Discussion

The results reported here of the crossbreeding investigations at Asela station provide several guidelines for dairy cattle breeding work in Ethiopia.

The importance of combining the more important components of dairy productivity before coming to decisions on breed comparisons is well illustrated in Table 21. On lactation milk yield alone, the ¾ Friesian ¼ Arsi, ¾ Friesian ¼ Zebu and ½ Friesian ½ Zebu are considered superior to all other crosses.

When the reproductive performance component is added, these three crosses remain in the top four, but the ¾ Exotic ¼ Arsi moves into second place. The ¾ grades thus occupy the first three rankings.

The butterfat component of total milk yields provides guidelines for the choice of breed groups most suited to a dairy products industry. In Ethiopia, problems related to the efficient marketing of fluid milk from remote rural areas may justify the choice of breed groups with higher total annual fat production. When this component is added to lactation milk yield and reproductive performance, the ½ Friesian ½ Zebu, ¾ Exotic ¼ Arsi, and ¾ Friesian ¼ Arsi lead the rankings, with the ½ Jersey ½ Arsi becoming fourth equal with the ¾ Friesian ¼ Zebu.

A successful dairy industry is highly dependent on the quantity and quality of available feeds. Guidelines in this context rely on indices that take into account the feed requirements of animals of different body sizes. Since dairy animals are fed for maintenance and milk production, feed costs become crucial to choices between breeds. Productivity indices based on annual fat-corrected milk yield per unit of metabolic body weight provide clear guidelines to breeding policy relative to feed availability. When this component is added, the smaller animals with varying amounts of Jersey ancestry come to the fore. Based on the index incorporating all four components, the ½ Jersey ½ Arsi and ¾ Exotic ¼ Arsi are ranked first and second, with the ½ Exotic ½ Arsi and ½ Friesian ½ Zebu third and fourth. Five general implications from this study of dairy productivity are summarized in Tables 24 and 25 and illustrated in Figure 3.

1. The clear superiority of all crossbreds over the indigenous breed groups, culminating in 105% for the productivity index covering all four components (Table 25).

2. The similarity in performance of the 75% Bos taurus and the 50% Bos taurus. While milk yields were 13% higher in the 75% grades, their overall productivity was identical to that of the 50% grades (Table 25).

3. The lack of superiority of the Friesian cross over the Jersey cross. While the Jersey cross was 12% inferior to the Friesian cross in total milk yield, it was 14% superior in overall productivity (Table 25).

4. The similarity in performance between the indigenous Arsi and Zebu, based on overall productivity for both purebred and crossbred use (Table 25).

5. The major advantages of calving in the wet season. For all evaluation criteria, calving from June to September gave higher productivity than any other period of the year. A 12% increase in overall productivity was achieved for June - September calvings compared with those during the rest of the year (Table 26).

Thus decisions on genotypes most suited to a particular production situation must take careful account of factors such as whether the major target is liquid milk or milk products, annual pasture availability, and the feed supplement resources.

Table 24. Ranking of breed groups according to different evaluation criteria.

a Index is percentage relative to Arsi, which is maintained at 100.

Figure 3. Breed group evaluation by four criteria of productivity.

The transferability of research station technologies to the smallholder situation is a key aspect of technology development and related extension work. Thus, it is pertinent to compare the productivity of the crossbred cows when kept under station and smallholder conditions. Table 27 shows the means for the performance traits of four breed groups as measured on smallholder farms and on Asela station.

The production levels were rather similar in each situation, with a lower smallholder farm lactation yield, lactation length, and calving interval, leading to a 4% lower daily yield over the lactation period and an 8% lower annual milk yield.

Breed group rankings according to annual milk yield on smallholder farms and Asela station are presented in Table 28. The rankings of the breed groups on smallholder farms were identical to their rankings on Asela station, although the sizes of the differences between them, reflected by the indices, varied.

Overall, the rather similar production levels and identical ranking of breed groups at Asela and on smallholder farms (Tables 27 and 28) implies that, when farmers manage a few (one or two) cows and are given sufficient extension support, dairy productivity remains satisfactory. Similar observations were made by Stotz (1979) on smallholder dairy farms in Kenya. The general implications arising from the dairy productivity study on Asela station are thus equally applicable to the smallholder farm situation.

Table 25. Differences between genotypes according to different evaluation criteria.

Table 26. Differences between calving season according to different evaluation criteria.

Table 27. Overall comparison of performance traits on smallholder farms and Asela station.

Table 28. Breed group comparisons of annual milk yield on smallholder farms and Asela station.

a Index is percentage relative to respective column mean only.