Genetic evaluation for longevity of Dutch dairy bulls.

Parameters needed for survival analysis of longevity records of cows to predict breeding values of their sires were estimated with data on Dutch Black and White and Red and White cows. The heritabilities of functional productive life were 0.041 and 0.036 on the log scale for Black and White and Red and White cows, respectively. Although the heritabilities and other parameters differed between both breeds, the resulting breeding values were hardly affected: the correlation between breeding values of Red and White bulls using either Red and White parameters or Black and White parameters was 0.992. Genetic correlations between the direct breeding value for functional longevity (based solely on longevity of sires' daughters) and breeding values for conformation, health, and fertility traits were calculated. Several alternative selection indices were investigated using these correlations. Based on the resulting reliabilities, it was concluded that the Dutch breeding value for functional longevity should be based on longevity, rump angle, teat placement, udder depth, feet and legs, and somatic cell count. The index was expressed on a scale with average of 100 and a standard deviation of 4 points (at 80% reliability). The economic value was Dfl. 65 per genetic standard deviation, which was 0.46 times the economic value of INET (Net Milk Revenue Index). For the breeding value for functional longevity that was first published in August 1999, slight modifications in the model were made.

Relationships between mastitis and functional longevity in Danish Black and White dairy cattle estimated using survival analysis.

The relationship between mastitis and functional longevity was assessed with survival analysis on data of Danish Black and White dairy cows. Different methods of including the effect of mastitis treatment on the culling decision by a farmer in the model were compared. The model in which mastitis treatment was assumed to have an effect on functional longevity until the end of the lactation had the highest likelihood, and the model in which mastitis treatment had an effect for only a short period had the lowest likelihood. A cow with mastitis had 1.69 times greater risk of being culled than did a healthy herdmate with all other effects being the same. A model without mastitis treatment was used to predict transmitting abilities of bulls for risk of being culled, based on longevity records of their daughters, and was expressed in terms of risk of being culled. The correlation between the risk of being culled and the national evaluations of the bulls for mastitis resistance was approximately -0.4, indicating that resistance against mastitis was genetically correlated with a lower risk of being culled and, thus, a longer functional length of productive life.

A comparison of breeding value predictors for longevity using a linear model and survival analysis.

A comparison was made among breeding values of sires for longevity that were obtained by different methods: phenotypic averages of daughters using only uncensored records, BLUP using only uncensored records, survival analysis using only uncensored records, and survival analysis using both censored and uncensored records. Two data files were used: one contained data from small herds, and the other contained data from large herds. The results from both data files were similar. Different methods of predicting breeding values resulted in different rankings of sires. The results obtained using phenotypic averages were weakly correlated (< or = 0.46) with those results obtained using the other methods of prediction. The REML BLUP had strong correlations (< or = -0.91) with the survival analysis predictor if the same data were used, and correlations weakened (< or = -0.60) when censored records were included in the survival analysis. The correlations are negative because the linear method analyzed longevity, and survival analysis measured the risk of being culled, which has an antagonistic relationship with longevity. The results from REML BLUP and survival analysis methods differed mainly because of the different data that were used (uncensored only versus both censored and uncensored).

Genetic correlations between longevity and conformation traits in an upgrading dairy cattle population.

Genetic correlations between longevity and conformation traits were estimated using data on Dutch Black and White cows born in 1978 (11,558 records), 1982 (39,252 records), and 1989 plus 1990 (58,864 records). Longevity traits considered were number of lactations, herd life, and stayabilities until 36 and 48 mo of age and their functional equivalents (i.e., the longevity traits corrected for production). For the 1989 plus 1990 data file, only stayabilities until 36 and 48 mo of age were considered. Conformation traits were rear legs set, front teat placement, udder depth, suspensory ligament, and subjective scores for udder, feet and legs, and type. Also investigated was a possible nonlinear relationship between conformation and longevity traits. Genetic correlations between conformation and longevity traits differed between years of birth, mainly because farmers practiced large-scale upgrading with Holstein-Friesian bulls during the period considered, which caused a change in desired type. Therefore, the predictive value of conformation traits for longevity based on data from an upgrading population, might be limited. Estimates of genetic parameters should be based on the most recent data possible, and these parameters should be reestimated over time. From the 1989 plus 1990 data file, subjective scores for udder and feet and legs had the highest predictive values for functional longevity. Quadratic relationships between conformation and longevity traits did exist, but generally the linear relationships prevailed.

Genetic parameters of longevity traits of an upgrading population of dairy cattle.

Longevity reflects the ability of a cow to avoid being culled for low production, low fertility, or illness. Longevity could be used in breeding programs if genetic parameters were known. Various measures are used for longevity. In this study, lifetime measures including number of lactations, total milk production, number of days in lactation, herd life, and length of productive life were analyzed. Also analyzed were stayability measures (dead or alive) to 36, 48, 60, or 72 mo of age and to 12, 24, 36, or 48 mo of productive life. Measures of longevity were also analyzed after correction for milk production during first lactation (functional longevity traits). Data on 1,72,988 cows were used to calculate means for longevity traits per year of birth. All cows were known to have been culled. Longevity decreased from 1978 through 1984 and increased in 1985. Possible causes for the decrease of longevity were implementation of the quota system and introduction of Holstein genes. heritabilities of longevity traits were estimated for cows born in 1985 (38,957 records), 1982 (166,324 records), and 1978 (94,935 records) after data were edited to require at least 25 daughters per sire and 10 cows per herd. Phenotypic and genetic correlations were estimated for the 1985 data. Heritability estimates differed between years of birth, and estimates of functional traits were lower than those of uncorrected longevity traits. Genetic correlations between uncorrected longevity traits were high (0.733 to 1.000); phenotypic correlations were lower (0.131 to 0.980). Genetic correlations between uncorrected and functional longevity traits were high (0.577 to 0.975).

Estimation of variance components with dominance and inbreeding in dairy cattle.

SUMMARY: The five variance components in the genetic (co)variance among inbred relatives for a quantitative trait with additive and dominance genetic variation were estimated by equating variances among and within different types of families of inbred cows to their expectations. The data used were milk and fat yields of 85,433 U.S. Holstein cows with inbreeding coefficients of 6.25% or higher. When all five parameters were estimated, unrealistic results were obtained. If all quantitative trait loci are biallelic, genetic (co)variance depends on only four parameters. More realistic estimates were obtained under this assumption. There was a substantial negative covariance among breeding values and dominance effects under inbreeding, and the dominance variance in inbred cows was larger than the dominance variance in the noninbred base population. ZUSAMMENFASSUNG: Varianzkomponenteneinschätzung bei Dominanz und Inzucht von Milchvieh Die fünf Varianzkomponenten in der genetischen (Ko)Varianz zwischen ingezüchteten Verwandten in einem quantitativen Merkmal wurden geschätzt durch Gleichsetzen von Varianzen zwischen und innerhalb verschiedener Familien von ingezüchteter Kühen zu ihren Erwartungswerten. Das Datenmaterial bestand aus den Milch- und Fettmengen von 85,433 U.S. Holstein Kühen mit Inzuchtkoeffizienten von 6.25% oder höher. Die gleichzeitige Schätzung aller fünf Parameter führte zu unrealistischen Ergebnissen. Wenn an allen Genorten des quantitativen Merkmals nur zwei Allele vorkommen, gehen nur vier Parameter in die genetische (Ko)Varianz ein. Die Schätzwerte, die unter dieser Annahme berechnet wurden, waren plausibler. Eine beträchtliche negative Kovarianz zwischen den Zuchtwerten und den Dominanzwerten bei Inzucht wurde gefunden, und die Dominanzvarianz war unter Inzucht gróßer als in der Basispopulation.