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Increases in genetic merit for milk yield are associated with increases in mobilization of body reserves. This study assessed the effects of genotype by environment (GxE) interactions on milk yield and energy and protein balances. Heifers (n = 100) with high or low genetic merit for milk yield were milked 2 or 3 times a day and received rations of low or high caloric density. The management factors were selected to induce substantial differences in milk production levels and model different management strategies. The 2 x 2 x 2 factorial arrangement enables the assessment of the effects of genotype, environment, and GxE interactions. Mean daily energy-corrected milk production in the first 100 d in milk varied between 21.8 and 35.2 kg among the groups. The experimental factors affected milk production in the presumed direction. Ration was the most determinant factor on milk production. Effects of milking frequency and genetic merit were significant only in the groups that were fed rations with high caloric density. Signs for severe negative energy balances, protein balances, and low body condition scores, all of which may be indicative of health risks, were not concentrated in the highest producing cows. Feed caloric density and milking frequency had stronger effects on energy balances and protein balances, with unfavorable effects of low caloric density feed and an extra milking. This emphasizes the possible effect of mismanagement on animal health risks. High genetic merit cows had significantly lower postpartum body condition scores. Genotype x environment interactions existed, but more information is needed to determine if cows of different genetic merit for milk yield are differently at risk for disease under specific conditions. High milk production levels per se will increase allostatic load, but need not compromise the health status of relatively young cows. Ongoing one-sided selection for high yield may be combined with good animal health, but because high g

Estimates of genetic parameters for organic dairy farming have not been published previously, and neither is information available on the magnitude of genotype by environment interaction (GxE) between organic and conventional farming. However, organic farming is growing worldwide and basic information about genetic parameters is needed for future breeding strategies for organic dairy farming. The goal of this study was to estimate heritabilities of milk production traits under organic farming conditions and to estimate the magnitude of GxE between organic and conventional dairy farming. For this purpose, production records of first-parity Holstein heifers were used. Heritabilities of milk, fat and protein yield, and somatic cell score (SCS) were higher under organic farming conditions. For percentages of fat and protein, heritabilities of organic and conventional production were very similar. Genetic correlations between preorganic and organic, and organic and conventional milk production were 0.79 and 0.80, respectively. For fat yield, these correlations were 0.86 and 0.88, and for protein yield, these were 0.78 and 0.71, respectively. Our findings indicate that moderate GxE was present for yield traits. For percentage of fat and protein and SCS, genetic correlations between organic and conventional and preorganic production were close to unity, indicating that there was no GxE for these traits.

The aim of this study was to describe and analyze effects of parity, stage of lactation, milkability (3 groups of cows with differing peak flow rates), time of milking, and quarter position on milk production and milk flow measures at udder and quarter levels. Particular emphasis was put on changes to the decline phase and in duration of overmilking. More than 75,800 quarter milk flow curves and more than 19,300 udder milk flow curves obtained from 38 cows throughout lactation were analyzed. Stage of lactation significantly influenced all studied variables at both udder and quarter levels. At the quarter level, the duration of decline phase and the decline ratio (decline phase as a percentage of milking time) decreased from mo 1 to 2 and then gradually increased as lactation advanced. In contrast, at the udder level, duration of decline phase decreased throughout lactation but beginning at mo 2, the decline ratio increased as lactation advanced. The duration of the overmilking phase of quarters increased from mo 1 to 3 and then decreased in the course of lactation. Parity did not influence peak and average flow rates, the duration of increase phase, or the decline ratio at either udder or quarter levels. All milk flow measures were higher during morning milking except the duration of increase and decline phases at the quarter level and the duration of increase phase at the udder level. Milk yield and the duration of increase phase were not affected by milkability at either level. Quarters from udders with high milkability had longest duration of decline phase and the shortest overmilking phase. Milkability did not influence duration of the decline phase at the udder level. Quarter position influenced all measured variables of milk yield and milk flow. Rear quarters had significantly higher milk yield, longer time of milking, higher peak, and higher average flow rates than front quarters. Front quarters had shorter duration of increase and decline phases than rear qu

The objective of this paper was to investigate the importance of a genotype x environment interaction (G x E) for somatic cell score (SCS) across levels of bulk milk somatic cell count (BMSCC), number of days in milk (DIM), and their interaction. Variance components were estimated with a model including random regressions for each sire on herd test-day BMSCC, DIM, and the interaction of BMSCC and DIM. The analyzed data set contained 344,029 test-day records of 24,125 cows, sired by 182 bulls, in 461 herds comprising 13,563 herd test-days. In early lactation, considerable G x E effects were detected for SCS, indicated by 3-fold higher genetic variance for SCS at high BMSCC compared with SCS at low BMSCC, and a genetic correlation of 0.72 between SCS at low and at high BMSCC. Estimated G x E effects were smaller during late lactation. Genetic correlations between SCS at the same level of BMSCC, across DIM, were between 0.43 and 0.89. The lowest genetic correlation between SCS measures on any 2 possible combinations of BMSCC and DIM was 0.42. Correlated responses in SCS across BMSCC and DIM were, on some occasions, less than half the direct response to selection in the response environment. Responses to selection were reasonably high among environments in the second half of the lactation, whereas responses to selection between environments early and late in lactation tended to be low. Selection for reduced SCS yielded the highest direct response early in lactation at high BMSCC.

The objective of the current study was to determine the consequences of using indirect carcass measurements on the genetic response and rate of inbreeding in broiler breeding programs. In the base breeding scheme, selection candidates were evaluated based on direct carcass measurements on relatives. The possibilities of using indirect carcass measurements were investigated in alternative breeding schemes. Three alternative schemes, including indirect and own performance information for carcass traits on selection candidates, were evaluated by deterministic simulation. In the first scheme, indirect carcass traits were measured on male selection candidates. In the second scheme, indirect carcass traits were measured on male selection candidates, and direct carcass traits were measured on relatives. In the third scheme, indirect carcass traits were measured on male and female selection candidates, and direct carcass traits were measured on relatives. In the base scheme, the genetic response for breast muscle percentage (BMP) was 0.3%, and the rate of inbreeding was 0.96% per generation. In the third alternative scheme, the response for BMP increased by 66.2% compared with the base scheme, and the rate of inbreeding decreased to 0.79% per generation. The improved genetic gain resulted from increased accuracy of selection. The use of own performance information for selection candidates reduced the rate of inbreeding in alternative schemes, which is desirable for long-term selection. The accuracy of the indirect carcass measurements had consequences on the response for BMP and the rate of inbreeding. In most cases, an accuracy of 30% was sufficient to result in a higher gain for BMP and a lower rate of inbreeding as compared with the base scheme

Longevity is an increasingly important trait in beef cattle. Increased longevity decreases costs for the farmer and increases revenue. The objective of this research was to investigate the phenotypic relationship between type traits and longevity in Chianina beef cattle, and the relationship between production and longevity, to analyze the effect of voluntary culling. Data included records on reproductive, productive, and type traits provided by the National Association of Italian Beef Cattle Breeders from 6,395 Chianina cows. The average length of productive life was 1,829 d. The herd-year had a strong effect on the risk of culling. The effects of 22 type traits were analyzed. All the muscularity traits analyzed were highly significant (P <0.01) and as a group had the largest, effect on longevity followed by dimension, refinement, and leg traits. Cows that calved before 35 mo of age had a lower probability of being culled than cows calving after 35 mo of age. Variation in herd size had a strong effect on risk ratio, with lower risk for intermediate classes. Cows with approximately one calf per year remained in the herd longer than did cows with fewer calves. Straight-legged animals had a 59% greater probability of being replaced than cows with a moderate angle to the hock, whereas sickle-legged animals had only a 3% higher probability of being culled than average cows. Udder conformation had no effect on longevity. In summary, results of this study indicate that herd-year effects and muscularity traits were the most important factors for longevity for Chianina cows among the factors studied.

Electrical conductivity (EC) of milk has been introduced as an indicator trait for mastitis over the last decade, and it may be considered as a potential trait in a breeding program where selection for improved udder health is included. In this study, various EC traits were investigated for their association with udder health. In total, 322 cows with 549 lactations were included in the study. Cows were classified as healthy or clinically or subclinically infected, and EC was measured repeatedly during milking on each quarter. Four EC traits were defined; the inter-quarter ratio (IQR) between the highest and lowest quarter EC values, the maximum EC level for a cow, IQR between the highest and lowest quarter EC variation, and the maximum EC variation for a cow. Values for the traits were calculated for every milking throughout the entire lactation. All EC traits increased significantly (P

A cross between 2 genetically different outcross broiler dam lines, originating from the White Plymouth Rock breed, was used to produce a large 3-generation broiler population. This population was used to detect and localize QTL affecting fatness in chicken. Twenty full-sib birds in generation 1 and 456 full-sib birds in generation 2 were typed for microsatellite markers, and phenotypic observations were collected for 3 groups of generation 3 birds (~1,800 birds per group). Body weight, abdominal fat weight, and percentage abdominal fat was recorded at the age of 7, 9, and 10 wk. To study the presence of QTL, an across-family weighted regression interval mapping approach was used in a full-sib QTL analysis. Genotypes from 410 markers mapped on 25 chromosomes were available. For the 3 traits, 26 QTL were found for 18 regions on 12 chromosomes. Two genomewise significant QTL (P <0.05) were detected, one for percentage abdominal fat at the age of 10 wk on chicken chromosome 1 at 241 cM (MCW0058 to MCW0101) with a test statistic of 2.75 and the other for BW at the age of 10 wk on chicken chromosome 13 at 9 cM (MCW0322 to MCW0110) with a test statistic of 2.77. Significance levels were obtained using the permutation test. Multiple suggestive QTL were found on chromosomes 1, 2, 4, 13, 15, and 18, whereas chromosomes 3, 7, 10, 11, 14, and 27 had a single suggestive QTL

The research with respect to displacement of the abomasum (DA) in dairy cattle is reviewed. Evaluated articles describe epidemiological and experimental studies. The occurrence is elevated with regard to breed, gender, age, concurrent diseases, environmental aspects and production levels as contributing factors and emphasis is placed on the effects of nutrition and metabolism. Reviewing the experimental work, distinction is made between the research into gas production in the abomasum and hypomotility of the abomasum, since both represent presumed pathways in the development of DA. Although the different fields of research have positive contributions to the understanding of the pathogenesis of DA, contradictions in the different studies are present. This is partly due to extrapolation of results from sheep to cows, or because of a low number of cows in the experiments. Finally, general suggestions are made for further research in the field of the pathogenesis of DA.