Effects of Grape Pomace on Sow Blood, Colostrum and Milk Parameters

Abstract

This study was performed to assess the effects of grape pomace feeding on the immunoglobulin concentration in mammary gland secretions and the biochemical parameters of sows’ blood. This study presents unique results of sow blood parameters obtained during the first day postpartum. Sixteen gestating sows were included in the experiment. The experimental group (DGP) received a supplement of dried grape pomace in the amount of 1% of the basal diet from the 7th day antepartum until the end of lactation. Blood, colostrum, and milk were taken from the sows. On the 1st day postpartum, in the sows’ blood, higher values of total proteins and globulins, as well as lower values of aspartate aminotransferase, creatinine, and the albumin/globulin ratio, were recorded in DGP. There were no significant differences in the concentration of immunoglobulins in the blood of sows between the groups. Also, differences in the concentrations of immunoglobulins in the colostrum and milk of sows throughout lactation were not statistically significant. It can be stated that the feeding of dried grape pomace did not have a negative effect on the biochemical parameters of the sows’ blood, colostrum, and milk. In addition, there is a potential suggestion that the addition of dried grape pomace could have a positive effect on the antioxidant status of sows.

1. Introduction

As viticulture is an important agricultural activity in many countries and produces a large amount of grape pomace, the inclusion of grape pomace in the feed rations of sows is justified, as it is currently used only marginally [1]. The amount of grape pomace produced in wine production depends on the grape cultivar and the pressing process [2], but several studies have shown that they generally make up 20–30% of the original grape mass [3,4]. It is estimated that only about 3% is currently used in animal nutrition [4]. Different types of fruits, berries, and pomace contain high concentrations of polyphenols. The immunomodulatory effects have been attributed to resveratrol, a polyphenol found mainly in grapes, peanuts, and other berries [5].

Colostrum and milk production by sows are the primary limiting factors influencing piglet survival, growth, and performance [6,7]. The death of one out of seven piglets between birth and weaning is a reality on most European farms. Approximately two-thirds of these deaths occur within the first 72 h after birth [8]. According to KilBride et al. [9], the two most common causes of death in piglets are low viability (14%) and starvation (up to 7%). Therefore, quality colostrum and milk are important for newborn piglets. While colostrum is important for pig survival, sow milk is a limiting factor influencing the piglet growth rate [10]. Immunoglobulins (Igs) secreted in colostrum and milk are a major factor in providing immune protection to neonates. Immunoglobulins in milk represent the cumulative immune response of a lactating mammal to exposure to pathogens and other sources of antigenic stimulation that occur when interacting with the environment [11]. Because the sow’s placenta is of an epitheliochorial nature, the piglet must obtain maternal immunoglobulins from the ingested colostrum for passive immune protection until it has fully developed its immune system [12]. The most abundant immunoglobulins in a sow’s mammary gland secretions are IgG, IgA, and IgM. The IgG concentration in colostrum is highest at the time of parturition and decreases during the first day of lactation [13]. Immunoglobulins received from colostrum in the first days after birth are used in the immunological defense of piglets. IgA in colostrum and milk protects the intestinal mucosa from pathogens, thus reducing neonatal diarrhea. This class is about 18% in colostrum at the onset of lactation, and its percentage gradually increases as it becomes the dominant immunoglobulin in milk at the end of lactation, with about 60% [14]. Several studies indicate that the nutrient and immunological compositions of colostrum and milk are different between breeds and are influenced by several factors, such as sow parity, the endocrine system, health status, the breeding environment, and the nutrition of pregnant and lactating sows [15]. The experiment by Wang et al. [16] showed that the addition of phytogenic additives to the feed rations of pregnant and lactating sows increased the IgG content in the colostrum. Wang et al. [17] fed sows, in their experiment, dietary polyphenols from grape seeds and reported an increase in IgG and IgM in the colostrum of sows, which, according to them, led to a reduced mortality of piglets in the experimental group. Monitoring health status through blood parameters is essential in husbandry practice [18]. Also, observation of the antioxidant status and blood β-hydroxybutyrate levels can help assess a pig’s fitness and health. Monitoring metabolic ketosis in pigs is not generally realized. However, early detection of ketosis can prevent the problem of reduced milk production by sows. Ketosis is caused by a negative energy balance in pigs [19]. It is pregnancy and the perinatal period that are a source of considerable stress for pigs and cause oxidative stress, which negatively affects the performance of pigs [20]. Polyphenols found in grape pomace are attributed to having antioxidant and immunomodulatory effects [20,21]. In pig production, there is a growing interest in natural feed additives, which have a positive impact on pig health and performance.

In relation to the positive effects of grape pomace on the immunological parameters of sows, colostrum, and milk, an experiment was carried out, and the following hypothesis was proposed: the addition of grape pomace to the feed rations of sows at the end of pregnancy and throughout lactation will change the immunoglobulin concentrations in colostrum and milk at the same time without negatively affecting blood parameters.

2. Materials and Methods

Throughout this experiment, the animals were under veterinary supervision and kept in line with Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 on the protection of animals used for scientific purposes [22]. Experienced and trained staff took care of the animals. At the beginning of the experiment, all sows were examined by a veterinarian and evaluated as clinically healthy animals. This experiment was carried out as part of an experiment on feeding grape pomace to pigs. The influence on the blood cell count parameters of sows and their offspring is published in the article [23].

2.1. Animals and Feeding

The experiment was carried out in cooperation with the commercial pig farm in Dubovany (SPD Veselé, Veselé, Slovakia). The experiment included 16 highly pregnant sows that were crossbred (Large White x Landrace) and mated by a boar of the Duroc breed. The sows were at the same stage of gestation. The sows were moved from free housing to the farrowing pens on the 7th day antepartum, when they were randomly divided into two groups. The control group (CON) and the experimental group (DGP) were housed in one farrowing room with controlled environmental conditions. On the day of transfer to the farrowing pens, the feeding of dried grape pomace to the experimental group was also started. The basic feed ration, from the 7th day ante partum, consisted of a feed mixture for lactating sows (3.5 kg per sow/day), and this was fed to a control group of sows. The DGP group received the same feed ration enriched with 1% dried grape pomace (0.035 kg) per sow and day. After farrowing, the diets in both groups were fed ad libitum, with an average intake of 9 kg per sow per day. Thus, in the DGP group, sows received an average of 0.090 kg of dried grape pomace per day during lactation. Throughout the experiment, sows were fed twice a day (50% of the diet in the morning and 50% of the diet in the evening). A weighed amount of dried grape pomace was added as a “top dressing” to the diet. Throughout the experiment, the sows had ad libitum access to water (nipple drinker). Grape pomace was obtained from white Pinot Gris vine, a variety grown at the Academic Winery of the Slovak University of Agriculture in Nitra. The grape pomace contained parts of skins, seeds, and pulp. After pressing the must, the grape pomace was pre-dried at 55 ± 5 °C and stored in paper bags. Prior to feeding, the pre-dried grape pomace was ground in a laboratory powder grinder with particles smaller than 1 mm.

2.2. Analysis of Feeds and Their Nutrient Composition

The concentrations of individual nutrients in the feed samples were determined in the Laboratory of Quality and Nutritional Value of Feeds at the Institute of Nutrition and Genomics, Department of Animal Nutrition, SUA in Nitra using standard laboratory procedures and techniques [24]. The nutritional characteristics of the compound feed and the compound feed enriched with dried grape pomace are given in

Table 1. Nutritional characteristics of the sow diet [23].

	Control Group	Dried Grape Pomace Group
Ingredients of diet (%)
Barley grain	33.0	32.69
Maize grain	33.0	32.69
Soybean meal	15.8	15.6
Wheat grain	7.0	6.93
Rapeseed meal	3.0	2.97
Vitamin mineral premix 1	3.0	2.97
Sunflower oil	2.6	2.57
PKK energy 2	1.5	1.49
Abrocel RC 3	1.0	0.99
Neutox 4	0.1	0.1
Dried grape pomace powder	0	1.0
Nutritional characteristics
Dry matter (g/kg)	893	892
Crude protein (g/kg)	174	173
Ether extract (g/kg)	20.8	21.3
Crude fiber (g/kg)	46.7	48
Ash (g/kg)	56.2	56
Nitrogen free extract (g/kg)	595	594
Starch (g/kg)	408	404
Total sugar (g/kg)	41.3	42.6
Non-fiber saccharides (g/kg)	508	505
Net energy (MJ/kg)	9.29	9.37
Ca (g/kg)	8.78	8.73
P (g/kg)	6.24	6.21
Mg (g/kg)	2.59	2.58
Na (g/kg)	2.97	2.94
K (g/kg)	9.37	9.4
Cu (mg/kg)	25.9	25.7
Fe (mg/kg)	354	351
Mn (mg/kg)	84.7	84
Threonine (g/kg)	6.18	6.15
Lysine (g/kg)	9.37	9.31
Cysteine (g/kg)	2.01	1.99
Methionine (g/kg)	1.74	1.72

¹ Tekromix PKK, Tekro Nitra s.r.o., Slovakia; one kilogram of premix contained: Ca 193 g; P 60 g; Mg 9 g; Na 50 g, Vitamin A 312,000 U.I.; Vitamin D3 65000 U.I.; Vitamin E 3200 mg; Vitamin B1 65 mg; Vitamin B2 170 mg; Vitamin B6 135 mg; Vitamin B12 1 mg; Vitamin K3 100 mg; Biotin 10 mg; Folic acid 145 mg; Niacin amide 1000 mg; Calcium pantothenate 685 mg; Choline chloride 5000 mg; Lysine 50 g; Fe 4000 mg; Cu 450 mg; Zn 3900 mg; Mn 2000 mg; I 45 mg; Se 10 mg; ² Tekro Nitra s.r.o., Slovakia: one kilogram contained: E 551a Silicic acid 9 g; Crude protein 20 g; Ether extract 279 g; Crude fiber 2 g; Ash 102 g; Ca 2 g; P 0.50 g; Na 0.1 g; ME 11.5 MJ. ³ JRS GmbH + Co KG, Germany: Crude fiber concentrate for sows. ⁴ Bioferm, Czech Republic, is a broad-spectrum toxin scavenger with additional mold control.

. The nutritional composition of the compound feeds and grape pomace was also published in the article by Mixtajová et al. [23] (2022), which was solved in the same project. The content of polyphenols in the grape pomace used was published in the article by Vašeková et al. [25], where the total polyphenol content was 27.38 ± 1.38 mg GAE/g, the total phenolic acid content was 13.27 ± 0.62 mg CAE/g, the total flavonoid content was 0.12 ± 0.01 mg QE/g, and the antioxidant activity was 9.17 ± 0.15 mg TEAC/g.

2.3. Sampling and Analysis of Blood, Colostrum, and Milk Samples

Blood samples were taken from the sows in sterile tubes for the first time at the beginning of the experiment, on the 7th day antepartum (7 d a.p.) and on the 1st day postpartum (1d p.p.). Blood was collected by a veterinarian from the vena cava cranialis to a test tube with an H-03 needle (Gama group a.s., Czech Republic). After clotting, the blood was centrifuged, and the resulting blood serum was transferred to 1.5 mL microtubes and frozen at −20 °C for further processing. Colostrum and sow milk (volume approx. 2 mL) were collected by manual milking into sterile tubes and then frozen for further processing. Milk samples were taken without oxytocin application. The milk ejection reflex was induced by the piglets of the sow. Piglets were not separated from the mother during colostrum and milk sampling. Colostrum samples were taken immediately after the birth of the first piglet (d0), and milk samples were subsequently taken on the 1st, 2nd, 3rd, 7th, and 28th days after parturition (d1, d2, d3, d7, and d28). Blood serum was used to determine biochemical parameters (ALB–albumin, CHOL–total cholesterol, TRIGS–triglycerides, GLU–glucose, TP–total proteins, DBIL–direct bilirubin, CREAT–creatinine, AST–aspartate aminotransferase, ALT–alanine aminotransferase, ALP–alkaline phosphatase, GGT–γ-glutamyl transferase, Ca–calcium, Mg–magnesium, P–phosphorus BHB–β-hydroxybutyrate and TAS–total antioxidant status) via a fully automated analyzer RX-Monaco (Randox Laboratories, UK) as per the manufacturer instructions. GLOB–globulin was calculated according to the following formula: GLOB = TP-ALB. A/G ratio–albumin/globulin ratio. Blood serum, colostrum, and milk were used to quantify immunoglobulins G, A, and M. They were measured using a swine ELISA kit (Bethyl Laboratories Inc., Montgomery, TX, USA), and the final IgG, IgA, and IgM concentrations were expressed in mg/mL. All laboratory procedures and analyses followed the kit manufacturer’s instructions. All samples were analyzed in duplicate, and the average of the duplicates of individual samples was used for statistical evaluation.

2.4. Statistical Analysis

Statistical processing of the results was performed using the statistical program IBM SPSS v. 26.0. The statistical significance of the differences between the observed groups at the sampling time, as well as between the sampling times within the groups, was evaluated using the Tukey HSD test. To express the interrelationships between immunoglobulin concentrations from sows’ blood on the 1st day postpartum and colostrum collected after the birth of the first piglet (d0), Pearson’s correlation coefficient was used.

3. Results

3.1. Biochemical Profile

Table 2. Biochemical profile and immunoglobulin concentration of sow serum 7 days ante partum and 1 day postpartum (mean ± SEM).

	Group	7d a.p.	1d p.p.
ALT (U/L)	DGP	35.2 ± 3.63	23.7 ± 3.56
	CON	41.0 ± 3.35	31.3 ± 1.52
AST (U/L)	DGP	25.0 ± 3.11	21.7 ± 2.12 a
	CON	19.9 ± 0.68	34.3 ± 5.07 b
ALP (U/L)	DGP	21.9 ± 2.83	26.9 ±3.87
	CON	22.4 ± 1.84	22.1 ± 2.41
GGT (U/L)	DGP	34.4 ± 1.49	42.7 ± 1.44
	CON	38.4 ± 1.62	42.2 ± 1.96
CREAT (μmol/L)	DGP	202.8 ± 8.0	172.8 ± 8.78 a
	CON	197.1 ± 3.95	197.4 ± 2.76 b
DBIL (μmol/L)	DGP	1.4 ± 0.09	0.7 ± 0.15
	CON	1.1 ± 0.13	0.5 ± 0.06
TP (g/L)	DGP	67.6 ± 1.81	73.0 ± 1.31 a
	CON	63.2 ± 1.74	64.4 ± 1.30 b
ALB (g/L)	DGP	40.2 ± 0.96	41.3 ± 1.28
	CON	40.6 ± 1.19	41.3 ± 0.63
GLOB (g/L)	DGP	27.4 ± 2.67	31.7 ± 2.30 a
	CON	22.6 ± 2.63	23.0 ± 1.69 b
A/G ratio	DGP	1.7 ± 0.19	1.4 ± 0.16 a
	CON	2.1 ± 0.24	1.9 ± 0.17 b
UREA (mmol/L)	DGP	8.0 ± 0.25	9.5 ± 0.58
	CON	7.9 ± 0.20	10.7 ± 0.52
CHOL (mmol/L)	DGP	1.5 ± 0.04	1.7 ± 0.07
	CON	1.6 ± 0.03	1.7 ± 0.06
TRIG (mmol/L)	DGP	0.8 ± 0.05	0.5 ± 0.10
	CON	0.7 ± 0.05	0.3 ± 0.04
GLUC (mmol/L)	DGP	4.4 ± 0.20	4.1 ± 0.17
	CON	4.1 ± 0.10	4.1 ± 0.06
Ca (mmol/L)	DGP	2.5 ± 0.07 a	2.7 ± 0.08
	CON	2.6 ± 0.05 b	2.5 ± 0.03
Mg (mmol/L)	DGP	1.1 ± 0.02	1.0 ± 0.04
	CON	1.1 ± 0.02	1.0 ± 0.02
P (mmol/L)	DGP	1.9 ± 0.07	2.3 ± 0.06
	CON	2.0 ± 0.05	2.4 ± 0.06
BHB (mmol/L)	DGP	0.009 ± 0.002	0.008 ± 0.002
	CON	0.008 ± 0.001	0.005 ± 0.002
TAS (mmol/L)	DGP	0.646 ± 0.015	0.684 ± 0.022
	CON	0.609 ± 0.024	0.575 ± 0.016
IgG (mg/mL)	DGP	11.1 ± 0.76	10.2 ± 0.35
	CON	10.3 ± 0.21	12.3 ± 2.13
IgA (mg/mL)	DGP	1.0 ± 0.24	1.2 ± 0.20
	CON	1.3 ± 0.24	1.7 ± 0.38
IgM (mg/mL)	DGP	5.6 ± 0.64	6.0 ± 0.68
	CON	7.0 ± 1.22	6.8 ± 1.47

7d a.p.—7th day antepartum; 1d p.p.—1st day postpartum; CON–control group of sows (n = 8); DGP–group of sows fed with an addition of dried grape pomace (n = 8); ^{a, b}—the values are statistically significant between groups within the same sampling timepoint (p-value < 0.05); SEM–Standard Error of the Mean.

shows the results of the biochemical profile, antioxidant status, and content of immunoglobulins (IgA, IgA, and IgM) determined in the blood of sows taken 7d a.p. and 1d p.p. At 7d a.p. we recorded a significant difference only in the biochemical profile in terms of Ca content (p < 0.05). For the other parameters, there was no significant difference between the groups at the beginning of the experiment (7d a.p.), which indicates good balance of the monitored parameters of the sows’ blood. Statistical differences between groups at 1d p.p. were recorded in parameters such as AST, CREAT, TP, GLOB, and the A/G ratio. None of the changes in blood immunoglobulins were significant (p ˃ 0.05).

3.2. Immunoglobulin Concentration in Colostrum and Milk of Sows

The results of the determination of the immunoglobulins in the sows’ colostrum and milk are shown in

Table 3. Immunoglobulin concentrations in sows’ colostrum and milk from the beginning of farrowing to weaning (mean ± SEM).

	Group	d0	d1	d2	d3	d7	d28
IgA (mg/mL)	DGP	12.9 ± 3.45	6.1 ± 1.42	7.0 ± 2.85	3.4 ± 0.59	4.0 ± 0.46	3.8 ± 1.09
	CON	13.6 ± 2.83	5.6 ± 1.45	4.8 ± 1.90	3.7 ± 0.72	4.2 ± 0.97	1.8 ± 0.40
IgM (mg/mL)	DGP	6.8 ± 1.00	2.6 ± 0.28	3.1 ±0.34	2.1 ± 0.49	1.4 ± 0.08	1.4 ± 0.19
	CON	7.4 ± 0.54	3.0 ± 0.58	2.5 ± 0.29	1.7 ± 0.26	1.6 ± 0.25	1.4 ± 0.20
IgG (mg/mL)	DGP	111.3 ± 7.2	20.7 ± 3.49	14.2 ± 4.99	5.3 ± 0.48	1.9 ± 0.19	4.0 ± 1.25
	CON	100.7 ± 2.2	18.3 ± 5.00	14.2 ± 5.42	5.4 ± 0.54	1.5 ± 0.29	3.8 ± 0.79

The difference in the mean value of the immunoglobulin concentration was not statistically significant at each time interval of colostrum sampling (day 0) or milk sampling (day 1, day 2, day 3, day 7, and day 28) (p > 0.05); SEM–Standard Error of the Mean.

. The differences between the groups were not statistically significant for any of the immunoglobulins examined. The concentration of IgG was the highest in colostrum (d0) and subsequently decreased over time in both groups. In the DGP group, there was a 58-fold decrease in IgG from 111.3 mg/mL (d0) to 1.9 mg/mL in milk on day 7 of lactation. In the CON group, the decrease was up to 67-fold from 100.7 mg/mL (d0) to 1.5 mg/mL in milk on day 7 of lactation. From d7 to d28, the IgG concentration increased slightly in both groups. The concentrations of IgA and IgM were also the highest at the beginning of lactation (d0), but the decrease was not as pronounced for IgG in either group.

The percentages of individual immunoglobulins according to the time of collection are shown in Figure 1. The percentage of IgG decreased almost threefold during lactation, from more than 84% at d0 to 25% at d7 of lactation. However, on d28, its percentage increased again to 42% in the DGP group. In the CON group, the percentage of IgG also decreased from 82% to 19% on d7 of lactation. Similarly, in the DGP group, between d7 and d28, the IgG in the CON group increased to 54%. The percentage of IgM increased in both lactating groups until d7 of lactation. The relative IgA proportion in the DGP group increased from 11% on d0 up to 56% on d7 of lactation. The IgA of the CON group showed an increasing trend of the percentage that was also recorded until d7 of lactation at the level of 58% from 11% on d0. Between d7 and d28, a decrease to 26% was recorded.

For IgG (−0.832) in DGP and IgA (0.925) in CON, a significant (p < 0.05) correlation between the sow’s blood on 1d p.p. and colostrum (d0) was observed.

4. Discussion

The values of biochemical parameters are influenced by several different factors, such as the age of the sow, diet, and stage of pregnancy and lactation [18]. And it is the period around parturition and lactation that may result in an increase in the levels of some indicators, such as AST, TP, and GLOB, or a decrease in CREAT. Within the enzymatic profile, the results showed a significant (p ≤ 0.05) difference between the groups at 1d p.p. in the AST. The monitored ALT and GGT parameters were within the reference values published by Heath et al. [26] and Friendship et al. [27]. AST was slightly below these reference values in the CON group at 7d a.p. and in the DGP group at 1 d p.p. The increase in AST concentration in the CON group (from 19.9 to 34.3 U/L) may be due to muscle cell degradation caused by mobilization of body reserves, as reported by Verheyen et al. [18] and Pietrzak and Grela [28]. ALP values were outside the swine reference values published by Heath et al. [26] and Friendship et al. [27] but within the reference values for pregnant and lactating sows published by Verheyen et al. [18]. It is possible that the values of the reference intervals vary, as different methods of determination are used in older publications compared to newer ones. From the nitrogen profile, TP values were below the reference values for pregnant and lactating sows [18]. ALB and CREAT were within published values for a given parameter. Only in the DGP group at 1d p.p. did the GLOB concentration reach the reference value for lactating sows [18]. Compared to Friendship et al. [27] and Elbers et al. [29], the A/G ratio value was higher in both groups and both sampling times. Dupak et al. [30] found a positive effect of grape pomace supplementation on the cholesterol levels of broiler chickens. On the other hand, the results of this study revealed no effect of grape pomace feeding on cholesterol levels. Disorders of energy metabolism are closely related to the feeding regime, especially during the last period of pregnancy. Its disorders must be assessed in terms of increased lipomobilization and lipolysis during the reproductive cycle. Physiological lipolysis, the negative energy balance just after parturition, and the onset of lactation depend on the postpartum supply of energy components in the feed ratio. The changes in glucose concentration that occur during the transition from pregnancy to lactation are the result of physiological changes in metabolic processes [31]. The BHB levels in this experiment were low and therefore it can be stated that sows did not develop ketosis. In their study, Perri et al. [32] considered ketotic pigs whose BHB value was higher than 0.1 mmol/L. The results show that sows had enough energy from the feed ration and that there was no increase in ketones in the blood, which occurs during the breakdown of fat stores [32]. The overall antioxidant status tended to decrease in the CON group from 7d a.p. compared to 1d p.p., but in the DGP group, it was the opposite. Compared to the results published by Lipiński et al. [20], the TAS values in this study are lower. They recorded TAS values of about 1.20 mmol/L and 1.14 mmol/L in the control group in the experiment with different doses of vit E and polyphenols. Also, Flis et al. [33] reported higher TAS values in both the control (1.12 mmol/L) and experimental groups (1.07 mmol/L), where they also examined the effects of polyphenols on the antioxidant status of pigs. The improvement in the antioxidant status of the sows in the experimental group can therefore be attributed to the polyphenols found in the grape pomace, which was also confirmed by Lipiński et al. [20]. The concentrations of the determined Ca, P, and Mg in sow serum in both groups were within the reference values published by several authors [26,27]. Chedea et al. [34] reported an increase in serum phosphorus levels when feeding grape pomace. The phosphorus values in this study increased in both groups, so it is not possible to attribute this increase to the feeding of grape pomace. Similarly, Kolláthová et al. [35] reported that serum minerals were not affected by a diet supplemented with grape pomace.

The immunoglobulin concentration in colostrum is the highest during parturition and decreases during the first day of lactation [13], which is confirmed by the results of this study, especially regarding IgG. However, there are few studies dealing with the effect of polyphenols on the immunoglobulin concentration in the blood of pregnant sows, colostrum, and milk of lactating sows. Immunoglobulins are crucial for the growth and health of offspring. Wang et al. [17] reported an increase in the concentrations of IgG and IgM in the colostrum of the experimental group when polyphenols from grape seeds were ingested. These results are comparable to the results of this study. Wang et al. [16] monitored the effects of a phytogenic additive and reported the concentrations of sow serum IgG during parturition (5.6 to 6.4 mg/mL) and one day after parturition (6.2 to 6.9 mg/mL). The concentration of IgG determined in this study at 1 d p.p. was higher (Table 2). Compared to this study, Segura et al. [36] reported higher concentrations of immunoglobulins, namely, IgG 21.9 mg/mL, IgM 9.8 mg/mL, and IgA 1.5 mg/mL, in pregnant sows. Foisnet et al. [37] confirmed that the IgG content is different between sows and set the mean value at 12.1 mg/mL in the sow’s serum at the end of pregnancy, which is in accordance with the results of this study.

Colostrum contains the highest concentrations of each immunoglobulin during or immediately after parturition [38]. According to Hurley [39], it is, on average, IgG 65 mg/mL, IgA 13 mg/mL, and IgM 8 mg/mL, but Markowska-Daniel and Pomorska-Mol [14] reported higher concentrations of IgG 98 mg/mL, IgA 23 mg/mL, and IgM 9 mg/mL in colostrum. Compared to these published values, an even higher IgG concentration in the colostrum was recorded in this study (Table 3). The IgG concentrations determined in this study in the colostrum samples from the DGP group are almost double those reported by Hurley and Theil [6] and Hurley [39], but they are comparable to the concentrations reported in the study by Segura et al. [36], which revealed the following immunoglobulin values at the start of parturition: IgG 94.3 mg/mL, IgM 5.0 mg/mL, and IgA 9.9 mg/mL. Segura et al. [36] also recorded a significant drop in the concentration of immunoglobulins after only a few hours. However, the IgG levels were higher at 24 h (37.3 mg/mL) compared to the results of this study. In a study published by Segura et al. [36], an average IgG concentration of 74.2 mg/mL was detected in colostrum, and a decrease of up to 23% in the sixth hour was reported. Then, 24 h from the beginning of parturition, they determined an average IgG concentration of 13.9 mg/mL, which is a lower value than that determined in both groups of sows in this study (Table 3). The percentages of immunoglobulins determined in this study differ from the percentages published by Foisnet et al. [37]. The dominant proportion of IgG at the beginning of lactation was in both groups. At the end of lactation, IgG remained dominant only in the CON group (53%). The percentage of milk IgG (d28) in the DGP group was comparable to that of IgA, 44% versus 41%. The proportion of milk IgA (d28) in the control group was 26%, which is lower than that reported by authors Markowska-Daniel and Pomorska-Mol [14]. As the reference values of colostral and milk immunoglobulins are not precisely established, it is difficult to assess their adequate concentration, but the increased IgG concentration in colostrum increases the IgG level in piglets and potentially improves the survival rate of piglets [40]. Kielland et al. [40] also determined an average colostral IgG concentration of 53.9 mg/mL, which is lower than the IgG concentration in colostrum from this study. In an experiment by Wang et al. [17], the IgM concentration ranged from 6 to 8 mg/mL, and the IgG concentration ranged from 70 to 80 mg/mL in the experimental group when fed 200 or 300 mg/kg DGP. IgG concentrations in this study are higher, while the concentration of IgM is similar compared to the results of Wang et al. [17]. Several authors have confirmed the increase in individual immunoglobulin concentrations in colostrum and milk after the addition of various plant or synthetic additives [16,17,41,42]. The IgA concentration is approximately 4 mg/mL in mature milk, the IgG concentration is 1 mg/mL, and the IgM concentration is 1.6 mg/mL. Similar concentrations of IgA, IgG, and IgM were detected in milk samples collected on 7d (Table 3).

According to Segura et al. [36], the IgG concentration in a sow’s blood at the end of pregnancy has a strong correlation with IgG and IgM in the colostrum. They attributed this to the origin of colostral IgG, which comes mainly from sow serum, whereas colostral IgA is synthesized mostly directly in the mammary gland. The concentrations of immunoglobulins determined in the serum of sows at the beginning of lactation and immunoglobulins in colostrum are strongly correlated. It can be hypothesized that the negative correlation of IgG in the relationship between sow blood and colostrum is a good sign. The lower the IgG content in the blood, the higher the content in the colostrum, as evidenced by the average IgG content in the colostrum (d0) and serum of sows at the beginning of lactation (1d p.p.). Rooke and Bland [12] reported that the IgG concentration is several times higher in colostrum than in sow plasma. In contrast, Foisnet et al. [37] did not confirm the correlation between IgG concentrations in sow plasma and colostrum.

5. Conclusions

The hypothesis that the addition of grape pomace to the diets of pregnant and lactating sows would change the concentration of immunoglobulins in the colostrum and milk, and the blood parameters of sows, was not confirmed. The higher concentration of immunoglobulin G in the colostrum of sows fed dried grape pomace supplementation was not significant. The blood biochemical parameters evaluated in sows that consumed dried grape pomace-supplemented diets remained within the physiological optimum. Based on the results of this study, it can be suggested that dried grape pomace is a usable feed for sows at the end of gestation and during lactation. The potential of dried grape pomace to increase the immunological quality of sows’ colostrum needs to be verified in further studies.