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PubMed1992

Genetic parameters of conformation traits, milk yield, and herd life in Holsteins.

Genetic parameters were estimated simultaneously for 5 herd-life traits, 15 conformation (type) traits, and milk yield measured in first lactation for 128,601 Holstein cows. Heritabilities of all traits were higher in registered than in grade cows. Genetic correlations of linear type traits with first lactation yield ranged from -.48 for udder depth to .54 for dairy form. Genetic correlations among milk yield and herd-life traits were all positive except for milk-corrected herd life in grade cows. Udder traits had largest absolute genetic correlations with herd-life traits, followed by body traits and feet and leg traits. Some traits associated with body size and foot angle differed between registered and grade cows. Estimates of genetic trends from obtained parameters revealed greatest progress for milk yield from single-trait selection but also the largest changes for some type traits and milk-corrected herd life in an undesirable direction. Relative milk to type ratios of between 2:1 and 3:1 yielded 90% of the gain in milk yield with no change or slight improvement in type traits and functional herd life. Selection for type traits associated with herd life appears to be warranted to improve days of functional herd life or to decrease involuntary culling of dairy cows.

Animals↗
PubMed1993

Effect of increasing ruminal butyrate on milk yield and blood constituents in dairy cows fed a grass silage-based diet.

The effects of increased ruminal supply of butyrate on milk yield, milk composition, and blood metabolites were studied in four lactating cows in a 4 x 4 Latin square design. The basal diet comprised grass silage, hay, and concentrate (34:22:42, DM basis) and was supplemented with isoenergetic VFA infusions (3.58 Mcal/d). A 3:1 molar mixture of acetate and propionate was replaced gradually with butyrate at the rates of 0, 200, 400, or 600 g/d. When the amount of infused butyrate increased, isobutyrate, butyrate, and isovalerate in plasma and acetoacetate and beta-hydroxybutyrate in whole blood increased linearly, but plasma glucose concentration decreased. The latter was associated with a trend toward higher plasma urea concentration, suggesting that more AA were used for gluconeogenesis as the supply of propionate decreased and that of butyrate increased. Milk yield was not changed. The concentrations of milk fat and protein increased, and that of lactose decreased linearly, with the rate of butyrate infusion. Milk fat yield increased, and lactose yield tended to decrease, with increased butyrate infusion. These results indicate that changes in the supply of butyrate do not affect markedly milk yield in cows yielding less than 20 kg/d but cause marked changes in milk composition. The increase in ruminal butyrate supply increased ketogenesis and decreased gluconeogenesis in the liver of lactating dairy cows.

3-Hydroxybutyric Acid↗
PubMed1993

Interactions of high milk yield and reproductive performance in dairy cows.

Correlations between reproductive traits and measures of milk yield indicate that higher yield is associated phenotypically and genetically with reduced reproductive performance in lactating cows. Numerous recent studies have reported that reproductive performance is compromised, primarily through delayed ovarian activity and reduced conception rates, by the demands of high milk yield. However, daily managerial decisions to obtain efficient reproductive performance have considerable impact. Management can offset depression in fertility, because high yielding herds often achieve the fewest days open. Selection for milk yield has increased blood concentrations of somatotropin and prolactin, stimulators of lactation, and decreased insulin, a hormone that is antagonistic to lactation and may be important for normal follicular development. These changes in hormone concentrations promote higher milk yield but may be potentially detrimental to other physiological functions, such as reproduction, if the management is not adequate to meet the metabolic demands of lactation. Timing and magnitude of negative energy balance apparently interact to determine the extent to which negative energy balance alters hypothalamic secretion of GnRH and its effect on gonadotropin secretion and, therefore, ovarian secretion of progesterone, which affects expression of estrus and support of the uterus during early pregnancy.

Animals↗
PubMed1994

Factors influencing variation of test day milk yield, somatic cell count, fat, and protein in dairy sheep.

Between January and July 1992, 8403 monthly test day records were obtained from 3202 ewes from 22 Churra dairy flocks in the Castilla-León region of Spain. Variables measured were milk yield, SCC, and fat and protein percentages; means were 912 ml, 1501 x 10(3) cells/ml, 6.76%, and 6.28%. Analysis of variance showed significant effects of flock, stage of lactation, parity, and type of birth on milk yield, SCC, and composition. Variability in SCC among flocks was high and ranged from 420 to 2719 x 10(3) cells/ml. During lactation, SCC and fat and protein percentages showed increases of 31.2, 37.6, and 20.3%. Twin birth ewes had higher SCC (8.6%) and yield (4.4%) than single birth ewes. However, fat and protein fell 1.7 and .8% in twin birth ewes. The parity effect was highly significant for yield, SCC, and fat; first lactation was always lower. A statistical model similar to that for dairy cattle was used to predict milk yield on the basis of flock, ewes within the flock, lactation stage, parity number, type of birth, and SCC. The model predicted 73% of the variation in milk yield.

Animals↗
PubMed1994

Effects of calving season and milk yield on pregnancy risk and income in North Carolina Holstein cows.

Effects of season of calving and milk yield and their potential interaction on days from calving to last breeding were investigated using survival analysis and an economic model in 2000 Holstein cows that calved during 1989 and 1990. The final Cox proportional hazards model included lactation number, calving season, and herdmate deviation FCM. The interval from calving to last breeding ranged from 40 to 570 d. Compared with cows that calved in fall, cows that calved in summer were two-thirds as likely to become pregnant. Conversely, cows calving in winter or spring were more likely to become pregnant. Milk yields beyond approximately 8025 kg lowered the risk of pregnancy. The interaction of season and yield was nonsignificant, suggesting that these factors may act independently to affect reproduction. Lower pregnancy rates associated with high yield were detected earlier postpartum than were lower rates associated with calving in summer. Within each season, higher yield offset the lower income over feed costs associated with poorer reproductive performance. Nevertheless, summer calving lowered income over feed costs per cow per year by $98, $2, $176, and $68 for low, medium to low, medium to high, and high yielding cows, respectively.

Animal Feed↗
PubMed1994

Genetic parameters of test day measures for somatic cell count, milk yield, and protein percentage of milking ewes.

Records from monthly test days for milk yield, natural log-transformed SCC, and protein percentage of 10,171 records of 3832 Spanish Churra ewes in 24 herds were analyzed to estimate genetic parameters. Heritabilities and genetic and phenotypic correlations for test day records were estimated using multivariate REML with an animal model, accounting for the effects of litter size, test day within herd group, age at lambing, and month in milk. Heritabilities for test day records of milk, log SCC, and protein percentage were .34, .04, and .13, respectively. Genetic correlations of test day measures of SCC with milk yield and protein percentage were -.37 and .37, respectively; phenotypic correlations were -.05 and .19. Considered as a random effect, test day within herd accounted for 28 and 17% of the total variance of test day milk yield and test day SCC, respectively. The correlation between milk yield and SCC because of the test day within herd, the covariation factor, was estimated to be -.16. Results indicate a moderately high heritability for milk yield, a low heritability for SCC, and moderate, negative genetic relationships between measures of SCC in milk and milk yield.

Animals↗
PubMed1994

Deaths and disposals in lines selected for milk yield and control lines of Jersey cattle.

Deaths and disposals of Jerseys from birth to 120 d of first lactation during a selection experiment were summarized. Cows were randomly assigned to the high milk yield and young sire lines. Service sires were bulls with the highest estimated breeding value for milk for the high milk line and a collection of all young unproven bulls available in AI in 1967. Cattle that were unsuitable for conditions of normal herd management were candidates for culling. Culling of uncalved heifers and of lactating cows was also permitted to maintain group sizes. Culling for herd reduction was random. Culling for low milk yield was permitted after cows reached 120 d of first lactation. Death and disposal data were analyzed through 120 d of first lactation. By 120 d of first lactation, 29.6% of females born to the young sire line had died or been involuntarily removed compared with 29.8% born to the high milk yield line. Deaths were 54.8% of total losses for the high milk yield line compared with 58.4% for the young sire line. Stillbirths were a larger proportion of total losses for animals in the high milk yield line (21.4%) than for those in the young sire line (15.3%). The most frequent cause of death was scours and pneumonia during 1st mo of life for animals in both lines. Selection of sires for high milk yield does not decrease total survival rates through the early first lactation.

Animal Husbandry↗
PubMed1995

The association between previous 305-day milk yield and disease in New York State dairy cows.

Logistic regression was used to examine the association between milk yield and disease. We studied 8070 cows of second or higher parity from 25 New York State Holstein herds, calving between June 1990 and November 1993. Previous 305-d mature equivalent milk yield was used because most of the disorders studied occurred too early in lactation for current milk yield to be considered. Seven disorders were studied: retained placenta, metritis, ovarian cyst, milk fever, ketosis, abomasal displacement, and mastitis. A separate model was used for each disorder. Each model included, in additional to milk yield, parity, calving season, and heard. Results showed that higher milk yield was not a risk factor for any disease except mastitis. However, the association between higher previous milk yield and mastitis does not necessarily imply causation.

Animals↗
PubMed1996

Estimates of genetic trend for yield traits of the registered Jersey population.

Data for American Jersey cattle from 1960 to 1990 were used to study genetic progress achieved by four paths of selection (sires of bulls, dams of bulls, sires of cows, and dams of cows). Possible methods of obtaining optimal genetic gain for the breed were suggested by the analysis. The generation interval by year of birth for parents of AI bulls was greater from 1975 to 1984 than for most recent 5 yr (1983 to 1987) because previously the use of old proven bulls was greater. Sires of bulls tended to have a longer average generation interval (9.3 yr) than the more nearly optimal interval reported in the literature for AI populations (7.0 yr). Selection differentials for the last 5 yr were larger than the average over all years for milk yield, fat yield, protein yield, and fat percentage. More intense selection for sires of bulls gave a larger increase in PTA over time than did other paths of selection. When all paths of selection were combined, estimated annual genetic change for the Jersey breed was greater from 1983 to 1987 than from 1960 to 1987 for milk yield, fat yield, protein yield, and fat percentage. Potential genetic response from the sires and dams that were available to produce sons was greater than the response from parents actually used. Therefore, better sires and dams were available for genetic enhancement of their progeny than those actually used to produce young sires and replacement females.

Animals↗
PubMed1996

Phenotypic relationship of yield and type scores from first lactation with herd life and profitability.

Milk records from Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn cows that first calved between 18 and 35 mo were combined with scores for linear type traits collected before 43 mo during first lactation to study herd life and lifetime profitability. Profitability (discounted relative net income) was the value of milk, calves, and cow salvage minus fixed costs, operating costs, and cow depreciation costs. Cows were included if they appeared only in a single herd and if the herd remained on test for 72 mo after birth date of the cow. Phenotypic correlations were computed for milk and fat yields and for 14 type traits during first lactation with nine variables for lifetime performance from 3895 Ayrshire, 7997 Brown Swiss, 20,179 Guernsey, 71,731 Jersey, and 628 Milking Shorthorn cows. Multiple correlations for predicting discounted relative net income for the four breeds with the most data were 0.43 to 0.46 from milk and fat yields (linear and quadratic effects) during first lactation, 0.11 to 0.29 from final score, and 0.21 to 0.33 from all type traits. Type scores had considerably less predictive ability than yield during first lactation for predicting profitability and had limited predictability after yield was included. Final score increased multiple correlations only 0.00 to 0.02 above that for yield for the same four breeds. Final score plus 13 type traits (linear, quadratic, and interaction effects) increased multiple correlations only 0.02 to 0.04 above that for yield. Because of the limited value of some of the linear type traits, an effort should be initiated to eliminate them from programs of breed associations.

Aging↗
PubMed1996

Change in body condition score of Holstein cows as affected by parity and mature equivalent milk yield.

Cows from 25 dairy herds were scored for body condition at 3-mo intervals for over 2 yr to study the pattern of changes during lactation and the effects of parity and milk yield capability of cows on changes in body reserves. Data were recorded for 1395 Holstein cows grouped into three parity classes and five classes of mature equivalent milk yield. The analysis model accounted for nearly 70% of the variation in body condition score. Body reserves decreased during early lactation until about 100 DIM and were restored during mid and late lactation. The pattern of change in body condition score varied among lactations and dairy merit of cows. Depletion and subsequent recovery of body reserves were less intense for primiparous cows than for multiparous cows. Loss of body condition scores was higher and more prolonged for cows of higher dairy merit. The minimum body condition score occurred at 3 mo after calving for the worst yielding cows and at 4 mo after calving for the best yielding cows; the highest yielding cows had twice the loss in body condition as the lowest yielding cows. General equations are presented as a proposed guideline to examine changes in body condition score of Holstein cows of different parities and dairy merit.

Adipose Tissue↗
PubMed1997

Yield response of lactating Holstein dairy cows to dietary fish meal and bone meal.

Experiments were conducted to examine the effects of the source and amount of dietary protein on yield and composition of milk from Holstein dairy cows. Study 1 used 36 multiparous cows at 125 +/- 59 d in milk in, a replicated 2 x 2 Latin square design. Treatments were diets formulated to contain 16% crude protein (CP) in which 11% was fish meal or meat and bone meal supplied 11% of dietary CP. Intakes of dry matter, CP, and net energy for lactation; yields of milk; and percentage of milk fat were not affected by treatment. Fish meal increased contents of milk total N, casein N, and noncasein N but did not increase contents of NPN; fish meal also tended to increase milk CP yields. Study 2 used 78 cows (31 primiparous) at 31 +/- 2 d in milk in a randomized block design. Two treatment diets were formulated to contain 16 or 18.5% CP, and soybean meal was the sole source of supplemental protein in those diets. The two other treatment diets were, formulated to contain 16% CP; in these diets, fish meal or meat and bone meal partially replaced soybean meal. Treatments did not influence yield or composition of milk from multiparous cows. Compared with a soybean meal diet containing 16% CP, a soybean meal diet containing 18.5% CP or diets containing 16% CP and containing meat and bone meal or fish meal increased the milk, yield of primiparous cows similarly. Fish meal or meat and bone meal increased the efficiency of protein utilization for milk yield.

Animals↗
PubMed1997

Pit-1 gene polymorphism, milk yield, and conformation traits for Italian Holstein-Friesian bulls.

The growth hormone factor-1/pituitary-specific transcription factor Pit-1 is responsible for the expression of growth hormone in mammals. Mutations in Pit-1 have been found in growth hormone disorders of mice and humans. We studied the eventual association between Pit-1 polymorphism using the HinfI enzyme and the milk yield and conformation traits of 89 Italian Holstein-Friesian bulls. A strategy employing polymerase chain reaction was used to amplify a 451-bp fragment from semen DNA. Digestion of polymerase chain reaction products with HinfI revealed two alleles: allele A was not digested (451-bp fragment), and allele B was cut at one restriction site, generating two fragments of 244 and 207 bp. Three patterns were observed; frequencies were 2.2, 31.5, and 66.3% for AA, AB, and BB, respectively. Fixed and mixed linear models were fitted on daughter yield deviations for milk yields and on deregressed proofs for conformation traits. Predictions were weighted using the inverse of the estimated variance of records. The models used contained mean and gene substitution effects for Pit-1 A allele as fixed effects and random sire effect for the mixed model. The A allele was found to be superior for milk and protein yields, inferior for fat percentage, and superior for body depth, angularity, and rear leg set, which is difficult to explain. A canonical transformation revealed that Pit-1 had three actions, one linked to milk yield traits and angularity, a second linked to body depth and rear leg set, and a third linked to lower fat yields and to higher angularity.

Animals↗
PubMed1998

Genetic parameters of health disorders, and relationships with 305-day milk yield and conformation traits of registered Holstein cows.

A total of 4368 first lactation records for Holstein cows from 30 herds was used to estimate genetic parameters for yield, conformation traits, and the binary coded disease traits of udder edema, milk fever, retained placenta, metritis, displaced abomasum, ketosis, cystic ovary, mastitis, and lameness. Data on health, parentage, and yield came from an on-farm program for record keeping and management. Test day production data were obtained from British Columbia DHI. Type classification data were received from the Holstein Association of Canada. Heritabilities of disease traits were low ranging from 0 to 0.05. Exceptions were lameness (0.16) and ketosis (0.39). Correlations of disease traits with 305-d milk yield and of selected type traits with retained placenta, displaced abomasum, mastitis, and lameness were estimated. Phenotypic correlations did not substantially differ from 0 except for the correlation between lameness and rear leg set (0.37). Genetic correlations between disease traits and milk yield were mostly positive (0.02 to 0.44). Only retained placenta had a negative genetic correlation with milk yield (-0.28). Genetic correlations ranged from 0 to 0.37 between udder conformation traits and mastitis, from -0.38 to 0.09 between leg conformation traits and lameness, and from -0.11 to 0.38 between rump conformation and retained placenta. The results suggest that selection based solely on yield may increase the incidence of disease. Selection on conformation traits can help reduce the incidence of disease, although genetic correlations are low.

Abomasum↗
PubMed1998

Heritability of test day somatic cell counts and its relationship with milk yield and protein percentage in dairy ewes.

A total of 6620 monthly test day records of SCC, milk yield, and protein percentage from single lactations of 2374 Spanish Churra ewes from 10 flocks was used to estimate genetic and environmental parameters. A subset of 4278 records containing data from healthy udders (SCC < or = 250,000 cells/ml) was also analyzed. Genetic parameters were estimated by REML using an animal model. Herd test date, parity, and lactation stage contributed significantly to variation of most variables, and birth type significantly affected milk yield only. The SCC increased markedly as parity number and stage of lactation increased. Heritabilities (+/- SE) for test day milk yield, log SCC, protein percentage, and log SCC (< or = 250,000 cells/ml) were 0.18 (0.03), 0.09 (0.02), 0.16 (0.03), and 0.03 (0.02), respectively. The corresponding repeatabilities were 0.54, 0.38, 0.38, and 0.10. Genetic correlations of log SCC with milk yield and protein percentage were -0.23 and 0.18, respectively. Phenotypic correlations were -0.15 and 0.16. Genetic and environmental reduction of SCC for dairy ewes could be achieved using practices similar to those for dairy cows. The negative genetic correlation between milk yield and SCC suggested that selection for increased milk yield alone is expected to result in a decrease in SCC.

Animals↗
PubMed1999

Comparison of test interval and best prediction methods for estimation of lactation yield from monthly, a.m.-p.m., and trimonthly testing.

A method with best prediction properties that condenses information from all test days into measures of lactation yield and persistency has been proposed as a possible replacement for the test interval method and projection factors. The proposed method uses previously established correlations between individual test days and includes inversion of a matrix for each lactation. Milk weights that were representative of monthly, a.m.-p.m., and trimonthly test plans were examined to compare the accuracy of best prediction and test interval methods for estimating lactation yield. Individual milk weights or daily yields of 658 Canadian cows in 17 herds were selected to correspond to test intervals for 100,000 US cows. For a.m.-p.m. testing, the initial milk weight that was credited was selected randomly from the a.m. or p.m. milking and was alternated thereafter. Trimonthly credits were from one of the first three designated test day weights, selected randomly, and each third designated test weight thereafter. Correlations between 305-d actual lactation yield and lactation estimates by the test interval method were 0.97, 0.96, and 0.93 for monthly, a.m.-p.m., and trimonthly testing, respectively. Corresponding correlations for the best prediction method were 0.97, 0.97, and 0.93. Standard deviations of differences between estimated and 305-d actual yields for monthly, a.m.-p.m., and trimonthly testing were 373, 400, and 546 kg, respectively, for best prediction regressed on herd mean, which was a reduction in estimation error of 4, 6, and 10% over the test interval method. The advantage of best prediction was moderate if two milk weights were recorded monthly and was larger if testing was less frequent. Advantages also were found for fat and protein yields estimated by multitrait best prediction for records with reduced component sampling.

Animals↗
PubMed1999

Genetic parameters of lactation cell counts and milk and protein yields in dairy ewes.

A total of 3231 lactation records of somatic cell counts (SCC), milk yield, and protein percentage for 2379 Spanish Churra ewes from 10 flocks were used to estimate genetic and environmental parameters. Genetic parameters were estimated by REML with a multitrait repeatability animal model. A lactation measure of SCC was obtained as the mean of test day log SCC adjusted for stage of lactation. Heritabilities for SCC, milk yield, and protein percentage were 0.12, 0.24, and 0.17, respectively. The corresponding repeatabilities were 0.35, 0.49, and 0.38. Heritability and repeatability estimates of SCC obtained from this study fell within the range frequently reported for dairy cows. Therefore, as practiced for dairy cattle, future possibilities for sire evaluation to improve udder health status using lactation measures of SCC for dairy sheep are not rejected, although hygienic practices are regarded as more important. Genetic correlations of SCC with milk yield and protein percentage were -0.15 and -0.03, respectively. The genetic correlation between milk yield and protein percentage was -0.47. The low genetic correlations of SCC with milk yield and protein percentage may indicate that breeding decisions to improve milk and protein yields of Churra ewes are not expected to have an effective correlated response in SCC.

Analysis of Variance↗
PubMed1999

Effects of photointensity and photoperiod on milk yield and reproductive performance of Norwegian red cattle.

Relationships between light exposure, milk yield, and reproductive traits in Norwegian Red cattle were studied using data from 1538 farms in southern Norway during the darkest part of the year (November 1 to February 28). Production level was expressed as milk yield at first artificial insemination (AI) and 305-d milk yield. Reproductive performance was calculated using the following dependent variables: age at first AI, age at first calving, days open, calving interval, number of AI per cow, and nonreturn rate at 60 d. Days open and calving interval were both 4.0 d shorter, number of AI per cow was 0.07 less, non-return rate was 3.1% greater, and daily milk yield at first AI was 0.5 kg greater in herds that used dim illumination at night compared with herds that used no illumination at night. Milk yield at first AI was 0.5 kg greater in herds with photoperiods > 12 h. Photoperiods > 12 h were associated with a reduction in age at first AI by 4.8 d and age at first calving by 6.6 d. We concluded that dairy cattle kept at high latitudes during winter should be exposed to dim illumination at night and a minimum photoperiod of 12 h to stimulate reproductive performance and milk yield.

Animals↗