Biological aspects of genetic differences in piglet survival

The objective of this thesis was to gain insight in the biological background of differences in the direct genetic (piglet) component of piglet survival. Estimations of the direct genetic component of piglet survival were obtained by calculation of estimated breeding values for piglet survival (EBVps), which predict survival from onset of farrowing until weaning. The results in this thesis show that differences in survival as a consequence of differences in EBVps are already apparent in the perinatal period (i.e. in the period around birth). Both farrowing survival and survival during the first days after birth significantly increase with increasing EBVps of the litter. Differences in the course of farrowing (i.e. duration of farrowing and birth intervals) do not account for EBVps-related differences in farrowing survival and postnatal survival. Increased postnatal survival with increasing EBVps is not due to differences in early piglet behavior, such as the time from birth until first colostrum uptake. Explanations for increasing farrowing survival and postnatal survival with increasing EBVps are more likely to be found in a higher degree of fetal development or maturity during late gestation. This is substantiated by increased relative organ weights (liver, adrenals, and small intestine), increased serum cortisol levels, increased glycogen reserves in liver and muscle, and an increased carcass fat percentage in litters with high EBVps. The strong positive relationship between fetal cortisol and EBVps possibly caused the majority of the observed differences in fetal development and maturity. Knowing that cortisol plays a major role in the preparation for the transition from intrauterine to extrauterine life, piglets with a higher genetic merit for piglet survival may have an improved ability to cope with hazards during birth and within the first days of life.The results in this thesis contribute to our understanding of the practical consequences of selection for increased piglet survival.</p

Breeding replacement gilts for organic pig herds

In this study, breeding structures and commercial sow lines were evaluated by economic and genetic simulation studies for their suitability to provide the Dutch organic pig sector with replacement gilts. Sow and litter performance from over 2000 crossbred sows from 2006 to 2007 were collected on 11 to 14 Dutch organic pig herds, respectively, and compared with conventional herds. Results showed that organic herds had lower farrowing rates (3.6% to 7.5%), more live born piglets per litter (0.4% to 1.2%) and higher preweaning mortality rates (7% to 13%) compared to conventional herds. These results were used to simulate economic performance of various combinations of breeding structures and sow lines under organic conditions, under the assumption of absence of genotype-environment interactions. Sow and litter performance data under organic conditions (total piglets born/litter, stillborn piglets/litter, mortality until weaning, lactation length, interval weaning-oestrus and sow culling rate) and the costprice calculation for the Dutch organic pig sector were used as input for the economic simulation studies. The expected genetic progress was simulated for three potential breeding structures of the organic sector: organic breeding herds producing F1 gilts (OrgBS), a flower breeding system (FlowerBS) and a two-line rotation breeding system (RotBS). In FlowerBS, an organic purebred sow line is bred, using on-farm gilt replacement. The OrgBS with a Yorkshire X Landrace cross had the highest margin per sow place ((sic)779), followed by RotBS with Yorkshire X Landrace cross ((sic)706) and FlowerBS with Yorkshire sow line ((sic)677). In case that an organic purebred sow population of 5000 sows would be available, FlowerBS gave the highest genetic progress in terms of cost price reduction ((sic)3.72/slaughter pig per generation), followed by RotBS and OrgBS ((sic)3.60/slaughter pig per generation). For FlowerBS, additional costs will be involved for maintaining a dedicated breeding programme. In conclusion, OrgBS using conventional genetics is economically the most viable option for the organic pig sector. However, this structure has clear disadvantages in terms of risks with regard to disease transmission and market demand. FlowerBS using a dedicated purebred organic line will only be cost-effective if sow population size is sufficiently large. RotBS might be a viable alternative, especially in combination with artificial insemination (AI) boars that are ranked according to an organic selection index. Regardless of breeding structure, the Yorkshire sow line gave the highest prolificacy and the highest economic returns on organic herds