J.A.M. van Arendonk

Genetic aspects of feed intake and efficiency in lactating dairy heifers

Abstract In 1982, an experiment was initiated to study the relationships between feed intake and feed efficiency of young AI bulls, growing heifers and lactating heifers. This paper focuses on the genetic parameters for feed intake, production, and efficiency of lactating heifers. Measurements of feed intake, body weight and production were taken on 360 heifers during the first 105 days of lactation. The heifers were progeny of 38 sires; 125 of the heifers also had measurements on their dam. Heifers were fed a diet of 6 kg of concentrates and roughage ad libitum. Genetic parameters were estimated by REML fitting an animal model using a derivative-free algorithm. Heritability for roughage dry matter intake was 0.46. Heritability was 0.37 for gross feed efficiency and 0.19 for residual feed intake, which reflects the differences in energy intake after correcting for differences in metabolic body weight, weight change and production. The genetic correlation of 105-day production of fat- and protein-corrected milk with roughage intake was 0.61, with gross feed efficiency was −0.93, and with residual feed intake was close to zero. The correlated response in roughage intake when selection is on production is not large enough to cover the additional requirements due to the increased production. Intake capacity might be considered as an additional trait in the selection goal to avoid an increase in negative energy balance during early lactation.

Milk Fatty Acid Unsaturation : Genetic Parameters and Effects of Stearoyl-CoA Desaturase (SCD1) and Acyl CoA: Diacylglycerol Acyltransferase 1 (DGAT1)

With regard to human health aspects of milk fat, increasing the amount of unsaturated fatty acids in milk is an important selection objective. The cows diet has an influence on the degree of unsaturation, but literature suggests that genetics also plays a role. To estimate genetic variation in milk fatty acid unsaturation indices, milk fatty acid composition of 1,933 Dutch Holstein Friesian heifers was measured and unsaturation indices were calculated. An unsaturation index represents the concentration of the unsaturated product proportional to the sum of the unsaturated product and the saturated substrate. Intraherd heritabilities were moderate, ranging from 0.23 +/- 0.07 for conjugated linoleic acid (CLA) index to 0.46 +/- 0.09 for C16 index. We genotyped the cows for the SCD1 A293V and DGAT1 K232A polymorphisms, which are known to alter milk fatty acid composition. Both genes explain part of the genetic variation in unsaturation indices. The SCD1 V allele is associated with lower C10, C12, and C14 indices, and with higher C16, C18, and CLA indices in comparison to the SCD1 A allele, with no differences in total unsaturation index. In comparison to the DGAT1 K allele, the DGAT1 A allele is associated with lower C10, C12, C14, and C16 indices and with higher C18, CLA, and total indices. We conclude that selective breeding can contribute to higher unsaturation indices, and that selective breeding can capitalize on genotypic information of both the SCD1 A293V and the DGAT1 K232A polymorphism.

Studies on the replacement policies in dairy cattle II.Optimum policy and influence of changes in production and prices

Abstract A dynamic programming model was developed to determine the optimum replacement policy of dairy cows. In the model cows were described in terms of lactation number, stage of lactation and the level of milk production during the previous and present lactations. The objective in determining the optimum replacement policy was to maximize the present value of net revenues from the present and subsequent replacement cows over a 20-year planning horizon. Milk and calf revenues, feed costs, carcass value, cost of replacement heifers and the probability of and financial loss associated with involuntary replacement were considered. The optimum replacement decisions corresponded with an average herd life of 42.9 months. Voluntary replacement accounted for 26% of all replacements. Changes in the price of a replacement heifer or the carcass price for culled cows had a considerable effect on the optimum replacement policy. A reduction in the difference between the carcass value of culled cows and the replacement costs resulted in a higher rate of voluntary replacement. Changes in the price of milk, calves or feed, the production level of the herd or the rate of genetic improvement did not greatly affect the optimum replacement policy. The financial advantage of a reduction in involuntary disposal rates increased when voluntary replacement of cows according to the optimum policy took place. These changes in voluntary replacement rates however reduced the effect on the optimum average herd life of cows.

Effects of milk protein variants on the protein composition of bovine milk.

The effects of beta-lactoglobulin (beta-LG), beta-casein (beta-CN), and kappa-CN variants and beta-kappa-CN haplotypes on the relative concentrations of the major milk proteins alpha-lactalbumin (alpha-LA), beta-LG, alpha(S1)-CN, alpha(S2)-CN, beta-CN, and kappa-CN and milk production traits were estimated in the milk of 1,912 Dutch Holstein-Friesian cows. We show that in the Dutch Holstein-Friesian population, the allele frequencies have changed in the past 16 years. In addition, genetic variants and casein haplotypes have a major impact on the protein composition of milk and explain a considerable part of the genetic variation in milk protein composition. The beta-LG genotype was associated with the relative concentrations of beta-LG (A >> B) and of alpha-LA, alpha(S1)-CN, alpha(S2)-CN, beta-CN, and kappa-CN (B > A) but not with any milk production trait. The beta-CN genotype was associated with the relative concentrations of beta-CN and alpha(S2)-CN (A(2) > A(1)) and of alpha(S1)-CN and kappa-CN (A(1) > A(2)) and with protein yield (A(2) > A(1)). The kappa-CN genotype was associated with the relative concentrations of kappa-CN (B > E > A), alpha(S2)-CN (B > A), alpha-LA, and alpha(S1)-CN (A > B) and with protein percentage (B > A). Comparing the effects of casein haplotypes with the effects of single casein variants can provide better insight into what really underlies the effect of a variant on protein composition. We conclude that selection for both the beta-LG genotype B and the beta-kappa-CN haplotype A(2)B will result in cows that produce milk that is more suitable for cheese production.

Application of Gibbs sampling for inference in a mixed major gene-polygenic inheritance model in animal populations

The application of Gibbs sampling is considered for inference in a mixed inheritance model in animal populations. Implementation of the Gibbs sampler on scalar components, as used for human populations, appeared not to be efficient, and an approach with blockwise sampling of genotypes was proposed for use in animal populations. The blockwise sampling of genotypes was proposed for use in animal populations. The blockwise sampling by which genotypes of a sire and its final progeny were sampled jointly was effective in improving mixing, although further improvements could be looked for. Posterior densities of parameters were visualised from Gibbs samples; from the former highly marginalised Bayesian point and interval estimates can be obtained.

Effect of lactation stage and energy status on milk fat composition of Holstein-Friesian cows

The effects of lactation stage, negative energy balance (NEB), and milk fat depression (MFD) were estimated on detailed milk fat composition in primiparous Holstein-Friesian cows. One morning milk sample was collected from each of 1,933 cows from 398 commercial Dutch herds in winter 2005. Milk fat composition was measured using gas chromatography, and fat and protein percentage were measured using infrared spectrometry. Each fatty acid changed 0.5 to 1 phenotypic standard deviation over lactation, except odd-chain C5:0 to C15:0, branched-chain fatty acids, and trans-10, cis-12 conjugated linoleic acid (CLA). The greatest change was an increase from 31.2 to 33.3% (wt/wt) for C16:0 from d 80 to 150 of lactation. Energy status was estimated for each cow as the deviation from each average lactation fat-to-protein ratio (FPdev). A high FPdev (>0.12) indicated NEB. Negative energy balance was associated with an increase in C16:0 (0.696 +/- 0.178) and C18:0 (0.467 +/- 0.093), which suggested mobilization of body fat reserves. Furthermore, NEB was associated with a decrease in odd-chain C5:0 to C15:0 (-0.084 +/- 0.020), which might reflect a reduced allocation of C3 components to milk fat synthesis. A low FPdev indicated MFD (<-0.12) and was associated with a decrease in C16:0 (-0.681 +/- 0.255) and C18:0 (-0.128 +/- 0.135) and an increase in total unsaturated fatty acids (0.523 +/- 0.227). The study showed that both lactation stage and energy balance significantly contribute to variation in milk fat composition and alter the activity of different fatty acid pathways.

Detection and characterization of quantitative trait loci for growth and reproduction traits in pigs

Abstract A genome scan was performed on F 2 animals of a cross between Meishan and Dutch commercial pigs. Phenotypic data were available for growth traits and ultrasonic backfat thickness on 942–1151 animals, and for litter size on 249 and 206 animals at first and second parity, respectively. QTL analyses were performed using interval mapping by regression under the line-cross approach complemented by tests for genomic imprinting and sex-specific QTL effects. For backfat thickness, the analyses revealed significant QTL on chromosomes 2, 7, 14, and X, with significant imprinting for chromosomes 2 and 14. Significant QTL were detected for the different growth traits on chromosomes 1, 4, 7, and 8. Both the QTL on chromosome 4 and chromosome 8 showed maternal expression for a specific growth stage. The QTL analyses for litter size revealed one suggestive QTL for first parity and three suggestive QTL for the second parity. Analyses under a half-sib model did not reveal additional significant QTL, but confirmed several of the QTL detected under the line-cross models. This study provides confirmation of several QTL affecting growth and fat deposition in pigs and adds interesting new insight into their mode of expression. Furthermore, additional significant and suggestive QTL were identified.

Fine mapping and imprinting analysis for fatness trait QTLs in pigs

Abstract. Quantitative trait loci (QTL) for fatness traits were reported recently in an experimental Meishan × Large White and Landrace F2 cross. To further investigate the regions on pig Chr 2 (SSC2), SSC4, and SSC7, 25 additional markers from these regions were typed on 800 animals (619 F2 animals, their F1 parents, and F0 grandfathers). Compared with the published maps, a modified order of markers was observed for SSC4 and SSC7. QTL analyses were performed both within the half-sib families as well as across families (line cross). Furthermore, a QTL model accounting for imprinting effects was tested. Information content could be increased considerably on all three chromosomes. Evidence for the backfat thickness QTL on SSC7 was increased, and the location could be reduced to a 33-cM confidence interval. The QTL for intramuscular fat on SSC4 could not be detected in this half-sib analysis, whereas under the line cross model a suggestive QTL on a different position on SSC4 was detected. For SSC2, in the half-sib analysis, a suggestive QTL for backfat thickness was detected with the best position at 26 cM. Imprinting analysis, however, revealed a genome-wise, significant, paternally expressed QTL on SSC2 with the best position at 63 cM. Our results suggest that this QTL is different from the previously reported paternally expressed QTL for muscle mass and fat deposition on the distal tip of SSC2p.

Studies on the replacement policies in dairy cattle. III. Influence of variation in reproduction and production

Abstract The optimum policy of insemination and replacement of dairy cows was determined by the dynamic programming technique. The model used in the previous study was extended to allow variation in time of conception. From 2 to 7 months after calving three alternatives were considered for an open cow namely (a) inseminating the cow, with a calculated probability of success, (b) leaving her open, and (c) replacing her immediately. When it was profitable to leave a cow open, the optimum time for replacement during the lactation period was determined. The minimum production level for insemination to be the optimum choice depended on the stage of lactation and the parity of the cow. In the optimum situation the average calving interval was 371 days, while 13% of the cows had an interval of 14 months or longer. The optimum policy was greatly affected by changes in the replacement heifer price. Changes in the probability of conception and persistency of milk production had significant but smaller effects. In herds with a smaller decline in production after the peak, insemination should be continued for longer than in herds with a larger decline. The relation between production and calving interval that resulted from the optimum policy was determined. When a measure of milk production was used that was not affected by gestation, the average correlation was 0.09. The correlation increased to 0.35 when the total 305-day production was used.

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.