By Zhenbin Zhang
Editor’s note: Zhenbin Zhang is a swine nutritionist for Cargill Animal Health. He can be contacted at zhenbin_zhang@cargill.com.
The swine industry has achieved significant advancements across various aspects, such as enhancing litter sizes, accelerating growth and improving feed efficiency in commercial grower-finisher pigs. These achievements can be attributed to extensive research and development efforts from both academia and industry. However, there remains ample room for enhancing pig livability.
When considering the cumulative losses from stillborn and mummified fetuses (eight to 10 per cent of piglets), pre-weaning mortality (14 per cent of losses), nursery mortality (four per cent) and grower-finisher mortality (four per cent), it becomes apparent that nearly one-third of pigs perish following pregnancy assessment. Many of these mortality factors can be correlated with birth weight.
Birth weights decline with larger litters
While producers are enjoying litter size increases, at a rate of about 0.3 piglets more per year, there is a downward trend in birth weights. When litter size is increased by one piglet, birth weight is reduced by 20 grams, and birth weight within-litter variation is increased by 0.38 per cent. The literature from five years ago consistently reports average birth weight above 1.4 kilograms, whereas birth weight today is closer to 1.2 to 1.3 kilograms.
Researcher George Foxcroft associated low birth weights with uterine capacity and maternal uterine nutrition. Moreover, gilts tend to give birth to lighter piglets than sows. The augmented rate of sow herd replacement over time could be partially responsible for this downward trend in birth weight. The health status of the pigs also plays a role in determining birth weight. Nutrient appropriation by parasites and the constraints posed by reproductive pathogens like Parvovirus and Porcine Reproductive and Respiratory Syndrome (PRRS) can also hinder fetal development.
The reduction in birth weight bears economic repercussions for pig producers. Firstly, a correlation exists between birth weight and pre-weaning mortality. The critical birth weight threshold for heightened pre-weaning mortality risk has been identified as 1.1 kilograms. Research conducted by Kansas State University several years ago revealed that 15 per cent of piglets exhibited birth weights of 1.11 kilograms or less. This subgroup demonstrated a 34 per cent pre-weaning mortality rate, contributing to 43 per cent of overall pre-weaning mortalities. Piglets with birth weights below 500 grams seldom survive.
Secondly, low birth weight compromises growth performance. As demonstrated in Table 1, lighter piglets at birth exhibit a reduction in body weight of one kilogram at weaning, 2.5 kilograms at the conclusion of the nursery phase, and five kilograms at the end of the finishing phase. Additionally, these lighter piglets demonstrate a two per cent lower feed efficiency from weaning to finishing. It is worth noting that birth weight has no discernible influence on carcass quality or meat characteristics. Given the significance of mortality and growth performance as key economic indicators, the decline in piglet birth weight undermines the profitability of producers.
Finding solutions to common problems
Industry experts have been working tirelessly to improve birth weight and mitigate their negative impacts. Swine geneticists are exploring ways to enhance uterine capacity, while nutritionists are focusing on improving uterine nutrition for placenta development and fetal growth. Much research into late-gestation nutrition has encouraged the industry to use a late-gestation diet or ‘bump feeding’ to increase nutritional intake. However, there is a need to raise awareness of the importance of nutrition in early gestation. There’s also nutritional technology like Profert, developed by Cargill Animal Nutrition, which can improve follicle maturation and development in weaned sows. This technology results in better-quality fertilized eggs, which translates into higher and more uniform birth weights and more piglets born alive.
From a production management point-of-view, the practice of split-feeding helps low-birth-weight piglets obtain the colostrum they need for life-readiness. At the same time, some producers have used a milk replacer for herds with large litters. For example, if a sow farm has an average of 17 to 19 live-born piglets, but the sows have only 14 to 16 teats, the extra piglets can be fed a milk replacer. In this case, the primary objective is to save the piglets’ lives. In the light of this practice, it also makes sense to give milk replacer to low-birth-weight piglets or with large litters. Milk replacers like Cargill’s Rescue Milk are designed to provide nutrition comparable to that of sow’s milk.
The nutritional concept covers milk proteins, essential fatty acids comparable to milk fat composition, immune-enhancing compounds and gut health technology. The use of milk replacer results in low pre-weaning mortality and higher weaning weights. In addition, milk replacer can improve the body condition of sows at weaning, thus ensuring reproductive performance of the next litter. Therefore, the use of a milk replacer can be considered a standard management practice to improve productivity in herds with litter sizes greater than 14 live-born piglets.
Strategies targeting management, genetics and nutrition can help counter issues associated with lower birth weights. Integrating milk replacers can reduce pre-weaning mortality, improve weaning weight and sow condition, with the effect of enhancing profitability for producers.
