- Email: [email protected]
Behaviour and weight changes at weaning and regrouping of pigs in relation to teat quality
Applied Animal Behaviour Science, 26 (1990) 143-155
143
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Behaviour and Weight Changes at Weaning and Regrouping of Pigs in Relation to Teat Quality B. ALGERS, P. JENSEN and L. STEINWALL
Swedish University of Agricultural Sciences, Department of Animal Hygiene, P.O.B. 345, S-532 24 Skara (Sweden) (Accepted for publication 16 November 1989)
ABSTRACT Algers, B., Jensen, P. and Steinwall, L., 1990. Behaviour and weight changes at weaning and regrouping of pigs in relation to teat quality. Appl. Anim. Behav. Sci., 26: 143-155. One hundred and one individually marked healthy piglets in 10 litters were followed from birth to 9 weeks of age in order to elucidate the relationships between weight changes and behaviour at weaning and regrouping. The piglets were weighed once a week and additionally at extra instances just before and after weaning and regrouping. The pigs were weaned by removal of the mother 6 weeks post-partum and the litters were mixed two by two, 7 days later, so that the pigs with weight rank 1, 3, 5 etc. in one litter were mixed with the corresponding pigs of the other litter. The behaviour of the pigs was recorded on video during 24 h before and after weaning and regrouping, and at 9 weeks of age (before moving to the fattening unit) by obtaining 20 s of continuous recording every fifth minute. Both weaning and regrouping markedly increased the frequencies of eating, drinking, aggression and submission, although the latter was only substantially increased by regrouping. Piglets having had the largest weight gain between 3 and 4 weeks post-partum (indicating good teat quality) ate less solids on all observations, except just before moving to the fattening unit, and drank less water before weaning. The same piglets had a lower relative weight gain at regrouping than their litter mates. During weaning, those pigs gaining more weight than their litter mates were more submissive, but there was no effect on aggression. When the pigs were regrouped, the pigs gaining more weight than their pen mates were more aggressive and those gaining less weight were more submissive. Aggression and submission were not observed in all pigs. During regrouping, those pigs showing submission were those that had used more productive teats than those that performed both aggressive and submissive behaviour. Pigs that showed aggression at regrouping were heavier than their pen mates and had a higher weight gain. In general, we conclude that the teat quality determines the nutritional change of the piglet at weaning, and also the degree of agonistic interactions at weaning and subsequent regrouping.
INTRODUCTION
Artificial weaning is a potential source of behaviour and health problems in pigs. In semi-natural environments, piglets are weaned at ~ 17 weeks of age, and the weaning process is gradual and prolonged (Jensen, 1986, 1988a, b; 0168-1591/90/$03.50
© 1990 Elsevier Science Publishers B.V.
144
B. ALGERS ET AL.
Jensen and Recen, 1989). Algers (1984a,b) was able to relate an increase of injuries in groups of early weaned piglets (3 weeks post-partum) to an increase of abnormal behaviour such as belly nosing and tail biting. General behavioural changes in early weaned pigs was also found by Wood-Gush and Csermely (1981). Worsaae and Schmidt (1980) reported high levels of stress hormones in piglets weaned at 3 weeks. Weaning of piglets at 6 or 7 weeks of age, as is common in Sweden, also induces various problems. Intestinal function is impaired and a stress response, often leading to post-weaning diarrhoea in the weaned pigs, has been demonstrated (LSfstedt, 1986). Some piglets may develop the so-called runt syndrome, which is characterized by reduced weight gain or even loss of weight, and considerable physiological changes such as atrophy of intestinal villi (Martinsson, 1984). There is normally a large spread of weights within a piglet litter. McBride et al. (1964a) found that the weight at 8 weeks of age was determined to a large extent by the weight at 3 weeks and the social rank within the litter (as determined by competitive success at the feed trough). In another study, McBride et al. (1964b) failed to distinguish any specific behavioural characters of extremely low-gaining piglets and it has been concluded that probably pigs at any weight could be depressed in growth. It is therefore not clear which factors cause some piglets to react more than others on weaning. The possible negative factors that a pig is exposed to in connection with weaning could be divided into different categories. Firstly, weaning demands a nutritional change. Although piglets already voluntarily consume solid feed in appreciable quantities from ~ 4 to 5 weeks of age, they still rely on milk as an important food source for a long time (Mount, 1968). Secondly, the need to utilize the feeders more may increase the frequency of agonistic interactions between litter mates, particularly if feeding space is limited. Thirdly, there may be an effect of environmental change if the pigs are moved after weaning. Fourthly, the removal of the mother will, in itself, probably cause a broad spectrum of various psychological stresses. The nutritional change at any artificial weaning time may to a large extent be determined by the milk consumption of the piglets prior to weaning. Since piglets possess a specific teat order (Fraser, 1980) and the production between different teats on the same sow may differ by as much as 200% or more (Barber et al., 1955; Algers and Jensen, 1989), different piglets within the same litter can be assumed to be affected quite differently by the nutritional change. Mixing of pigs after weaning is another well-recognized stress. Mixing has been shown to increase fighting (Meese and Ewbank, 1973; Graves et al., 1978; Friend et al., 1983; McGlone and Curtis, 1985; Rundgren, 1988) and to reduce eating time (Graves et al., 1978). Different pigs appear to be unequally involved in the fights (Rundgren, 1988). Several methods of composing new groups of pigs in order to reduce aggression and weight gain depression have
CHANGES IN WEANED AND REGROUPED PIGS
145
been studied (e.g. Blackshaw et al., 1987; Spicer and Aherne, 1987), but it is not clear which causal relationships exist between intra-litter variations of agonistic behaviour and performance. For instance, it might be that pigs with a greater need to utilize the feeders might become involved in more fights. The present study was performed to investigate the behavioural changes of individual pigs caused by removing the mother at 6 weeks of age and subsequently mixing pigs from different litters, and to relate these changes to the production of the teats which the piglets had occupied and to the weight changes that occurred during weaning and mixing. MATERIALSAND METHODS
Animals One hundred and one clinically healthy piglets from 10 litters (range 8-14 piglets per litter) were studied from birth to 9 weeks of age. The animals were of a three-cross breed, Yorkshire + New Hampshire + Swedish Landrace.
Management The pigs were kept on a conventional farm in single-sow pens (2.25× 3.70 m). The pens were divided into an area for piglets,to which the sow did not have access,and an area where the sow could eat,restand nurse, and a dunging area. Creep feed with 50 p.p.m. Mecadox was offered ad libitum to pigletsfrom I week of age. The sows were fed a daily standard ration of 2.5 kg commercial concentrate plus 0.4 kg per pigletautomatically divided into two portions per day. Fresh straw was provided daily. Both sows and piglets had access to water ad libitum. Windows and lamps provided fullday lightand lightsof low intensitywere on during the nights. Iron was administered and the teeth of the pigletsclipped within 24 h postpartum. The male pigletswere castrated between i and 2 weeks of age. The pigletswere individuallyear-tagged within 24 h post-partum. In addition, they were painted with large individual numbers on their backs.
Experimental procedure All observation serieswere carried out on two parallellitters,born not more than I day apart. The pigletswere weighed once a week from birth onwards. In addition,extra weighings were performed the day before and the day afterthe day of weaning and regrouping, here referredto as weight gain during weaning and regrouping, respectively. Weaning was performed when the piglets were 42 days old ( _+1 day) by
146
B. ALGERS ET AL.
moving the sow to a dry sow unit. Seven days later, the pigs were regrouped. This was done by mixing half of each of the parallel litters. The pigs were ranked according to weight before regrouping and mixing was done so that the pigs with weight ranks 1, 3, 5, etc. were mixed with the corresponding pigs of the other litter, and similarly those with ranks 2, 4, 6, etc. were mixed with the corresponding pigs. Fourteen days after regrouping, all the pigs were moved into a fattening stable.
Observations During 24 h before and after weaning, before and after regrouping, and before moving the litter, the behaviour of the litter was recorded on video. This was achieved by obtaining a continuous record of 20 s every fifth minute. Each such 24-h sample was regarded as one observation for each pig. The video cameras were situated above the pens and the entire pen was visible on the picture obtained. All recordings were subsequently made by the same person. During each interval, all occurrences of eating from the feeder, drinking, aggression (head-to-head knock, head-to-body knock; Jensen, 1980 ) and submission (head tilt, retreat; Jensen, 1980) were recorded, as well as the identity of the pig performing the behaviour.
A nalyses As a parameter for the milk yield of the teat occupied by a piglet, the weight increase of the piglet from Week 3 to 4 was used. During this period, the teat order was well established {Fraser, 1980) and the piglets did not consume enough solids to affect the weight gain significantly {Mount, 1968). This parameter is called "teat quality" in this paper, using the terminology of Fraser and Lin {1984). The weight data were used in three different ways in different analyses. (1) Actual weight and weight changes were considered. (2) Relative weight changes of individual piglets were obtained by dividing the weight change between two successive observations by the actual weight on the first observation. (3) The weights were indexed within litters by dividing the actual weight of the individual by the average weight of the litter at the specific observation considered. Index changes between successive observations were then calculated. Behavioural data were expressed as the mean number of observations per pig per recorded interval. Since this does not correspond to any real frequency data, one should consider and treat this as a frequency index. For the purpose of analysing weight data of those piglets that were never
CHANGESIN WEANEDAND REGROUPEDPIGS
147
observed to be involved in agonistic encounters, the pigs were grouped into those that showed no aggression or submission at all, those that showed only aggression or only submission, and those that showed both behaviours at the specific observation considered. The statistical analyses were performed using the t-test and Pearson's correlation coefficient ( Statistical Analysis Systems, 1982 ). In order to illustrate the direction and magnitude of correlations observed between weight index changes and frequencies of agonistic interactions, the material was divided into three groups: the 10% of animals with the highest and lowest weight index changes each formed one group and the rest another group. For each group, average behaviour frequencies were calculated. In this analysis, it was possible to see the behaviour of the groups of pigs with extremely low and high weight changes in relation to the majority of the pigs. RESULTS
The average weight gain of the pigs is shown in Fig. 1 together with the standard deviations. The frequency of eating behaviour increased over weaning, remained fairly constant from weaning until 1 week after regrouping, whereafter it increased again (Fig. 2a). The drinking frequency was markedly increased after weaning, but decreased thereafter (Fig. 2b). Both weaning and regrouping markedly increased aggression, but submissive behaviour was only substantially increased after regrouping (Fig. 2c-d). Pigs using more productive teats had a
?o
r
/
~5
1'1 I
,
...... -i-it
[
o
1
2
,3
4 Age,
5
6
7
8
9
weeks
Fig. 1. Average weights of the 101 piglets ( _+1 SD ) at each week from 1 week of age to just before being moved into the fattening unit.
148
B. ALGERSET AL.
Eating
Drinking
Freq 10
Freq
-f
(a)
(b)
9
-I-
8 7 6
il i
BEF. WEAN.
AFTR WEAN.
8EF, REGR,
AFTR REGR,
BEF, MDV,
BEF. WEAN,
AFT• W[AN.
OBS
BEF, REGR.
AFTR REGR,
BEF, MOV,
OB
Aggression
Submission
4]
Freq 0
,I 0 (c)
(d)
i
05
,~' 2
BEF, WEAN,
AFTR WEAN,
BIF REGR, I][}; I
AFTI~ REGR,
BEF, NOV,
BIF. WEAN,
AFTR WEAN
BEF, REGR, (F[,
AFrR REGR,
BEF. "~OV.
Fig. 2. (a-d) Average frequenems of eating, drinking, aggression and submission (_+ S E M ) on each of the five observations (w = weaning, r = regrouping, m = moving).
lower frequency of eating behaviour before and after weaning as well as before and after regrouping (Table 1 ). However, the frequency of their drinking behaviour was lower only before weaning. Those pigs that had been using more productive teats during Week 3-4 had a significantly poorer relative weight gain during regrouping, but not during weaning (Table 2). Pigs that gained more weight during weaning than their litter mates were
CHANGESIN WEANEDAND REGROUPEDPIGS
149
TABLE 1 Pearson correlation coefficients between teat quality and eating and drinking behaviour on different observations Observations Before weaning After weaning Before regrouping After regrouping Before moving Eating
-0.43 P=0.001
-0.28 P=0.004
-0.29 P=0.003
-0.25 P=0.013
Drinking
-0.29 P=0.005
-0.11 n.s.
-0.05 n.s.
n.s.
0.07
-0.17 n.s. 0.02 n.s.
n.s. = not significant. TABLE 2 Pearson correlation coefficients between teat quality during suckling and relative weight changes during weaning and regrouping Relative weight change over Weaning
Regrouping
-0.12 n.s.
-0.43 P<0.001
n.s. = not significant. TABLE 3 Pearson correlation coefficients between weight index changes and agonistic behaviour during weaning and regrouping Behaviour Aggression Weaning Regrouping
0.12
Submission
n.s.
0.35 P<0.001
0.29 P = 0.004
- 0.22 P = 0.025
n.s. = not significant.
more submissive after weaning. There was no significant effect on aggression, although the tendency was the same (Table 3, Fig. 3a-b). When the pigs were regrouped, the pigs gaining more weight than their pen mates were more aggressive and those gaining less weight were more submissive than their pen mates (Table 3, Fig. 3 c-d).
150
B. ALGERS ET AL.
Aggression at weaning Freq 06-
Submission at weaning Freq 050
Ca) 0.5
0.25
0.4
0 20
03
015
I
0.2
01
00 Loosers
Neutral
(b)
010
005
0 O0 Gainers
Aggression at regrouping
Loosers
Neutral
Gainers
Submission at regrouping
Freq 0 5
o.s
(d)
{c} 0.4
0 4 0 ,3 0.5 0 2
0 1 0 1
@0
0 0 Loosers
Neutral
Gainers
oosers
Neutral
Gainers
Fig. 3. (a-d) Average frequencies ( _+1 SD) of aggression and submission after weaning and regrouping for three groups of pigs: the 10% gaining least in weight in relation to their pen mates ("loosers"), the 10% gaining most ("gainers") and the rest of the piglets ("neutral") at weaning and regrouping, respectively.
Whether pigs were aggressive or submissive during weaning, when data were grouped irrespective of the frequency of the behaviours, did not relate to either the quality of the teat they had been using, their relative weight or weight change within litter or their weight change in relation to body weight during weaning. During regrouping, the submissive pigs were those that had used more productive teats than those which performed both aggressive and submissive behaviour. Pigs that showed aggressive behaviour generally had a higher weight
CHANGES IN WEANED AND REGROUPED PIGS
151
TABLE 4 Weight data for pigs a i ~ r weaning and regrouping in four different categories based on whether or not they performed submissive or aggressive behaviour or both. 0 = a n i m a l s not displaying any agonistic behaviour
Weaning
Regrouping
Aggres- Submis- Aggressive+ 0 sire sive submissive
Aggressive
Mean teat quality 1.10 Mean weight index 1.04 Mean index +0.02 difference Mean relative +0.05 weight change (kg kg-'body weight) n 22
0.67 0.95 0.00
1.17 0.98 +0.16
+0.07
+0.07
2
3
Submis- Aggressive+ 0 sive submissive
1.29 1.17ab* 1.48a 0.99 1.09a 0.99ab 0.00 +0.05a -0.07b +0.05 +0.07
74
45
+0.10
17
0.99b 1.08a +0.03ac
1.26ab 0.89b -0.01bc
+0.08
+0.09
8
31
*Numbers followed by different letters are significantly different ( P < 0.05, t-test).
than their pen mates and tended to have a higher weight gain over regrouping than their pen mates (Table 4). DISCUSSION Weaning comprises a number of changes which can affect the weight gain of weaned pigs, e.g. the sources of nutrition are changed and the social bonds to the sow are broken. The results show that removing the mother when the piglets are 6 weeks of age induced a behavioural change in the piglets comparable with that caused by regrouping I week later. The frequencies of eating, drinking and aggression all increased markedly, and submission increased to some degree, indicating that weaning at 6 weeks was a strain on the piglets even when no change of environment was involved. The reason why eating and drinking increased is obvious; the piglets were forced to compensate for the loss of nutrients and water caused by not being able to suckle any more. The nutritional change at weaning is therefore verified by the results. However all piglets of the litter were not affected in the same way by the nutritional change. Eating was negatively correlated to teat quality on all observation instances except the last, and drinking before weaning was negatively correlated to teat quality. We interpret this as indicating that the piglets occupying more productive teats fulfilled a larger part of their nutritional demands with milk than their litter mates. It might be that these piglets were not frequently involved in fights at the feeder before weaning and thus did not effectively learn to compete for food with their litter mates. The results indicate that the piglets with better teats were not able to compensate for their loss of nutrients, since they continued to eat less frequently than their litter
152
B. ALGERS ET AL.
mates. This became crucial at the time of regrouping, when the piglets which had used more productive teats gained significantly less relative weight than their litter mates, perhaps because of a lack of experience in competing for feed. A weak tendency for a poorer relative weight was already noted over weaning. These findings are in accordance with the "fast food hypothesis", suggested by Jensen and Recen (1989). They showed that weaning in free-ranging pigs, which was completed at ~ 17 weeks of age, was to a large extent a result of the behaviour of the young, i.e. the piglets stopped suckling without any aggressive rejection by the mother. There were some signs that smaller piglets tended to stop suckling before the larger litter mates, which led the authors to suggest that weaning could be a result of an optimal foraging decision. If a piglet occupies a productive teat, it might, according to the hypothesis, be better off from an optimal foraging point of view if it composes its total diet of a larger amount of milk than those piglets occupying less productive teats. The piglets gaining most weight relative to their litter mates over weaning were those that tended to be involved in more agonistic interactions. This is consistent with the idea that weaning caused an increase in the need to utilize the feeder and that this competition may have been one reason why agonistic behaviour increased following weaning. Regrouping of the pigs resulted in a substantial increase in both aggressive and submissive behaviour, which is consistent with earlier findings (e.g. Meese and Ewbank, 1973). However our results show that these behaviours are not seen in all pigs. Those pigs in which aggressive behaviour was observed were those gaining more weight during regrouping in relation to their pen mates. These pigs had been using less productive teats and consumed more creep feed according to the above results. The pigs that gained less weight during regrouping were more submissive and had previously been using more productive teats. In a study of how different weaning methods affected weight gain, intestinal absorption, haematology and blood chemistry, LSfstedt (1986) observed a decrease in weight gain the first week after weaning. In one group, the effect of sufficient intake of creep feed (0.3 kg per piglet day-1, measured as an average of the litter) was studied. A weight gain retardation could not be prevented in this group. However no attempts were made to relate the findings to any withinlitter characteristics. Our results suggest some possible within-litter effects of teat quality on behaviour and weight changes. These effects, evidence for some of which has been given in this paper, are outlined in the model in Fig. 4. In conclusion, we suggest that an important factor for the growth depression generally seen in pigs after weaning and regrouping is a sudden change in the supply of nutrients, being of a greater magnitude for pigs which have been occupying more productive teats than for the others. Further, we suggest that the strategy of agonistic behaviour among the pigs is a function of the variation
CHANGES IN WEANED AND REGROUPED PIGS I GOOD TEAT 0UALITY
153
I POOR TEAT OUALITY
1
f~ORE SOLIDS
1
I LESS SOLIDS
......
..........
Weaning. . . . . . . . . .
......
LARGE NUTRITIONAL CHANGE
MINOR NUTRITIONAL i CHANGE ]
L
iI
LESS AGONISTIC BEHAVIOUR
MORE AGONISTIC BEHAVIOUR
POORER WEIGHT GAIN
BETTER WEIGHT GAIN
i
l
Regrouping
i MORE AGGRESSIVE BEHAVIOUR
MORE SUBMISSIVE BEHAVIOUR
I I POORER WEIGHT GAIN
i 1 J
i BETTER WEIGHT I GAIN l
Fig. 4. A model of teat quality sequels to weaned and regroupedpigs. The model is based on the findings in this study. of the productivity of the sow's teats, the within-litter variation of access to more productive teats and the subsequent within-litter variation of growth depression.
ACKNOWLEDGEMENTS
We thank Uddetorp Farm School for allowing us to use the experimental facilities and Ferrosan AB for financial support.
154
B. A L G E R S E T AL.
REFERENCES Algers, B., 1984a. Animal health in flatdeck rearing of weaned piglets. Zentralbl. Veterinaermed. Reihe A, 31: 1-13. Algers, B., 1984b. Early weaning and cage rearing of piglets: Influence on behaviour. Zentralbl. Veterinaermed. Reihe A, 31: 14-24. Algers, B. and Jensen, P., 1989. Teat stimulation and milk production in early lactation of sows. Effects of continuous noise. In: Vocal and Tactile Communication during Suckling in Pigs. Thesis, Swedish University of Agricultural Sciences, Department of Animal Hygiene, Report 25. Barber, R.S., Braude, R. and Mitchell, K.G., 1955. Studies on milk production of Large White Pigs. J. Agric. Sci., 46: 97-118. Blackshaw, J.K., Bodero, D.A.V. and Blackshaw, A.W., 1987. The effect of group composition on behaviour and performance of weaned pigs. Appl. Anim. Behav. Sci., 19: 73-80. Fraser, D., 1980. A review of the behavioural mechanism of milk ejection of the domestic pig. Appl. Anim. Ethol., 6: 247-255. Fraser, D. and Lin, C.S., 1984. An attempt to estimate teat quality of sows by hand milking during farrowing. Can. J. Anim. Sci., 64: 165-170. Friend, T.H., Knabe, D.A. and Tanksley, T.D., 1983. Behavior and performance of pigs grouped by three different methods at weaning. J. Anim. Sci., 57: 1406-1411. Graves, H.B., Graves, K.L. and Sherritt, G.W., 1978. Social behaviour and growth of pigs following mixing during the growing-finishing period. Appl. Anim. Ethol., 4: 169-180. Jensen, P., 1980. An ethogram of social interaction patterns in grouphoused dry sows. Appl. Anim. Ethol., 6: 341-350. Jensen, P., 1986. Observations on the maternal behaviour of free-ranging domestic pigs. Appl. Anim. Behav. Sci., 16: 131-142. Jensen, P., 1988a. Maternal behaviour and mother-young interactions during lactation in freeranging domestic pigs. Appl. Anim. Behav. Sci., 20: 297-308. Jensen, P., 1988b. Maternal behaviour of free-ranging domestic pigs. I: Results of a three-year study. Swedish University of Agricultural Sciences, Department of Animal Hygiene, Report 22, 58 pp. Jensen, P. and Recen, B., 1989. When to wean--observations from free-ranging domestic pigs. Appl. Anim. Behav. Sci., 23: 49-60. LSfstedt, M., 1986. Clinical and physiological effects of weaning in pigs with special reference to post-weaning growth depression. Thesis, Department of Medicine I, Swedish University of Agricultural Sciences, Uppsala. Martinsson, K., 1984. "Pellesyndromet" hos grisar. Sven. Veterin~irtidn., 36: 11-13, McBride, G., James, J.W. and Hodgens, N., 1964a. Social behaviour of domestic animals. IV. Growing pigs. Anim. Prod., 6: 129-139. McBride, G., Wyeth, G.S.F. and Hodgens, N.W., 1964b. Social behaviour of domestic animals. VI. A note on some characteristics of "Runts" in pigs. Anim. Prod., 6: 249-252. McGlone, J.J. and Curtis, S.E., 1985. Behavior and performance of weanling pigs in pens equipped with hide areas. J. Anim. Sci., 60: 20. Meese, G.B. and Ewbank, R., 1973. The establishment and nature of the dominance hierarchy in the domestic pig. Anim. Behav., 21: 326-334. Mount, L.E., 1968. The Climatic Physiology of the Pig. Camelot Press, London, 271 pp. Rundgren, M., 1988. Growing pig performance. Effects of dietary fibre, the halothane gene, transportation and mixing. Dissertation. Inst. fSr husdjurens utfodring och v~rd. Swedish University of Agricultural Sciences, Report 172, Uppsala. Spicer, H.M. and Aherne, F.X., 1987. The effects of group size/stocking density on weanling pig performance and behavior. Appl. Anita. Behav. Sci., 19: 89-98.
CHANGESIN WEANEDANDREGROUPEDPIGS
155
Statistical Analysis Systems, 1982. SAS User's Guide: Statistics, Version 5 Edition. SAS Institute Inc., Cary, NC, 956 pp. Wood-Gush, D.G.M. and Csermely, D., 1981. A note on the diurnal activity of early-weaned piglets in flat-deck cages at 3 and 6 weeks of age. Anita. Prod., 33: 107-110. Worsaae, H. and Schmidt, M., 1980. Plasma cortisol and behaviour in early weaned piglets. Acta Vet. Scand., 21: 640-657.
143
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Behaviour and Weight Changes at Weaning and Regrouping of Pigs in Relation to Teat Quality B. ALGERS, P. JENSEN and L. STEINWALL
Swedish University of Agricultural Sciences, Department of Animal Hygiene, P.O.B. 345, S-532 24 Skara (Sweden) (Accepted for publication 16 November 1989)
ABSTRACT Algers, B., Jensen, P. and Steinwall, L., 1990. Behaviour and weight changes at weaning and regrouping of pigs in relation to teat quality. Appl. Anim. Behav. Sci., 26: 143-155. One hundred and one individually marked healthy piglets in 10 litters were followed from birth to 9 weeks of age in order to elucidate the relationships between weight changes and behaviour at weaning and regrouping. The piglets were weighed once a week and additionally at extra instances just before and after weaning and regrouping. The pigs were weaned by removal of the mother 6 weeks post-partum and the litters were mixed two by two, 7 days later, so that the pigs with weight rank 1, 3, 5 etc. in one litter were mixed with the corresponding pigs of the other litter. The behaviour of the pigs was recorded on video during 24 h before and after weaning and regrouping, and at 9 weeks of age (before moving to the fattening unit) by obtaining 20 s of continuous recording every fifth minute. Both weaning and regrouping markedly increased the frequencies of eating, drinking, aggression and submission, although the latter was only substantially increased by regrouping. Piglets having had the largest weight gain between 3 and 4 weeks post-partum (indicating good teat quality) ate less solids on all observations, except just before moving to the fattening unit, and drank less water before weaning. The same piglets had a lower relative weight gain at regrouping than their litter mates. During weaning, those pigs gaining more weight than their litter mates were more submissive, but there was no effect on aggression. When the pigs were regrouped, the pigs gaining more weight than their pen mates were more aggressive and those gaining less weight were more submissive. Aggression and submission were not observed in all pigs. During regrouping, those pigs showing submission were those that had used more productive teats than those that performed both aggressive and submissive behaviour. Pigs that showed aggression at regrouping were heavier than their pen mates and had a higher weight gain. In general, we conclude that the teat quality determines the nutritional change of the piglet at weaning, and also the degree of agonistic interactions at weaning and subsequent regrouping.
INTRODUCTION
Artificial weaning is a potential source of behaviour and health problems in pigs. In semi-natural environments, piglets are weaned at ~ 17 weeks of age, and the weaning process is gradual and prolonged (Jensen, 1986, 1988a, b; 0168-1591/90/$03.50
© 1990 Elsevier Science Publishers B.V.
144
B. ALGERS ET AL.
Jensen and Recen, 1989). Algers (1984a,b) was able to relate an increase of injuries in groups of early weaned piglets (3 weeks post-partum) to an increase of abnormal behaviour such as belly nosing and tail biting. General behavioural changes in early weaned pigs was also found by Wood-Gush and Csermely (1981). Worsaae and Schmidt (1980) reported high levels of stress hormones in piglets weaned at 3 weeks. Weaning of piglets at 6 or 7 weeks of age, as is common in Sweden, also induces various problems. Intestinal function is impaired and a stress response, often leading to post-weaning diarrhoea in the weaned pigs, has been demonstrated (LSfstedt, 1986). Some piglets may develop the so-called runt syndrome, which is characterized by reduced weight gain or even loss of weight, and considerable physiological changes such as atrophy of intestinal villi (Martinsson, 1984). There is normally a large spread of weights within a piglet litter. McBride et al. (1964a) found that the weight at 8 weeks of age was determined to a large extent by the weight at 3 weeks and the social rank within the litter (as determined by competitive success at the feed trough). In another study, McBride et al. (1964b) failed to distinguish any specific behavioural characters of extremely low-gaining piglets and it has been concluded that probably pigs at any weight could be depressed in growth. It is therefore not clear which factors cause some piglets to react more than others on weaning. The possible negative factors that a pig is exposed to in connection with weaning could be divided into different categories. Firstly, weaning demands a nutritional change. Although piglets already voluntarily consume solid feed in appreciable quantities from ~ 4 to 5 weeks of age, they still rely on milk as an important food source for a long time (Mount, 1968). Secondly, the need to utilize the feeders more may increase the frequency of agonistic interactions between litter mates, particularly if feeding space is limited. Thirdly, there may be an effect of environmental change if the pigs are moved after weaning. Fourthly, the removal of the mother will, in itself, probably cause a broad spectrum of various psychological stresses. The nutritional change at any artificial weaning time may to a large extent be determined by the milk consumption of the piglets prior to weaning. Since piglets possess a specific teat order (Fraser, 1980) and the production between different teats on the same sow may differ by as much as 200% or more (Barber et al., 1955; Algers and Jensen, 1989), different piglets within the same litter can be assumed to be affected quite differently by the nutritional change. Mixing of pigs after weaning is another well-recognized stress. Mixing has been shown to increase fighting (Meese and Ewbank, 1973; Graves et al., 1978; Friend et al., 1983; McGlone and Curtis, 1985; Rundgren, 1988) and to reduce eating time (Graves et al., 1978). Different pigs appear to be unequally involved in the fights (Rundgren, 1988). Several methods of composing new groups of pigs in order to reduce aggression and weight gain depression have
CHANGES IN WEANED AND REGROUPED PIGS
145
been studied (e.g. Blackshaw et al., 1987; Spicer and Aherne, 1987), but it is not clear which causal relationships exist between intra-litter variations of agonistic behaviour and performance. For instance, it might be that pigs with a greater need to utilize the feeders might become involved in more fights. The present study was performed to investigate the behavioural changes of individual pigs caused by removing the mother at 6 weeks of age and subsequently mixing pigs from different litters, and to relate these changes to the production of the teats which the piglets had occupied and to the weight changes that occurred during weaning and mixing. MATERIALSAND METHODS
Animals One hundred and one clinically healthy piglets from 10 litters (range 8-14 piglets per litter) were studied from birth to 9 weeks of age. The animals were of a three-cross breed, Yorkshire + New Hampshire + Swedish Landrace.
Management The pigs were kept on a conventional farm in single-sow pens (2.25× 3.70 m). The pens were divided into an area for piglets,to which the sow did not have access,and an area where the sow could eat,restand nurse, and a dunging area. Creep feed with 50 p.p.m. Mecadox was offered ad libitum to pigletsfrom I week of age. The sows were fed a daily standard ration of 2.5 kg commercial concentrate plus 0.4 kg per pigletautomatically divided into two portions per day. Fresh straw was provided daily. Both sows and piglets had access to water ad libitum. Windows and lamps provided fullday lightand lightsof low intensitywere on during the nights. Iron was administered and the teeth of the pigletsclipped within 24 h postpartum. The male pigletswere castrated between i and 2 weeks of age. The pigletswere individuallyear-tagged within 24 h post-partum. In addition, they were painted with large individual numbers on their backs.
Experimental procedure All observation serieswere carried out on two parallellitters,born not more than I day apart. The pigletswere weighed once a week from birth onwards. In addition,extra weighings were performed the day before and the day afterthe day of weaning and regrouping, here referredto as weight gain during weaning and regrouping, respectively. Weaning was performed when the piglets were 42 days old ( _+1 day) by
146
B. ALGERS ET AL.
moving the sow to a dry sow unit. Seven days later, the pigs were regrouped. This was done by mixing half of each of the parallel litters. The pigs were ranked according to weight before regrouping and mixing was done so that the pigs with weight ranks 1, 3, 5, etc. were mixed with the corresponding pigs of the other litter, and similarly those with ranks 2, 4, 6, etc. were mixed with the corresponding pigs. Fourteen days after regrouping, all the pigs were moved into a fattening stable.
Observations During 24 h before and after weaning, before and after regrouping, and before moving the litter, the behaviour of the litter was recorded on video. This was achieved by obtaining a continuous record of 20 s every fifth minute. Each such 24-h sample was regarded as one observation for each pig. The video cameras were situated above the pens and the entire pen was visible on the picture obtained. All recordings were subsequently made by the same person. During each interval, all occurrences of eating from the feeder, drinking, aggression (head-to-head knock, head-to-body knock; Jensen, 1980 ) and submission (head tilt, retreat; Jensen, 1980) were recorded, as well as the identity of the pig performing the behaviour.
A nalyses As a parameter for the milk yield of the teat occupied by a piglet, the weight increase of the piglet from Week 3 to 4 was used. During this period, the teat order was well established {Fraser, 1980) and the piglets did not consume enough solids to affect the weight gain significantly {Mount, 1968). This parameter is called "teat quality" in this paper, using the terminology of Fraser and Lin {1984). The weight data were used in three different ways in different analyses. (1) Actual weight and weight changes were considered. (2) Relative weight changes of individual piglets were obtained by dividing the weight change between two successive observations by the actual weight on the first observation. (3) The weights were indexed within litters by dividing the actual weight of the individual by the average weight of the litter at the specific observation considered. Index changes between successive observations were then calculated. Behavioural data were expressed as the mean number of observations per pig per recorded interval. Since this does not correspond to any real frequency data, one should consider and treat this as a frequency index. For the purpose of analysing weight data of those piglets that were never
CHANGESIN WEANEDAND REGROUPEDPIGS
147
observed to be involved in agonistic encounters, the pigs were grouped into those that showed no aggression or submission at all, those that showed only aggression or only submission, and those that showed both behaviours at the specific observation considered. The statistical analyses were performed using the t-test and Pearson's correlation coefficient ( Statistical Analysis Systems, 1982 ). In order to illustrate the direction and magnitude of correlations observed between weight index changes and frequencies of agonistic interactions, the material was divided into three groups: the 10% of animals with the highest and lowest weight index changes each formed one group and the rest another group. For each group, average behaviour frequencies were calculated. In this analysis, it was possible to see the behaviour of the groups of pigs with extremely low and high weight changes in relation to the majority of the pigs. RESULTS
The average weight gain of the pigs is shown in Fig. 1 together with the standard deviations. The frequency of eating behaviour increased over weaning, remained fairly constant from weaning until 1 week after regrouping, whereafter it increased again (Fig. 2a). The drinking frequency was markedly increased after weaning, but decreased thereafter (Fig. 2b). Both weaning and regrouping markedly increased aggression, but submissive behaviour was only substantially increased after regrouping (Fig. 2c-d). Pigs using more productive teats had a
?o
r
/
~5
1'1 I
,
...... -i-it
[
o
1
2
,3
4 Age,
5
6
7
8
9
weeks
Fig. 1. Average weights of the 101 piglets ( _+1 SD ) at each week from 1 week of age to just before being moved into the fattening unit.
148
B. ALGERSET AL.
Eating
Drinking
Freq 10
Freq
-f
(a)
(b)
9
-I-
8 7 6
il i
BEF. WEAN.
AFTR WEAN.
8EF, REGR,
AFTR REGR,
BEF, MDV,
BEF. WEAN,
AFT• W[AN.
OBS
BEF, REGR.
AFTR REGR,
BEF, MOV,
OB
Aggression
Submission
4]
Freq 0
,I 0 (c)
(d)
i
05
,~' 2
BEF, WEAN,
AFTR WEAN,
BIF REGR, I][}; I
AFTI~ REGR,
BEF, NOV,
BIF. WEAN,
AFTR WEAN
BEF, REGR, (F[,
AFrR REGR,
BEF. "~OV.
Fig. 2. (a-d) Average frequenems of eating, drinking, aggression and submission (_+ S E M ) on each of the five observations (w = weaning, r = regrouping, m = moving).
lower frequency of eating behaviour before and after weaning as well as before and after regrouping (Table 1 ). However, the frequency of their drinking behaviour was lower only before weaning. Those pigs that had been using more productive teats during Week 3-4 had a significantly poorer relative weight gain during regrouping, but not during weaning (Table 2). Pigs that gained more weight during weaning than their litter mates were
CHANGESIN WEANEDAND REGROUPEDPIGS
149
TABLE 1 Pearson correlation coefficients between teat quality and eating and drinking behaviour on different observations Observations Before weaning After weaning Before regrouping After regrouping Before moving Eating
-0.43 P=0.001
-0.28 P=0.004
-0.29 P=0.003
-0.25 P=0.013
Drinking
-0.29 P=0.005
-0.11 n.s.
-0.05 n.s.
n.s.
0.07
-0.17 n.s. 0.02 n.s.
n.s. = not significant. TABLE 2 Pearson correlation coefficients between teat quality during suckling and relative weight changes during weaning and regrouping Relative weight change over Weaning
Regrouping
-0.12 n.s.
-0.43 P<0.001
n.s. = not significant. TABLE 3 Pearson correlation coefficients between weight index changes and agonistic behaviour during weaning and regrouping Behaviour Aggression Weaning Regrouping
0.12
Submission
n.s.
0.35 P<0.001
0.29 P = 0.004
- 0.22 P = 0.025
n.s. = not significant.
more submissive after weaning. There was no significant effect on aggression, although the tendency was the same (Table 3, Fig. 3a-b). When the pigs were regrouped, the pigs gaining more weight than their pen mates were more aggressive and those gaining less weight were more submissive than their pen mates (Table 3, Fig. 3 c-d).
150
B. ALGERS ET AL.
Aggression at weaning Freq 06-
Submission at weaning Freq 050
Ca) 0.5
0.25
0.4
0 20
03
015
I
0.2
01
00 Loosers
Neutral
(b)
010
005
0 O0 Gainers
Aggression at regrouping
Loosers
Neutral
Gainers
Submission at regrouping
Freq 0 5
o.s
(d)
{c} 0.4
0 4 0 ,3 0.5 0 2
0 1 0 1
@0
0 0 Loosers
Neutral
Gainers
oosers
Neutral
Gainers
Fig. 3. (a-d) Average frequencies ( _+1 SD) of aggression and submission after weaning and regrouping for three groups of pigs: the 10% gaining least in weight in relation to their pen mates ("loosers"), the 10% gaining most ("gainers") and the rest of the piglets ("neutral") at weaning and regrouping, respectively.
Whether pigs were aggressive or submissive during weaning, when data were grouped irrespective of the frequency of the behaviours, did not relate to either the quality of the teat they had been using, their relative weight or weight change within litter or their weight change in relation to body weight during weaning. During regrouping, the submissive pigs were those that had used more productive teats than those which performed both aggressive and submissive behaviour. Pigs that showed aggressive behaviour generally had a higher weight
CHANGES IN WEANED AND REGROUPED PIGS
151
TABLE 4 Weight data for pigs a i ~ r weaning and regrouping in four different categories based on whether or not they performed submissive or aggressive behaviour or both. 0 = a n i m a l s not displaying any agonistic behaviour
Weaning
Regrouping
Aggres- Submis- Aggressive+ 0 sire sive submissive
Aggressive
Mean teat quality 1.10 Mean weight index 1.04 Mean index +0.02 difference Mean relative +0.05 weight change (kg kg-'body weight) n 22
0.67 0.95 0.00
1.17 0.98 +0.16
+0.07
+0.07
2
3
Submis- Aggressive+ 0 sive submissive
1.29 1.17ab* 1.48a 0.99 1.09a 0.99ab 0.00 +0.05a -0.07b +0.05 +0.07
74
45
+0.10
17
0.99b 1.08a +0.03ac
1.26ab 0.89b -0.01bc
+0.08
+0.09
8
31
*Numbers followed by different letters are significantly different ( P < 0.05, t-test).
than their pen mates and tended to have a higher weight gain over regrouping than their pen mates (Table 4). DISCUSSION Weaning comprises a number of changes which can affect the weight gain of weaned pigs, e.g. the sources of nutrition are changed and the social bonds to the sow are broken. The results show that removing the mother when the piglets are 6 weeks of age induced a behavioural change in the piglets comparable with that caused by regrouping I week later. The frequencies of eating, drinking and aggression all increased markedly, and submission increased to some degree, indicating that weaning at 6 weeks was a strain on the piglets even when no change of environment was involved. The reason why eating and drinking increased is obvious; the piglets were forced to compensate for the loss of nutrients and water caused by not being able to suckle any more. The nutritional change at weaning is therefore verified by the results. However all piglets of the litter were not affected in the same way by the nutritional change. Eating was negatively correlated to teat quality on all observation instances except the last, and drinking before weaning was negatively correlated to teat quality. We interpret this as indicating that the piglets occupying more productive teats fulfilled a larger part of their nutritional demands with milk than their litter mates. It might be that these piglets were not frequently involved in fights at the feeder before weaning and thus did not effectively learn to compete for food with their litter mates. The results indicate that the piglets with better teats were not able to compensate for their loss of nutrients, since they continued to eat less frequently than their litter
152
B. ALGERS ET AL.
mates. This became crucial at the time of regrouping, when the piglets which had used more productive teats gained significantly less relative weight than their litter mates, perhaps because of a lack of experience in competing for feed. A weak tendency for a poorer relative weight was already noted over weaning. These findings are in accordance with the "fast food hypothesis", suggested by Jensen and Recen (1989). They showed that weaning in free-ranging pigs, which was completed at ~ 17 weeks of age, was to a large extent a result of the behaviour of the young, i.e. the piglets stopped suckling without any aggressive rejection by the mother. There were some signs that smaller piglets tended to stop suckling before the larger litter mates, which led the authors to suggest that weaning could be a result of an optimal foraging decision. If a piglet occupies a productive teat, it might, according to the hypothesis, be better off from an optimal foraging point of view if it composes its total diet of a larger amount of milk than those piglets occupying less productive teats. The piglets gaining most weight relative to their litter mates over weaning were those that tended to be involved in more agonistic interactions. This is consistent with the idea that weaning caused an increase in the need to utilize the feeder and that this competition may have been one reason why agonistic behaviour increased following weaning. Regrouping of the pigs resulted in a substantial increase in both aggressive and submissive behaviour, which is consistent with earlier findings (e.g. Meese and Ewbank, 1973). However our results show that these behaviours are not seen in all pigs. Those pigs in which aggressive behaviour was observed were those gaining more weight during regrouping in relation to their pen mates. These pigs had been using less productive teats and consumed more creep feed according to the above results. The pigs that gained less weight during regrouping were more submissive and had previously been using more productive teats. In a study of how different weaning methods affected weight gain, intestinal absorption, haematology and blood chemistry, LSfstedt (1986) observed a decrease in weight gain the first week after weaning. In one group, the effect of sufficient intake of creep feed (0.3 kg per piglet day-1, measured as an average of the litter) was studied. A weight gain retardation could not be prevented in this group. However no attempts were made to relate the findings to any withinlitter characteristics. Our results suggest some possible within-litter effects of teat quality on behaviour and weight changes. These effects, evidence for some of which has been given in this paper, are outlined in the model in Fig. 4. In conclusion, we suggest that an important factor for the growth depression generally seen in pigs after weaning and regrouping is a sudden change in the supply of nutrients, being of a greater magnitude for pigs which have been occupying more productive teats than for the others. Further, we suggest that the strategy of agonistic behaviour among the pigs is a function of the variation
CHANGES IN WEANED AND REGROUPED PIGS I GOOD TEAT 0UALITY
153
I POOR TEAT OUALITY
1
f~ORE SOLIDS
1
I LESS SOLIDS
......
..........
Weaning. . . . . . . . . .
......
LARGE NUTRITIONAL CHANGE
MINOR NUTRITIONAL i CHANGE ]
L
iI
LESS AGONISTIC BEHAVIOUR
MORE AGONISTIC BEHAVIOUR
POORER WEIGHT GAIN
BETTER WEIGHT GAIN
i
l
Regrouping
i MORE AGGRESSIVE BEHAVIOUR
MORE SUBMISSIVE BEHAVIOUR
I I POORER WEIGHT GAIN
i 1 J
i BETTER WEIGHT I GAIN l
Fig. 4. A model of teat quality sequels to weaned and regroupedpigs. The model is based on the findings in this study. of the productivity of the sow's teats, the within-litter variation of access to more productive teats and the subsequent within-litter variation of growth depression.
ACKNOWLEDGEMENTS
We thank Uddetorp Farm School for allowing us to use the experimental facilities and Ferrosan AB for financial support.
154
B. A L G E R S E T AL.
REFERENCES Algers, B., 1984a. Animal health in flatdeck rearing of weaned piglets. Zentralbl. Veterinaermed. Reihe A, 31: 1-13. Algers, B., 1984b. Early weaning and cage rearing of piglets: Influence on behaviour. Zentralbl. Veterinaermed. Reihe A, 31: 14-24. Algers, B. and Jensen, P., 1989. Teat stimulation and milk production in early lactation of sows. Effects of continuous noise. In: Vocal and Tactile Communication during Suckling in Pigs. Thesis, Swedish University of Agricultural Sciences, Department of Animal Hygiene, Report 25. Barber, R.S., Braude, R. and Mitchell, K.G., 1955. Studies on milk production of Large White Pigs. J. Agric. Sci., 46: 97-118. Blackshaw, J.K., Bodero, D.A.V. and Blackshaw, A.W., 1987. The effect of group composition on behaviour and performance of weaned pigs. Appl. Anim. Behav. Sci., 19: 73-80. Fraser, D., 1980. A review of the behavioural mechanism of milk ejection of the domestic pig. Appl. Anim. Ethol., 6: 247-255. Fraser, D. and Lin, C.S., 1984. An attempt to estimate teat quality of sows by hand milking during farrowing. Can. J. Anim. Sci., 64: 165-170. Friend, T.H., Knabe, D.A. and Tanksley, T.D., 1983. Behavior and performance of pigs grouped by three different methods at weaning. J. Anim. Sci., 57: 1406-1411. Graves, H.B., Graves, K.L. and Sherritt, G.W., 1978. Social behaviour and growth of pigs following mixing during the growing-finishing period. Appl. Anim. Ethol., 4: 169-180. Jensen, P., 1980. An ethogram of social interaction patterns in grouphoused dry sows. Appl. Anim. Ethol., 6: 341-350. Jensen, P., 1986. Observations on the maternal behaviour of free-ranging domestic pigs. Appl. Anim. Behav. Sci., 16: 131-142. Jensen, P., 1988a. Maternal behaviour and mother-young interactions during lactation in freeranging domestic pigs. Appl. Anim. Behav. Sci., 20: 297-308. Jensen, P., 1988b. Maternal behaviour of free-ranging domestic pigs. I: Results of a three-year study. Swedish University of Agricultural Sciences, Department of Animal Hygiene, Report 22, 58 pp. Jensen, P. and Recen, B., 1989. When to wean--observations from free-ranging domestic pigs. Appl. Anim. Behav. Sci., 23: 49-60. LSfstedt, M., 1986. Clinical and physiological effects of weaning in pigs with special reference to post-weaning growth depression. Thesis, Department of Medicine I, Swedish University of Agricultural Sciences, Uppsala. Martinsson, K., 1984. "Pellesyndromet" hos grisar. Sven. Veterin~irtidn., 36: 11-13, McBride, G., James, J.W. and Hodgens, N., 1964a. Social behaviour of domestic animals. IV. Growing pigs. Anim. Prod., 6: 129-139. McBride, G., Wyeth, G.S.F. and Hodgens, N.W., 1964b. Social behaviour of domestic animals. VI. A note on some characteristics of "Runts" in pigs. Anim. Prod., 6: 249-252. McGlone, J.J. and Curtis, S.E., 1985. Behavior and performance of weanling pigs in pens equipped with hide areas. J. Anim. Sci., 60: 20. Meese, G.B. and Ewbank, R., 1973. The establishment and nature of the dominance hierarchy in the domestic pig. Anim. Behav., 21: 326-334. Mount, L.E., 1968. The Climatic Physiology of the Pig. Camelot Press, London, 271 pp. Rundgren, M., 1988. Growing pig performance. Effects of dietary fibre, the halothane gene, transportation and mixing. Dissertation. Inst. fSr husdjurens utfodring och v~rd. Swedish University of Agricultural Sciences, Report 172, Uppsala. Spicer, H.M. and Aherne, F.X., 1987. The effects of group size/stocking density on weanling pig performance and behavior. Appl. Anita. Behav. Sci., 19: 89-98.
CHANGESIN WEANEDANDREGROUPEDPIGS
155
Statistical Analysis Systems, 1982. SAS User's Guide: Statistics, Version 5 Edition. SAS Institute Inc., Cary, NC, 956 pp. Wood-Gush, D.G.M. and Csermely, D., 1981. A note on the diurnal activity of early-weaned piglets in flat-deck cages at 3 and 6 weeks of age. Anita. Prod., 33: 107-110. Worsaae, H. and Schmidt, M., 1980. Plasma cortisol and behaviour in early weaned piglets. Acta Vet. Scand., 21: 640-657.