Effects of L-citrulline supplementation on lactation performance of sows in summer

Facilitating improved heat dissipation in sows may improve lactation performance in summer by reducing the negative effects associated with heat stress. Vasodilation is one adaptive strategy pigs can use to dissipate heat when exposed to high temperatures. Nitric oxide is required for thermal-induced vasodilation in skin (Charkoudian 2003) and a previous study showed supplementing a nitric oxide donor, L-citrulline, reduced respiration rates in heat-stressed pigs (Kvidera et al. 2016), suggesting it has the potential to reduce heat stress. Therefore, we hypothesised that supplementing 1% L-citrulline in lactation diets may reduce heat stress and improve lactation performance of sows in summer.

A total of 221 mixed parity sows (Large White × Landrace, PrimeGro™ Genetics, Corowa, NSW) were allocated to two dietary treatments with a similar parity distribution (2.4 ± 1.76 days, mean ± s.d.). The wheat-based control lactation diet contained 14.9 MJ/kg digestible energy (DE) and 15% crude protein (CP). The L-citrulline diet was similar to the control diet but 1% wheat was replaced with 1% L-citrulline. The diet contained similar DE and 16% CP. The sows were fed either a control diet (n = 111) or L-citrulline diet (n = 110) at entry to the farrowing house (5.8 ± 1.78 days before farrowing) until weaning (26.4 ± 1.53 days lactation). Sows were restrict fed 2.5 to 4.0 kg from entry until d 3 after farrowing and then fed ad libitum. The experiment was conducted over summer at Corowa, NSW from 20 January to 6 March 2017. The average daily minimum temperature of 15.6 ± 4.56°C (mean ± s.d.) and maximum temperature of 32.6 ± 5.49°C were beyond the thermo-neutral zone for sows (12 to 22°C) (Black et al. 1993). A total of 64 sows were monitored for signs of heat stress by measuring respiration rate and rectal temperature every 3 h from 0800 h until 1700 h on d 19 post-farrowing (maximum shed temperature was over 30°C). Bodyweight and P2 backfat thickness of sows was measured at entry and weaning. Feed intake of sows was recorded daily. Litter size and weight were recorded after cross-fostering and at d 21 post-farrowing. Lactation performance and physiological data were analysed by univariate and repeated-measures procedure of General Linear Model (SPSS v24.0, IBM, Armonk, NY, USA) respectively for the effects of parity (gilt or sow), diet and their interaction. The main effects of dietary treatment are presented. Rectal temperature was similar between the treatments on the days when maximum shed temperature was over 30°C; however, respiration rates tended to be lower in those sows supplemented with L-citrulline compared to controls (P = 0.095) (Table 1). L-citrulline did not affect sow daily feed intake, bodyweight loss or backfat loss over lactation. Number of piglets born alive and post-foster was similar between the treatments. L-citrulline supplementation tended to increase (P = 0.094) litter size from 9.5 to 10.1 at 21 days post-farrowing but did not affect piglet average daily gain (ADG).

Table 1.  Physiology and lactation performance of sows fed a Control or L-citrulline diet in summer

In conclusion, supplementation of 1% L-citrulline tended to reduce the sign of heat stress and improve lactation performance of sows in summer.