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.

Relationships between linear type scores, objective type measures, and indicators of mastitis.

Objectives were to examine the usefulness of objective measures of conformation and linear scores for type for predicting indicators of mastitis. Approximately 300 cows in five herds were scored in the experimental linear classification program of the Holstein-Friesian Association of America, measured objectively for numerous components of conformation, and evaluated for four indicators of mastitis. Indicators of mastitis were average natural logarithm of somatic cell counts during the lactation, percent of samples (taken approximately every 3 mo) infected during a lactation, percent of samples infected with Staphylococcus aureus, Streptococcus agalactiae, Escherichia coli, Klebsiella, and percent of samples with signs of mastitic milk. Relationships between conformation and mastitis often were inconsistent because of moderate or low correlations between indicators of mastitis. Indicators of mastitis were predicted from results of multiple regression analyses with subjective scores and objective measures of type as independent variables. Largest differences of predicted indicators of mastitis from variation in any single type trait were sufficient to be important economically, but average differences were much smaller. Selection to reduce frequencies of cows with deep udders, especially low rear udders, widely placed teats, rear teats too far back, and teats that are short and wide, may augment, modestly, efforts to reduce incidence of mastitis through improved sanitation, antibiotic treatment, and proper milking procedures.

Genetic evaluation of dairy goat bucks for daughter milk and fat.

Genetic evaluations were computed for milk and fat for 3,181 Alpine, 1,039 LaMancha, 4,455 Nubian, 1,449 Saanen, and 1,546 Toggenburg bucks. These evaluations were based on 58,562 lactations of 43,913 does that kidded from 1976 through 1982. Best linear unbiased predictions were computed with relationships among multiherd bucks and information from all lactations included. An interaction between herd and sire was included in the model. Evaluations were computed across breed, which allowed does of different breeds to be herdmates. Bucks were grouped by breed and herd usage (single herd versus multiherd). Correlations between evaluations computed with and without relationships were only .84 to .88, which indicates that relationships had a significant effect. Evaluations of 2,491 bucks with Repeatability 15% or more were released to the industry.

Projecting health cost from research herds.

Health costs by categories were summarized from 1,999 lactations of 863 cows in three dairy herds. These costs were projected to Dairy Herd Improvement data. Health categories were mammary, reproduction, locomotion, digestion, respiration, other, and total. The largest estimated total health cost of $67.63 was associated with postpartum length (days in milk and dry) greater than 420 days, an average 98 days dry, and milk production greater than 8,250 kg in fourth or later terminal lactations. The smallest estimated total health cost of $22.25 per lactation was associated with production between 5,750 and 6,999 kg in the nonterminal first lactation with postpartum length less than 300 days. For nonterminal first lactations of intermediate length, the estimated total health cost represented 3 to 6% of the value of milk production. First-calf heifers with milk production less than 5,750 kg and postpartum length 300 to 419 days had the least mammary cost. Cows in their fourth or later lactations with postpartum length greater than 420 days and milk production less than 5,750 kg had the highest reproductive cost. Mammary cost increased and reproductive cost decreased with increased days dry. Cows in terminal lactations had $11.38 more total health cost, $4.33 more mammary cost, and $6.31 more reproductive cost than cows in complete nonterminal lactations. Relatively more reproductive than mammary cost occurred in terminal lactations compared to nonterminal lactations. Mammary cost remained the largest component of total health cost. Multiparous cows had more total health, mammary, and reproductive costs than first parity cows. The repeatibility of total health cost was .12 +2- .03.

Genetic aspects of lactation curves.

Parameters of lactation curves were defined by a gamma-type function for 113,705 lactations from the California Dairy Herd Improvement Association. Heritabilities and genetic correlations were estimated from a mixed-model analysis of paternal half sisters for first, second, third, and later lactations. Daily milk production on day 6 postpartum was estimated from production at first test-day to reduce the percentage of atypical lactations to less than 1% instead of an expectation of 30% without estimating production for day 6. The natural logarithm of the gamma-type function was ln(yt) = ln(a) + b ln(t) - ct, where yt was daily milk production in the tth week and ln(a), b, and c were coefficients. Persistency (c-(b+1)), week of peak yield (b/c), peak yield (a(b/c)be-b), and coefficient of determination were estimated from coefficients for each lactation. Heritabilities in first lactation were: ln(a) . 10 +/- .01, b .06 +/- .01, c .14 +/- .02, persistency .02 +/- .01, week of peak yield .02 +/- .01, peak yield .23 +/- .02, and determination .03 +/- .01. Heritabilities for later lactations were similar. Cows in first lactation had lower ln(a), lower peak yield, lower c, greater persistency, and took longer to reach peak yield than did cows in later lactations. Genetic and phenotypic correlations indicated that selection for increased peak yield would be associated with increased ln(a), b, and c without changing persistency or week of peak yield.

Postpartum distribution of costs and disorders of health.

More than 17,000 events from 1,305 lactations of 551 cows in two herds were analyzed to quantify the distribution of costs and disorders of health during a lactation. Categories were mammary, reproduction, locomotion, digestion, respiration, other, insemination, and total. The largest costs and most disorders were associated with initiation of lactation rather than period of peak daily milk yield. Mammary and reproductive costs were 71% of total health cost in the first 30 days postpartum. Mammary and reproductive costs were 55% of the total health cost in an average 30-day interval. Insemination cost was 50% of the total health cost between 60 to 89 days postpartum. Parturition and extended days open were periods of large reproductive cost. Postpartum distributions of health cost and health disorders were similar implying that the prices assigned for severity added little information to counting disorders.

Alternative genetic bases for sire summaries and cow indexes.

The need is discussed for understanding the interpretation of Predicted Differences in relation to the 1974 genetic base. Merits of moving, fixed, and stepwise genetic bases are discussed in relation to genetic progress in the United States dairy industry. A moving genetic base has little merit, because too many animals are evaluated and published in each sire summary. Either a fixed or stepwise base could be used effectively if dairymen and industry personnel were educated on the relation of current genetic evaluations to the genetic base and the need to continue genetic improvement in individual breeds.