Open AccessJournal Article
Genetic Trends for Milk Yield, Persistency of Milk Yield, Somatic Cell Count and Calving Interval in Holstein Dairy Cows of Iran
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TLDR
Although not significant, favorable genetic trends for most studied traits were reported and selection emphasis in Iran was on lactation milk yield, so progress was low during the years of the study.Abstract:
The objective of the present study was to estimate genetic trends for lactation milk yield, persistency of milk yield, somatic cell count and interval between first and second calving in Holstein dairy cows of Iran. The dataset consisted of 210,625 test day and 25,883 first parity cows with milk yield recorded from July 2002 to September 2007 comprising 97 herds in Iran. Breeding values of animals were predicted with Best Linear Unbiased Prediction methodology under multi-trait animal model. Model included region, herd–year–season of calving and age at first calving as fixed effects and Holstein percentage (covariate) and random animal additive effect. Genetic trends of studied traits were estimated by regressing mean of breeding values on calving year. Phenotypic trends were estimated using annual averages of first lactation traits on calving year weighted by the number of animals in each year. Genetic trend was positive and significant for lactation milk yield (21 kg/yr; p < 0.01).Although not significant, favorable genetic trends for most studied traits were reported. Considering that selection emphasis in Iran was on lactation milk yield, progress for this trait was low during the years of the study.read more
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References
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TL;DR: In this article, the general shape of the curve, defined by the locus of weekly yield of a single lactation, remains substantially unchanged, and it is shown that the animal which produces milk at a moderate level steadily throughout her lactation is preferred to one which produces a great deal of milk at her peak but little thereafter.
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Factors Affecting the Shape of Lactation Curves of Holstein Cows from the Balikesir Province of Turkey
TL;DR: Effects of farm operation, calving year, calve season, parity, and service period were significant for the various lactation curve traits and peak and lactation yields were higher for cows that calved in fall and winter, and persistency was higher for cattle that calve in summer and fall.
Journal ArticleDOI
Yield and Fertility Relationships in Dairy Cattle
TL;DR: In this paper, the authors obtained measures of yield and fertility from breeding receipts of artificial insemination and records of test-day yield, using the Henderson Method 3, maximum likelihood, and restricted maximum likelihood.
Journal ArticleDOI
Trends in calving ages and calving intervals for dairy cattle breeds in the United States.
E. Hare,H.D. Norman,J.R. Wright +2 more
TL;DR: Breed differences for calving age and calving interval were evident for all parities; current mean age at first calving ranged from 24 mo for Jerseys to 28 mo for Ayrshires.
Journal ArticleDOI
Genetic Relationships Between Persistency and Reproductive Performance in First-Lactation Canadian Holsteins
TL;DR: Estimates of genetic relationships between lactation persistency and reproductive performance in first lactation and relationships with day in milk at peak milk yield and estimated 305-d milk yield found heifers younger than average when first inseminated and/or conceived successfully at first inSEmination tended to have a more persistentFirst lactation.
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