Identifying, understanding and harnessing the beneficial impact of nutritional interactions to optimise the performance and carcass quality of low birth weight pigs

  • Samuel Hawe

Student thesis: Doctoral ThesisDoctor of Philosophy


This research study was undertaken to determine the key characteristics of low birth weight pigs in a commercial setting as well as to investigate a number of intervention strategies within a research setting to uplift the lifetime growth and carcass performance of low birth weight pigs to levels comparable to average birth weight pigs. Particular emphasis was placed on increased nutrient supply to pigs through enhanced sow lactation feed intake, as well as tailored post-weaning feeding regimes. 

The significance of low birth weight pigs on farms 

Due to the lack of recent data reporting the lifetime performance of commercially reared pigs born into large litters (>14 piglets), this research initially aimed to quantify the growth and mortality rate of low and average birth weight pigs throughout their lifetime on commercial farms in Northern Ireland. Low birth weight (Low BW; <1kg) (n=328) and average birth weight (Av BW; 1.3-1.7kg) (n=292) pigs across four commercial farms and one research farm were assessed from birth to slaughter on an individual pig basis. The Av BW pigs were heavier than Low BW pigs throughout the trial (P<0.001), with a weight advantage of 1.2kg at weaning increasing to over 9kg at a slaughter age of 22 weeks. Av BW pigs also recorded a superior average daily gain (ADG) to Low BW pigs throughout the trial (P<0.05), with the greatest differences recorded immediately post-weaning, i.e. between 4 to 8 weeks of age (77g/day) and between 8 to 12 weeks of age (85g/day). Pre-weaning mortality of Low BW pigs was over three times greater than that of Av BW pigs (21% vs 6%; P<0.001), with deaths of Low BW pigs occurring earlier (9.2 days vs 15.4 days; P<0.001) and at a lighter weight (1.2kg vs 2.4kg; P<0.001). The extent of pre-weaning mortality due to various causes differed with birth weight (P<0.05), with starvation (49%) and overlying (28%) accounting for the majority of Low BW mortalities. With regard to post-weaning mortality, birth weight had no effect on number of deaths or the age or weight of death (P>0.05). The alimentary tract (27%) and respiratory tract (27%) were the most common body systems associated with deaths following post-mortem examination of all post-weaning mortalities. This study quantified the inferior weight and growth rate of Low BW pigs, along with the major causes of mortality. The lactation and immediate post-weaning periods were identified as having greatest potential for reducing the negative effects of low birth weight on lifetime performance in terms of growth and mortality. 

Pre weaning intervention – the impact of sow lactation feed intake on piglet growth, suckling behaviour and feeding behaviour

Literature and on-farm data indicated that opportunity exists to increase the pre-weaning performance of low birth weight pigs. As such this study aimed to determine the effects of increased sow lactation feed intake on piglet pre- and post-weaning growth, mortality and feeding behaviour. Low (Low BW;<1kg) (n=224) and average (Av BW;1.3-1.7kg) (n=224) birth weight animals were reared in uniformly weighted litters of 14 piglets. Each litter was reared on a foster mother offered either a low (Low FA; average 6.2kg/day) or high (High FA; average 7.7kg/day) feed allowance over a 28 ± 1 day lactation. 

Pre weaning impact 

Sows offered a High FA consumed an average of 42.5kg more feed during lactation than those offered a Low FA, resulting in a greater total derived milk yield over the 28 day lactation (371kg vs 307kg; P<0.05). Animals of Av BW were heavier than those of Low BW throughout the trial (P<0.05). Piglets reared by sows offered a High FA were heavier at weeks 3 and 4 of lactation (P<0.05). Low BW animals reared on sows offered a High FA had comparable weaning weights to Av BW pigs reared on sows offered a Low FA (7.87kg vs 7.94kg; P>0.05). Piglets reared on sows offered a High FA expressed greater relative growth pre-weaning compared to piglets on sows offered a Low FA (6.1kg/kg vs 5.4kg/kg; P<0.05). Low BW animals reared on sows with a High FA recorded half the levels of pre-weaning mortality compared with that of Low BW pigs on sows offered a Low FA (11% vs 22%). During week 1 of lactation, Av BW litters recorded a greater total suckling duration to that Low BW litters (197mins/day vs 166mins/day; P<0.05), but there was no difference in suckling frequency (P>0.05). During week 3 of lactation High FA litters displayed a significantly lower suckling frequency (37 bouts/day vs 46 bouts/day; P<0.05), yet a greater total suckling duration (162 mins/day vs 130mins/day; P<0.001). In conclusion, rearing Low BW pigs on sows offered a High FA during lactation significantly increased total suckling duration, reduced piglet mortality and increased piglet weaning weights.

Post weaning impact

The performance of a cohort of pigs from the work described above was followed through to slaughter to investigate if the superior performance during lactation in pigs from sows offered a High FA was retained. During weeks 4 to 10, a total of 160 Low BW and 160 Av BW pigs were reared in pen groups of 10 and offered feed from dry multi-space feeders. Average daily gain (ADG) was greater for Av BW pigs during weeks 4 to 7 (P<0.001) but no difference was recorded between weeks 7 and 10 (P>0.05). Average daily feed intake (ADFI) was greater for Av BW pigs throughout weeks 4 to 10 compared with Low BW pigs (P<0.05), however feed-conversion ratio (FCR) did not differ from that of Low BW pens (P>0.05). Piglets reared by High FA sows were heavier at weeks 5 and 7 (P<0.05) but not at week 10 (P>0.05) compared with pigs reared by Low FA sows. Relative growth between weeks 4 and 10 was greater for piglets reared on sows offered a Low FA compared with pigs reared on sows offered a High FA (P<0.05), suggesting compensatory growth. 

From the above cohort, 128 Low BW pigs and 128 Av BW pigs remained on trial from 12 weeks of age until slaughter at 22 weeks of age. Low BW pigs were housed in pen groups of 16, with 8 Low BW animals which had been reared on sows offered a Low FA merging with 8 Low BW animals which had been reared on sows offered a High FA. This pen arrangement was repeated for Av BW pigs. All animals were offered feed from electronic feed intake stations so that individual feed intake, feeding behaviour and growth performance could be monitored. Animal birth weight had no effect on ADFI between weeks 12 and 22 (P>0.05). However, feed intake relative to bodyweight was greater for Low BW pigs during this finishing period (35.4g/kg vs 33.7g/kg; P<0.05). Av BW pigs were significantly heavier than Low BW pigs throughout, weighing 6.3kg more at slaughter (105.1kg vs 99.4kg; P<0.05). Also, Av BW pigs recorded a 2.2% superior FCR (2.19 vs 2.24; P<0.05) during the trial period which could be partially explained by their 42g/day greater ADG (1014g/day vs 972g/day; P<0.05). However, relative growth rate was greater for Low BW pigs during the finishing period (2.00kg/kg vs 1.89kg/kg; P<0.05). Linear regression analysis showed that, despite the Low BW pigs recording an inferior absolute FCR throughout the finishing period, the rate of FCR deterioration with increasing liveweight did not differ between Low BW and Av BW pigs (P>0.05). Therefore the projected 4.4kg of additional feed required by Low BW pigs compared to Av BW pigs to grow from 40kg to 120kg liveweight was a consequence of their poorer FCR and not as a result of an increased rate of FCR deterioration. Birth weight had no impact on any parameters of feeding behaviour (P>0.05). Sow lactation feed allowance had no effect on animal weight, relative growth, ADG, ADFI, relative feed intake or FCR from weeks 12 to 22 (P>0.05 respectively). Pigs reared on sows offered a Low FA recorded 0.72 more feeder visits per day between weeks 17 and 22 (8.11 visits/day vs 7.39visits/day; P<0.05) but a 27g reduction in feed intake per feed visit between weeks 12 to 22 (317g/visit vs 344g/visit; P<0.05). In conclusion, animals failed to build upon the pre-weaning benefits attained from an increased sow lactation feed intake, with piglet birth weight having a substantially greater impact on performance during the growing and finishing period. 

Impact of nutritionally tailored interventions post weaning

The above studies indicated that improvements in weaning weight were achievable, but these benefits were lost during the post-weaning period through to slaughter. The positive relationship between nutrient intake, in particular energy and lysine intake, and growth are well known. Therefore the main aim of this final experiment was to improve the lifetime performance of low birth weight pigs by tailoring energy and protein intakes to match their weight in a pen based, commercial-like setting. During lactation, low birth weight (Low BW; <1kg) and average birth weight (Av BW; 1.3kg-1.7kg) piglets were reared in uniformly weighted litters by a foster sow offered a high lactation feed allowance. Post-weaning, Low BW (n=220) or Av BW (n=220) animals were offered either a ‘standard’ (STAND) or ‘feed-to-weight’ (FTW) regime from weaning until slaughter. The STAND regime mirrored commercial production, where diet transitions occurred either after a pre-determined feed consumption target or time interval. In contrast, diet transitions in the FTW regime were carried out when the pen average weight met a target threshold. Av BW pigs were significantly heavier than Low BW animals at each stage of the trial (P<0.001), recording a superior average daily gain (ADG) (P<0.01), average daily feed intake (ADFI) (P<0.001) and average daily intake of energy (P<0.01) and lysine (P<0.01) during each time period monitored.  Birth weight had no effect on feed conversion ratio (FCR) (P>0.05), except between weeks 10 and 17, where Low BW animals recorded a superior FCR (1.97 vs 2.02; P<0.05). Av BW animals recorded a greater carcass weight (98.0kg vs 91.7kg; P<0.001) and kill-out percentage (81.7% vs 80.2%; P<0.01) than Low BW pigs at slaughter, but birth weight had no effect on back-fat depth at slaughter (P>0.05). Animals offered the FTW regime were significantly heavier than STAND pigs from week 7 through to slaughter, recording a greater carcass weight (P<0.05). FTW animals also recorded a superior ADG (466g/day vs 449g/day; P<0.05) and ADFI (657g/day vs 634g/day; (P<0.05) compared to STAND pigs from weeks 4 to 10. Similarly, pigs on the FTW regime exhibited a greater average daily intake of energy and lysine from weeks 4 to 10 (Energy = 10.2MJ/day vs 9.8MJ/day; Lysine = 9.36g/day vs 9.01g/day; P<0.05) and weeks 10 to 17 (Energy = 27.1MJ/day vs 26.2MJ/day; Lysine = 21.8g/day vs 21.2g/day; P<0.05). Feeding regime had no effect on FCR, except between weeks 10 and 17 where the FCR was superior for STAND pigs (1.97 vs 2.02; P<0.05). The age and weight of Av BW pigs at each diet transition did not differ significantly with feeding regime for the majority of transitions (P>0.05). However, Low BW animals offered the FTW regime were significantly older and heavier than those offered the STAND regime at each transition (P<0.05). Feeding regime had no effect on kill-out percentage or back-fat depth (P>0.05).Data collected from a subset of pigs (n=80) which underwent a series of three DEXA scans during the growth period of the pig showed that Low BW animals recorded lower total tissue and lean content at all stages of the study (P<0.01 respectively), as well as a lower fat content at weeks 4 (2.44kg vs 2.70kg; P<0.01) and 10 (6.7kg vs 7.2kg; P<0.01). However, Low BW animals had a greater percentage fat at weeks 4 (34.2% vs 32.5%; P<0.001) and 10 (27.8% vs 26.6%; P<0.001) which aligned with a lower percentage lean at weeks 4 (63.1% vs 64.6%; P<0.01) and 10 (69.6% vs 70.7%; P<0.01) compared to Av BW pigs. Despite the same numerical trend persisting to week 21, birth weight had no significant effect on percentage lean or fat at this final stage (P>0.05). Total or percentage lean and fat did not differ between FTW or STAND pigs at either weeks 10 or 21 (P>0.05). In conclusion, feeding Low BW animals on the basis of weight may have allowed a greater time for digestive development between each diet transition. This increased nutrient intake and, as a result, improved liveweight. As this regime had no detrimental effect on carcass characteristics or body composition it represents a commercial opportunity to increase the slaughter weight of all animals, improving output and profitability at farm level. 


This research project has advanced the knowledge and understanding of low birth weight pigs by quantifying their actual performance as well as the performance differential compared to average birth weight pigs on commercial farms. It also indicated the most prevalent time and cause of deaths for both birth weight categories on farms in NI. In contrast to much of the literature, effective intervention strategies employed in a research setting in this work showed that it was possible for low birth weight pigs to achieve the weight of average birth weight pigs. Finally, modelling the change of animal feeding efficiency with increasing liveweight, combined with analysis of animal feeding behaviour and body composition has furthered the understanding of the underlying mechanisms responsible for the elevated performance in low birth weight pigs given enhanced nutrient supply.

This work quantified that, on farms in NI, low birth weight animals exhibited a 15% greater level of pre-weaning mortality than average birth weight piglets, with starvation cited as the cause of death in almost 50% of cases. The weight differential between low birth weight animals and average birth weight counterparts increased from 1.2kg at weaning to over 9kg at slaughter, with low birth weight animals requiring an estimated additional 11 days to reach a comparable slaughter weight. Finally, the greatest divergence in growth rate was recorded in the weeks immediately following weaning, highlighting this period as a critical window for intervention.

For the first time, this work has found that increasing sow lactation feed allowance halved mortality amongst low birth weight animals compared to those reared on sows offered a low feed allowance or those reared commercially. Furthermore, when reared on sows offered a high feed allowance, low birth weight litters expressed the same suckling behaviour as average birth weight litters during later lactation and had the capacity to effectively utilise the additional milk yield to give an 11% increase in weaning weight. Low birth weight pigs recorded a superior relative growth and relative feed intake between weeks 12 and 22 of age, where FCR deterioration and feeding behaviour did not differ compared to average birth weight pigs. However an overall poorer FCR for low birth weight animals during this period, combined with a poorer feed intake immediately following weaning, meant any pre-weaning benefit was not built upon during the post-weaning period. 

With regard to post-weaning nutrition, this research project has shown that when dietary transitions were carried out on a weight basis, low birth weight animals were significantly older and heavier at each transition compared to those of an equivalent birth weight fed using a commercial regime. This novel data showed the former method of feeding improved growth to the extent that low birth weight animals fed on a weight basis post-weaning in the research setting were 3% (38.6kg vs 37.3kg) and 8% (71.7kg vs 65.7kg) heavier at week 12 and 17 respectively compared to average birth weight animals reared in the commercial setting. This indicates that it is not only the inferior physiology of compromised pigs which limits growth but also the production system employed. Whilst low birth weight animals were generally associated with a greater percentage of body fat and lower percentage of lean composition compared to average birth weight pigs throughout the growing period, this was not exacerbated by the enhanced feeding regime. Hence this method of intervention represents a commercial opportunity to maximise performance and profitability.  

This research project outlines a number of opportunities for pig producers to improve productivity and efficiency at farm level. Enhancing nutritional management of the sow during lactation can significantly improve growth and suckling behaviour of low birth weight pigs, whilst reducing pre-weaning mortality. Furthermore, this study highlights that offering a post-weaning feeding regime tailored to animal weight can minimise any post-weaning growth check in low birth weight animals, with no adverse effects on body composition or carcass quality.

Date of AwardDec 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsDepartment of Agriculture, Environment and Rural Affairs
SupervisorElizabeth Magowan (Supervisor) & Nigel Scollan (Supervisor)


  • low birth weight pig
  • lifetime growth
  • weaning
  • suckling behaviour
  • feeding behaviour
  • body composition
  • large litters
  • mortality

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