Relationship between bull dam herd characteristics and bias in estimated breeding value of bull

The objective of the study was to relate estimated breeding values (EBVs) of the parents’ 305-days protein production and the bull dam herd-year characteristics to the empirical bias in pedigree indices (difference between the pedigree index and the final proof) of young bulls. Two animal model evaluations were carried out; one included records up to 1990 and the other up to spring 1992. The final data set included 242 bulls with pedigree indices, final proofs, parents’ EBVs, production and herd information (the size, the average production and the intraherd standard deviation) of the dams. The average empirical bias in pedigree indices was 13.6 kg. The correlation between the final proof of the bull and the EBVs of the bull sire or dam were 0.45 and 0.17, respectively. The low correlation with bull dam EBV indicates the unreliability of the bull dam EBVs. Size of the herd and the standard deviation of production in the herd when bull dam produced its third lactation were correlated with the empirical bias in pedigree index. Pedigree indices of the bulls coming from small herds with high intraherd standard deviation were more biased than those from the big herds with low intraherd standard deviation. The best bulls, when grouped according to their final proofs, were sons of the highest EBV sires. EBVs of bull dams did not differ in the highest and the lowest final proof groups, but the dams of the best bull group had a higher first lactation record than the dams of the other bull groups.

A simulation study for optimizing the use of dairy bulls in breeding programs

Different breeding program alternatives in dairy cattle population were studied by simulation. Traits studied were milk production and a low heritability trait that is negatively correlated with milk production, e.g. fertility. The variable factors in the study were the number of young bulls to be tested, the number of daughters per bull in progeny testing, the number of tested bulls to be used and the weights for selected traits in an overall index of the bull’s breeding value. The influence of variable factors on genetic response in milk production and fertility was studied by calculating the average of real genotypic values on both traits for all cows born in the same year and having a complete first lactation record. This was done for a 25 year period. The population structure used in simulation was like the Finnish milk recorded Ayrshire population in which there are ca. 250000 cows. The genetic response in milk production was improved by increasing the selection intensity amongst bulls. The negative effect of selection for milk yield on fertility could be decreased by giving the fertility a larger indexed weight. If the milk production had a weight of 1 and genetic correlation between traits was —0.20 then increasing the weight of fertility from 0.1 to 0.3 did not affect significantly the response in milk production.

SEASONAL CALVINGS BY LACTATION IN R.O.P.-TESTED HOLSTEIN–FRIESIAN HERDS IN RELATION TO CONTEMPORARY COMPARISONS

Frequency distributions of number of herd calvings by lactation and season are given for the Canadian Holstein breed using recent official records of performance. A minimum of 14 and 15% first-lactation animals had no contemporaries for the two spring seasons studied and the corresponding percentage for two fall seasons were 4 and 5. Thirty-seven percent of all herds with first-lactation cows contained only one first-lactation record for both spring seasons and the frequency of such herds for the two fall seasons was 16 and 20 percent. The relative proportion of first-lactation animals per herd differed between seasons. The average number of calvings per herd was close to 10 for fall and spring seasons or 20 for a 12-month period.

Progeny Testing of Dairy Cattle Bulls Used in Artificial Insemination

In 1945 the Milk Marketing Board (M.M.B.) of England and Wales undertook responsibility for the development of an A.I. service to cover large areas of the two countries.By 1951, a total of 24 main Centres had been set up, housing some 600 dairy and beef bulls and supplying semen to 77 Sub-Centres. During the year ending 31st March, 1952, approximately 707,000 first inseminations were carried out, representing 25% of the available cattle population. Further progress continues to be made and it is estimated that this proportion will be raised to 30% for the corresponding year ending in 1953.From the outset it has been agreed that the rate of cattle improvement through A.I. will be largely dependent upon the use made of the older progeny-recorded bulls available to the scheme. Here it should be noted that the M.M.B. took over responsibility for milk recording under ‘ National Milk Records ‘ in 1943. By adopting a system based upon lactation record cards, it was possible to establish in 1947 a central clearing house for milk records of animals registered with Breed Societies, viz. the Bureau of Records. One of the main services operated by the Bureau is that of progeny recording for sires and summaries of bulls fulfilling certain requirements are now published annually.

465. Studies on variations in the solids-not-fat content of milk: I. Variations in lactation yield, milk-fat percentage and solids-not-fat percentage, that are due to the age of the cow

1. The coefficient of variation of lactation milk yield was approximately 25% for all age groups. That for lactation milk-fat percentage approximately 10% and that for lactation solids-not-fat percentage only 3%. The last two coefficients tended to increase with the age of the cow.2. Lactation milk yield was least with first calvers and rose to a maximum for sixth calvers. Milk quality was highest with first calvers.3. No tendency to vary with the season of calving could be found for any lactation record of any age group.4. During the first years of the herd's existence there was a small negative correlation between lactation milk yield and lactation milk-fat percentage. This has disappeared in more recent years.5. There was no correlation between lactation milk yield and lactation solids-not-fat percentage.6. There was a small (r = +0·40 approximately) positive correlation between lactation milk-fat percentage and lactation solids-not-fat percentage.

The variations in milk yields caused by season of the year, service, age, and dry period, and their elimination: Part I. Season of the year

Although the primary object of recording cows' milk yields is to provide a means of comparing one individual with another, it is not satisfactorily achieved when the records have been obtained, since yields are influenced to a large extent by environmental factors which vary from cow to cow. The lactation record is the result of two sets of factors—genetic and environmental—and for purposes of selection and breeding it is important to be able to make accurate allowance for the one, so as to arrive at a good estimate of the other.Leaving aside the variation due to feeding and management (which, whilst undoubtedly large, is minimised for the cows of the same herd, and which it is hardly possible to study statistically in the existing data) the chief factors operating on the lactation yield (i.e. the measurable environmental factors) are the following:(1) Season of the year; the lactation yield is influenced to a certain extent by the month of the year in which the cow calves.(2) Service; i.e. the stage of the lactation at which the cow again becomes pregnant. The interval between calving and the next fertile service is here termed the Service Period (S.P.); thus if a cow calves on June 1st, and becomes pregnant again on July 1st, her S.P. for that lactation is 30 days.