Records contributing to national genetic evaluations by year, registration status, herd size, and region

Accuracy of recorded birth and calving dates of dairy cattle in the United States

Frequencies of births that were reported for specific days of the month were documented for US dairy cattle born since 1987 by birth year, herd size, and registry status and compared with calving frequencies for those dates. Because birth dates are expected to be random and uniformly distributed throughout each month, percentages of births on individual dates were expected to be equal (3.3% for d 1 to d 28, 3.2% for d 29, 3.0% for d 30, and 1.9% for d 31). However, percentages of reported birth dates for d 1, 2, 10, 15, and 20 were higher than expected. The percentage of reported births for d 1 was highest (5.3%) of all days of the month regardless of herd size or registry status. The nonuniform distribution of birth dates within month indicated that a substantial number of birth dates were unknown and that estimated birth dates had been reported. About one-third of the birth dates recorded on d 1 appeared to have been estimated, or altered to gain an advantage in cattle shows. The highest frequencies for birth dates on d 1 (5.9 to 7.4%) were found for registered cows during months that initiated age groupings for dairy shows (March, June, September, and December). Birth dates for some registered cows were intentionally misreported as confirmed by comparison of birth dates of individual cows with calving dates of their dams. Reported calving dates appeared to be more accurate than reported births; the inflated frequency of recorded calvings on d 1 was only about 30% as large as the inflated frequency of recorded births. Because cow age is determined by birth date, proper reporting of birth dates is important to ensure the accuracy of standardized yield and fitness records and the genetic evaluations that are based on those records. When animals' recorded birth dates and their dams' calving dates differ, more credence should be given to the latter to improve accuracy.

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.

Herd and state means for somatic cell count from dairy herd improvement

To determine the impact of reducing the current legal limit of 750,000 cells/ml for somatic cell count (SCC) in US market milk, data were examined from 539,577 herd test days for Dairy Herd Improvement herds on test during 1996 and 1997. Somatic cell scores for individual cows were converted to SCC. The SCC for each cow was weighted by milk yield and used to compute herd mean on test day. The mean for each state was derived by weighting herd test-day SCC by herd test-day milk yield. State means were lowest in the West and highest in the Southeast. The percentage of herd test days with an SCC of >750,000 cells/ml ranged from 0 to 14% across states; the mean was 4%. Only 1% of the herd tests were >750,000 cells/ml on 2 consecutive test days. Mean SCC in the United States was 307,100 cells/ml for 1996 and 313,500 cells/ml for 1997. Mean SCC was lower during October through January (280,000 to 300,000 cells/ml) than during July and August (340,000 cells/ml). Herd size and SCC were negatively related; larger herds had lower SCC. Because records of some cows treated with antibiotics were included in the data, herd SCC means likely were higher than corresponding bulk tank SCC. Most herds had test-day SCC that were substantially below legal bulk tank limits and could have met lower limits (e.g., 500,000 cells/ml).

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.

Consideration of percentage of milk shipped for calculation of total lactation yields from various morning and evening plans of milk sampling

Milk yield recorded on DHI test day was compared with data on milk shipped from Texas and Minnesota herds for an innovative DHI test plan referred to as alternate a.m.-p.m. without a timer. Controls were yields for test day and for milk shipped from official DHI herds in Texas, Illinois, Minnesota, and several northeastern US states. Herd milk yield for a test day as a percentage of milk shipped was considered to be an indicator of the accuracy of the DHI recording plans. Mean percentage of milk shipped was 103 for all plans and regions. When herd test days with missing values were excluded, the percentage of herd test days within 96 to 110% of milk shipped were 77 for Texas and 82 for Minnesota innovative plans and 82 for Texas, 82 for Minnesota, 79 for Illinois, and 81 for northeastern official plans. Analysis indicated that the percentage of milk shipped was consistent across herd sizes, data source, and milk yield. Eight hypothetical testing plans were examined with or without adjustment of lactation yields for percentage of milk shipped. Estimates of variance components of lactation milk yields were computed and compared using a multitrait animal model. Adjustment of records for percentage of milk shipped would decrease mean milk yields by 3%, could result in better estimates of actual milk produced, but would have little effect on accuracy of genetic evaluations.

Age and seasonal effects on Holstein yield for four regions of the United States over time

Multiplicative factors to adjust Holstein yield for age and season of calving were calculated and analyzed from 20 data files for region and time. Regions were 1) California, 2) Minnesota and Wisconsin, 3) New York and Pennsylvania, and 4) six southern states (Texas, Louisiana, Mississippi, Alabama, Georgia, and Florida). Time periods were calving years of 1964 to 1968, 1971 to 1975, 1976 to 1980, 1981 to 1985, and 1986 to 1990. The same statistical model was used that had been used to derive current USDA factors from 1964 to 1968 data. The number of lactation records for each data file ranged from 81,394 to 2,238,201 and increased with time. Effect of calving season on milk yield generally decreased with time; the largest decrease was for the southern region. Effect of calving age also generally decreased for recent data, and the largest decreases were for California. Updated factors to adjust yield for calving age and season are indicated for some regions.