Introduction
Pre-weaning mortality in swine production remains a major drawback, especially neonatal mortality, with at least 50% of pre-weaning deaths occurring within 3 days of birth (Tuchscherer et al., Reference Tuchscherer, Puppe, Tuchscherer and Tiemann2000). Those piglets are characterised by a low birth weight and a low weight gain, which is related to a low colostrum intake (de Passillé and Rushen, Reference De Passillé and Rushen1989b; Milligan et al., Reference Milligan, Fraser and Kramer2002). Therefore, low colostrum intake appears to be a major cause of neonatal death (Edwards, Reference Edwards2002). The roles of colostrum for piglet’s thermoregulation, immunity and intestinal development are well established (see reviews by Xu et al., Reference Xu, Wang and Zhang2000; Rooke and Bland, Reference Rooke and Bland2002; Le Dividich et al., Reference Le Dividich, Rooke and Herpin2005). Colostrum intake by piglets depends not only on their ability to extract colostrum from teats but also on the ability of sows to produce enough colostrum for the whole litter (Hoy et al., Reference Hoy, Lutter, Puppe and Wahner1997). Indeed, negative effects of low birth weight and poor vitality (asphyxia during delivery, long time from birth to first suckling) on colostrum intake were demonstrated in several studies (Herpin et al., Reference Herpin, Le Dividich, Hulin, Fillaut, De Marco and Bertin1996; Tuchscherer et al., Reference Tuchscherer, Puppe, Tuchscherer and Tiemann2000).
Although the factors influencing sow milk production have been studied for a long time, few studies have focussed on the factors determining colostrum production. Factors that may influence milk production include: litter and sow characteristics, such as litter size, litter weight, genotype and parity (Boyce et al., Reference Boyce, Smits, Campbell and King1997; Etienne et al., Reference Etienne, Dourmad, Noblet, Verstegen, Moughan and Schrama1998); sow hormonal background, such as circulating concentrations of prolactin, progesterone and cortisol (see reviews by Devillers et al., Reference Devillers, Le Dividich and Prunier2006 and Farmer et al., Reference Farmer, Devillers, Rooke and Le Dividich2006); behaviour of the sow and piglets, such as alterations in nursing frequency (Auldist et al., Reference Auldist, Morrish, Eason and King2000); and environmental factors (Etienne et al., Reference Etienne, Dourmad, Noblet, Verstegen, Moughan and Schrama1998). The roles of prolactin and progesterone for the initiation of lactation and, consequently, for colostrogenesis have also been demonstrated (Taverne et al., Reference Taverne, Bevers, Bradshaw, Dieleman, Willemse and Porter1982; Farmer et al., Reference Fraser and Rushen1998). On the other hand, some studies suggest that litter size may not have any influence on colostrum yield (Milligan et al., Reference Milligan, Fraser and Kramer2001; Le Dividich et al., Reference Le Dividich, Martineau, Thomas, Demay, Renoult, Homo, Boutin, Gaillard, Surel, Bouetard and Massard2004). The present study used a method previously described (Devillers et al., Reference Devillers, Van Milgen, Prunier and Le Dividich2004b) for estimating colostrum intake by individual piglets and sow colostrum yield in order to determine factors that influence these two variables.
Material and methods
Animals and measurements
In all, 22 primiparous and 18 multiparous Landrace × Large White sows were inseminated with semen from Piétrain boars and were housed with their litters (526 piglets) in individual farrowing crates (2.0 m × 2.5 m) with straw bedding. During pregnancy, sows were fed 1.1 kg per 100 kg live weight daily of a diet containing 13.3% crude protein (CP), 2966 kcal/kg of metabolisable energy (ME) and 0.49% lysine. Throughout lactation, they were fed a diet providing 17.3% CP, 3062 kcal/kg of ME and 0.8% lysine. On the day of farrowing, sows were offered 2.0 kg of the lactation diet. Thereafter, this amount was increased by 1 kg daily until ad libitum feeding. Water was supplied ad libitum throughout the experiment. Sows were weighed upon entrance in the farrowing rooms (the week preceding farrowing, i.e. days 107 to 110 of gestation). Parturition was induced (in 63% of the cases) on day 114 of gestation with 1 ml of prostaglandins (Alphabedyl®, CEVA Santé Animale, Libourne, France). Parturitions were watched but observers interfered as less as possible in the farrowing process. The beginning (T0) and the end of parturition were considered as the birth of the first and the last piglets, respectively. At birth, piglets were weighed and time of day was recorded. Because of their link to hypoxia during delivery (Herpin et al., Reference Herpin, Le Dividich, Hulin, Fillaut, De Marco and Bertin1996), some birth characteristics were also recorded to assess vitality (umbilical cord already ruptured, difficulty to breathe (more than 5 s until first attempt to breathe), piglet still inside placental membranes). Piglets born in placental membranes were extirpated from them and reanimated, if necessary. No additional help or care was given. At 24 h after the onset of parturition (T24), piglets were weighed again and the presence of splayleg was recorded. No cross fostering was done before T24.
Colostrum intake by piglets between birth and T24 was estimated according to a previously described method (Devillers et al., Reference Devillers, Van Milgen, Prunier and Le Dividich2004b) whereby an equation was set up in similar environmental conditions (herd, housing, genetic lines) as in the present study to predict piglet’s colostrum intake (CI in g) based on birth weight (BWB in kg), weight gain [(BW−BWB) in kg], age (t in min) and the interval between birth and first suckling (t FS in min) (see Eq.
(1)).
Since the latency to suck was not recorded in the present study, the mean interval between birth and first suckling was estimated to be 30 min (De Passillé and Rushen, Reference De Passillé and Rushen1989a). The standardisation of this factor has been discussed previously (Devillers et al., Reference Devillers, Van Milgen, Prunier and Le Dividich2004b) and an error of 15 min in the estimation of the interval from birth to first suckling induces an average error in CI of approximately 6 g/kg BWB for a 25-h CI duration, which represents less than a 2% error. Colostrum yield by the sow was calculated as the sum of intakes from each piglet within a litter during the 24 h following the onset of parturition.
Sampling and analyses
A sample of colostrum (100 ml) was collected manually across all teats at T0, T2, T4 and T24. At T24 only, colostrum ejection was induced with a 0.5 ml intravenous injection of oxytocin (Ocytovem®, CEVA Santé Animale, Libourne, France). Colostrum was filtered through gauze and stored at 4°C. Within 24 h of collection, 5 ml of filtered colostrum was heated to 38°C, homogenised and ultra-centrifuged twice at 50 000 × g (0°C) for 1 h each time, before lactoserum was collected.
Colostrum samples were analysed for nutritional composition as well as hormonal and immunoglobulin G (IgG) concentrations. Prolactin (PRL) concentrations were determined using a previously described radio-immunoassay (Robert et al., Reference Robert, De Passillé, St-Pierre, Dubreuil, Pelletier, Petitclerc and Brazeau1989) with a sensitivity of 1.8 ng/ml. Progesterone (P4) and oestradiol-17β (E2) concentrations were determined using commercial kits (RIA kit, Immunotech, Marseille, France, ref. 2465 and 2464, respectively). Assay sensitivities were 0.6 ng/ml and 26 pg/ml, respectively. Nitrogen (N) content was determined according to the method of Dumas (Association of Official Analytical Chemists (AOAC) 7 024, 1831) based on sample pyrolysis and direct determination of N2 using an automatic device (Leco FP-428, LECO Corporation, St Joseph, MI, USA). Crude proteins were estimated as N × 6.38 (Gordon and Whittier, Reference Gordon, Whittier, Webb and Johnson1965) and total lipids were measured according to the Gerber method (AOAC, 1990). Lactose was assayed using an enzymatic method (Lactose/d-galactose test combination R-Biopharm – Roche, Darmstadt, Germany, ref. 0176303). Concentrations of IgG were measured by ELISA, as previously described (Devillers et al., Reference Devillers, Farmer, Mounier, Le Dividich and Prunier2004a) and assay sensitivity was 23 ng/ml.
Statistics and data analyses
Statistical analyses were done with Statistical Analysis Systems Institute (2002) software. When performing analyses within litter, data for individual colostrum intakes of piglets were corrected for litter effect (General Linear Model (GLM) procedure) and particular relationships between individual colostrum intake of piglets and vitality or performance variables are presented as residues or as least squares means. Analyses of variance were used to test special relationships between colostrum intake and vitality variables or birth rank (MIXED linear model procedure). Regression analyses were used to describe links between colostrum intake and birth weight (regression (REG) and correlation (CORR) procedures). Regression analyses were also used at the litter level to explore the relationships between mean colostrum intake for the litter and litter size, mean birth weight and variation in birth weight (CV), as well as total litter weight.
Data related to colostrum yield of the sow were analysed using multivariate analyses, which is appropriate for such descriptive studies. The partial least squares analysis (PLS procedure) was used to relate colostrum yield to other measured variables. PLS analysis works by extracting successive linear combinations of the predictors, called factors, thereby optimally explaining both the response variation (colostrum yield) and the predictors variation (covariates). Thereafter, special relationships between colostrum yield and variables mostly contributing to its modelling were explored using analyses of variance (parity, induction of farrowing) or regression analyses (duration of gestation, litter size, sow body weight, litter weight, colostrum composition).
Relationships between colostrum composition variables and performances were described using principal component analysis (PRINCOMP procedure) and Spearman correlations. Because of missing data, E2, P4 and PRL concentrations were pooled for T0 and T2 (T0–2). Verification has been done before that there were correlations between concentrations at times T0 and T2 (E2: r = 0.53, P < 0.001; P4: r = 0.71, P < 0.001; PRL: r = 0.88, P < 0.001) and that there were no differences between means from these times (E2: P = 0.32; P4: P = 0.15; PRL: P = 0.39). Data given in the text are means ± s.e.
Results
Reproduction performances
Reproduction performances of sows were generally consistent with national French results (Institut Technique du Porc (ITP), 2001). Average parity of the 40 sows was 2.2 ± 0.3, ranging from 1 to 6. Body weight, 1 week before expected farrowing (days 108 to 110 of gestation) averaged 257.4 ± 5.1 kg and farrowing occurred at 114.1 ± 0.2 days of gestation. The mean duration of farrowing was 191 ± 15 min and litter size averaged 13.5 ± 0.5, ranging from 8 to 21 piglets, with a mean of 0.35 stillbirths per litter. This particularly low number of stillbirths was probably due to supervision of farrowings. Average piglet birth weights and litter sizes were negatively linked (r = −0.32; P = 0.041) and an increase of one piglet per litter represented a decrease of 25 g in individual birth weight.
Colostrum intake by individual piglets and its variability
Among the 526 piglets born, 14 were stillborn and 23 died before T24. Mean birth weight was 1.34 ± 0.015 kg, ranging from 0.45 to 2.30 kg. Colostrum intake between birth and T24 was evaluated to be negative for 17 piglets (mean=−41 g). Those piglets had a mean birth weight of 1.1 kg and lost more than 78 g between birth and T24. Only two of them were still alive at weaning, and 14 died within 3 days of birth. Damm et al. (Reference Damm, Pedersen, Heiskanen and Nielsen2005) reported that 72% of piglets that die within the first 4 days post partum have not consumed any colostrum. Therefore, colostrum intake of those 17 piglets was estimated to be 0. Mean colostrum intake of piglets, which were still alive at T24, was 300 ± 7 g (217 ± 4 g/kg birth weight) with a maximum colostrum intake of 710 g (450 g/kg birth weight) in 19 h. At birth, 3.0%, 2.5% and 14.9% of piglets, respectively, had difficulty in breathing, were stuck in placental membranes or had their umbilical cord already ruptured. At T24, 11% of piglets had splayleg.
Analyses of intra-litter factors affecting colostrum intake by piglets were done on residues calculated from the litter effect analysis. Piglet birth weight was related to both individual colostrum intake (Figure 1; r = 0.62; P < 0.001) and relative colostrum intake (g/kg birth weight; r = 0.21; P < 0.001). Colostrum intake also differed between piglets with and without difficulty in breathing at birth, their umbilical cord already ruptured or splayleg (Figure 2). Analysis of the influence of birth order (divided into four categories) on colostrum intake and on birth weight showed no significant effect (Figure 3). Inter-litter regression analysis showed effects of average litter birth weight (R 2 = 0.29; P < 0.001), heterogeneity of litter birth weight (% CV; R 2 = 0.18; P < 0.01) and litter size (R 2 = 0.49; P < 0.001; Figure 4) on mean colostrum intake by the litter.
Intra-litter relationship between colostrum intake and birth weight. Data presented are residues calculated after correction from litter effect.
Effect of vitality traits on birth weight and colostrum intake. Numbers at bottom of bar graphs are numbers of piglets in each category. Data presented are least square means calculated after correction from litter effect. Error bars represent s.e. values. *P < 0.05, ***P < 0.001.
Effect of birth order divided in four categories on birth weight (black) and colostrum intake (white). Numbers at bottom and top of bar graphs are numbers of piglets in each category. Data presented are least square means calculated after correction from litter effect. Error bars represent s.e. values.
Effect of litter size on mean colostrum intake by piglets and sow colostrum yield.
Colostrum yield of sows and its variability
Colostrum yield during the 24 h following the beginning of parturition averaged 3.67 ± 0.14 kg, ranging from 1.91 to 5.31 kg. The PLS analysis first considered 17 variables related to sow characteristics (parity, number of functional teats, sow body weight upon entrance in maternity, induction of farrowing, duration of gestation, duration of farrowing), litter characteristics (litter size, total litter weight at birth, mean birth weight of piglets born alive, variation in piglets’ birth weights) and composition of colostrum (concentrations of E2, P4 and PRL at T0–2 and concentrations of CP, lactose, total lipids and IgG at T0). In this first PLS analysis, the first two principal factors summarised 42.3% of the variability in colostrum yield. In further PLS analyses, seven variables were removed because of their weak contribution in the modelling of colostrum yield. In particular, the absence of relationship between colostrum yield and litter size is shown in Figure 4. The 10 remaining variables are presented in Figure 5, the first two principal factors summarising 39.3% of the variability in colostrum yield. According to the first principal factor, on one hand, there was a positive relationship between colostrum yield, total and mean birth weight per litter, concentrations of IgG and protein at T0 and sow body weight and parity, and on the other hand there was a negative relationship between colostrum yield and induction of farrowing, duration of gestation and concentrations of lactose at T0 (Figure 5). According to the second principal factor, colostrum yield was negatively linked to variations in birth weights, but to a lesser extent than the associations noted with the first principal factor.
Result from partial least square analysis on colostrum yield. Lactose, immunoglobulin G and protein at T0 are measured in colostrum at the onset of farrowing. Factor 1 summarises 24.5% of the general model information and 32.5% of the colostrum production variability. Factor 2 summarises 17.9% of the general model information and 6.8% of the colostrum production variability.
Analyses of particular relationships between colostrum yield and each of these variables were carried out. Simple analysis of variance on the effect of induction of parturition on colostrum yield showed a lower yield when farrowing was induced (induced: 3366 ± 126 g; not induced: 4165 ± 281; P = 0.017; t-test). However, this effect was somewhat confounded with the duration of gestation since only sows farrowing after 114 days of gestation were induced (gestation length: when induced, 114.6 ± 0.1 and not induced, 113.3 ± 0.3; P < 0.001; t-test). Unfortunately, the unequal distribution of sows between durations of gestation and induction groups did not allow appropriate independent comparisons of these two variables on colostrum yield. Sow body weight and parity were strongly related (r = 0.72; P < 0.001) and duration of gestation showed negative correlations with parity (r = −0.29; P = 0.07) and body weight (r = −0.34; P = 0.03). Despite its contribution towards colostrum yield in the PLS analysis, body weight did not significantly influence colostrum yield (P = 0.35). On the other hand, when looking at the effect of parity (three categories were used, namely, primiparous, second or third parity, or parity 4 or more) on colostrum yield, sows of second and third parities had a greater colostrums production (means of 3435a ± 184 g, 4278b ± 288 g and 3616ab ± 288 g, respectively, for the three groups; overall effect of parity P = 0.059).
Spearman correlation coefficients between colostrum yield and mean birth weight of piglets, total litter birth weight and variability of piglets’ birth weights were 0.38 (P = 0.015), 0.28 (P = 0.085) and −0.34 (P = 0.030), respectively. There were no significant relationships between colostrum yield and concentrations of the various hormones at farrowing. However, the PLS analysis showed that colostrum yield was positively related to protein (r = 0.045; P = 0.78) and IgG (r = 0.10; P = 0.53) concentrations and negatively related to lactose (r = −0.26; P = 0.11) content in colostrum at the onset of farrowing. Colostrum composition and concentrations of various hormones in colostrum at farrowing, 2, 4 and 24 h post partum are shown in Figure 6. Relationships between colostrum composition and some sow characteristics, as determined by the principal components analysis, are shown in Figure 7 and a correlation matrix between those variables can be seen in Table 1. Figure 7 shows that a group of variables including P4, IgG and protein concentrations in colostrum around farrowing was diametrically opposed to lactose concentrations. A second group composed of protein, IgG concentrations at T24, sow weight and parity was opposed to duration of gestation and colostrum lipid content.
Concentrations of prolactin (PRL), progesterone (P4) and oestradiol-17β (E2) in colostrum at the onset of farrowing (T0) and 2, 4 and 24 h later. Values are means ± s.e. Different letters indicate significant differences (P < 0.05). Composition of colostrum (means of concentrations of lipids, lactose, proteins including immunoglobulin G (IgG)) at farrowing and 2, 4 and 24 h later.
Results from the principal components analysis on colostrum composition and some sow-performance variables. The biplot of the first two principal components jointly represent 44.6% of the total variation.
Matrix of correlations between concentrations of progesterone (P4) and oestradiol-17β (E2) at T0−2 (average of the two) and concentrations of lactose, crude proteins and IgG at T0 in colostrum (r=Spearman’s coefficient of correlation; P = P value for statistical difference; n=number of sows)
IgG = immunoglobulin G.
Discussion
Measurement of colostrum yield
Colostrum is produced by the mammary glands during a variable period ranging from 12 to 48 h after the onset of parturition. It is characterised by a high protein concentration, largely due to the presence of immunoglobulins, and a sharp drop (about 50%) in CP content occurs during the first 48 h (Klobasa et al., Reference Klobasa, Werhahn and Butler1987). In the present study, 60% of sows showed a drop in colostral CP greater than 50% within 24 h post partum and the mean overall decrease for all sows was 52%. The first 24 h following the onset of farrowing is therefore an appropriate period for the measurement of colostrum yield.
To our knowledge, this is the first study directly assessing sow colostrum yield through the evaluation of colostrum intake by the whole litter. Previous studies provided some idea of colostral production during the first 24 h following the onset of parturition, estimated at 3000 g, via the measurement of individual colostrum intake of only a few sow-reared piglets (Le Dividich and Noblet, Reference Le Dividich and Noblet1981; Milon et al., Reference Milon, Aumaitre, Le Dividich, Franz and Metzger1983). Yet, the weigh–suckle–weigh method used in those studies underestimates colostrum intake by approximately 31% (Rudolph, 1984). When accounting for this correction, a more precise estimate of sow colostrum yield would therefore be 4000 g, which is in agreement with the present results. Our measure of colostrum yield might also have underestimated values since colostrum intake by piglets dead within 24 h after the onset of farrowing was not measured. However, those piglets most likely did not consume any colostrum, as indicated by their weight loss (Milligan et al., Reference Milligan, Fraser and Kramer2001; Damm et al., Reference Damm, Pedersen, Heiskanen and Nielsen2005).
Variability of colostrum yield and intake
Piglet characteristics
Colostrum intake by piglets was calculated using an equation based on their birth weight and their weight gain within 24 h of birth, therefore accounting for the strong relationship between colostrum intake and birth weight. However, while there was an overall increase in colostrum intake of 28 g per 100 g increase in birth weight, the equation used to estimate colostrum intake would suggest a 7-g increase in colostrum intake per 100-g increase in piglet birth weight (Devillers et al., Reference Devillers, Van Milgen, Prunier and Le Dividich2004b). Therefore, the impact of birth weight on colostrum intake is greater than what would be expected from the equation itself. Le Dividich et al. (Reference Le Dividich, Martineau, Thomas, Demay, Renoult, Homo, Boutin, Gaillard, Surel, Bouetard and Massard2004) noted an increase of 18 g in piglet weight gain per 100-g increase in birth weight, which is equivalent to 30 g of colostrum intake and is very close to the present results (1 g CI = 0.6 g birth weight; Devillers et al., Reference Devillers, Van Milgen, Prunier and Le Dividich2004b). Furthermore, relative colostrum intake (i.e. corrected for birth weight in g/kg) in the present study was also related to birth weight, indicating that heavier piglets may have a competitive advantage over lighter ones for colostrum access.
Although piglets being born later during farrowing have less time to consume colostrum, birth order was not related to either colostrum intake or birth weight, showing that piglets born later did catch up with others in terms of the amount of colostrum ingested (Bland et al., Reference Bland, Rooke, Bland, Sinclair and Edwards2003). Indeed, piglets tend to consume up to 30% of their 1st day colostrum intake during the first nursing bouts following birth (Fraser and Rushen, Reference Farmer, Robert and Rushen1992) and during the first 6 h post partum, less than 75% of the litter is present at most nursing bouts (De Passillé and Rushen, Reference De Passillé and Rushen1989a). It is likely that after ingestion of a large amount of colostrum during the phase of continuous secretion, early-born piglets are asleep, thereby allowing late-born piglets the opportunity to suck. The negative influence of low vitality at birth, especially hypoxia during delivery, on the piglet’s ability to suckle (Herpin et al., Reference Herpin, Damon and Le Dividich2002) is confirmed by the lower colostrum intake of piglets with splayleg, ruptured umbilical cord or difficulty in breathing at birth. Those characteristics can therefore be useful to identify piglets at risk. In conclusion, low vitality and low birth weight impair the piglets’ ability to successfully extract colostrum from the teats and reduce their chances of suckling later on, as nursings become synchronised (Pluske and Williams, Reference Pluske and Williams1996; Hoy et al., Reference Hoy, Lutter, Puppe and Wahner1997).
Litter characteristics
Contrary to what is seen with milk production (Auldist et al., Reference Auldist, Carlson, Morrish, Wakeford and King1998), litter size did not affect colostrum yield, thereby confirming the absence of a litter size effect on piglets’ growth during the first postnatal days (Milligan et al., Reference Milligan, Fraser and Kramer2001; Le Dividich et al., Reference Le Dividich, Martineau, Thomas, Demay, Renoult, Homo, Boutin, Gaillard, Surel, Bouetard and Massard2004). Piglets from larger litters therefore have less colostrum available on an individual basis. Higher litter birth weights tended to be related with higher colostrum yield and a greater heterogeneity in piglets’ birth weights was negatively related to colostrum yield. These results are consistent with previous findings that greater heterogeneity in birth weights leads to poorer growth and higher mortality of piglets (Milligan et al., Reference Milligan, Fraser and Kramer2002; Quiniou et al., Reference Quiniou, Dagorn and Gaudré2002). Therefore, the main factor determining colostrum intake by piglets was their body weight at birth, which is also the major determinant of their vitality and their ability to stimulate the udder in order to extract colostrum from the teats.
Sow characteristics
Colostrum intake does not depend solely on characteristics of the piglets but also on the sow’s ability to produce it. In the PLS analysis, the duration of gestation, induction of farrowing, parity and sow weight all contributed to the variation in colostrum yield. However, no clear effects were shown when the influence of each variable was analysed independently.
The effects of gestation length and induction of farrowing on colostrum yield are somewhat contradictory to earlier reports. Indeed, a lower colostrum yield was observed in sows with early-induced parturitions (day 109 of gestation) and this seemed to be due to lower birth weight and vitality of piglets (Milon et al., Reference Milon, Aumaitre, Le Dividich, Franz and Metzger1983). Moreover, studies on the influence of prostaglandins on induction of lactation showed that sows with induced farrowings presented less risk of agalactia or mastitis (Einarsson et al., Reference Einarsson, Gustafsson and Larsson1975) and had only a slightly lower colostrum yield (Maffeo et al., Reference Maffeo, Redaelli, Ballabio and Baroni1986). Nevertheless, it is important to consider that the distribution of sows across gestation lengths was not uniform in the present study and the effects of gestation length and farrowing induction were confounded to some extent. A study using a larger number of sows varying in gestation lengths is therefore needed to clearly determine their exact influences. Despite its contribution to the variation in colostrum yield, sow body weight was not, by itself, related to colostrum yield. On the other hand, parity had a slight influence on colostrum yield, with second and third parity sows having a higher yield of colostrum than sows from other parities. The same tendency was observed for milk production (Boyce et al., Reference Boyce, Smits, Campbell and King1997).
There is strong evidence for a role of progesterone (Liptrap, Reference Liptrap1980; De Passillé et al., Reference De Passillé, Rushen, Foxcroft, Aherne and Schaefer1993) and prolactin (Farmer et al., Reference Fraser and Rushen1998) in the initiation of lactation, yet no relationships between colostral concentrations of these hormones and colostrum yield were established. Although hormonal concentrations in colostrum and plasma are well correlated during parturition (Devillers et al., Reference Devillers, Farmer, Mounier, Le Dividich and Prunier2004a), the concentrations measured in colostrum reflect an average of plasma concentrations during an undetermined period and slight differences may therefore go unnoticed. A positive relationship between milk production and milk lactose concentrations was previously reported in sows (White et al., Reference White, Head, Bachman and Bazer1984), yet the inverse relationship found with the PLS analysis suggests that mechanisms regulating the synthesis of colostrum are different from those regulating milk synthesis.
Colostrum composition
Data on composition of colostrum was in accordance with previous reports (Le Dividich et al., Reference Le Dividich, Rooke and Herpin2005). Hormonal concentrations in colostrum were also comparable with previously obtained results (Devillers et al., Reference Devillers, Farmer, Mounier, Le Dividich and Prunier2004a), with the exception that E2 concentrations were greater during farrowing in the present study. Hormonal status regulates the synthesis of colostrum components and the PCA analysis provides a good summary of the relationships between hormone concentrations and colostrum composition. The negative correlations between lactose, and CP and IgG levels in colostrum confirmed the opposite relationship between the synthesis of lactose and the transfer of immunoglobulins in the mammary gland (Devillers et al., Reference Devillers, Farmer, Mounier, Le Dividich and Prunier2004a). Moreover, P4 concentrations were positively correlated with IgG and CP and negatively correlated with lactose content in colostrum, confirming its stimulatory influence on the transfer of IgG from plasma to colostrum in the sow (Jackson et al., Reference Jackson, Hurley, Easter, Jensen and Odle1995) and its inhibitory effect on lactose synthesis (Whitely et al., Reference Whitely, Hartmann, Willcox, Bryant-Greenwood and Greenwood1990). Oestradiol-17β was also shown to stimulate the transfer of IgG from plasma to colostrum in cows (Darton and McDowell, Reference Darton and McDowell1979) and this could also be the case in sows since a relationship between IgG and E2 concentrations in colostrum was observed.
Conclusion
This descriptive study provides the first estimate of colostrum yield using a method based on the measure of colostrum intake of the whole litter. Results demonstrate a large variability in colostrum yield among sows and suggest that determination of the factors affecting colostrum yield can be looked at based on two different hypotheses. In the event that sows do not limit the amount of colostrum available to the piglets, individual characteristics of the piglets, particularly birth weight and vitality, and consequently litter characteristics (heterogeneity of litter weight), would be the major determinants of colostrum intake by individual piglets. On the other hand, in the event that sows are limiting colostrum intake by the piglets, hormonal, environmental and nutritional factors could be responsible for the great variability in colostrum production.
In the present study, litter size, which is known to have a strong influence on milk production, did not affect colostrum yield. On the other hand, piglet weights, either individual or total litter weights, were slightly related to colostrum yield suggesting that, irrespective of litter size, vitality of the litter could be the major factor in determining colostrum yield. At this early stage of lactation, the impact of udder stimulation by piglets is not likely in place yet and most of the colostrum is consumed in the few hours following parturition. A low colostrum yield may therefore be mainly attributed to a poor ability of the sow to produce colostrum, making the supply inadequate to meet the piglets’ needs. However, we did not find any sow-related factor that clearly affected colostrum yield. The influences of parity, induction of farrowing and duration of gestation need to be confirmed and further studies are needed to investigate the endocrine regulation of colostrum secretion, especially the possible negative impacts of hormonal and metabolic disorders around parturition on the initiation of the lactation process.
Acknowledgement
The authors wish to acknowledge M. Lefebvre, A.M. Mounier, F. Thomas, L. Gaillard, D. Boutin, Y. Surel, R. Bouetard, C. Homo and B. Duteil from INRA-SENAH and L. Thibault and S. Horth from the Lennoxville Dairy and Swine R&D Centre for expert technical assistance. The authors also thank S. Méthot, from Agriculture & Agri-Food Canada, for his invaluable help in statistical analyses. PhD studentship was funded by ITP (Paris, France) and INRA (Paris, France).
