Single-step genomic predictions for heat tolerance of production yields in US Holsteins and Jerseys.

The physiological stress caused by excessive heat affects dairy cattle health and production. This study sought to investigate the effect of heat stress on test-day yields in US Holstein and Jersey cows and develop single-step genomic predictions to identify heat tolerant animals. Data included 12.8 million and 2.1 million test-day records, respectively, for 923,026 Holstein and 153,710 Jersey cows in 27 US states. From 2015 through 2021, test-day records from the first 5 lactations included milk, fat, and protein yields (kg). Cow records were included if they had at least 5 test-day records per lactation. Heat stress was quantified by analyzing the effect of a 5-d hourly average temperature-humidity index (THI5d¯) on observed test-day yields. Using a multiple trait repeatability model, a heat threshold (THI threshold) was determined fowr each breed based on the point that the average adjusted yields started to decrease, which was 69 for Holsteins and 72 for Jerseys. An additive genetic component of general production and heat tolerance production were estimated using a multiple trait reaction norm model and single-step genomic BLUP methodology. Random effects were regressed on a function of 5-d hourly average (THI5d¯) and THI threshold. The proportion of test-day records that occurred on or above the respective heat thresholds was 15% for Holstein and 10% for Jersey. Heritability of milk, fat, and protein yields under heat stress for Holsteins increased, with a small standard error, indicating that the additive genetic component for heat tolerance of these traits was observed. This was not as evident in Jersey traits. For Jersey, the permanent environment explained the same or more of the variation in fat and protein yield under heat stress indicating that nongenetic factors may determine heat tolerance for these Jersey traits. Correlations between the general genetic merit of production (in the absence of heat stress) and heat tolerance genetic merit of production traits were moderate in strength and negative. This indicated that selecting for general genetic merit without consideration of heat tolerance genetic merit of production may result in less favorable performance in hot and humid climates. A general genomic estimated breeding value for genetic merit and a heat tolerance genomic estimated breeding value were calculated for each animal. This study contributes to the investigation of the impact of heat stress on US dairy cattle production yields and offers a basis for the implementation of genomic selection. The results indicate that genomic selection for heat tolerance of production yields is possible for US Holsteins and Jerseys, but a study to validate the genomic predictions should be explored.

Heritability estimates associated with alternative definitions of mastitis and correlations with somatic cell score and yield.

The objectives of this study were to compare alternative mastitis definitions and to estimate genetic correlations of producer-recorded mastitis with somatic cell score (SCS) and yield. Cow health events and lactation records from June 2002 through October 2007 were provided by Dairy Records Management Systems (Raleigh, NC). First- through fifth-lactation records from cows calving between 20 and 120 mo of age and that calved in a herd-year with at least 1% of cows with a clinical mastitis event were retained. The edited data contained 118,516 lactation records and 1,072,741 test-day records of 64,893 cows. Mastitis occurrence (1 = at least one mastitis event during lactation or test-day interval, 0 = no mastitis events), number of mastitis events during lactation, SCS, and yield were analyzed with animal models (single trait) or sire-maternal grandsire models (multiple trait) in ASREML. Comparisons were made among models assuming a normal distribution, a binary distribution, or Poisson distribution (for total episodes). The overall incidence of clinical mastitis was 15.4%; and heritability estimates ranged from 0.73% (test-day interval mastitis with a linear model) to 11.07% (number of mastitis episodes with a Poisson model). Increased mastitis incidence was genetically correlated with higher SCS (range 0.66 to 0.88) and was generally correlated with higher yield (range -0.03 to 0.40), particularly during first lactation (0.04 to 0.40). Significant genetic variation exists for clinical mastitis; and health events recorded by producers could be used to generate genetic evaluations for cow health. Sires ranked similarly for daughter mastitis susceptibility regardless of how mastitis was defined; however, test-day interval mastitis and a total count of mastitis episodes per lactation allow a higher proportion of mastitis treatments to be included in the genetic analysis.

Voluntary waiting period management practices in dairy herds participating in a progeny test program.

A survey was mailed to approximately 4,000 herds participating in a young sire progeny test program to estimate the percentage of herds that selectively alter the voluntary waiting period (VWP) for individual cows or groups of cows. Responses were received from 673 herds (17%; 583 Holsteins, 55 Jerseys, 35 other dairy breeds). The mean VWP cited by respondents was 56 +/- 0.6 d (range = 30 to 90 d) and did not differ by breed. Among responding herds, 64% (432/673) indicated the VWP was selectively altered for one or more reasons. The most frequently cited reasons for altering the VWP were postpartum health (50%), season (18%), milk yield (18%), parity (14%), and other reasons (14%). In Holstein herds that altered the VWP based on milk yield, the highest production group averaged 14 more days to first service than the lowest production group (> or =40 vs. <20 kg of energy-corrected milk, respectively). In contrast, days to first service were nearly identical for all production groups in Holstein herds that did not vary the VWP based on milk yield. In conclusion, management decisions to selectively alter the VWP led to differences in days to first service and may have a confounding effect on genetic estimates of daughter fertility. Opportunities to improve the accuracy of daughter pregnancy rate estimates may reside in models that adjust for VWP management decisions on a within-herd basis.

Timeliness and effectiveness of progeny testing through artificial insemination.

Progeny-test (PT) programs of US artificial-insemination (AI) organizations were examined to determine timeliness of sampling, PT daughter distribution, rate of return of PT bulls to widespread service, and genetic merit of PT bulls compared with AI-proven and natural-service (NS) bulls. Bull age at semen release and at birth and calving of PT daughters was documented by breed (Ayrshire, Brown Swiss, Guernsey, Holstein, Jersey, and Milking Shorthorn) for bulls that entered AI service since 1960. Mean Holstein bull age at semen release (16 mo) changed little over time, but standard deviations (SD) decreased from 4.0 mo during the 1960s to 2.4 mo during the 1990s. Most Holstein bulls (80%) had semen released by 18 mo. Mean age of Holstein bulls at birth and calving of PT daughters during the 1990s was 29 and 56 mo, respectively (a decline of 4 mo from the 1960s); SD decreased from 6 to 3 mo. Bulls of other breeds usually were older at birth and calving of PT daughters, and SD were larger. Mean Holstein bull age when 80% of PT daughters had been born declined from 36 mo during the 1960s to 31 mo during the early 1990s; for other breeds, bulls showed the same trend but at older ages. Mean Holstein bull age when 80% of PT daughters had calved declined from 65 mo during the 1960s to 59 mo during the 1990s; for other breeds, bulls were older. Percentage of herds with PT daughters has increased over time. For Holsteins, herds with five or more usable first-parity records that had PT daughters with usable records increased from 15% during 1965 to 61% during 1998; percentage of herds with from 1 to 19% PT records increased from 11 to 38%, and percentage of herds with >50% PT daughters increased from 1 to 5%. Percentage of Holstein PT bulls returned to AI service declined to about 12% for bulls with PT entry around 1990; for other breeds, 12 to 23% of most recent PT bulls were returned to service. Percentage of milking daughters that had records usable for genetic evaluation that were sired by PT bulls increased steadily from 10 to 18%, whereas percentage of daughters with usable records that were sired by NS bulls declined from 14 to 7%. Milk yield of daughters of AI-proven bulls was 107 to 200 kg greater than for daughters of PT bulls and 366 to 444 kg greater than for daughters of NS bulls for all years. More extensive and rapid sampling and increased selection intensity of PT programs have led to more rapid genetic progress. More extensive use of AI could increase US producer income by millions of dollars annually.

Overview of progeny-test programs of artificial-insemination organizations in the United States.

Characteristics of progeny-test (PT) programs of artificial insemination (AI) organizations in the United States were examined for changes since 1960. Mean number of bulls that were progeny tested annually by major AI organizations during the mid 1990s was 11 for Ayrshires, 24 for Brown Swiss, 21 for Guernseys, 1261 for Holsteins, 112 for Jerseys, and 3 for Milking Shorthorns. Mean parent age at progeny-test (PT) bull birth decreased except for Milking Shorthorns; mean age of maternal grandsire at bull birth decreased for Holsteins and Jerseys but increased for other breeds. For Holsteins, mean ancestor ages at PT bull birth were 85 mo for sires, 47 mo for dams, and 136 mo for maternal grandsires during the mid 1990s. Percentage of PT bulls that resulted from embryo transfer increased to 78% for Brown Swiss and 80% for Holsteins by 1999. Inbreeding in PT bulls increased over time and ranged from 3.8% for Brown Swiss to 6.4% for Jerseys (5.6% for Holsteins) during the mid 1990s. Mean numbers of daughters and herds per PT bull generally declined except for Holsteins, which increased during the early 1990s to 61 daughters and 44 herds. Mean number of states in which PT daughters are located increased; for Holstein PT bulls during 1994, 22% of daughters were in California, 13% in Wisconsin, 12% in New York, and 10% in Pennsylvania and Minnesota. Percentage of first-lactation cows that were PT daughters increased and ranged from 6% for Milking Shorthorns to 22% for Ayrshires (14% for Holsteins) during 1998. Percentage of PT daughters that were registered declined and was 19% for Holsteins and around 80% for other breeds.

Genetic evaluation of Holstein sires and maternal grandsires in the United States for perinatal survival.

Stillbirth, defined as a calf that dies just prior to, during, or within 48 h of parturition, represents a reoccurring concern among breeders of dairy cattle in the United States. About 11% of parturitions of primiparous Holstein cows result in the death of a calf; 5.7% in multiparous cows. Genetic evaluations can be reported as perinatal survival to 48 h to emphasize the positive information about the trait. The purpose of this research was to: 1) estimate genetic parameters by restricted maximum likelihood for perinatal survival rates; 2) characterize the genetic evaluation of sires for the perinatal survival of their progeny and maternal grandsires for the perinatal survival of their daughters progeny; and 3) estimate genetic trends from 1984 to 1994. Data (n = 666,339) were from the National Association of Animal Breeders calving ease database. Over 600 new young sires were available each year. The binomial response variable, 1 = alive, 0 = stillborn within 48 h of parturition was analyzed by using a sire-maternal grandsire linear mixed model. The model included fixed effects for sex of calf, dystocia, and season of birth, and gestation length as a covariate; correlated random effects of sire and maternal grandsire; and uncorrelated random effects of herd-years. Parturitions of primiparous and multiparous cows were analyzed separately. In primiparous cows, heritability estimates were 1.1 and 2.2% for sire of the calf and maternal grandsire, respectively. The genetic correlation between sire and maternal grandsire predicted transmitting ability (PTA) for perinatal survival, was 0.31; simple product moment correlations among sire-MGS PTA were 0.43 and 0.46 for primiparous and multiparous cows, respectively. The PTA for sire of the calf ranged from -2.9 (lower survival) to 2.8% (higher survival). Mean PTA from 1984 to 1994 was quite variable from year to year. Evidence showed a slightly negative, but nonsignificant, genetic trend in perinatal survival (-0.04% per year for sires and -0.02% per year for maternal grandsires). Estimates of genetic parameters and genetic trends for data from multiparous cows are also reported. Correlations among PTA for perinatal survival, milk yield, and calving ease are given.

Phenotypic trends in incidence of stillbirth for Holsteins in the United States.

The objectives for this study were to determine 1) if there was a trend in stillbirths for the U.S. Holstein population, 2) if stillbirths are the same trait in primiparous and multiparous cows, and 3) what was the role of dystocia in stillbirths. A sample of 666,341 births from the MidStates Dairy Records Processing Center and the National Association of Animal Breeders was used to examine the influence of sire, herd, year, season, sex of calf, parity of dam, calving ease, and gestation length on the survival of the calf. Parity was scored as an ordered variable (1, 2, 3+). Calving ease was scored on a scale of 1 (no assistance) to 3+ (needed assistance). An increasing trend in stillbirths was found in primiparous and multiparous cows. The percentage of stillborn calves in primiparous cows increased from 9.5 in 1985 to 13.2 in 1996. Stillbirths in multiparous cows increased from 5.0 to 6.6% from 1985 to 1996. Variation about the trend was greater in primiparous cows than in multiparous cows. Dystocia was a major determinant of stillbirth incidence, but the association was stronger in primiparous cows. Sex of calf had different associations with stillbirth incidence in primiparous and multiparous cows. Gestation length and season of birth also had significant associations with stillbirth incidence. Logistic regression models with fixed and random effects were fit to the data to preserve the binary nature of the stillbirth response. The expected probability of stillbirths for an average herd and sire was 10% for primiparous cows and 5% for multiparous cows. Replacement of stillborn calves is a substantial cost to the dairy industry at more than $125.3 million per year. Because of the increasing incidence of stillbirths, these costs have increased by $75.9 million from 1985 to 1996.

Usability for genetic evaluations of records from herds participating in progeny test programs of artificial insemination organizations.

Thirteen AI organizations provided identification of herds that participated in their progeny test programs in 1989 and 1990; 15% of those herds participated in programs of more than one AI organization, but only 2.6% participated in programs of more than two AI organizations. Of the 19,589 participating herds, 82 and 76% were enrolled in DHI test plans that were considered to be usable for genetic evaluations during 1991 and 1992. For herds that had participated in AI progeny test programs, mean percentages of usable records were 77% in 1991 and 78% in 1992; the mean percentages of usable records for nonparticipating herds were 62% in 1991 and 60% in 1992. Participating herds had larger mean herd sizes, higher means and standard deviations of milk yields, younger cows, and a lower percentage of registered cows than did nonparticipating herds. Analysis of variance was used to explain the variation in the percentage of records that were usable for genetic evaluations. Herds that participated in AI progeny test programs or that had smaller herd sizes, higher mean milk yields, younger cows, or larger percentages of registered cows had higher percentages of records that were usable for genetic evaluations. Improved usability of records for genetic evaluations would increase the efficiency of AI progeny testing, and consideration of herd characteristics associated with higher percentages of usable records should aid AI organizations in evaluating prospective herds for progeny test programs.