English abstract
The main objective of this research was determining the effect of sire of cow, year and season of freshening, lactation number, and their different interactions on 305-day mature equivalent (ME) milk yield of Holstein Friesian cows in the United Arab Emirates (UAE). It also aimed to estimate sire and error variance and heritability of 305-day ME milk yield. The data was collected from AL Salamat Dairy Farm in Al Ain. The average size of the herd was 1000 animals during the experimental period. The Dairy Comp 305 computer program was used for compiling the data. The data under the study covered the years 2004 to 2007. The climatic temperature during the summer (April to September) varied from moderate to very hot. The winter (October to March) had lower temperature and higher relative humidity than the summer. All the effects were fixed except for random sire and residual error term. The overall least-square mean of the 305-day ME milk yield was 11060±355 kg/305 days. The data showed a significant effect of sire of cow
(p≤0.001), year of freshening (p≤0.001), lactation number (p≤0.01), year x season of freshening (p≤0.01), and year of freshening x lactation number (p≤0.001) on milk yield. However, the effect of season of freshening showed non signify-cant effect. No significant seasonal differences were found in 2004. However, in the year 2005 and 2006, the summer fresheners had significantly higher yield than those of the winter season. The 305-day ME pertaining to summer vs. winter were 11691±400 kg vs. 11483±410 kg and 11522±369 kg vs. 11041±374 kg for the year 2005 and 2006, respectively. However, the reverse was true in 2007 with the fresheners during summer that have lower 305-day ME (10286±372kg) than those freshening during winter (10672±388 kg). The differences among the three lactations were relatively high in 2004 (9837 to 12116 kg), compared to 2005 - 2006 (11267 to 11747 kg) and 2007 (9853 to 11355 kg). The heritability of 305-day ME was 0.31 indicating that a significant response to selection would be achieved through a well-designed progeny testing and cow evaluation program.
