Milk production, feed intake, and liveweight records were available on individual animals from a high yielding Holstein-Friesian herd in which selection had been practised on fat plus protein yield using nationally available AI sires. Unlike most other studies, animals were fed <i>ad libitum</i> thus making this data ideal for investigating genetic relationships. In total, the data comprised 475 26-week and 293 38-week (a subset of the 26-week data) lactation records. The relationship between sires and maternal grandsire's transmitting ability (ICC), expressed as a pedigree index (sire ICC + 0.5 maternal grandsire ICC), and offspring performance for milk production traits, feed intake, and gross efficiency (milk energy (MJ)/total intake (MJ)) was investigated. Regressions of fat plus protein yield, fat yield, protein yield, and milk yield, of heifers, on their corresponding pedigree index were not far from the theoretical expectation (for a full lactation) of 1. A genetic increase of 10% in fat plus protein yield of daughters of sires of high genetic merit for fat plus protein yield was accompanied by a genetic increase of 2.0% in feed intake and a 7.9% genetic increase in efficiency. The genetic relationships among milk production, feed intake, feed efficiency and liveweight traits were investigated. Restricted Maximum Likelihood analyses were carried out, fitting an Animal Model, with repeat lactations as an additional random effect. Univariate analyses were done after approximate canonical transformation of the traits. Heritability estimates for fat plus protein yield, feed efficiency and feed intake ranged from 0.45±0.22 to 0.15±0.12, 0.48±0.21 to 0.13±0.09, and 0.52±0.14 to 0.30±0.15, respectively. Genetic correlations between milk production traits and efficiency were generally less than 0.65. Genetic correlations between liveweight traits and efficiency were very high and negative. The results indicate that when selection is on yield, the correlated responses in efficiency may be smaller under <i>ad libitum</i> feeding, compared with published values where cows were fed according to yield. Including liveweight in the selection criterion may give higher responses in efficiency compared to selection on yield alone. In nucleus schemes (based on Multiple Ovulation and Embryo Transfer) it may be worthwhile to include feed intake or efficiency directly in the selection criteria.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660546 |
| Date | January 1990 |
| Creators | Persaud, Pooran |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15633 |
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