J. Anim. Sci. 2004. 82:1919-1924
© 2004 American Society of Animal Science
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
Viability of Iberian x Meishan F2 newborn pigs. I. Analysis of physiological and vitality variables1
J. Casellas*,
W. M. Rauw
,
J. Piedrafita*,2,
A. Sánchez*,
M. Arqué and
J. L. Noguera
* Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain and
and
Àrea de Producció Animal, Centre UdL-IRTA, 25198 Lleida, Spain
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Abstract
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Eight physiological and vitality variables related to the first minutes of the life of Iberian x Meishan F2 piglets were analyzed. Variables included rectal temperature, arterial oxygen saturation, heart rate (all were monitored at birth and 60 min later), time to reach the udder, and time to the first colostrum intake. Litter effect within boar, a random source of variation, influenced all variables, whereas the random boar effect was not significant for heart rate and arterial oxygen saturation at birth and the time to reach the udder. Birth weight influenced rectal temperature at birth (P < 0.01) and 60 min later (P < 0.001), arterial oxygen saturation 1 h after birth (P < 0.05), heart rate 1 h after birth (P < 0.001), time to reach the udder (P < 0.05), and time to the first suckle (P < 0.01), whereas viability score influenced rectal temperatures (at birth and 60 min later; P < 0.001), and time to reach the udder (P < 0.001) and to suckle (P < 0.001). Finally, the order of birth showed significant effects for rectal temperature 1 h after birth (P < 0.001) and time to first colostrum intake (P < 0.001). Correlation coefficients between physiological variables were generally low, with the exception of the ones for rectal temperature 1 h after birth and arterial oxygen saturation 1 h after birth (0.38; P < 0.001), and for rectal temperature at birth and rectal temperature 1 h after birth (0.34; P < 0.001). Times to reach the udder and to suckle were highly correlated (0.67; P < 0.001) and also were moderately and negatively correlated with rectal temperature 1 h after birth (–0.36 and –0.38 respectively; P < 0.001). Heart rates at birth and 1 h later, as well as arterial oxygen saturation at birth and 1 h later, were not correlated, showing that the values at birth do not necessarily provide information about the physiological status of the pig 1 h after birth. The recording of physiological variables, birth weight, and viability score may be useful to identify weak piglets quickly and to establish palliative measures.
Key Words: Physiological Variables • Piglets • Postnatal Period • Viability
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Introduction
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Birth is a crucial moment in a piglet’s life. Environmental conditions change quickly and drastically, and newborn piglets have to adapt to the new environment and to compete with their siblings for access to resources (Fraser and Thompson, 1991
). Piglets need to reach the udder and suckle colostrum early because a delay could decrease their survivability (Christison et al., 1997; Tuchscherer et al., 2000) and their subsequent growth (Donovan and Dritz, 2000). During delivery, a moderate asphyxia is normal in all fetuses, but some piglets suffer a greater degree of asphyxiation because of the cumulative effects of successive contractions; the occlusion, damage, or rupture of the umbilical cord; or the detachment of the placenta as delivery progresses (Herpin et al., 1996). This period of hypoxia interacts with the postnatal metabolism and behavior of the piglets and may also be related to survivability (Herpin et al., 1996, 1998). Birth originates drastic changes in various physiological variables, but only body temperature has been extensively studied (see revision of Herpin and Le Dividich, 1995). Conversely, some authors have analyzed the behavior of newborn pigs as the time taken to find the udder or for the first suckle (Herpin et al., 1996; Tuchscherer et al., 2000), but the relationships of these variables to the physiological ones have not been established.
The aim of the current study is to augment our understanding of physiological and vitality variables of piglets and to relate them to observations on piglet suckling behavior in the first hour of life. Our results will contribute to the understanding of piglets’ metabolism after birth, their adaptation to the external environment, and their initial feeding behavior, as a previous step in the survival analysis.
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Materials and Methods
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Animals
Between November, 2001, through May, 2002, 108 primiparous Iberian x Meishan F1 sows farrowed in climate-controlled rooms (24°C) at the Nova Genètica farm of Solsona (Catalonia, Spain). Gilts were penned during farrowing and lactation in standard farrowing crates, which were provided with heating plates for piglets (38°C). During parturition, veterinary interventions were kept to a minimum. Oxytocin (20 I.U.) was administered intramuscularly when the interval between births was greater than 30 min. Additionally, sows that did not deliver before the 113th gestational day received 175 µg of cloprostenol through an intravulvar injection to elicit farrowing.
Measurements
For each pig, time of birth and presentation (anterior or posterior) were recorded. To determine the viability score (VS), three variables were monitored, simplifying the method proposed by Randall (1971): time to the onset of respiration; muscle tone; and attempts to stand. A score of 0, 1, or 2 was assigned to each variable, depending on a subjective evaluation (see Table 1), the VS being the sum of these three values. Randall’s (1971) VS also included the color of the piglet and the heart rate at birth, but because all piglets had a black skin, and heart rate was not monitored right after birth (but 1 to 5 min after), these measurements could not be included. Afterwards, the umbilical cord was broken if it was intact and the piglet was monitored for heart rate (HR-0), rectal temperature (RT-0), and arterial oxygen saturation (OS) using a Vet/Ox 4404 monitor pulsoxymeter (Heska Corp., Fort Collins, CO). Given that the piglets had a black skin, measurements on heart rate and arterial oxygen saturation were taken in the tongue, using an Exotic Reflectance Sensor (Heska Corp.).
Because Herpin et al. (1998) observed a great increase in arterial oxygen saturation during the first seconds of life, the time interval between birth and the measurement of OS was also recorded (TOS), which was used to adjust OS to 90 s after birth (OS-0), applying the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). In this regard, we estimated the population mean (µ = 73.014, P < 0.001) and the regression coefficient for TOS (ß = 0.023, P < 0.001), and the OS-0 adjustment for the ith animal was carried out following the equation OS-0i = µ + 90ß + ei. Physiological variables were not monitored for animals with viability scores lower than 3 because they died before establishing the respiratory function correctly. All piglets were ear-tagged for identification purposes, weighed, and placed in the caudal region of the sow, near the vulva. This process allowed for the registration of the time interval between birth and first udder contact (TU) as well as first suckle (TS). Sixty minutes after birth, heart rate (HR-1), rectal temperature (RT-1), and arterial oxygen saturation (OS-1) were monitored again.
Data Analysis
This study analyzed the influences received by the following eight variables, as well as their interrelations: RT-0, RT-1, HR-0, HR-1, OS-0, OS-1, TU, and TS. The preliminarily model tested for all variables (Y) was
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where OBm is the order of birth including six intervals (first or second, third or fourth, fifth or sixth, seventh or eighth, ninth or tenth, and eleventh or later); PBn is the presentation at birth (anterior or posterior); SXo is the sex; BWp is the birth weight; VSq is viability score; PTr is the total number of piglets born excluding mummies (<7, 7 to 10, 11 to 14, and >14); PSs is the presence or absence of stillborn piglets; PMt is the presence or absence of mummified piglets; AOu is the administration of oxytocin to the dam (yes, no); ACv is the administration of cloprostenol to the dam (yes, no); CCw is the corporal condition of the dam as the dorsal fat thickness (millimeters) 7 d before delivery measured through ultrasounds; BOx is the random effect of boar; LEy(BOx) is the random litter effect within boar; and em,n,o,p,q,r,s,t,u,v,w,x,y,z is the error term. For the viability score, Levels 3 and 4 were grouped into the same category because the number of piglets with a score of 3 was small. Variables BWp and CCw were treated as continuous, fixed effects. Interactions were excluded from the final model because they led to low significance levels, and their inclusion implied the exclusion of other fixed effects. Before rejecting the nonsignificant fixed effects, each of them was tested with the group of fixed effects initially significant to determine whether any became significant.
Pearson’s correlation coefficients between all variables were calculated using the correlation procedure of SAS to detect relations between physiological and vitality variables.
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Results
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Sows had an average backfat thickness of 40.8 ± 0.23 mm. Average number of piglets born alive was 9.73 ± 0.32, and there was an average of 0.25 ± 0.08 stillborn piglet and 0.24 ± 0.06 mummified piglet in a litter. Piglets were born with an average birth weight of 1.11 ± 0.01 kg and an average viability score of 5.63 ± 0.03. Average values for the analyzed variables are shown in Table 2. The average body temperature was higher at birth than 60 min after, whereas the average heart rate and arterial oxygen saturation was lower at birth than 60 min after.
Table 2
also shows which of the 13 variables of the preliminarily model were significant and therefore retained in model that was used for analyzing the different traits. The variables PB, SX, PT, PS, PM, AO, AC, and CC had no significant effect (P > 0.1) on any of the traits. The litter effect within boar (LE[BO]) was significant (P < 0.1) for all traits, whereas boar effect did not influence heart rate, arterial oxygen saturation at birth, and time to first suckle. Birth weight was associated (P < 0.05) with RT-0, RT-1, OS-1, HR-1, TU, and TS, viability score (VS) influenced significantly (P < 0.001) RT-0, RT-1, TU, and TS, and the order of birth reached the statistical significance (P < 0.001) for RT-1 and TS (Table 2).
Animals with a viability score of 3 or 4 had lower rectal temperatures (both at birth and 60 min after), and they reached the udder later, postponing their first colostrum intake (Table 3). Rectal temperatures 1 h after birth increased, and the interval from birth to first suckle decreased with the order of birth (Table 4). Rectal temperatures at birth and 60 min after, arterial oxygen saturation 60 min after birth, and heart rate 60 min after birth increased (P < 0.05) with birth weight, whereas the time interval from birth to first udder contact and to first suckle decreased (P < 0.05) with birth weight (Table 5).
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Table 4. Number of animals and least squares means ± SEM of rectal temperature 1 h after birth and time interval from birth to first suckle for each level of birth order
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Table 5. Estimates of regression coefficients and standard errors of the regression coefficients for birth weight
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Correlation coefficients for physiological variables at birth (HR-0, OS-0, and RT-0) were in general low or not significant, with the exception of the one between RT-0 and RT-1 (0.34, P < 0.001). A similar tendency was observed between physiological variables 1 h after birth, where only the correlation between RT-1 and OS-1 reached a moderate value (0.38, P < 0.001). On the other hand, the highest correlation coefficient was observed between vitality variables, TS and TU (0.67, P < 0.001), and these were also negatively and moderately correlated with RT-1 and OS-1 (Table 6).
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Table 6. Correlation coefficients between dependent variables (upper-right diagonal) and number of records used (lower-left diagonal)
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Discussion
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Heart rate, rectal temperature, and arterial oxygen saturation characterized the piglet’s metabolism after birth, showing the degree of asphyxiation suffered during delivery and as well as the piglet’s ability of recovery physiological levels (Herpin et al., 1996, 1998). The evolution of piglet body temperature during the early-postnatal period has been extensively studied (Herpin and Le Dividich, 1995), and recent research have been focused on arterial oxygen saturation during first minutes of life (Herpin et al., 1996, 1998). Notwithstanding, information about initial feeding behavior is limited (Tuchscherer et al., 2000), and our knowledge concerning heart rate is practically nil, although this variable has historically been included in viability scores (Randall, 1971). Moreover, the interactions between these variables have never been analyzed, with the exception of research by Herpin et al. (1998), who showed a positive relation between oxygen saturation at birth and the subsequent heat production of the piglet. Our results contribute to the knowledge of early postnatal metabolism and suggest the need for a new research area dealing with the interrelationships among physiological and vitality variables of the neonate piglet.
Average rectal temperature decreased and average arterial oxygen saturation increased 1 h after birth, in accordance with observations by Herpin et al. (2001). The hypoxemia generated during parturition depresses the myocardial contractility (Detweiler, 1998), decreasing heart rates to 147.0 beats per minute. Fortunately, the fast increase of arterial oxygen saturation allows for a quick recuperation of cardiac activity, which reached an average of 218.2 beats per minute 1 h after birth.
Newborn piglets get an unusually low level of care from their mothers; they receive little physical guidance to direct them to her teats (Rohde Parfet and Gonyou, 1991). The piglets of the current study took on average 24.2 min to reach the udder. This agrees with results by Christison et al. (1997) and is faster than the average observed by Herpin et al. (1996, 32 min). After reaching the vicinity of the udder, the teat-seeking phase begins. The interval from birth to the first suckle was approximately twice the time taken from birth to the first udder contact, as described by Christison et al. (1997) and Tuchscherer et al. (2000). Our results were similar to those of Christison et al. (1997, 40 min after birth), lower than those of Herpin et al. (1996, 44 min after birth), and higher than those obtained in German Landrace newborn pigs by Tuchscherer et al. (2000). It seems noteworthy that the time to the first suckle decreased with increasing position in the birth order. This effect may be related to the mother’s behavior because sows were very anxious and changed their position constantly at the beginning of parturition, but they remained relatively still as time progressed, as described Jensen (1986) and Fraser et al. (1998). Rectal temperature 1 h after birth increased with increasing order of birth, showing that an earlier colostrum intake is beneficial for piglet thermoregulation, as previously reported Noblet et al. (1997) and Herpin et al. (2002).
Piglets with high viability scores had increased rectal temperatures at birth and 60 min after birth. They also reached the udder and started suckling faster, which agrees with results described by Fraser et al. (1998). The lower rectal temperature at birth for piglets with a low viability score may be partially related to the protocol followed for data collection. Given that the temperature was measured after monitoring the necessary variables for evaluating the viability score, the time elapsed between birth and recording was greater for low-viability-scored piglets than for the high-viability-scored, allowing a greater heat loss due to evaporation.
In the current study, birth weight was positively related to rectal temperatures both at birth and 60 min after birth. The existence of such a relationship has been described by a number of authors (e.g., Leenhouwers et al., 1999 and Herpin et al., 2002). Bate (1993) indicated that smaller piglets tend to have weaker thermoregulatory mechanisms, which may be explained by the greater surface-to-mass ratio, resulting in greater heat loss (Herpin et al., 2002). Furthermore, their metabolism could suffer from a certain degree of underdevelopment. Birth weight was not related to arterial oxygen saturation at birth, partially contradicting the results of Herpin et al. (1996), but lighter piglets had a lower level of arterial oxygen saturation 60 min after birth. Smaller piglets needed more time to reach the udder and, consequently, to ingest colostrum, than larger piglets, as was previously described by Herpin et al. (1996). Increased litter size generally results in more lightweight piglets with a decreased probability of survival (Roehe and Kalm, 2000). However, litter size was not related to any of the physiological traits or to viability score, the time interval from birth to reach the udder, and interval to the first suckle.
Pearson’s correlation coefficients showed that the variables TU and TS were highly correlated, and they also reached negative and highly significant correlation coefficients with RT-1 (–0.36 and –0.38, respectively), corroborating the importance of colostrum intake for thermoregulation purposes that was previously reported by Noblet et al. (1997) and Herpin et al. (2002). The variables TS and RT-1 have been historically considered as piglet survival indicators (Herpin and Le Dividich, 1995; Christison et al., 1997). The moderate correlations between TU and OS-1 suggest that these variables also may be related to piglet survival, although future studies will be necessary to verify this result. Rectal temperature at birth and at 1 h after were moderately correlated. This relationship in time was not observed between arterial oxygen saturation or heart rate, and it may be partially related to significant fixed and random effects of each variable. Rectal temperature at birth and 1 h later received practically the same influences, whereas models for heart rates and arterial oxygen saturations were clearly different at birth than 1 h later. Thus, HR-0 and OS-0 did not provide information about the physiological status of the pig 1 h after birth. They were, furthermore, not correlated with RT-1 or TU and TS, indicating that pulse-oxymetry measurements at birth did not provide useful information about the posterior feeding behavior or the thermoregulatory ability of piglet.
The results of this study highlight the influence of body weight and viability score at birth on the physiology of the newborn pig, and its ability to reach the udder and to obtain colostrum. Furthermore, correlation estimates have been reported between variables, showing that feeding behavior and metabolism 1 h after birth were significantly related, probably characterizing piglet viability.
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Implications
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Birth weight and viability score highly influenced physiological variables and the time to reach the udder or to the first colostrum intake, characterizing the early postnatal piglet vitality. Their consideration in standard management techniques may be useful in identifying weak piglets quickly and to establish palliative measures like cross-fostering or selective tooth clipping. Moreover, piglet vitality and physiological variables 1 h after birth were moderately correlated, showing the importance of early teat access and colostrum intake to keep piglet metabolism within physiological levels, and most likely characterizing early piglet survivability. The recording of physiological variables may be useful for identifying undernourished piglets. Future studies are needed to analyze the effect of these physiological variables on piglet survival allowing an indirect genetic improvement of neonatal survival.
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Footnotes
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1 Financial support was provided by Ministerio de Ciencia y Tecnología, Spain (Grant AGL2000-1229-C03). The authors are indebted to the staff of Nova Genètica for cooperating in the experimental protocol, in particular to E. Ramells, F. Márquez, I. Riart, R. Malé, F. Rovira, and M. González, and to M. Fina and J. Tarrés for their active and friendly collaboration during data collection. The authors gratefully acknowledge the contributions of the Institut National de la Recherche Agronomique (France) and the SIA El Dehesón del Encinar (Spain) for providing the purebred Meishan sows and Iberian boars, respectively. The English revision of C. Simmons is also acknowledged. 
2 Correspondence—phone: 34935811399; e-mail: jesus.piedrafita{at}uab.es.
Received for publication November 7, 2003.
Accepted for publication March 29, 2004.
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Abstract
Introduction
