By Jeff Wiegert and Mark Knauer, North Carolina State University
Genetic selection for greater litter size, without emphasis on piglet quality, has reduced piglet birth weight (Lund et al., 2002). Light-birth-weight piglets are slower-growing and a greater mortality risk before reaching market weight (Fix et al., 2010a; Fix et al., 2010b).
Significant fetal growth and protein accretion occurs in the last trimester of pregnancy, when the sow’s dietary amino acid and energy requirements are greatest (Kim et al., 2009; Goodband et al., 2013).
However, increasing sow feeding levels in late-gestation has shown mixed effectiveness as a strategy to improve piglet birth weight. Yet uterine, fetal and placental tissues are not the only nutrient-consumers in the sow.
Mammary development also occurs in late gestation to prepare for colostrum and milk production (Ji et al., 2006). Colostrum is the fluid harvested from the sow within the first 24 hours of farrowing and provides energy, immune cells and growth factors that piglets need to thrive. Previous studies have reported positive associations between piglet colostrum intake in the first 24 hours of life and piglet survival to weaning and pig body weight at both weaning and finishing (Declerck et al., 2016).
Yet, few studies have considered the effects of sow late gestation nutrient intake on colostrum production and composition (Decaluwé et al., 2014; Mallman et al., 2019; Swanson et al., 2019). Therefore, the study evaluates increasing sow nutrient intake during late gestation to enhance piglet colostrum intake and colostrum composition.
Four experiments, encompassing 376 sows and 5,017 piglets, were conducted to evaluate the impact of practically changing late gestation diets to enhance piglet colostrum intake. Three of the experiments were conducted at the North Carolina Department of Agriculture Tidewater Research Station near Plymouth, N.C., using second-parity Landrace × Large White composite females. The fourth study was conducted on a commercial sow farm in eastern North Carolina using multiparous sows.
Sow reproduction and colostrum measurements were the same across all experiments. Farrowings were attended, and piglets were weighed immediately after birth and again at 24 hours of age. Individual piglet colostrum intake was calculated according to Theil et al. (2014), as was the pig’s Day 1 growth rate, adjusted for birth weight and time spent suckling the dam.
Sow colostrum yield was calculated as the sum of the individual piglet colostrum intakes within a litter. A 50-milliliter sample of colostrum was collected during farrowing and analyzed for percent fat, protein and lactose content. The sow functional teat number, or the number of teats capable of producing colostrum during farrowing, was recorded.
The total number born and number born alive were recorded at farrowing, and litter size of the biological dam at weaning and piglet weaning weight were recorded at 20.6 days in lactation. Piglet survival was calculated as litter size at weaning divided by total number of piglets born.
Across experiments, nutrition treatment variables consisted of sow diet, feeding level and the duration of treatment feeding. The diets were a gestation diet (0.58% standard ileal digestible lysine, 2,979 kilocalories/kilogram metabolizable energy), a lactation diet (0.99% SID lysine, 3,322 Kcal/kg ME, 2.5% added fat), or the gestation diet supplemented daily with additional soybean meal or fat to achieve the component lysine or fat content of the lactation diet. Treatment diets were initiated between 93 and 107 days of pregnancy and were fed until farrowing. Feeding levels in the experiments ranged from 3.3 to 9.9 pounds per day. A meta-analysis of all four studies was conducted by calculating each sow’s total lysine intake, total added fat intake and total ME intake from Day 93 to farrowing.
The objectives of the meta-analysis were to determine the effects of sow late-gestation nutrient intake on piglet colostrum intake, colostrum macronutrient composition and litter performance. Data was analyzed in Statistical Analysis System software with experiment, sow parity, day of feeding initiation and total number born included as model effects. Lactation length was also included as a covariate in weaning trait analyses. One sow was the experimental unit.
Summary statistics of reproduction and colostrum traits are presented in Table 1.
In Table 2, the results of a 1-gram addition in total lysine intake, total added fat intake or a 1-megacalorie addition in total metabolizable energy intake on sow reproduction and colostrum traits are shown. Increasing nutrient intake in late gestation had no effect on piglet birth weight.
However, a 1-g increase in total lysine intake and total added fat intake improved piglet colostrum intake by 0.12 g and 0.03 g, respectively, and a 1-Mcal increase in total ME intake improved piglet colostrum intake by 0.4 g. A 1-g increase in total lysine intake and a 1-Mcal increase in total metabolizable energy intake also resulted in a 1.3-g and 3.4-g increase in average piglet weaning weight, respectively (Figure 1). However, no dietary effects on piglet survival or litter size at weaning were observed.
Sow nutrient intake did not influence colostrum macronutrient composition (Table 2). No individual colostrum macronutrients were associated with piglet survival or piglet growth (Figure 2). Yet, piglet colostrum intake and sow colostrum yield were positively associated with litter throughput. A 1-g increase in piglet colostrum intake enhanced average piglet weaning weight by 3.3 grams.
Piglet colostrum intake was greatly impacted by both litter size and sow functional teat number. Each additional piglet born into the litter reduced average piglet colostrum intake by 23.7 grams, while a one-nipple increase in sow functional teat number improved piglet colostrum intake by 13.3 grams. A one-nipple increase in sow functional teats number improved sow colostrum yield, litter size at weaning and litter weaning weight by 287 g, 0.31 pigs, and 1.85 kg, respectively.
Collectively, the results of the meta-analysis suggest that increasing sow amino acid and energy intake in late gestation enhances individual piglet colostrum intake and piglet weaning weight. Yet, production systems should consider the additional sow nutrient costs against the value of additional weaning weight to determine cost-effective levels of amino acid and fat inclusion in their herds.
The correct time to increase sow nutrient intake was not clear from the study results. In three of the experiments, piglet colostrum intake was numerically greatest when sow feeding level was increased between Days 104 and 107 of gestation.
Perhaps this is real, as immunoglobulin accumulation in the mammary gland is thought to begin near this time in gestation (Feyera et al., 2019). Yet additional studies are required to validate the timing of nutrient intake on colostrum yield.
Greater piglet colostrum intake was associated with a greater likelihood of survival to weaning. Yet piglet survival was not associated with the percent concentration of any individual macronutrient. No measurements of individual fatty acids, oligosaccharides or proteins were made. Perhaps strategies to increase piglet calorie intake in the first 24 hours of life would enhance piglet survival.
Functional teat number key
Teat count is a commonly used metric to evaluate underline quality at replacement gilt selection, and a minimum number of teats (typically 14) is commonly suggested as a requirement for entry into the breeding herd. The average number of functional teats on sows included in this analysis was 14.7.
These results suggest that litter throughput is improved when sow functional teat number is greater than the generally recommended requirement. These results are likely to be more evident in modern, hyperprolific sows.
The fact that a one-nipple increase in sow functional teat number improved litter size at weaning by 0.31 pigs should provide sufficient incentive for greater attention to replacement gilt underline quality, cross-fostering piglets based on sow functional teat number, and incorporation of these traits into maternal line selection indices.
Scientists at North Carolina State University are continuing research efforts in this field. Current and future projects are focused on the genetics of functional teat number, validating the economic value of a functional teat and continued efforts to enhance piglet quality.
Jeff Wiegert is a North Carolina State University doctoral candidate and swine Extension associate in the animal science department. Mark Knauer is an NCSU associate professor and Extension swine specialist.