T. van der Lende

Effects of genetic selection for milk yield on energy balance, levels of hormones, and metabolites in lactating cattle, and possible links to reduced fertility ☆

Selection for a higher milk yield increases metabolic load via a higher yield per se and/or via physiological processes that facilitate milk yield, and it is difficult to differentiate between these two. Here, we aim to identify important pathways that contribute to the reduction in fertility following selection for higher yield. The associations between milk yield and fertility may run via pleiotropic effects, i.e. via functional pathways (for example related to intake), or linkage of genes and may involve changes in levels of hormones and metabolites. A number of studies have investigated the effects of genetic merit for milk yield on fertility, feed intake, energy balance and levels of metabolic and fertility hormones or metabolites. Differences in genetic merit were associated with differences in: (1) feed intake; (2) energy balance; and (3) plasma levels especially of GH, IGF-I, prolactin, progesterone, insulin, glucose, NEFAs and ketones. In the discussion we focus on the possible roles that energy balance, the growth hormone axis, and glucose together with insulin may have in the reduced fertility that is associated with high yield. The overall conclusion is that many minor pathways probably contribute, but that reduced metabolic fuel availability, rather than direct effects of hormone concentrations, is an important cause of poorer fertility with increasing genetic merit.

Genetic aspects of piglet survival

Amongst all fully formed piglets at the end of gestation, piglet survival until weaning (PS) is on average 81%. Selection for fast lean growth and increased litter size tends to decrease piglet survivability. Estimated heritabilities for PS and its component traits are generally low, on average around 0.04. Despite this, selection for improved survival is possible since the genetic variance for the trait is substantial. Genetic analyses indicated significant genetic correlations between PS on one side and litter size, gestation length, within-litter variation in birth weight, feed intake, gain, and backfat on the other. Genetic correlation of PS with birth weight, however, was low. Selection on birth weight as an indirect way to improve PS is doubtful. Genetic differences between piglets in survivability will be reflected in differences in body composition rather than in differences in birth weight. Experimental work on litters with high versus low genetic merit for PS, results of various selection experiments and experimental work with Meishan pigs support these findings.

Direct, maternal and nurse sow genetic effects on farrowing-, pre-weaning- and total piglet survival

Abstract Peri- and postnatal survival data, including birth weights and cross-foster information from two line/farm combinations with 33 717 and 29 200 piglets, respectively, were analyzed to find the best genetic model to describe piglet survival. This was done in terms of direct (piglet), maternal and nurse sow genetic effects, maternal to cover uterine quality and nurse sow to cover mothering ability. The two component traits, farrowing and pre-weaning survival and — birth weight, the most important factor for survival — were similarly analyzed. As fixed effects, Year/Season, cross, parity, birth weight in classes of 100 g, litter size as such, and sex were included in the analyses. Models combining the different genetic effects were compared on the basis of the log-likelihood. A maternal/nurse sow model fitted the data best for pre-weaning survival, a direct/maternal model for birth weight, a direct model for farrowing survival in the dam line and a direct/maternal model for farrowing survival in the sire line. Including nurse sow effect in a model for piglet survival as a whole gave erratic results, making it difficult to define an optimal model. Estimated heritabilities for pre-weaning survival, measured on the binary scale, in the dam line were 0.02±0.005 for both maternal and nurse sow effects. Heritabilities for birth weight were, on average for the two lines, 0.04±0.01 for the direct effect and 0.20±0.03 for the maternal effect. In conclusion, selection for increased component traits of piglet survival is possible.

Critical periods for foetal mortality in gilts identified by analysing the length distribution of mummified foetuses and frequency of non-fresh stillborn piglets

The objective of this study was to investigate the timing of foetal mortality in gilts of a segregating F2 cross of Large White and Meishan pigs on the basis of the length distribution of mummified foetuses and the frequency of non-fresh stillborn piglets in order to establish whether critical periods for foetal mortality exist. All expelled conceptuses and placentae of 192 farrowing gilts with a normal health status were meticulously investigated to recover all mummified foetuses. The length of each mummified foetus was measured. The predicted number of foetuses present per gilt at the early foetal stage of gestation was calculated as the sum of numbers of mummified foetuses and non-fresh stillborn, fresh stillborn and liveborn piglets. Foetal loss was calculated as the sum of mummified foetuses and non-fresh stillborn piglets. The average foetal mortality rate per gilt was 8.7%. In total 162 mummified foetuses were found (average 0.84 per litter), ranging in length from 0.4 to 33.0 cm. This indicates a range in foetal age at death of approximately 35-100 days. Although mummified foetuses of all lengths within the above mentioned range were found, relatively many had a length of less than 4 cm or of 10-21 cm. The total number of non-fresh stillborn piglets (i.e. late foetal deaths) was 58 (average 0.30 per litter). It can be concluded that foetal mortality occurred in these gilts throughout the period from day 35 to term, with relatively high incidences at the early foetal stage (days 35-40), shortly after mid-pregnancy (days 55-75) and after approximately day 100 of gestation. These three periods coincide with reported periods of change in porcine placental growth.

Progress of farrowing and early postnatal pig behavior in relation to genetic merit for pig survival.

The objective of this study was to investigate whether pigs with different genetic merit for survival differed in birth weight, progress of farrowing, early postnatal behavior, or rectal temperature within 24 h after birth. On a nucleus farm in Rio Verde, Brazil, information was collected on 280 pigs, originating from 25 litters with known estimated breeding values for pig survival (EBVps). Litters were selected in such a way that a continuous range of EBVps with a maximum genetic contrast was achieved. Birth weight was recorded for all pigs. Indicators for progress of farrowing were birth intervals and duration of farrowing. Behavioral indicators of pig vitality were time until first upright standing (FUS), time until first udder contact (FUC), time until first teat in mouth (FTM), and time until first colostrum uptake (FCU). Rectal temperature was measured within 24 h after birth. Farrowing survival and early postnatal survival (within 3 d after farrowing) were registered. Farrowing survival and early postnatal survival both increased with increasing EBVps (farrowing survival: P = 0.007; early postnatal survival: P = 0.027). Birth weight decreased with increasing EBVps (P = 0.01). Birth intervals tended to increase with increasing EBVps (P = 0.10) and duration of farrowing was not related to EBVps. Time until first teat in mouth increased with increasing EBVps (P = 0.05), but the other behavioral indicators of pig vitality were not related to EBVps. Rectal temperature within 24 h after birth was not related to EBVps. Pigs with a higher genetic merit for survival have a lower birth weight but nevertheless have an increased farrowing survival and early postnatal survival. Their increased survival cannot be explained by differences in progress of farrowing, early postnatal behavior, or rectal temperature within 24 h after birth.

Death risk and preweaning growth rate of piglets in relation to the within-litter weight distribution at birth

Abstract This study investigated whether the death risk of piglets and the preweaning growth rate of the surviving piglets depend on the within-litter weight distribution at birth. The litters were produced either by sows from one of six commercial breeds (n = 363) or by Dutch Landrace sows (n = 456). The birth weight and sex of all piglets and the weight and age at weaning of piglets which survived the suckling period were known. All litters were classified as one of five litter types on the basis of the within-litter birth weight distribution. The results indicate that the within-litter birth weight distribution is neither an important determinant of the within-litter variation in birth weight, nor an important determinant of the preweaning death risk of liveborn piglets. The average preweaning growth rate differed between litter types, but this was entirely due to differences in average litter size at birth. Within each of the four litter types with two discrete subpopulations, the average growth rate of the piglet type with the lower average birth weight was less than that of the piglet type with the higher average birth weight. In two litter types this difference was still significant after correction for litter size and birth weight.

Leptin gene polymorphisms and their phenotypic associations

In an era of rapidly increasing prevalence of human obesity and associated health problems, leptin gene polymorphisms have drawn much attention in biomedical research. Leptin gene polymorphisms have furthermore drawn much attention from animal scientists for their possible roles in economically important production and reproduction traits. Of the polymorphisms reported for exonic, intronic, and promoter regions of the leptin gene, 16 have been included in association studies in humans, 19 in cattle, and 6 (all exonic or intronic) in pigs. In humans, associations have been found with overweight or (early-onset) obesity, non-insulin-dependent diabetes mellitus, prostate cancer, and non-Hodgkins lymphoma. In cattle, associations have been found with feed intake, milk yield traits, carcass traits, and reproduction-related traits, and in pigs with feed intake, average daily gain, carcass traits (backfat/leanness), and reproduction performance traits. Many of the polymorphisms were only included in a limited number of association studies, or the phenotypes studied varied largely for a given polymorphism between studies. Therefore, many of the associations found for these polymorphisms need to be confirmed in future studies before firm conclusions can be drawn.

Weight distribution within litters at the early foetal stage and at birth in relation to embryonic mortality in the pig

Abstract This study investigated whether the within-litter weight distribution at birth is already established by the end of the embryonic stage of pregnancy (Day 35) and whether it is related to embryonic mortality rate. All data were obtained from Dutch Landrace gilts which had been inseminated with semen of Dutch Landrace boars. A total of 373 foetal litters (Day 27–Day 110) and 826 litters at term were classified into one of five litter types on the basis of the within-litter weight distribution. Independent of stage of pregnancy, within-litter weights were normally distributed in approximately 67% of all litters. The within-litter weight distribution at birth was already established by the end of the embryonic stage. Embryonic mortality rate was lower in litters with two discrete subpopulations than in litters with a normal distribution, except for litters with giants (growth-enhanced foetuses). The latter had the highest average embryonic mortality rate. The type of within-litter weight distribution might be a consequence of the very early existence of variation in embryonic development and the functioning of an intrauterine mechanism of selective mortality to reduce developmental variation before implantation.

Genetic analysis of the service sire effect on litter size in swine

Abstract REML methodology was applied to estimate the heritability of service sire effect on total number of piglets born (TNB) and number of piglets born alive (NBA) in a dataset containing records of 36 708 litters of three purebred lines (a boar line and two sow lines) and a line cross. The litters originated from a total of 1044 service sires. Data were analyzed within lines using a univariate animal model containing the genetic effect of service sire and dam of the litter as well as the permanent environmental effect of the dam. Heritability estimates for service sire effect on TNB and NBA varied between lines from 0 to 0.04 and 0.01 to 0.03, respectively. This study confirms earlier reports indicating a low heritability for service sire effect on litter size in swine.

The relationship between ovulation rate and litter size before and after Day 35 of pregnancy in gilts and sows: An analysis of published data

Abstract The relationships between the average number of corpora lutea and the average number of embryos or foetuses and the average prenatal survival rate were studied in data obtained from 78 publications for 139 (sub)populations. Before Day 35 of pregnancy, number of embryos increased linearly with an increase in number of corpora lutea. This increase was significant for non-induced and hormonally induced gilts and sows. In non-induced gilts and sows this increase was still significant after Day 35, but of a lower magnitude. No information was available for induced gilts and sows for the period after Day 35. In non-induced gilts and sows the prenatal survival rate did not change significantly with the number of corpora lutea before Day 35, but decreased significantly with an increasing number of corpora lutea after Day 35. Before Day 35 the latter was also true for the induced gilts and sows. It is concluded that an increase in average ovulation rate can result in an increase of average litter size.