age, pigs were transferred to finishing accommodations (0.61 m2/pig) with fully slatted concrete flooring, where they remained until slaughter (105 kg). In the finishing accommodation pigs were offered feed via a ‘wet and dry’ single space verba feeder (Verba, Verbakel™, The Netherlands). One feeder was used per pen i.e. per 10 pigs. During the trial, all pigs were offered water from bowl drinkers (10 pigs per drinker). They were exposed to natural lighting through windows and artificial lighting during feeding. 2.3. Experimental design and treatments The experiment was designed as a 2 × 2 × 2 factorial (group structure (uniform vs mixed) × post weaning starter diet allowance (high vs low) × finishing diet (special vs normal)). Pigs in uniform groups all had a similar weight whereas pigs in mixed weight groups spanned the full range of weights which can be observed at weaning. Post weaning starter diet allowance treatments compared the practice of offering post weaned pigs a ‘High’ allowance of starter diets (12 kg/pig) or a ‘low’ allowance (6 kg/pig). The 12 kg included 4 kg of ‘starter 1’ diet followed by 8 kg of ‘starter 2’ diet. The 6 kg included 2 kg of ‘starter 1’ diet followed by 4 kg of ‘starter 2’ diet. In practice, each pen of 20 pigs was allocated 20 times the required allowance. For example, for the 4 kg of starter 1 diet, in the ‘high’ allowance treatment, each pen of 20 pigs was offered 80 kg of starter 1 diet. When pens of pigs finished their allocation of starter diets they were offered a grower diet to 11 weeks of age. The finishing diets differed in energy and lysine content creating a ‘special’ (S) and ‘normal’ (N) finishing diet. All diets were offered ad libitum and their compositions are reported in Table 1. Dietary treatments in the finishing period were balanced across the treatments from the post weaning period, so that carryover effects could be tested. Pigs were on experiment from weaning to 20 weeks of age.
2.1. Pre weaning management
2.4. Post weaning period
Piglets received creep feed (DE 15.8 MJ/kg fresh, CP 200 g/kg fresh, lysine 16 g/kg fresh; Devenish Nutrition Ltd, Belfast) ad libitum from 18 ± 2 days of age. The creep feed was offered on the floor of the heated forward creep area, and was the same as the starter 1 diet used in the trial (Table 1). Pigs were vaccinated for Mycoplasma hyopneumoniae at weaning. At the time of the trial, Porcine Circovirus 2 (PCV2) was identified at high levels in some pigs and it was suspected that Post weaning Multi-systemic Wasting Syndrome (PMWS) was apparent at a low level in finishing pigs within the herd (mortality = 6%). Zinc Oxide and Tylan® (Elanco) were included in all diets.
Over six time periods (replicates) a total of 960 pigs (1/4 Landrace × ¾ Large White) were weaned at 28 ± 2 days of age and randomly allocated into groups of 20 according to their weight and sex (groups were balanced for sex (entire boars and gilts)). Within each replicate, eight groups were formed at weaning. Six represented uniform weight groups while the remaining two represented mixed weight groups. Therefore two groups of light weight pigs (average weight 7.1 kg, SD 0.85 kg), two groups of medium weight pigs (average weight 8.9 kg SD 0.50 kg), two groups of heavy weight pigs (average weight 10.4 kg, SD 0.75 kg) and two groups of mixed weight pigs (i.e. light, medium and heavy pigs grouped together,
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Table 1 The ingredients and composition of the diets used from weaning to finish. Diet
Ingredient (g/kg) Wheat Barley Maize Cooked cereal Soya Rice protein Sugar Whey Molaferm Vegetable oil blend Soya oil Limestone Mono DCP Salt Lysine Methionine Devicare (Mins and vits) Emulsifier Lignosulphate binder Chemical analysis as formulated Dry matter (g/kg) Digestible energy (MJ/kg) Crude protein (g/kg) Oil A (g/kg) Fibre (g/kg) Ash (g/kg) Total lysine (g/kg)
Starter 1
Starter 2
Grower
Normal finisher
Special finisher
✓
✓
700
360 394
500 227
217
188
185
30
20 10
✓ ✓ ✓ ✓
(Toasted)
✓
✓ ✓ ✓ ✓ ✓ ✓ ✓
✓ ✓ ✓ (Toasted) ✓ ✓ ✓
✓
✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
904 15.8 200 9.7 18 65 16
888 15.5 200 8.4 22 55 15
20 11 7.5 1.5 4.6 1.4 5
11.5 6.1 2.8 2.3 0.4 5
20 15 26 8.5 6.5 1.2 4.5 0.4 5
867 14.0 186 32 24 48 12
870 13.5 167 25 34 48 9.5
872 14.5 166 55 30 42 11
⁎The diets were commercially manufactured by Devenish Nutrition Ltd. (Belfast) (Starter diets 1 & 2) and John Thompson and Sons Ltd. (Grower, normal and special finisher). The exact amount of each ingredient cannot therefore be disclosed, however a ‘tick’ represents the presence of the raw material in the diet.
average weight 8.8 kg, SD 1.60 kg) were formed per replicate. Starter diet allowance was then balanced across the groups. 2.5. Finishing period At 10 weeks of age, pigs were transferred to finishing accommodation. At this stage, each group of 20 pigs was split to form two similar groups of 10 pigs (balanced for weight and sex (entire boars and gilts)) and the original assignment of ‘light’, ‘medium’, ‘heavy’ or ‘mixed’ remained with the group. All pigs were offered the grower diet to 11 weeks of age and each pen was then randomly allocated to receive either the ‘special’ or ‘normal’ finishing diet, so that diet was balanced across grouping and starter diet allowance. 2.6. Measurements Pigs were weighed and feed intakes were recorded at wean, 7, 10, 11, 15 and 20 weeks of age. Average daily gain (ADG), average daily feed intake (ADFI), feed conversion ratio (FCR), coefficient of variation for weight and the coefficient of variation for average daily gain were subsequently calculated. On a pen basis, pig performance data (weight, ADG, ADFI and FCR) for the uniform group structure treatment was combined and represented the average of the light, medium and heavy weight uniform groups. Coefficients of variation (CV) were calculated by dividing the standard deviation of the data set by the average of the data set. The coefficient of variation for the uniform groups of pigs was calculated in two ways:
1) individual pig weight and ADG data for the heavy, medium and light pigs in the uniform groups were combined as one data set and therefore represented 60 pigs and the same spread in weights as the mixed weight group, and 2) similar to the performance data, CV per pen was calculated for each uniform group and the three ‘pen’ values were averaged resulting in a low coefficient of variation for the uniform groups. 2.7. Statistical analysis Data were analysed on a pen mean basis by Analysis of Variance (ANOVA) using Genstat version 10.1 statistics package (Genstat 10.1, Lawes Agricultural Trust, Rothamsted Experimental Station). Data were analysed according to the 2 × 2 × 2 design (group structure × starter diet allowance × finishing diet). Values for the uniform groups were the average of the three uniform groups unless otherwise stated. All statistical analyses were conducted at a significance level of 5%. No covariates were applied. 3. Results 3.1. Treatment effects on pig weight There were no significant effects of starter diet allowance, finishing diet or group structure on the weight of pigs at any stage of group (Table 2).
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Table 2 Effects of starter diet allowance, finishing diet and method of grouping on the weight of pigs between weaning and 20 weeks of age. Group structure
Weight (kg) at: Wean 7 weeks 10 weeks 11 weeks 15 weeks 20 weeks
Starter diet allowance
Finishing diet
Uniform
Mixed
SEM
P
Low
High
SEM
P
Special
Normal
SEM
P
8.8 15.3 29.1 33.2 54.4 86.3
8.8 15.4 29.2 33.3 53.9 85.3
0.21 0.27 0.38 0.41 0.59 0.73
NS NS NS NS NS NS
8.8 15.3 28.9 32.8 53.6 85.5
8.8 15.4 29.3 33.6 54.9 86.7
0.19 0.24 0.34 0.37 0.53 0.65
NS NS NS NS NS NS
8.8 15.3 29.1 33.1 54.3 86.5
8.8 15.4 29.2 33.3 54.2 85.7
0.19 0.24 0.34 0.37 0.53 0.65
NS NS NS NS NS NS
NS: P N 0.05.
3.2. Treatment effects on pig performance The FCR of pigs offered a high allowance of starter diets post weaning was significantly (P b 0.001) improved between wean and 7 weeks of age compared with those offered a low allowance (Table 3). There was an interaction between starter diet allowance and method of grouping on the ADG and FCR of pigs between 7 and 10 weeks of age (P b 0.01 and P b 0.001 respectively) (Table 3). The ADG and FCR of mixed weight groups of pigs was poorer when they were offered a high allowance of starter diets (633 g/day and 1.64) compared with a low allowance (672 g/day and 1.57) which was in contrast to uniformly grouped pens of pigs whose ADG was similar and FCR was improved when they were offered a high allowance (669 g/day and 1.54) compared with a low allowance (647 g/day and 1.62) (Table 3). The ADG of pigs between 11 and 20 weeks of age was significantly (P b 0.05) higher when pigs were offered a special finishing diet (860 g/day) compared with a normal finishing diet (827 g/day) (Table 3). There was a significant interaction (P b 0.01, SEM 26.5) between starter diet allowance and finishing diet on the ADFI of pigs between 11 and 20 weeks of age. When pigs were offered a high allowance of starter diets, their ADFI was similar between 11 and 20 weeks of age whether they were offered a special or normal finishing diet (2042 and 2072 g/day respectively). However, when they were offered a low allowance of starter diets, the ADFI of pigs between 11 and 20 weeks of age was significantly lower (1935 g/day) when they were offered a special compared with a normal finishing diet (2052 g/day). A significant three-way interaction (P b 0.01, SEM 0.039) between method of grouping, starter diet allowance and finishing diet was observed for FCR between 11 and 20 weeks of age (Table 3). When pigs were offered a high allowance of starter diets followed by a special finishing diet, FCR was significantly lower in uniform groups (2.30) than in mixed weight groups of pigs (2.53). In addition when pigs in uniform groups were offered a low allowance of starter diets and a normal finishing diet their FCR was similar (2.45) to that of uniformly grouped pigs offered a low allowance of starter diets followed by a special finishing diet (2.35). However, for pigs in mixed weight groups, the FCR between 11 and 20 weeks of age was similar whether pigs were offered a normal or special finishing diet when they had previously been offered a high allowance of starter diets (2.54 and 2.53 respectively). This is in contrast to when they were offered a low allowance of starter diets, in this case FCR was significantly increased when a normal finishing diet was used
(2.63) compared with a special finishing diet (2.35). Overall the best FCR was observed when uniformly grouped pigs were offered a high allowance of starter diets followed by a special finishing diet whereas the poorest FCR was observed when mixed weight pens of pigs were offered a low allowance of starter diets and a normal finishing diet. Overall between weaning and 20 weeks of age, there were no significant effects on ADG. However, the ADFI of pigs between weaning and 20 weeks of age offered a special finishing diet was significantly lower (P b 0.05, 1817 g/day) compared with those offered a normal finishing diet (1861 g/ day). Furthermore, the ADFI of pigs between weaning and 20 weeks of age in uniform groups was significantly lower (P b 0.001, 1784 g/day) than those in mixed weight groups (1891 g/day). A significant three-way interaction (P b 0.01, SEM 0.031) was observed for FCR between weaning and 20 weeks of age (Table 3). The pattern of the interaction reflected that described above for the interaction on FCR between 11 and 20 weeks of age. 3.3. Treatment effects on the coefficient of variation As expected, the CV of wean weight for pigs in uniform groups was significantly lower (P b 0.001) than that of pigs in mixed weight groups (Table 4). The CV of weight for 10, 11 and 15 weeks was also significantly lower (P b 0.001). Method of grouping had no significant effect (P N 0.05) on the CV of ADG at any stage of growth (Table 4). There was a three-way interaction between starter diet allowance, finishing diet and method of grouping on the CV of 20-week weight (P b 0.01), ADG between 11 and 20 weeks of age (P b 0.05) and ADG between weaning and 20 weeks of age (P b 0.05) (Table 4). Although the CV of 20-week weight of pigs in uniform groups was statistically similar, it was numerically lowest when these pigs were offered a low allowance of starter diets post weaning and a normal finishing diet (0.101), however the same dietary regime when offered to mixed weight groups of pigs resulted in the highest CV of 20 week weight (0.169). In addition, offering the dietary regime which included a low allowance of starter diets post weaning and a special finishing diet resulted in the lowest CV of 20 week weight for mixed weight groups (0.120) but the highest for uniform weight groups (0.139). Overall between wean and 20 weeks of age, the lowest CV of ADG was observed when uniformly grouped pigs were offered a high allowance of starter diets post weaning and a special finishing diet or when mixed weight pigs were offered a high allowance of starter diets post weaning and a normal
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Table 3 Interactions and effects of starter diet allowance (SD), finishing diet (FD) and group structure (GS) on pig performance between weaning and 20 weeks of age. Mixed
Starter diet allowance
Low
Finishing diet*
N
Average daily gain (g/day) Wean–7 weeks 345 7–10 weeks 665 10–11 weeks 551 11–20 weeks 801 Wean–20 weeks 661 Average daily feed intake (g/day) Wean–7 weeks 417 7–10 weeks 1023 10–11 weeks 1123 11–20 weeks† 2012 Wean–20 weeks 1910 Feed conversion ratio Wean–7 weeks 1.33 7–10 weeks 1.57 10–11 weeks 2.33 ‡ 11–20 weeks 2.63 Wean–20 weeks‡ 2.70
Uniform High S
N
Low S
N
High S
N
S
Interaction
Direct effects of
SD × GS
SD 3
FD
GS
SEM
P
SEM
P
P
SEM
P
314 678 595 858 696
338 632 553 823 682
341 634 527 869 706
319 647 596 862 701
324 646 518 847 680
328 667 621 821 687
327 671 603 864 709
8.2 10.8 24.5 12.5 8.2
NS b0.01 NS NS NS
5.2 6.8 15.5 7.9 5.2
NS NS NS NS NS
NS NS NS b 0.05 NS
5.8 7.6 17.3 8.9 5.8
NS NS NS NS NS
417 1023 1218 1967 1812
413 1026 1119 2053 1874
413 1026 1144 2108 1968
420 1013 1162 2091 1829
420 1013 1095 1903 1754
401 1005 1222 1977 1820
401 1005 1185 1976 1734
9.7 13.3 38.8 29.6 27.8
NS NS NS NS NS
6.1 8.5 24.6 18.8 17.6
NS NS NS NS NS
NS NS NS 0.01 b 0.05
6.8 9.4 27.4 20.9 19.7
NS NS NS NS b 0.001
b0.001 b0.01 NS NS NS
NS NS NS b 0.001 b 0.001
1.33 1.57 2.18 2.38 2.53
1.26 1.64 2.31 2.54 2.66
1.26 1.64 2.51 2.53 2.65
1.35 1.62 2.04 2.45 2.58
1.35 1.62 2.32 2.35 2.52
1.24 1.54 2.02 2.51 2.57
1.24 1.54 2.11 2.30 2.43
0.017 0.014 0.096 0.028 0.022
NS b0.001 NS NS b0.05
0.011 0.010 0.061 0.018 0.014
0.012 0.011 0.068 0.020 0.015
NS NS b 0.05 b 0.001 b 0.001
†
Interaction between starter diet allowance and finishing diet (SD × FD) ADG 11–20, P b 0.01 with SEM 26.5. Interaction between starter diet allowance, finishing diet and method of grouping (SD × FD × GS), FCR 11–20 P b 0.01 with SEM 0.039, FCR wn-20 P b 0.01 with SEM 0.031; NS: P N 0.05; * N: Normal finishing diet, S: Special finishing diet. ‡
3
SEM for effect of SD and FD is the same.
E. Magowan et al. / Livestock Science 136 (2011) 216–224
Group structure
E. Magowan et al. / Livestock Science 136 (2011) 216–224
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Table 4 Interactions and effects of starter diet allowance (SD), finishing diet (FD) and group structure (GS) on the coefficient of variation (CV) for weight and growth rate of pigs between weaning and 20 weeks of age. Group structure:
Mixed
Interactions †
Uniform High
Low
High
SD × FD
Direct effect of ‡
Starter diet allowance:
Low
SD × FD × GS
GS
Finishing diet*:
N
S
N
S
N
S
N
S
SEM
P
SEM
P
SEM
P
CV of: Wean weight 10 wk weight 11 wk weight 15 wk weight 20 wk weight Wean–10 wk ADG 10–11 wk ADG 11–20 wk ADG Wean–20 wk ADG
0.181 0.167 0.166 0.172 0.169c 0.186 0.347 0.145ab 0.162b
0.170 0.169 0.154 0.157 0.120ab 0.204 0.407 0.128ab 0.127ab
0.196 0.172 0.163 0.163 0.142bc 0.207 0.454 0.162ab 0.111a
0.183 0.166 0.147 0.149 0.144bc 0.187 0.375 0.160ab 0.154ab
0.070 0.129 0.112 0.112 0.101a 0.178 0.293 0.115a 0.152ab
0.078 0.134 0.123 0.146 0.139abc 0.179 0.358 0.149ab 0.149ab
0.076 0.128 0.118 0.138 0.130abc 0.174 0.329 0.172b 0.144ab
0.083 0.133 0.112 0.116 0.109ab 0.176 0.322 0.130ab 0.117a
0.0089 0.0099 0.0096 0.0082 0.0084 0.0132 0.0327 0.0106 0.0092
NS NS NS b 0.05 b 0.05 NS NS b 0.01 b 0.05
0.0125 0.0156 0.0152 0.0129 0.0132 0.0208 0.0516 0.0167 0.0145
NS NS NS NS b0.01 NS NS b0.05 b0.05
0.0063 0.0078 0.0076 0.0064 0.0066 0.0104 0.0258 0.0083 0.0073
b 0.001 b 0.001 b 0.001 b 0.001 b 0.05 NS NS NS NS
NS: P N 0.05; * N: Normal finishing diet, S: Special finishing diet. † There were no significant (P N 0.05) interactions between SD and GS or FD and GS. ‡ There were no significant (P N 0.05) direct effects of SD or GS. a, b, c numbers with common superscripts are not significantly different (P>0.05).
finishing diet. However, the highest CV of ADG between wean and 20 weeks of age was observed when pigs were in mixed weight groups and offered a low allowance of starter diets post weaning and a normal finishing diet. The data for uniform groups were combined as if the three uniformly grouped pens of pigs represented one pen, therefore, small, medium and large pigs were represented in one group in the same proportion as present in the mixed weight groups (Fig. 1). When these data were analysed, no three-way interactions were observed and as expected the CV of wean weight was similar for mixed and uniform groups (0.181 and 0.174 respectively). However, the CV of 10 and 20week weight was numerically lower and the CV of 15-week weight was significantly lower (P b 0.05) in uniform groups compared with mixed weight groups (Fig. 1).
7 weeks of age, it is estimated that pigs offered a low allowance of starter diets would have moved onto the grower diet approximately 5 days before they were 7 weeks of age whereas pigs on a high allowance would still have had approximately 3.5 kg/pig of starter 2 diet to consume at 7 weeks of age and would have transferred to grower diet by 8 weeks of age. In agreement with a number of previous workers, the feed conversion ratio of pigs in the current study was significantly improved between weaning and 7 weeks of age when a high allowance of starter diet was offered compared with a low allowance (Lawlor et al., 2002; Dritz et al., 1996; Danielson, 1988; Chiba, 1995). This was mainly due to the high allowance being more nutrient dense than the low allowance. The aforementioned workers also found improvements in growth rate which is in contrast to the findings of this study although it is noted that the differences between ‘high’ and ‘low’ dietary regimes used in the aforementioned literature were more extreme than those used in the current study. A high allowance of starter diets also improved FCR between 7 and 10 weeks of age but only of uniformly grouped pigs. Previous research is contradictory regards the effect of grouping on performance of
4. Discussion The dietary regime during the post weaning period, involved pigs being offered a high or low allowance of starter diets. Using the values of feed intake between wean and
Coefficient of variation for weight
0.17 0.16 NS, SEM 0.0042
0.15 NS, SEM 0.0064
0.14
P<0.05, SEM 0.0065
0.13
NS, SEM 0.0067
0.12 0.11
Mixed Uniform
0.1 4 (wean)
10
15
20
Age (weeks) Fig. 1. The effect of method of grouping when the uniform pigs were considered as one group.
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post weaned pigs. McGlone et al. (1987) found no effect but Bruininx et al. (2001) reported that post weaned pigs in uniform groups had a 3% improved FCR compared with pigs in mixed weight groups. This study suggests that an effect of group structure on FCR is related to the dietary regime used. In agreement with previous research (Azain, 2001; Brumm and Miller, 1996; Henry and Walker 1994), the special finishing diet (high lysine and energy) improved feed efficiency and growth rate during finishing (11 to 20 weeks of age) compared with the normal finishing diet. However, the digestible energy intake per kilogram gain was similar when either the normal (35.0 MJ/kg gain) or special (35.4 MJ/kg gain) diets were offered. This suggests that the main reason for the improved feed efficiency when the special diet was offered was the higher energy density provided by the special diet. In this study it was also found that a special finishing diet lowered feed intake, but only when a low allowance of starter diets had been offered post weaning. This is similar to a result observed by Chiba (1995) who found significant interactions between starter and grower diets on the feed intake of growing pigs. In their study they compared simple starter diets with complex starter diets and high or low lysine/MJ energy grower diets. They suggested that the digestive system of the pigs offered the simple diet was not developed adequately to cope with the high lysine/MJ energy grower diet and therefore feed intake was reduced. However, in the current study the same diets were used and the difference arose from the amount of diet pigs were allocated. The second suggestion put forward by Chiba (1995) for the observed interaction therefore seems more likely in that pigs obtained adequate amounts of amino acids during the grower phase (in this study the finisher phase) in accordance with their degree of muscle tissue development, even though their feed intake was reduced. Group structure had no effect on the ADG or ADFI of pigs during finishing which is in agreement with O'Connell et al. (2005) and Wolter et al. (2002). However, in this study the feed intake of uniformly grouped pigs was lower overall between weaning and 20 weeks of age compared with pigs in mixed weight groups. In addition, O'Connell et al. (2005) and Wolter et al. (2002) found no effect of group structure on FCR. In the current study, a three-way interaction was observed on the FCR of pigs during finishing, again suggesting that the effect of group structure on pig performance is dependent on dietary regime. It was interesting to note that the most efficient FCR and lowest CV of ADG between weaning and 20 weeks of age was achieved when uniformly grouped pigs were offered a high allowance of starter diets post weaning and a special finishing diet whereas the poorest FCR and highest CV of ADG were observed when mixed weight groups of pigs were offered a low allowance of starter diets and a normal finishing diet. It is not possible to comment if these two measurements are linked and if they are, more detailed data regarding individual pig feed intake and FCR would be required to aid explanation. Wolter et al. (2002), O'Quinn et al. (2001) and Tindsley and Lean (1984), using a variety of group sizes and start weights (54 pigs/pen, average 31 kg; 12 pigs/pen, average 34 kg and 4 pigs/pen, average 18 kg respectively) did not find any differences in the variation of slaughter weight when pigs were in either uniform or mixed weight groups at the start of
the grow/finish period. O'Connell et al. (2005) also found that pigs placed in uniform groups at weaning (4 weeks of age) had similar variation in weight at slaughter and variation in growth rate from wean to slaughter compared with pigs grouped in mixed weight groups at weaning. The results of the current study agree with those of O'Connell et al. (2005) observed post weaning, in that CV of weight was lower in uniform groups compared with mixed weight groups at 10 weeks of age. However, they are in contrast with the results observed by O'Connell et al. (2005) during the finishing period and with previous studies as the current study found that CV of weight of uniformly grouped pigs at 15 and even 20 weeks was still lower than that of mixed weight groups. In the current study pigs were in groups of 20 post weaning and split into similar groups of 10 during the finishing period whereas in the study by O'Connell et al. (2005) pigs were in the same group of 10 from weaning to finish. This management difference may have been a key aspect with regards to the variable weight of pigs within the uniform groups remaining low to 20 weeks of age in the current study. In addition, the CV of start (wean) weight differed more between uniform and mixed weight groups in the current study than that in the study by Wolter et al., (2002). In agreement with O'Connell et al. (2005) and Wolter et al. (2002) the CV of ADG was similar whether pigs were in uniform or mixed weight groups. Furthermore, results of this study agree with Hastad et al. (2005) who found no difference in the variation of growth rate of finishing pigs grouped in uniform or mixed weight groups and offered a high energy diet. The present results also agree with Chiba (1995) who found no difference in the variation of growth rate between post weaned pigs when they were offered a range of diets varying in nutrient density. However, this study found a significant interaction between these three factors i.e. post weaning starter diet allowance, finishing diet and group structure on the CV of 20-week weight and the CV of ADG between weaning and 20 weeks of age. The CV of 20 week weigh was, as expected, highest in the mixed weight pens but when these pigs were offered a low allowance of starter diets post weaning and a normal finishing diet, the CV of 20 week weight and CV of ADG (weaning to 20 weeks) was highest of all treatments. On the other hand, when uniform weight groups were offered a high allowance of starter diet post weaning and a special finishing diet, the CV of ADG was low which supported the result of a low CV of 20 week weight. It appears that high variation in growth rate equates to high variation in end weight when pigs are initially placed in mixed weight groups but not when uniformly grouped. Furthermore, dietary regime can exaggerate the effects both positively and negatively. Patterson (1985) noted dramatic changes in feed intake when nutrient density of the diet changed e.g. from ‘high’ to ‘medium’ or vice versa. The higher degree of variable growth rate in the current study probably reflects a high level of variation in feed intake (Nyachoti et al., 2004; Bruininx et al., 2001) which may have been related to the change in nutrient density of the diet e.g. change from high allowance of starter diets to normal finishing diet or low allowance of starter diets to special finishing diet. Although Patterson (1985) found no difference in feed intake when the entire finishing period was considered, in the current study, as has been discussed, the
E. Magowan et al. / Livestock Science 136 (2011) 216–224
finishing diet had a significant effect on feed intake and feed efficiency. Unfortunately the coefficient of variation for feed intake could not be determined since feed intakes were measured on a pen basis. It is therefore difficult to explain the above interaction, but this is clearly an area which should be further investigated to test if the result is repeatable and if so tries to establish reasons for it. In agreement with O'Connell et al. (2005), the coefficient of variation for 20-week weight of pigs in uniform groups was almost twice the CV of wean weight but in the mixed weight groups the CV for 20-week weight was lower than that of wean weight. It is also noted that the CV of ADG between wean and 10 weeks of age was similar for mixed and uniform groups of pigs which suggests that the variation in growth rate within a batch of small, or medium or large pigs is just as much as the variation in growth rate between small, medium and large pigs. This result supports previous suggestions that a degree of weight variation is required for the social dynamics of a group to be formed and if variation in weight is not present when the group is formed, it will develop (Tindsley and Lean, 1984; Payne et al., 1999). When the individual pig data for the uniform groups were pooled the resultant CV values represented the group of 60 pigs from the three uniform groups and were similar at weaning to that of the mixed weight groups. When the data was analysed in this form, no three-way interactions were noted and it was found that uniformly grouped pigs, although starting with a similar CV of weight at weaning had a decreased CV of weight at 10, 15 and 20 weeks of age (Fig. 1) compared with mixed weight groups. In practice this result is more commercially applicable and demonstrates that the uniform grouping of pigs at weaning, with further splitting at 10 weeks of age, should lower the variation in weight of pigs at slaughter. It is estimated that the lower CV found in this study equates to a reduced spread in slaughter weight of 7.5 kg (95% confidence limits minimum to maximum). 5. Conclusions A high allowance of starter diets offered post weaning improved the FCR of pigs post weaning and, in combination with uniform grouping, the early effects on FCR appear to be retained after transfer to the finishing accommodation. A higher energy and lysine finishing diet was found to improve growth rate and FCR although the effects on FCR were dependent on the group structure and the post weaning starter diet allowance. Variation in slaughter weight can be reduced by forming uniform weight groups at weaning when the groups are split at 10 weeks of age. However, variation in slaughter weight and variation in growth rate is affected by dietary regime and effects differ for uniformly and mixed weight groups of pigs. It was interesting to note that the most efficient FCR between weaning and 20 weeks of age corresponded with the lowest variation (CV) in ADG whereas the poorest FCR corresponded with the highest variation (CV) in ADG. Acknowledgements The authors gratefully acknowledge John Thompson and Sons Ltd, Devenish Nutrition Ltd and the Department of
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Agriculture and Rural Development for Northern Ireland for their support. We are also thankful for the technical assistance of Agri-Food and Biosciences Institute staff in the care of the animals and the statistical expertise provided by David Kilpatrick.
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