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

Abstract

This researchstudy was undertaken to determine the key characteristics of low birth weightpigs in a commercial setting as well as to investigate a number of interventionstrategies within a research setting to uplift the lifetime growth and carcassperformance of low birth weight pigs to levels comparable to average birthweight pigs. Particular emphasis was placed on increased nutrient supply topigs through enhanced sow lactation feed intake, as well as tailoredpost-weaning feeding regimes. 

The significance of low birth weight pigs on farms 

Due to the lack of recent data reporting the lifetimeperformance of commercially reared pigs born into large litters (>14piglets), this research initially aimed to quantify the growth and mortalityrate of low and average birth weight pigs throughout their lifetime oncommercial 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 fourcommercial farms and one research farm were assessed from birth to slaughter onan individual pig basis. The Av BW pigs were heavier than Low BW pigsthroughout the trial (P<0.001), with a weight advantage of 1.2kg at weaningincreasing to over 9kg at a slaughter age of 22 weeks. Av BW pigs also recordeda 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 greaterthan that of Av BW pigs (21% vs 6%; P<0.001), with deaths of Low BW pigsoccurring 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 tovarious causes differed with birth weight (P<0.05), with starvation (49%)and overlying (28%) accounting for the majority of Low BW mortalities. Withregard to post-weaning mortality, birth weight had no effect on number ofdeaths 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 withdeaths following post-mortem examination of all post-weaning mortalities. Thisstudy quantified the inferior weight and growth rate of Low BW pigs, along withthe major causes of mortality. The lactation and immediate post-weaning periodswere identified as having greatest potential for reducing the negative effectsof low birth weight on lifetime performance in terms of growth and mortality. 

Preweaning intervention – the impact of sow lactation feed intake on pigletgrowth, suckling behaviour and feeding behaviour

Literature and on-farm data indicated that opportunity existsto increase the pre-weaning performance of low birth weight pigs. As such thisstudy aimed to determine the effects of increased sow lactation feed intake onpiglet pre- and post-weaning growth, mortality and feeding behaviour. Low (LowBW;<1kg) (n=224) and average (Av BW;1.3-1.7kg) (n=224) birth weight animalswere reared in uniformly weighted litters of 14 piglets. Each litter was rearedon 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 morefeed during lactation than those offered a Low FA, resulting in a greater totalderived 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 3and 4 of lactation (P<0.05). Low BW animals reared on sows offered a High FAhad comparable weaning weights to Av BW pigs reared on sows offered a Low FA (7.87kgvs 7.94kg; P>0.05). Piglets reared on sows offered a High FA expressedgreater relative growth pre-weaning compared to piglets on sows offered a LowFA (6.1kg/kg vs 5.4kg/kg; P<0.05). Low BW animals reared on sows with a HighFA recorded half the levels of pre-weaning mortality compared with that of LowBW pigs on sows offered a Low FA (11% vs 22%). During week 1 of lactation, AvBW 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 insuckling frequency (P>0.05). During week 3 of lactation High FA littersdisplayed a significantly lower suckling frequency (37 bouts/day vs 46bouts/day; P<0.05), yet a greater total suckling duration (162 mins/day vs130mins/day; P<0.001). In conclusion, rearing Low BW pigs on sows offered aHigh 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 describedabove was followed through to slaughter to investigate if the superiorperformance 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 inpen groups of 10 and offered feed from dry multi-space feeders. Average dailygain (ADG) was greater for Av BW pigs during weeks 4 to 7 (P<0.001) but nodifference was recorded between weeks 7 and 10 (P>0.05). Average daily feedintake (ADFI) was greater for Av BW pigs throughout weeks 4 to 10 compared withLow BW pigs (P<0.05), however feed-conversion ratio (FCR) did not differfrom that of Low BW pens (P>0.05). Piglets reared by High FA sows wereheavier at weeks 5 and 7 (P<0.05) but not at week 10 (P>0.05) compared withpigs reared by Low FA sows. Relative growth between weeks 4 and 10 was greaterfor piglets reared on sows offered a Low FA compared with pigs reared on sowsoffered a High FA (P<0.05), suggesting compensatory growth. 

From the above cohort, 128 Low BW pigs and 128 Av BW pigsremained on trial from 12 weeks of age until slaughter at 22 weeks of age. LowBW pigs were housed in pen groups of 16, with 8 Low BW animals which had beenreared on sows offered a Low FA merging with 8 Low BW animals which had beenreared on sows offered a High FA. This pen arrangement was repeated for Av BWpigs. All animals were offered feed from electronic feed intake stations sothat individual feed intake, feeding behaviour and growth performance could bemonitored. 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 BWpigs during this finishing period (35.4g/kg vs 33.7g/kg; P<0.05). Av BW pigswere significantly heavier than Low BW pigs throughout, weighing 6.3kg more atslaughter (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 bepartially 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 duringthe finishing period (2.00kg/kg vs 1.89kg/kg; P<0.05). Linear regressionanalysis showed that, despite the Low BW pigs recording an inferior absoluteFCR throughout the finishing period, the rate of FCR deterioration withincreasing 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 pigscompared to Av BW pigs to grow from 40kg to 120kg liveweight was a consequenceof their poorer FCR and not as a result of an increased rate of FCRdeterioration. Birth weight had no impact on any parameters of feedingbehaviour (P>0.05). Sow lactation feed allowance had no effect on animalweight, relative growth, ADG, ADFI, relative feed intake or FCR from weeks 12to 22 (P>0.05 respectively). Pigs reared on sows offered a Low FA recorded0.72 more feeder visits per day between weeks 17 and 22 (8.11 visits/day vs7.39visits/day; P<0.05) but a 27g reduction in feed intake per feed visitbetween 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 anincreased sow lactation feed intake, with piglet birth weight having asubstantially greater impact on performance during the growing and finishingperiod. 

Impact of nutritionally tailored interventions post weaning

The above studies indicated that improvements in weaningweight were achievable, but these benefits were lost during the post-weaningperiod through to slaughter. The positive relationship between nutrient intake,in particular energy and lysine intake, and growth are well known. Thereforethe main aim of this final experiment was to improve the lifetime performanceof low birth weight pigs by tailoring energy and protein intakes to match theirweight in a pen based, commercial-like setting. During lactation, low birthweight (Low BW; <1kg) and average birth weight (Av BW; 1.3kg-1.7kg) pigletswere reared in uniformly weighted litters by a foster sow offered a highlactation feed allowance. Post-weaning, Low BW (n=220) or Av BW (n=220) animalswere offered either a ‘standard’ (STAND) or ‘feed-to-weight’ (FTW) regime fromweaning until slaughter. The STAND regime mirrored commercial production, wherediet transitions occurred either after a pre-determined feed consumption targetor time interval. In contrast, diet transitions in the FTW regime were carriedout when the pen average weight met a target threshold. Av BW pigs weresignificantly 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 ofenergy (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), exceptbetween weeks 10 and 17, where Low BW animals recorded a superior FCR (1.97 vs2.02; P<0.05). Av BW animals recorded a greater carcass weight (98.0kg vs91.7kg; P<0.001) and kill-out percentage (81.7% vs 80.2%; P<0.01) thanLow BW pigs at slaughter, but birth weight had no effect on back-fat depth atslaughter (P>0.05). Animals offered the FTW regime were significantlyheavier than STAND pigs from week 7 through to slaughter, recording a greatercarcass weight (P<0.05). FTW animals also recorded a superior ADG (466g/dayvs 449g/day; P<0.05) and ADFI (657g/day vs 634g/day; (P<0.05) compared toSTAND pigs from weeks 4 to 10. Similarly, pigs on the FTW regime exhibited a greateraverage 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 weeks10 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 17where the FCR was superior for STAND pigs (1.97 vs 2.02; P<0.05). The ageand weight of Av BW pigs at each diet transition did not differ significantlywith feeding regime for the majority of transitions (P>0.05). However, LowBW animals offered the FTW regime were significantly older and heavier thanthose offered the STAND regime at each transition (P<0.05). Feeding regimehad no effect on kill-out percentage or back-fat depth (P>0.05).Datacollected from a subset of pigs (n=80) which underwent a series of three DEXAscans during the growth period of the pig showed that Low BW animals recordedlower total tissue and lean content at all stages of the study (P<0.01respectively), 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 agreater percentage fat at weeks 4 (34.2% vs 32.5%; P<0.001) and 10 (27.8% vs26.6%; 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 nosignificant 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 ateither weeks 10 or 21 (P>0.05). In conclusion, feeding Low BW animals on thebasis of weight may have allowed a greater time for digestive developmentbetween each diet transition. This increased nutrient intake and, as a result,improved liveweight. As this regime had no detrimental effect on carcasscharacteristics or body composition it represents a commercial opportunity toincrease the slaughter weight of all animals, improving output andprofitability at farm level. 

Summary

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

This work quantified that, on farms in NI, low birth weightanimals exhibited a 15% greater level of pre-weaning mortality than averagebirth weight piglets, with starvation cited as the cause of death in almost 50%of cases. The weight differential between low birth weight animals and averagebirth weight counterparts increased from 1.2kg at weaning to over 9kg atslaughter, with low birth weight animals requiring an estimated additional 11days to reach a comparable slaughter weight. Finally, the greatest divergencein 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 sowlactation feed allowance halved mortality amongst low birth weight animalscompared to those reared on sows offered a low feed allowance or those rearedcommercially. Furthermore, when reared on sows offered a high feed allowance,low birth weight litters expressed the same suckling behaviour as average birthweight litters during later lactation and had the capacity to effectivelyutilise the additional milk yield to give an 11% increase in weaning weight.Low birth weight pigs recorded a superior relative growth and relative feedintake between weeks 12 and 22 of age, where FCR deterioration and feedingbehaviour did not differ compared to average birth weight pigs. However anoverall poorer FCR for low birth weight animals during this period, combinedwith a poorer feed intake immediately following weaning, meant any pre-weaningbenefit was not built upon during the post-weaning period. 

With regard to post-weaning nutrition, this research projecthas shown that when dietary transitions were carried out on a weight basis, lowbirth weight animals were significantly older and heavier at each transitioncompared to those of an equivalent birth weight fed using a commercial regime.This novel data showed the former method of feeding improved growth to theextent that low birth weight animals fed on a weight basis post-weaning in theresearch setting were 3% (38.6kg vs 37.3kg) and 8% (71.7kg vs 65.7kg) heavierat week 12 and 17 respectively compared to average birth weight animals rearedin the commercial setting. This indicates that it is not only the inferiorphysiology of compromised pigs which limits growth but also the productionsystem employed. Whilst low birth weight animals were generally associated witha greater percentage of body fat and lower percentage of lean compositioncompared to average birth weight pigs throughout the growing period, this wasnot exacerbated by the enhanced feeding regime. Hence this method of interventionrepresents a commercial opportunity to maximise performance andprofitability.  

This research project outlines a number of opportunities forpig producers to improve productivity and efficiency at farm level. Enhancingnutritional management of the sow during lactation can significantly improvegrowth and suckling behaviour of low birth weight pigs, whilst reducingpre-weaning mortality. Furthermore, this study highlights that offering apost-weaning feeding regime tailored to animal weight can minimise anypost-weaning growth check in low birth weight animals, with no adverse effectson body composition or carcass quality.