Comparison of milk produced by cows cloned by nuclear transfer with milk from non-cloned cows

Cloning technologies, including embryo splitting and nuclear transfer, were introduced into dairy cattle breeding in the early 1980s. With the recent worldwide attention on the cloning of sheep ("Dolly") and cows ("Gene"), the potential food safety concerns for food products derived from cloned animals needs to be addressed. There has been no study of the composition of milk produced by cloned cows. In this preliminary study, we evaluated the composition of milk from 15 lactating non-embryonic cell cloned cows and six non-cloned lactating cows over a single season. The cloned cows came from five unique genetic lines and three distinct breeds. Milk samples were analyzed for total solids, fat, fatty acid profile, lactose, protein and compared to non-cloned and literature values. Gross chemical composition of milk from cloned cows was similar to that of the non-cloned cows and literature values. Our results lead us to conclude that there are no obvious differences in milk composition produced from cloned cows compared to non-cloned cows.     

Association of the DGAT1 gene polymorphism in stud bulls with milk productivity in cows

The substitution of lysine for alanine (K232A) in the acyl-CoA-diacylglycerol acyltransferase, which is encoded by the DGAT1 gene, was tested for the significance for breeding evaluation of stud bulls of the holsteinized Black-and-White breed. The breeding value (deviation of milk productivity in daughters compared with cows of the same age) was estimated by the DYDC (daughter yield deviation to contemporary) method with modification. The frequency of allele 232K in the bulls examined was 0.28, lower than in Holstein bulls (0.4-0.6). The greatest effect of the A232K substitution was observed for the percent fat content in milk (1.4 sigma) and milk yield (0.76 sigma), and a lower effect was established for the milk protein yield (0.47 sigma) and percent protein content in milk (0.44 sigma). In the case of milk fat yield, the effect was nonsignificant. A method was proposed for converting the data on fat yield in order to obtain significant results in this case as well. The effect of the A232K substitution was estimated at 154 kg for milk yield, 2.8 kg for protein yield, 0.079% for percent fat content, and 0.015% for percent protein content. The results are discussed in the context of multiple pleiotropic effects of the K232A substitution in the DGAT1 gene. It is proposed that the K232A substitution of the DGAT1 gene be used as a golden standard in comparisons of the effect on milk productivity for the total gene set. This approach will allow a meta-analysis of the gene effects in spite of the differences in dairy cattle breeds and methods used to analyze their breeding value. In view of more than 30-year experience of using sperm of Holstein stud bulls, including those bred in North America, it was noted that the effect of the A232K substitution on milk productivity traits agreed well with the data reported for the North American commercial population of Holstein cattle.     

Characterization of DGAT1 Allelic Effects in a Sample of North American Holstein Cattle

A putative causative mutation underlying a QTL was identified as a lysine to alanine non-conservative substitution at amino acid 232 of the gene encoding the acylCoA:diacylglycerol acyltransferase (DGAT1) protein. Our goal was to characterize the allelic substitution effects of this DGAT1 mutation in a large sample of Holstein bulls from North America. Statistically significant effects were identified for all of the milk production traits and somatic cell scores. Estimated average effects of substituting the lysine allele for the alanine variant on Holstein bull daughter yield deviations were ?81 kg, 3.7 kg, ?1.1 kg, 0.063%, 0.012%, and ?0.023 units for milk yield, fat yield, protein yield, fat component, protein component, and SCS, respectively. These estimates were largely in agreement with previous studies; however, the magnitudes of the estimates were much smaller in this study. Impacts on economic indices for net merit, cheese merit, and fluid merit were modest. Because of the strong antagonism between fat and protein yield and how those traits influence economic indices, selection for DGAT1 genotypes will likely not find widespread application in the U.S.     

Genetic correlations between yield traits or days open measured in cows and semen production traits measured in bulls

We used a bivariate animal model to investigate the genetic correlations between yield traits or days open (DO) as characters measured in cows and semen production traits as characters measured in bulls. Lactation records of 305-day milk, fat, and protein yields, and DO, from 386 809 first-lactation Holstein cows in Hokkaido, Japan, that calved between 2008 and 2014 were used. Semen production records were collected between 2005 and 2014 and included volume per ejaculate (VOL), sperm concentration (CON), number of sperm per ejaculate (NUM), progressive motility index of sperm (MOT), and MOT after freeze-thawing (A-MOT). Number of sperm per ejaculate was log-transformed into a NUM score (NUMS). A total of 30 373 semen production records from 1196 bulls were obtained. The pedigree file used for analysing the records was involving 885 345 animals. Heritability was estimated for VOL (0.42), CON (0.12), NUMS (0.37), MOT (0.08), and A-MOT (0.11). Weak and negative genetic correlations were recorded between yield traits measured in cows and VOL, CON or NUMS measured in bulls. Moderate and negative genetic correlations were obtained between DO and MOT (–0.42) or A-MOT (–0.43). Selection focused on MOT or A-MOT measured in bulls may therefore improve DO measured in cows.     

Association of the <Emphasis Type="Italic">DGAT1</Emphasis> gene polymorphism in bulls with cow milk performance

The substitution of lysine for alanine (K232A) in the acyl-CoA:diacylglycerol acyltransferase, which is encoded by the DGAT1 gene, was tested for the significance for breeding evaluation of bulls of the holsteinized Black-and-White breed. The breeding value was estimated by the DYDC (daughter yield deviation to contemporaries) method with modification. The frequency of allele 232K in the bulls examined was 0.28, lower than in Holstein bulls (0.4–0.6). The greatest effect of the A232K substitution was observed for the percent fat milk yield (1.4σ) and milk yield (0.76σ), and a lower effect was established for the milk protein yield (0.47σ) and percent protein milk yield (0.44σ). In the case of milk fat yield, the effect was nonsignificant. A method was proposed for converting the data on fat yield in order to obtain significant results in this case as well. The effect of the A232K substitution was estimated at 154 kg for milk yield, 2.8 kg for milk protein yield, 0.079% for percent milk fat, and 0.015% for percent milk protein yield. The results are discussed in the context of multiple pleiotropic effects of the K232A substitution in the DGAT1 gene. It is proposed that the K232A substitution of the DGAT1 gene may be used as a golden standard in comparisons of the effect on milk production traits for the total gene set. This approach will allow a meta-analysis of the gene effects in spite of the different dairy cattle breeds and methods used to analyze their breeding value. In view of more than 30-year experience of using sperm of Holstein bulls, including those breeds in North America, it was noted that the effect of the A232K substitution on milk production traits agreed well with the data reported for the North American commercial population of Holstein cattle.     

Ability of dairy cows to be inseminated according to breed and genetic merit for production traits under contrasting pasture-based feeding systems

Strong genetic selection on production traits is considered to be responsible for the declined ability of dairy cows to ensure reproduction. The present study aimed to quantify the effect of genetic characteristics (breeds and genetic merit for production traits) and feeding systems (FS) on the ability of dairy cows to be inseminated. An experiment was conducted during 9 years on Normande and Holstein cows assigned to contrasted pasture-based FS. Diets were based on maize silage in winter and grazing plus concentrate in spring in the High FS; and on grass silage in winter and grazing with no concentrate during spring in the low FS. Within breed, cows were classified into two genetic groups with similar estimated breeding values (EBV) for milk solids: cows with high EBV for milk yield were included in a Milk-Group and those with high EBV for fat and protein contents were included in a Content-Group. Holstein produced more milk throughout lactation than Normande cows (+2294 kg in the High FS and +1280 kg in the Low FS, P<0.001) and lost more body condition to nadir (−1.00 point in the High FS and −0.80 kg in the Low FS, P<0.001). They also showed a poorer ability to be inseminated because of both a delayed commencement of luteal activity (CLA) and delayed first service (more days from start of the breeding season to first service, DAI1). Cows in the Milk-Group produced more milk than cows in the Content-Group, but milk solids production was similar. Cows in the Content-Group had earlier CLA than cows in the Milk-Group (P<0.01). Genetic group neither affected ovulation detection rate nor DAI1. Within breed and FS, cows with high genetic merit for milk yield had later CLA and DAI1. Cows in the High FS produced more milk and lost less condition to nadir than cows in the Low FS. FS did not affect dairy cows’ ability to be inseminated. However, cows with higher milk protein content, and presumably better energy balance, had earlier CLA (P<0.01) and DAI1 (P<0.10). In addition, higher milk yield was associated with poorer ovulation detection rate and oestrus intensity (P<0.05). The study showed that at similar EBV level for milk solids, selection for increased milk fat and protein content resulted in improved cyclicity and similar oestrous expression and submission rates compared with selection for increased milk yield.     

Genetic merit for milk production and reproductive success in dairy cows

The effect of genetic merit for milk production traits - fat, protein and milk yield - in dairy cows on milk production, body condition, blood metabolites, reproductive hormones, feed intake and reproductive performance was studied over a period of 2 years. Cows were grouped into two categories, based on calculated pedigree indices using multiple-trait across country evaluation (MACE). Cows of high genetic merit (HGM, n = 48 in year 1 and n = 46 in year 2) had a mean predicted difference +/- standard deviation for milk production of 475 +/- 76kg. The cows of medium genetic merit (MGM, n = 48 in both years) had a mean predicted difference for milk production of 140 +/- 68kg.The cows calved between January and April, and were offered grass silage ad libitum plus 9kg concentrates per cow per day, irrespective genetic merit, from calving to turnout in March, when they were subjected to one of three grazing systems. Cows were available for rebreeding from late April until late July of each year.High genetic merit cows had higher milk production, incurred greater body condition loss between calving and first service and had lower plasma glucose and insulin-like growth factor-1 (IGF-1) concentrations than medium genetic merit cows. Furthermore, HGM cows had lower first and second service and overall conception rates, and required more services per conception than the MGM cows.Cows that did not conceive to first service were retrospectively compared to those that conceived to first service within each genetic merit group. There were no significant differences between the HGM cows that did not conceive to first service and those that conceived to this service in terms of milk production, body condition score change between calving and first service, feed intake at first service, or in plasma concentrations of glucose, non-esterified fatty acids (NEFA) or IGF-1. Medium genetic merit cows that did not conceive to first service lost more body condition between calving and first service than did those that conceived to this service.In the present study, HGM cows had higher milk production and reduced reproductive performance in comparison with MGM cows. However, reproductive performance was not associated with milk production, feed intake or plasma concentrations of glucose, NEFA or IGF-1 between calving and first service, since there were no significant differences in these variates between high or medium genetic merit cows that did not conceive to first service and those that conceived to this service. Therefore, these variates are unlikely to be useful predictors of reproductive performance, under the conditions of the present study.     

A simple method for genomic selection of moderately sized dairy cattle populations

An efficient algorithm for genomic selection of moderately sized populations based on single nucleotide polymorphism chip technology is described. A total of 995 Israeli Holstein bulls with genetic evaluations based on daughter records were genotyped for either the BovineSNP50 BeadChip or the BovineSNP50 v2 BeadChip. Milk, fat, protein, somatic cell score, female fertility, milk production persistency and herd-life were analyzed. The 400 markers with the greatest effects on each trait were first selected based on individual analysis of each marker with the genetic evaluations of the bulls as the dependent variable. The effects of all 400 markers were estimated jointly using a 'cow model,' estimated from the data truncated to exclude lactations with freshening dates after September 2006. Genotype probabilities for each locus were computed for all animals with missing genotypes. In Method I, genetic evaluations were computed by analysis of the truncated data set with the sum of the marker effects subtracted from each record. Genomic estimated breeding values for the young bulls with genotypes, but without daughter records, were then computed as their parent averages combined with the sum of each animal's marker effects. Method II genomic breeding values were computed based on regressions of estimated breeding values of bulls with daughter record on their parent averages, sum of marker effects and birth year. Method II correlations of the current breeding values of young bulls without daughter records in the truncated data set were higher than the correlations of the current breeding values with the parent averages for fat and protein production, persistency and herd-life. Bias of evaluations, estimated as a difference between the mean of current breeding values of the young bulls and their genomic evaluations, was reduced for milk production traits, persistency and herd-life. Bias for milk production traits was slightly negative, as opposed to the positive bias of parent averages. Correlations of Method II with the means of daughter records adjusted for fixed effects were higher than parent averages for fat, protein, fertility, persistency and herd-life. Reducing the number of markers included in the analysis from 400 to 300 did not reduce correlations of genomic breeding values for protein with current breeding values, but did slightly reduce correlations with means of daughter records. Method II has the advantages as compared with the method of VanRaden in that genotypes of cows can be readily incorporated into the Method II analysis, and it is more effective for moderately sized populations.     

Milk yield response of dairy cows fed fat along with protein

The influence of a fat-coated protein on milk production of Holstein dairy cows was determined using a 4×4 Latin square experiment. Twelve cows were fed a control diet or test diets supplemented with fat, fat plus ruminally undegraded protein (RUP), or a fat-coated protein (Duets™). Cows fed test diets received 0.55 kg of more fat per day than cows in the control treatment. Daily intakes of feed, energy, and protein were the same in all treatments. Cows produced 36.5, 37.3, 37.9, and 39.3 kg of energy-corrected milk per day in control, fat, fat plus RUP, and fat-coated protein treatments, respectively. Cows fed fat-supplemented diets produced an average 1.7 kg more milk daily compared with cows in the control treatment. Feeding RUP along with fat or fat-coated protein provided no further improvement in milk yield compared with fat alone, but partially alleviated the depression in protein content caused by supplemental fat and increased the daily yield of milk protein. In the present experiment, cows fed fat-coated protein produced daily an average 60 g of milk protein more than cows fed fat alone. Since, there was no advantage in milk yield, the decision to include fat-coated protein in dairy rations should be based on its price compared to fat alone and the return in terms of milk protein yield.     

Comparison of pure Holsteins to crossbred Holsteins with Norwegian Red cattle in first and second generations

A total of 1922 first generation crossbred cows born between 2005 and 2012 produced by inseminating purebred Israeli Holstein cows with Norwegian Red semen, and 7487 purebred Israeli Holstein cows of the same age in the same 50 herds were analyzed for production, calving traits, fertility, calving diseases, body condition score, abortion rate and survival under intensive commercial management conditions. Holstein cows were higher than crossbreds for 305-day milk, fat and protein production. Differences were 764, 1244, 1231 for kg milk; 23.4, 37.4, 35.6 for kg fat, and 16.7, 29.8, 29.8 for kg protein; for parities 1 through 3. Differences for fat concentration were not significant; while crossbred cows were higher for protein concentration by 0.06% to 0.08%. Differences for somatic cells counts were not significant. Milk production persistency was higher for Holstein cows by 5, 8.3 and 8% in parities 1 through 3. Crossbred cows were higher for conception status by 3.1, 3.6 and 4.7% in parities 1 through 3. Rates of metritis for Holsteins were higher than the crossbred cows by 7.8, 4.6 and 3.4% in parities 1 to 3. Differences for incidence of abortion, dystocia, ketosis and milk fever were not significant. Holstein cows were lower than crossbred cows for body condition score for all three parities, with differences of 0.2 to 0.4 units. Contrary to comparisons in other countries, herd-life was higher for Holsteins by 79 days. A total of 6321 Holstein cows born between 2007 and 2011 were higher than 765 progeny of crossbred cows backcrossed to Israeli Holsteins of the same ages for milk, fat and protein production. Differences were 279, 537, 542 kg milk; 10.5, 17.7, 17.0 kg fat and 6.2, 12.9, 13.2 kg protein for parities 1 through 3. Differences for fat concentration were not significant, while backcross cows were higher for protein percentage by 0.02% to 0.04%. The differences for somatic cell score, conception rate, and calving diseases other than metritis, were not significant. Holstein cows were lower than backcross cows by 1.5% to 2.5% for conception status in parities 1 to 3 and lower for body condition score for parities 1 and 2, with differences in the range of 0.06 to 0.09 units. Culling rates were higher, and herd-life lower for the crossbred cows. The gains obtained in secondary traits for crossbred cows did not compensate for the major reduction in production.     

Ovarian structures and uterine environment are associated with phenotypic and genetic merit for performance in lactating dairy cows

The objective of this study was to estimate the association between detailed reproductive phenotypes for cows categorized as divergent for phenotypic and genetic performance. The hypothesis was that higher yielding animals, either phenotypically or genetically, would have compromised ovarian and uterine reproductive performance. Detailed reproductive traits including multiple ovulations, cystic ovarian structures, corpus luteum (CL) presence, and uterine environment were available on 9675 ultrasound records from 8174 dairy lactating cows, calved between 10 and 70 days. Cows were categorized, within parity, into low, average, or high for each of the performance traits. There was a greater likelihood of multiple ovulations in cows with greater phenotypic yields (odds ratio: 1.53–1.81) and greater genetic merit for yield (odds ratio: 1.31–1.59) relative to lower performing contemporaries. After adjustment for genetic merit, a similar trend of increased odds (odds ratio: 1.29–1.87) of multiple ovulations in higher yielding cows was observed compared with the lowest yielding category. There was no association between either phenotypic milk composition or genetic merit for milk composition with the likelihood of multiple ovulations. The likelihood of cystic ovarian structures was highest in cows with greatest phenotypic milk yields (odds ratio: 2.75–3.24), greater genetic merit for milk yield (odds ratio: 1.30–1.51), and even after adjustment for genetic merit there was a greater likelihood of cystic ovarian structures in cows with the highest milk yields (odds ratio: 2.71–2.95), compared with cows in the lowest category for each of the milk traits. Cows with average phenotypic milk yields were more likely to have a CL, compared with the lowest yielding category (odds ratio: 1.20–1.23), and these associations remained after adjustment for genetic merit of the trait. The likelihood of CL presence was highest in cows with the lowest genetic merit for milk. Lower fat:protein ratio was associated with an increased likelihood of CL presence compared with cows with greater fat:protein ratio and cows with the highest phenotypic milk composition were more likely to have a CL compared with cows in the lowest composition category. Genetic predisposition to higher somatic cell score was associated with a reduced risk of multiple ovulations (odds ratio: 0.69; 95% CI: 0.55–0.87) but an increased likelihood of CL presence (odds ratio: 2.66; 95% CI: 2.09–3.37) and poorer uterine health score (odds ratio: 1.36; 95% CI: 1.20–1.55). There was a lower likelihood of multiple ovulations, cystic ovarian structures, and poorer uterine health and an increased likelihood of CL presence in cows with superior genetic merit for reproductive performance and survival.     

Study of the association between alleles of the growth hormone receptor and prolactin receptor genes of bulls and the milk productivity of their daughters

A substitution of thyrosine for phenylalanine (F297Y) in the transmembrane domain of the growth hormone receptor (GHR) was tested for significance for breeding evaluation of bulls of the holstenized Black-and-White breed. The breeding value was estimated by the method of daughter yield deviation to contemporaries with modification. The frequency of genotype FF in the bulls examined was 0.37, lower than in Holstein bulls (0.67). The F297Y substitution exerted the greatest effect on the milk fat content (1.5??) and milk yield (0.8 ??) and a lower effect on the milk fat yield (0.6 ??), milk protein yield (0.5 ??), and milk protein content (0.6 ??). The GHR4.2 single nucleotide substitution (SNP) in the promoter of the GHR gene did not affect the milk production traits. A substitution of asparagine for serine (S18N) in the transmembrane domain of the prolactin receptor (PRLR) was also examined, but it did not significantly affect the milk production traits. The results are discussed in the context of the hypothesis that multiplicity of causal mutations of a particular gene is common and should be taken into account in the genetics of quantitative traits.     

中国荷斯坦牛IL8基因遗传多态性与泌乳性状以及体细胞评分的关联

以上海某奶牛场30个公牛家系的610头中国荷斯坦牛为试验材料,采用聚合酶链式反应-单链构象多态性(PCR-SSCP)技术对Interleukin-8(IL8)基因的遗传多态性进行了分析,采用混合动物模型分析了IL8基因突变位点与测定日产奶量、测定日乳脂率、测定日乳蛋白率、305d校正产奶量、305d乳脂量、305d乳蛋白量及测定日体细胞评分7个性状的相关性,寻找可用于生产实际的分子标记。共检测到KK、KA和AA3种基因型,频率分别为0.187、0.451和0.362,等位基因K和A的频率分别为0.412和0.588。该位点突变对测定日产奶量、305d乳蛋白量、305d校正产奶量和305d乳脂量以及体细胞评分影响达到极显著水平(P0.01),对测定日乳蛋白率的影响达到显著水平(P0.05),对测定日乳脂率影响不显著(P0.05)。多重比较表明:KK基因型对测定日产奶量、305d校正产奶量、305d乳蛋白量和305d乳脂量极显著高于AA和KA基因型(P0.01)。KK基因型的体细胞评分(SCS)最小二乘均值极显著低于KA、AA基因型(P0.01)。对于测定日的乳蛋白率AA基因型显著低于KA、KK型(P0.05)。IL8基因遗传突变对中国荷斯坦牛泌乳性状和乳房炎抗性有较大的遗传效应,可用于中国荷斯坦牛的分子标记辅助选择。     

Assessing the quality of products from cloned cattle: an integrative approach

Scientific expertise was developed during a 3-year study to evaluate a large number of bovine female clones (n=37; from 4 to 36 months of age) and their products through a multidisciplinary approach and compare them to non-cloned breed, age and sex-matched contemporary control animals (n=38) maintained under the same conditions at the same experimental farm of INRA. In clone and control groups, most parameters measured for health and development of the animals as well as evaluation of milk and meat products were within the normal range for the breed. The strict comparison between cloned animals and controls allowed us to detect slight significant differences between the two groups. Cloned heifers reached puberty significantly later (+62 days) and at higher body weight (+56kg) than controls. There were slight differences in antigen-specific induced proliferation of lymphocytes after vaccination with ovalbumin before 10 months of age, but responses were normal responses in older animals. There were differences in the fatty acid (FA) composition of milk and muscle arising from two families of clones, suggesting a possible deviation in lipid metabolism as assessed by higher Delta-9 desaturase activity indices in both milk and muscle from clones compared to controls. Nutritional evaluation of milk and meat using the rat model did not reveal any difference between products derived from clones versus controls.     

Effects of DGAT1 and GHR on milk yield and milk composition in the Chinese dairy population

Previous studies have demonstrated that the p.Lys232Ala substitution in the acylCoA: diacylglycerol acyltransferase ( DGAT1 ) gene and the p.Phe279Tyr mutation in the growth hormone receptor ( GHR ) gene are the causative quantitative trait loci underlying milk yield and composition on BTA14 and BTA20 respectively. To examine their applications in the genetic improvement of Chinese dairy cattle productivity, we herein investigated the effects of the DGAT1 p.Lys232Ala and GHR p.Phe279Tyr mutations on milk, fat and protein yield, as well as fat and protein percentage in the milk of 1222 Holstein cows. Genotyping was performed using PCR-RFLP for DGAT1 or primer-introduced restriction analysis (PCR-PIRA) for GHR . With a mixed animal model, the significant associations of the DGAT1 p.Lys232Ala substitution with 305-day milk, fat and protein yield were identified ( P  =   0.0001). The DGAT1 allele that encode lysine at position 232 was associated with increased 305-day milk fat yield, but with decreased 305-day milk and protein yield, whereas the GHR p.Phe279Tyr mutation was found to be significantly associated with protein percentage ( P  =   0.0014). The allele substitution effect of p.279Phe by p.279Tyr may lead to a significant increase in protein percentage. Our findings indicate that DGAT1 p.232Ala and GHR p.279Phe could be used to increase milk yield and protein yield of Chinese Holstein cows.     

Genetic correlations between production and disease traits during first lactation in Holstein cows

The aim of this study was to estimate genetic correlations between milk yield, somatic cell score (SCS), mastitis, and claw and leg disorders (CLDs) during first lactation in Holstein cows by using a threshold–linear random regression test-day model. We used daily records of milk, fat and protein yields; somatic cell count (SCC); and mastitis and CLD incidences from 46 771 first-lactation Holstein cows in Hokkaido, Japan, that calved between 2000 and 2009. A threshold animal model for binary records (mastitis and CLDs) and linear animal model for yield traits were applied in our multiple trait analysis. For both liabilities and yield traits, additive genetic effects were used as random regression on cubic Legendre polynomials of days on milk. The highest positive genetic correlations between yields and disease incidences (0.36 for milk and mastitis, 0.56 for fat and mastitis, 0.24 for protein and mastitis, 0.32 for milk and CLD, 0.44 for fat and CLD and 0.31 for protein and CLD) were estimated at about the time of peak milk yield (36 to 65 days in milk). Selection focused on early lactation yield may therefore increase the risk of mastitis and CLDs. The positive genetic correlations of SCS with mastitis or CLD incidence imply that selection to reduce SCS in the early stages of lactation would decrease the incidence of both mastitis and CLD.     

Effect of pregnancy on the genetic evaluation of dairy cattle

We investigated the effect of stage of pregnancy on estimates of breeding values for milk yield and milk persistency in Gyr and Holstein dairy cattle in Brazil. Test-day milk yield records were analyzed using random regression models with or without the effect of pregnancy. Models were compared using residual variances, heritabilities, rank correlations of estimated breeding values of bulls and cows, and number of nonpregnant cows in the top 200 for milk yield and milk persistency. The estimates of residual variance and heritabilities obtained with the models with or without the effect of pregnancy were similar for the two breeds. Inclusion of the effect of pregnancy in genetic evaluation models for these populations did not affect the ranking of cows and sires based on their predicted breeding values for 305-day cumulative milk yield. In contrast, when we examined persistency of milk yield, lack of adjustment for the effect of pregnancy overestimated breeding values of nonpregnant cows and cows with a long days open period and underestimated breeding values of cows with a short days open period. We recommend that models include the effect of days of pregnancy for estimation of adjustment factors for the effect of pregnancy in genetic evaluations of Dairy Gyr and Holstein cattle.     

Compositional analysis of dairy products derived from clones and cloned transgenic cattle

Cloning technology is an emerging biotechnological tool that could provide commercial opportunities for livestock agriculture. However, the process is very inefficient and the molecular events underlying the technology are poorly understood. The resulting uncertainties are causing concerns regarding the safety of food products derived from cloned livestock. There are similar concerns for livestock produced by biotechnologies which enable the purposeful introduction of genetic modifications. To increase the knowledge about food products from animals generated by these modern biotechnologies, we assessed compositional differences associated with milk and cheese derived from cloned and transgenic cows. Based on gross composition, fatty acid and amino acid profiles and mineral and vitamin contents, milk produced by clones and conventional cattle were essentially similar and consistent with reference values from dairy cows farmed in the same region under similar conditions. Whereas colostrum produced by transgenic cows with additional casein genes had similar IgG secretion levels and kinetics to control cows, milk from the transgenic cows had a distinct yellow appearance, in contrast to the white color of milk from control cows. Processing of milk into cheese resulted in differences in the gross composition and amino acid profiles; 'transgenic' cheese had lower fat and higher salt contents and small but characteristic differences in the amino acid profile compared to control cheese.     

Relationship between the magnitude of the inbreeding coefficient and milk traits in Holstein and Jersey dairy bull semen used in Brazil

Artificial insemination has been used to improve production in Brazilian dairy cattle; however, this can lead to problems due to increased inbreeding. To evaluate the effect of the magnitude of inbreeding coefficients on predicted transmitting abilities (PTAs) for milk traits of Holstein and Jersey breeds, data on 392 Holstein and 92 Jersey sires used in Brazil were tabulated. The second-degree polynomial equations and points of maximum or minimal response were estimated to establish the regression equation of the variables as a function of the inbreeding coefficients. The mean inbreeding coefficient of the Holstein bulls was 5.10%; this did not significantly affect the PTA for percent milk fat, protein percentage and protein (P = 0.479, 0.058 and 0.087, respectively). However, the PTAs for milk yield and fat decreased significantly after reaching inbreeding coefficients of 6.43 (P = 0.034) and 5.75 (P = 0.007), respectively. The mean inbreeding coefficient of Jersey bulls was 6.45%; the PTAs for milk yield, fat and protein, in pounds, decreased significantly after reaching inbreeding coefficients of 15.04, 9.83 and 12.82% (P < 0.001, P = 0.002, and P = 0.001, respectively). The linear regression was only significant for fat and protein percentages in the Jersey breed (P = 0.002 and P = 0.005, respectively). The PTAs of Holstein sires were more affected by smaller magnitudes of inbreeding coefficients than those of Jersey sires. It is necessary to monitor the inbreeding coefficients of sires used for artificial insemination in breeding schemes in Brazil, since the low genetic variability of the available sires may lead to reduced production.