| dc.description.abstract | The main purpose of the present study was to compare the milk yields of crossbred ayrshire x sahiwal cows with those of high grade ayshires kept at Kilifi Plantations Limited in the coas province of Kenya. All lactations included in the study were started and completed under Kilifi conditions. Both complete and 305 day mille yields were used. Comparisonof milk yields, ages at calving,lactation lengths and preceding calving intervals were done within lactations. In the first analysis which was done
with the aid of an electronic desk calculator, only the first five lactations were used and only the first three lactations were age corrected. In the second, more complete analysis all the data, i.e. the first eight lactations were used. In this second analysis a least squares program written for an IBM 370/155 computer was used.
The main findings were:-
1. In the eight lactations, the 3/4 Ayrshire: 1/4 Sahiwal gave more milk than the other groups except in lactations 2, 6 and 7 when they were intermediate to high grade Ayrshire and 1/2 Sahiwal: 1/2 Ayrshire. The 1/2 Sahiwal: 1/2 Ayrshire were the poorest in the first five lactations but improved in the later lactations. High grade Ayrshires were almost always intermediate.
2. Breed influence on milk yields was significant in lactations 1, 2, 3 and 8 and in lactations 1, 2, 7 and 8 for complete and 305 day milk records, respectively , The variance components were usually low, on average 4.7% for 305
and 3.5% for complete lactation lactation yields.
3. The variation due to year of calving had greater influence on milk yields than the other
classified factors. Its effects was significant in all lactations except the 7th for the 305 day records and in all but 3, 5, 7 and 8 for the complete milk yields.
4. Influence of season and breed by season interaction was small and in many cases not
significant.
5. The correlation between 305 day and complete lactation records wa s over 0.8 on average and was statiptically significant in all lactaticns. Hence in this summary only 305 day records will be referred to.
6. The unweighted average for the eight lactations of the 305 day milk yields corrected for
year of calving,season of calving and breed x season interaction was 6006 (100), 6076 (101.2) and 6377, (106.2) for pure ayrshire, 1/2 Sahiwal: 1/2 Ayrshire and 3/4 Ayrshire: 1/4 Sahiwal.
7. There were no sibnificant differences between the breed groups as regards age at first
calving, the average being about 36 months for all groups. Age at calving in the subsequent lactation was however , influenced by year and breed.
8. The differences in lactation Lengths between the breed groups were significant only in
the second and the third lactations. In the early analysis where there were no corrections for systematic on the first five lactations. Except in the first in the first lactation,the length. of lactation was always the longest for the pure Ayrshire. In most lactations, the 3/4 A: 1/4 S had the shortest lactation lengths. Year of calving, had significant influences in all lactations except the last while only the first lactation length was influenced by
season and breed x season interaction•
9. The differences in calving interval between the breeds were significar:t only in the
first two lactations. In the first analysis they were significant in the first five lactations. Year
of calving influenced the length of the preceding calving interval Significantly. The calving interval was longest for high grade Ayrshires except for the last one. The 1/2 Sahiwal: 1/2 Ayrshire had the shortest first four calving interval while the 3/4 Ayrshire: 1/4 Sahiwal had the shortest last three calving intervals.
10. When comparing the two statistical analyses it can be concluded tha.t at least a
correction for year of calving is required to get unbiased results.
11. The main conclusion from this study is that although the differences between the breed groups were not large, a fair proportion of Bosindicus genes seems to be required in this envronment for optimal production especially if the feeding and management standards are below that of Kilifi Plantations Limited. | en |
