Nurse sows display altered reproduction in the next gestation

An increase in the total number of piglets born alive has resulted in excess piglets in relation to available functional teats (Baxter et al. 2013). Nurse sows are now commonly employed to accommodate excess piglets born and those that are not thriving on their birth sow. To do this, sows receive foreign piglets after weaning their biological litter. In hyper prolific sows, this practice increases number of pigs born in the next litter, most likely due to the extended lactation length, and stockperson bias in sow selection (Bruun et al. 2016). We hypothesised that the subsequent reproductive output of a nurse sow would differ to that of a non-nurse sow.

Data was extracted from the herd management software for the years 2015 and 2016 for a large commercial breeder unit located in South Australia. Nurse sows were identified in the dataset as being those with a second lactation subsequent to a single gestation (n = 849), and were randomly paired with sows recording a single lactation (n = 723). All data were analysed in SPSS v24.0 (IBM, Armonk, NY, USA) with year and shed as random terms, parity group (1, 2–4 and 5+), season (summer, autumn, winter and spring), and treatment (control and nurse) as fixed effects. Weaning to service interval, number of piglets born, and piglets born alive were analysed using a general linear model. Percent bred by <10 days, pregnancy rate and farrowing rate were analysed using a generalised linear model with binary distribution. Number of piglets born dead was analysed using a generalized linear mixed model with Poisson distribution.

Nurse sows were on average younger (3.1 ± 0.1) than controls (3.6 ± 0.1; P < 0.001). There was no difference in the total number of piglets born before treatment (12.3 ± 0.2; P > 0.05). First lactation length was reduced in nurse sows (25.1 ± 0.2 and 25.8 ± 0.2 for controls, P < 0.001), and nurse sows averaged 13.8 ± 0.3 days in the second lactation. Weaning to service interval was increased in nurse sows, and percent bred <10 days, pregnancy rate and farrowing rate were reduced (Table 1). Total number of piglets born and piglets born alive were increased in nurse sows, but piglets born dead were similar to controls.

Table 1.  Mean ± s.e.m. reproductive output for Control and Nurse sow in the subsequent gestation

Our hypothesis was supported. Using the predicted means for farrowing rate and total piglets born alive (Table 1), the number of piglets per 100 sows bred would be 899 for control and 842 for nurse sows. Given the usage of nurse sows is probably low in the Australian herd, this result would have little impact on the total productivity and output of breeder units. Future research will explore population dynamics of nurse sows to exploit reproduction advantages. This will be of high importance as the use of nurse sows is increased.