Piglets are born with limited energy reserves, agammaglobulinemic and with an immature gastro-intestinal tract. Colostrum is the sole external nutrient resource for piglets after birth, provides the piglets with maternal immunity and also contains several factors that stimulate the development of the gastro-intestinal tract and other organs (chapter 1). Colostrum thus has important functions and insufficient CI is a major cause of pre-weaning mortality and reduced daily weight gain (chapter 3.4.), both causing major economic losses in modern sow herds. Approximately 30% of sows do not produce sufficient colostrum for their litter (chapter 3.1.) and the CY is independent of litter size (chapter 3.4.). Consequently, insufficient CY in sows is a major problem and becomes even more pronounced in high-prolific sows.
Research on CY in sows is scarce and mainly focused on the hormonal regulation (chapter 1). Very limited information is available on how the sow’s use of energy and protein derived from the feed or body reserves affects CY. The general aim of this thesis was to investigate the use of energy and protein from feed or body reserves during gestation in relation to CY in sows.
In a first study (chapter 3.1.), we identified 2 periods in late gestation during which the use of body energy reserves was correlated with CY. The BF change between d 85 and 108 of gestation was negatively correlated with CY (r = -0.346, P = 0.032) whereas the BF change the week prior to farrowing was positively correlated with CY (r = 0.391, P = 0.017). In this study, we also collected sow serum samples 3-4 days before farrowing and at d 1 of lactation and blood analyses confirmed that the use of body energy and protein reserves just prior to farrowing was negatively correlated with CY. This study also showed that there was no correlation between CY and colostrum composition, which is interesting as this suggests that improving CY should not be at cost of the colostrum composition. Causal relationships between CY and the change of body reserves could not be established with this study design. Therefore, the 2 identified periods of interest were further investigated.
In the second study (chapter 3.2.), we focused on the positive correlation between CY and the BF change 1 week before farrowing. Sows were randomly divided into 2 treatment groups at d 108 of gestation. The first group (L, n = 28) received 1.5 kg feed per day, the second group (H, n = 22) received 3 times 1.5 kg feed per day until farrowing. Based on BF at d 108, sows were divided into 3 BC groups: skinny ( 23 mm, n = 14). The H-group tended to have a greater total CY (P = 0.074) and had a greater CY per kg liveborn piglet (P = 0.018) than the L-group. Compared to sows in moderate BC, fat sows had a lower total CY (P = 0.044), and a lower CY per kg liveborn piglet (P = 0.005). The H-group had a greater concentration of lactose (P = 0.009) and n-3 PUFA (P < 0.001) but a lower concentration of protein (P = 0.040) in colostrum than the L-group. The concentration of IgG and IgA did not differ between treatment and BC groups. The H-group mobilized less body fat (NEFA: P = 0.002) and protein (creatinine: P < 0.001, C4: P = 0.016) reserves but had a greater ratio urea:NEFA (P < 0.001) and less ketone bodies (3-OH-C4: P < 0.001) compared to the L-group before farrowing. This indicates a more balanced entry of metabolites in the citric acid cycle and thus a better support of the maternal peripartal metabolism in the H-group. This study showed that both CY and composition can be influenced by the peripartal feeding strategy and BC. Management of the peripartal feeding strategy and BC thus offer short-term strategies to improve the CY and composition.
In the third study (chapter 3.3.), we tried to unravel the negative correlation between CY and the BF change between d 85 and 108 of gestation. We proposed 2 hypotheses based on literature (chapter 1) 1) the BF change was an indicator of energy use for mammogenesis and a BF loss thus indicated more gestational mammogenesis resulting in a higher CY during the observed period, and 2) the BF change was correlated with the sow’s insulin sensitivity and as such might affect the direction of glucose towards the mammary gland. At d 85 of gestation, 47 sows were stratified for BF and parity, and randomly divided into 6 groups differing in daily feed allowance between d 85 and 108 of gestation. Group 1 was allowed 1.8 kg feed per sow per day. Feed allowance for each next group increased with 300 g feed per sow per day and reached 3.3 kg feed per sow per day in group 6. From d 108 of gestation until weaning, all sows were managed and fed similarly. The CY was correlated with BF change between d 85 and 108 of gestation (r = -0.446, P = 0.002) but not with daily feed allowance between d 85 and 108 of gestation (r = -0.156, P = 0.312). We found 3 indications to support the hypothesis of mammogenesis: 1) gestational mammogenesis occurs between d 85 and 108 of gestation. A BF loss between d 85 and 108 of gestation might partially evolve from an increased mammogenesis; 2) colostrum composition was not correlated with CY or BF change between d 85 and 108 of gestation (P > 0.10) which is indicative for more functional mammary tissue; 3) piglets’ daily weight gain was correlated with BF change between d 85 and 108 of gestation up to d 3 of lactation (r = -0.359, P = 0.019) which is right before the start of lactational mammogenesis. Although BF change between d 85 and 108 of gestation and daily feed allowance between d 85 and 108 of gestation affected the glucose and insulin metabolism, CY was not correlated with the changes in insulin (r = 0.025, P = 0.876) and glucose (r = -0.149, P = 0.359) between d 85 and 108 of gestation which makes this hypothesis less evident. Improving mammogenesis in sows thus seems promising as a long term strategy to increase CY in sows.
In the fourth study (chapter 3.4.) we investigated the effects of CI on piglet performance (survival and daily weight gain) during lactation. All piglets born to 37 PIC sows were observed until weaning and 4 piglets per litter were randomly selected for serum collection 24-30 h after birth. The daily weight gain was positively correlated with BWB and CI/kg BWB, and negatively with time between birth and first suckle until d 3 of lactation (R² = 0.39, P 60 min (P < 0.01). The CI/kg BWB was negatively correlated with urea (P = 0.002), positively to some free AA (P < 0.05) but not to creatinine, NEFA, IgG and IgA in piglets’ serum. The daily weight gain was negatively correlated with urea and positively to leucine until d 3 of lactation (R² = 0.19, P < 0.001), until d 7 of lactation (R² = 0.13, P < 0.001) and until weaning (R² = 0.08, P < 0.001). A lower CI/kg BWB was accompanied by a higher catabolism of protein that did not seem to originate from the piglets’ body reserves. It seems that piglets with a lower CI/kg BWB use a larger proportion of colostral protein as a substrate for energy production rather than for other purposes such as lean growth, as there was a negative correlation between parameters indicating protein catabolism and daily weight gain at least until weaning. Sufficient CI is thus essential for piglet performance at least until weaning. This underlines the importance of improving CY in sows and distribution of the available CY within a litter.
In conclusion, this thesis showed that CY in sows and CI in piglets are highly variable and also insufficient for a considerable number of the animals. The results also documented the importance of sufficient CI for piglet’s performance during the entire lactation period. Next to elucidating the importance of insufficient CY and intake, the thesis also showed that the use of body reserves during late gestation is correlated with CY. A negative energy balance the week prior to farrowing should be avoided. A high peripartal feeding strategy the week prior to farrowing resulted in decreased negative energy balance, less imbalance at the entry of the citric acid cycle and a higher CY. The use of body energy reserves between d 85 and 108 of gestation was negatively correlated with CY and several indications were presented showing that this correlation might be due to better gestational mammogenesis. The thesis provided opportunities for both short-term and long-term strategies to improve CY in sows
