Post-weaning growth response and feeding behaviour of low and average birth weight pigs to sow lactation feed intake

Application Low birthweight piglets have the capacity to achieve acceptable weaning weights when reared on sows offered a high feed allowance. This weight advantage at weaning was lost in the post-weaning period through a poorer feed conversion efficiency since the intake and feeding behaviour of low and average birthweight pigs was similar. This work demonstrates a need to understand the differences in the biological drivers of feed efficiency between low and average birthweight pigs, as well as the need to provide further interventions post-weaning to maximise the performance of compromised pigs. Introduction Previous work has shown that when compromised pigs are reared on sows offered a high lactation feed allowance, they will achieve reduced mortality with weaning weights equivalent to average birthweight counterparts reared under commercial conditions (Hawe et al, 2019). This work aimed to assess if benefits achieved at weaning were retained through the growing and finishing stage. Material and methods This two (birth weight) x two (lactation feed allowance) factorial arrangement study complied with the Animals (Scientific Procedures) Act 1986. Litters comprised of either 14 low birthweight (Low BW;<1kg) or 14 average birthweight (Av BW;~1.5kg) piglets were reared by sows offered either a low (Low FA) or high (High FA) feed allowance (Hawe et al, 2019). It is worthy of note that the Low FA treatment during lactation was comparable to that used commercially. This study focused on the post-weaning period with animals remaining in their litter groups until slaughter at week 22 and performance monitored throughout the growing and finishing stages. All animals followed a standard feeding regime post-weaning. Animals were individually weighed at week 5, 7, 12, 15, 17 and 22. Feeding behaviour was recorded on an individual basis using electronic ‘FIRE’ feeders between weeks 12 and 22. Statistical analysis Data was analysed using a linear mixed model. Birthweight and feed allowance were fitted as fixed effects. Replicate, birth mother or foster mother were incorporated as a random effect. In certain instances ‘treatment’ was fitted as a fixed effect in order to compare and contrast each treatment group. A significance level of 0.05 was used. Results There were no significant interactions (P>0.05) between treatments on any performance parameters recorded (Table 1). The average liveweight and ADG was greater for Av BW pigs than Low BW animals throughout the trial (P<0.05). Sow FA during lactation did not influence piglet weight or ADG post-weaning (P>0.05). Relative growth from week 4-10 was higher for pigs from sows offered Low FA (P=0.006). ADFI was greater for Av BW pigs from week 4 to 10 but was not influenced by BW from week 12 to 22. Av BW pigs recorded a superior FCR from week 12 to 22 (P<0.05). From week 12 to 22, BW and FA had no effect on the time spent in feeder per day, feeder visits per day, average time of each feed interval or eating velocity (P>0.05). However from week 17 to 22 Low FA pigs entered the feeder a significantly greater number of times per day (P=0.038). Feed intake per interval during week 12 to 22 was greater for animals offered High FA (P=0.028). Analysis comparing the individual sow treatments on pig performance found that, despite there being no difference in weaning weight, Low BW pigs offered a High FA had a lower ADG from week 4 to 10 than Av BW pigs offered a Low FA, resulting in a significantly lower piglet weight at week 7 (P=0.02) and 12 (P=0.013). Furthermore there was no significant difference in the weight, ADG or ADFI of Low BW pigs offered Low FA or High FA from week 7 to slaughter (P>0.05). Conclusion Pre-weaning benefits of enhanced sow lactation intake on piglet weight were not retained at slaughter, with results suggesting compensatory growth occurred post-weaning. The 5.4% reduced slaughter weight of compromised pigs can be explained by their 2.2% reduction in FCR during the finishing period. Low BW pigs require post-weaning intervention in order to maximise lifetime performance. Furthermore, more focussed research on the biological drivers of FCR in compromised pigs is required.