Heritability Estimates for First Lactation Milk Yield of Registered and Nonregistered Holstein Cows

Heritabilities of milk yield and fat test were estimated from first lactation records of 196,672 Holstein daughter-dam pairs separately for registered and nonregistered cows for four milk yield groups and by years of freshening of the daughter. The model included herd-season and sire of the daughter. Heritability estimates were similar for registered and nonregistered cows averaging about .33 for milk yield and .62 for fat test. Estimates of heritability increased slightly over time for both milk yield and fat test. Heritability of fat test was similar for all groups. Heritability estimates for milk yield, however, averaged about .25 in low, about .35 in middle, and about .40 in high groups.     

Comparison of Heritability and Variation for Milk Yield of Registered and Nonregistered Holstein Cows

First lactation milk records of AI Holstein cows in the northeastern United States were analyzed for among and within-sire variation separately by year of freshening, class of herd production, and registry status of registered or non-registered with a model that included effects of herd-seasons, sires of sampling daughters, and sires of daughters of proven sires. Heritability from the paternal half-sib correlation among records of daughters of sampling sires was similar for registered and nonregistered cows. Differences in heritability in different years and class of herd production were similar to those found in previous analyses that ignored registry status. Residual variances were similar for records of registered and nonregistered cows. Differences in variances by year and class of herd production also were similar to those found in previous analyses. Residual variances of milk records increased with time and class of herd production and in the same year were distinctly larger in herds with higher production than in herds with lower production. Residual variances of logarithms of milk records changed little with time but in the same year were distinctly smaller in herds with higher production than in herds with lower production. Residual variances of square roots of milk records increased somewhat with time but in the same year were similar in different classes of herd production.     

Genetic and Phenotypic Relationships Between Lactation Cell Counts and Milk Yield and Composition of Holstein Cows

Monthly somatic cell count data were collected between February 1977 and February 1982 for Holstein cows in 928 herds enrolled on the Quebec Dairy Herd Analysis Service. The geometric mean of the log monthly cell counts was calculated for each lactation. Official lactation records for 305-day milk, fat, and protein yields, and fat and protein percents were obtained for same cows. There were 18,189 cows in first lactation representing 257 sires, 13,225 in second lactation representing 206 sires, and 8,683 in third lactation representing 151 sires. Heritabilities of yield traits and protein percent increased across three lactations. Heritability of fat percent was similar in first and third lactations but decreased slightly in second lactations. Heritability of lactation cell count was small, being least in second lactations. Genetic correlations between lactation cell count and yield traits were positive in first lactations, small and negative in second lactations, and small and positive in third lactations. Genetic correlations between lactation cell count and fat and protein contents were small in the three lactations. Phenotypic correlations between lactation cell count and production traits were small in each of the three lactations. Genetic correlations between yield traits in early lactation and lactation cell count in a subsequent lactation were positive. The genetic correlation between protein percent in an early lactation and cell count in a later lactation was large between first and second lactations, decreased between second and third lactation, and small between first and third lactations. Genetic correlations were small and negative for fat percent.     

Influence of Intake of Rumen Undegradable Protein on Milk Production of Late Lactation Holstein Cows

Twenty Holstein cows, in late lactation, were assigned to five equal groups in an orthogonal design to determine effects of a rapidly rumen degraded protein source (canola meal) low in estimated rumen undegradable protein substituted for a slowly rumen degraded protein source (corn gluten meal) high in rumen undegradable protein on feed intake, milk production, and milk composition. Cows were fed total mixed rations based upon barley silage, haycrop silage, barley grain, and supplemental protein in three 4-wk periods, subsequent to a 4-wk covariate period. In situ rumen incubation of extreme diets and estimation of intermediate diets indicated that all diets exceeded Agricultural Research Council (United Kingdom) recommendations for rumen degradable and undegradable protein as well as NRC recommendations for rumen degradable protein. However, two to four diets, dependent upon assumed ruminal turnover rates, did not meet NRC recommendations for undegradable protein. Dry matter intake and milk yield were not influenced by substitution of canola meal with corn gluten meal to increase dietary undegradable protein content. Daily yield and milk percent of lactose, fat, and protein were not influenced by substitution. Results do not support NRC recommendations to supplement diets based upon these ensiled forages and barley grain for late lactation cows with protein sources resistent to rumen degradation. Results broadly support lower amounts of rumen undegraded protein recommended by the Agricultural Research Council.     

Insoluble Nitrogen for Milk Production in Holstein Cows via Increases in Voluntary Intake and Nitrogen Utilization

Influences of insoluble and soluble N on milk production and N use were studied in 24 Holstein cows. The basal diet (grain: corn silage plus urea, 1:1 dry matter) contained 12% crude protein (60% insoluble N). Urea or soybean meal was added to the basal diet, increasing the crude protein to 15% with 43 and 67% insoluble N, respectively. Balance studies were performed during wk 4, 10, and 22 of lactation. Multiple regression analyses were performed on balance data adjusted for metabolic size to determine coefficients of soluble and insoluble N use. Intake of N, partitioned into insoluble and soluble N, accounted for 76, 30, 61, and 10% of the variation in dry matter intake, milk yield, milk N, and body weight^.75, respectively. Utilization coefficients for insoluble N were higher for dry matter intake, milk N, and weight^.75 but lower for milk yield. Urea supplementation increased dry matter intake; however, much of the milk yield by cows fed urea was attributed to a greater weight^.75 loss. In contrast, cows fed soybean meal as a source of insoluble N maintained both weight^.75 and higher milk production because of higher dry matter intake and more efficient use of N.     

Variation in Coagulation Properties of Milk from Individual Cows,

Milk samples from 50 Holstein cows were tested monthly for 10 mo for total protein, casein, fat, somatic cells, and pH. A Formagraph was used to measure chymosin coagulation properties. Significant variations in coagulation time and curd firmness were observed in relation to period of lactation, individual cows, and milk pH. A high negative correlation coefficient (?.86) was observed between coagulation time and curd firmness measured 30 min after addition of chymosin. The mean coagulation time generally increased as lactation progressed and milk yield decreased. Curd firmness was generally greatest in midlactation samples.Milk from 38% of the cows did not coagulate in 30 min 1 mo prior to their dry periods. The frequency of failure to coagulate was 68% in winter and 32% in fall. Milk pH was the most significant factor that affected coagulation time and curd firmness. Simulated cheese making procedures were utilized to estimate recovery of fat and protein in curd. Curd yield calculated from the recovery data ranged from 5.4 to 14% with a mean of 9.2%.     

Profitability in Daughters of High Versus Average Holstein Sires Selected for Milk Yield of Daughters

Data from 778 cows with 2,461 lactations through three generations of selection at the Iowa State University research herd were used to study differences between daughters of sires selected for high and breed-average Predicted Difference Milk. A profitability function, income minus expense, was calculated for each cow. A fixed, linear model was used to describe lifetime profitability. Daughters of high Predicted Difference Milk sires had 49% higher semen costs, 1% higher reproductive health costs, less than 1% fewer breedings, and less than 1% more reproductive examinations. They had 9% more respiratory costs, 6% more digestive costs, and 8% more skin and skeletal costs. Daughters of high Predicted Difference Milk sires produced 16% more milk, had 26% more mammary costs, and 42% more discarded milk costs. Disregarding breeding costs, they had 21% higher total health costs. Including breeding costs, total health costs were 32% higher. With 9% increased feed costs, they netted 18% more lifetime profit and 18% more profit per day of life. Use of a mixed model, which adjusted for fixed effects and included cows as random variables, showed daughters of high Predicted Difference Milk sires to have 12.5% more milk and 15.5% more profit per lactation. Number of breedings and reproductive examinations increased in later lactations and also in later generations as milk production increased in the daughters of high Predicted Difference Milk sires.     

Relation between Mastitis Test Score,Mineral Composition of Milk,and Blood Electrolyte Profiles in Holstein Cows

The relationship between mastitis, mineral composition of milk, and blood electrolyte profiles was investigated in 54 Holstein cows. Sodium potassium, calcium, magnesium, and chloride in blood and milk were compared under two indices of mastitis, a milk quality test and a milk somatic cell count. Milk from cows with evidence of udder infection had higher sodium and chloride and lower potassium than cows free of mastitis. Although there was a correlation between blood calcium and milk calcium and between milk calcium and milk somatic cell count, as well as differences in mean potassium and calcium in blood between mastitic and nonmastitic cows, there was no direct relationship between the indices of mastitis and electrolyte profiles of blood.     

Characteristics of Milk and Butter from Cows Fed Sunflower Seeds

Composition of milk and butter was evaluated from cows fed either control or experimental diets containing added fat of partially unsaturated fatty acid composition. The control diet concentrate mix consisted mainly of corn and soybean meal. The two experimental diets substituted either 20% high oleic sunflower seeds (>79% of fatty acids as oleic acid) or 20% regular sunflower seeds (>67% of fatty acids as linoleic acid) for part of the corn and soybean meal in the concentrate mix. Feeding lactating dairy cattle sunflower seeds resulted in lower concentrations of short and medium chain and higher concentrations of long-chain fatty acids in milk fat and butter. Milk unsaturated fatty acid concentrations were (28.9, 38.8, 45.6%), and butter unsaturated fatty acid concentrations were (29.6, 38.1, 44.3%) for control, high oleic sunflower seed, and regular sunflower seed treatment milk, respectively. Organoleptic evaluation indicated the high oleic sunflower seed and regular sunflower seed treatment butters were equal or superior in flavor to the control butter. The high oleic sunflower seed and regular sunflower seed treatment butters were softer, more unsaturated, and exhibited acceptable flavor, manufacturing, and storage characteristics.     

Selection of Young and Proven Holstein Artificial Insemination Sires to Maximize Profits from Milk

Net present values of genetic investments in young and proven artificial insemination Holstein sires were calculated to determine profit-maximizing proportions of these genetic resources. The sensitivity of profit from young sires was evaluated by varying semen cost from 0 to $5 per unit and comparing average net present values of young and proven sires. Data for proven sires were retail semen prices and Predicted Differences (1974 base) for yields of milk and fat of 449 bulls available for purchase after the July 1983 USDA sire summary. Data for young sires concurrently used in fall 1983 were Predicted Differences of sires and maternal grandsires of 260 bulls for random sampling and 32 bulls-in-waiting from four artificial insemination organizations. Net present values of milk income were calculated using a real interest rate of 3% with alternative conception rates to first service (30 and 50%) and number of generations (one and infinite) of descendants in the planning horizon.Relative rankings of young and proven bulls were same for each conception rate and planning horizon; thus, only net present values for 50% conception rate and one generation planning horizon are reported. Average profitability of young sires for sampling was equal to average profit from proven bulls when young sire semen cost $5/unit and was $36 (.7 standard deviation) more profitable than average proven sires when young sire semen cost was nil. Mean net present value of young sires for sampling ranked at 42nd percentile of proven sires when semen cost $5/unit or 69th percentile of proven sires when semen cost was nil. Therefore, profit-maximizing dairy producers have no economic incentive to mate cows to random young sires when free to select and obtain semen from at least the top 30% of proven bulls at current prices. For semen cost of $5/unit, there was incentive to replace with young sires up to 40% of the least profitable proven bulls. Decreases (increases) in cost of semen of young sires relative to the less profitable proven bulls would increase (decrease) the proportion of proven sires that should be replaced by random young sires.     

Relationship of Temperature and Humidity to Conception Rate of Holstein Cows in Hawaii

Weather data and breeding records for a Holstein herd of 1300 cows in Hawaii were evaluated to determine effects of climate on reproductive performance. The dairy is in a coastal climate near latitude 21°N. Average maximum temperature, relative humidity, and resulting temperature-humidity index for the warmest month of the year were 31 C, 44%, and 79. Average minimum temperature and attending values for the same period were 20 C, 96%, and 68. From late April to November, conception rates were correlated negatively with the average temperature-humidity index of each day of the estrous cycle beginning 11 days prior to breeding. Slopes of regression lines differed, suggesting varying sensitivity of conception rate to heat stress on different days of the cycle. The temperature-humidity index of the 2nd day prior to breeding was most closely correlated with conception rate. Conception rates declined from 66% to 35% as the index increased from 68 to 78. Only the temperature-humidity index of the 2nd day prior to breeding had a significant partial correlation coefficient when the index of the 2nd and 1st day prior to breeding, the day of breeding, and the day following breeding were each evaluated with the index of the others held constant.     

牛初乳中可的松和氢化可的松质量分数变化

选择了5头荷斯坦牛利用液相-气质谱法分析了产后7 d内牛初乳中和常乳中可的松和氢化可的松质量分数变化.结果表明,不同天数的牛初乳中可的松质量分数无显著差异(P＜0.05),与常乳相比也无差异.牛初乳和常乳中可的松质量分数变化范围为2.16～0.51 μg/kg同样,不同天数的牛初乳中氢化可的松质量分数无显著差异(P＜0.05).与常乳相比也无差异.经统计相关分析表明,可的松含量与泌乳时间显著负相关(r=0.93,P=0.003).只有产后5 d内乳汁中氢化可的松含量与泌乳时间正相关(r=0.91,P=-0.03),随着泌乳时间的延长无相关性.     

Relationships Between Milk Protein Polymorphisms and Major Milk Constituents in Holstein-Friesian Cows

Milk samples from 1,908 Holstein Friesian cows were phenotyped for genetic variants of α_s1 -casein, β-casein, κ-casein, and β-lactoglobulin. The relationships between milk protein polymorphism and test day milk yield and composition were investigated. After adjustments were made for environmental effects of herd, parity number, month of test, stage of lactation, age of sample at testing, and somatic cell count, milk protein phenotypes were found to be associated with milk yield; concentrations in fat, protein, casein, and whey protein; and proportion of casein in protein. Higher test-day milk production was associated with α_s1-casein BB, β-casein A1A3, κ-casein AA, and β-lactoglobulin AA phenotypes. Fat and protein concentrations were highest in milk from cows of α_s1-casein BC, β-casein A1B, and κ-casein BB phenotypes. β-Lactoglobulin BB milk was associated with higher percentages of fat and casein and with lower percentages of total protein and whey protein. Based on desirable fat and casein contents of milk for cheese production, it would be advantageous to select for cows bearing κ-casein BB and β-lactoglobulin BB phenotypes.     

不同锌源对奶牛产奶量和乳品质的影响

本试验采用3×3拉丁方设计,将9头中国荷斯坦奶牛分为3组,分别饲喂对照组基础日粮,补加蛋氨酸锌日粮(锌含量400mg),补加氧化锌日粮(锌含量400mg),研究补饲不同锌源对奶牛产奶量及乳品质的影响。结果表明,不同来源的锌对奶牛产奶量均有不同程度提高,蛋氨酸锌提高幅度大于氧化锌,但差异不显著(p>0.05);对乳脂率无明显影响;补锌可增加乳中锌的含量,蛋氨酸锌比氧化锌明显(p<0.05)。     

灌注法生产α - 亚麻酸牛奶的氧化稳定性研究

在泌乳奶牛十二指肠中增量灌注富含游离亚麻酸的紫苏油,采集获得的实验奶样,将其分别放置在4℃和20℃条件下避光保存0、72h 和120h,观察贮存条件对于实验奶样氧化稳定性的影响。结果发现：实验奶样在0h 保存时,其氧化稳定性随着灌注剂量的增加具有降低趋势;在4℃保存72h,其氧化稳定性伴随灌注剂量的增加呈显著降低,而在保存120h 后,其氧化稳定性又趋于平稳状态;在20℃中保存72h,随着灌注剂量的增加,其氧化稳定性出现降低趋势,而在保存120h 后,其氧化稳定性显著降低。结果表明：通过十二指肠灌注紫苏油生产的富含亚麻酸牛奶,其氧化稳定性受到乳中脂肪酸组成的影响。     

Milk protein polymorphisms in Holstein cattle†

Milk samples from 203 Holstein cows were phenotyped for genetic variants α_s1‐casein, β‐casein, κ‐casein and β‐lactoglobulin using starch‐gel electrophoresis. All of the four milk protein loci exhibited polymorphism with allele frequencies of 0.862 ± 0.017 for α_s1‐casein B, 0.966 ± 0.0009 for β‐casein A, 0.712 ± 0.0224 for κ‐casein A and 0.567 ± 0.0245 for β‐lactoglobulin B. The mean heterozygosity estimated over all the four milk protein loci was 0.3015. Genetic equilibrium was observed among all of the loci investigated, except κ‐casein. Chi‐squared tests revealed that there was no significant linkage among studied milk protein phenotypes.     

Factors Associated with Variation in Milk Fat Depression Resulting from High Grain Diets Fed to Dairy Cows

Thirty lactating Holstein cows were used in a crossover design with 4-wk periods to establish the relationship between chewing activity, molar proportions of ruminal volatile fatty acids, and milk fat depression resulting from feeding high grain-low forage diets. Milk production and dry matter intake were not affected by treatment. When cows were fed the high grain-low forage diet, milk fat decreased from 3.39 to 2.87%, ruminal acetate plus butyrate:propionate ratio decreased from 2.7 to 2.0, and total chewing time decreased from 659 min/24 h to 472 min/24 h. Percentage change in milk fat test between treatments was correlated to percentage change in the ruminal molar proportion of acetate, propionate, acetate plus butyrate:propionate ratio, and percentage change in total chewing time per kilogram neutral detergent fiber intake (n = 30, r = .38, −.50, .53, and −.30, respectively). More correlation coefficients were significant and correlations were higher if only cows that proceeded from control to high grain-low forage treatment were considered. As milk fat depression was increased by high grain feeding, magnitude of depression in chewing activity was decreased. Within treatment, time spent chewing increased as milk fat percentage decreased.     

Rates of Milk Flow and Milking Times Resulting from Selection for Milk Yield,

Responses to selection for milk yield for rates of milk flow and times for milking were studied using data from an experimental herd of Holsteins. In 1964, foundation cows were paired by sire and randomly split into two genetic groups, selection and control. Four highest bulls for Predicted Difference milk were mates for selection cows each year and replaced annually. Twenty bulls near breed average for milk in 1964 were mated continuously to control cows. Beginning in 1972, milk yield at 15-s intervals was recorded by using a stopwatch and milk meter. Lactations for 130 selection and 162 control cows were observed over 10 yr. Selection cows did not differ from controls during first lactation for rate of milk flow but took longer to milk until stripping. When adjustment was made for milk yield at the observed milking, pedigree groups did not differ for milking time until stripping. Data from all cows suggested that rates of milk flow were also greater for selection cows. First parity heritabilities were .46 (peak rate), and .68 (milking time until stripping). Genetic and phenotypic correlations of milk yield with rates of flow and milking times were positive.