Data were analyzed from Sahiwal and East African Zebu herds maintained by the Roman Catholic Church as part of the Ilkerin Development Scheme. The project staff manage the Ilkerin farm in the Loita Hills of southwestern Kenya near Morijo. The ranch lies at a latitude of 1.7º S and an elevation of approximately 2200 m. Annual rainfall from 1974 through 1978, when data were collected, averaged 610 mm, falling in a bimodal pattern with the main rainy season from April through June and a rainy period from October through November.
This study involved the analysis of lactation records on 29 East African Zebu and 102 Sahiwal cows collected from 1974 through 1976. Also, lactation data were collected in 1978 on 37 East African Zebu and 53 Sahiwal cows. From 1974 through 1976, cows were milked once a day in the morning after being separated from their calves overnight and were suckled once later in the day. After the first two and one-half months of lactation, the cows were milked twice a day. For the lactation records obtained in 1978, calves were separated from their dams and the cows were fully milked out twice a day with calves allowed to suckle the limited amounts available afterwards.
Birth weights were recorded on 53 Sahiwal × East African Zebu cross calves and on 106 straightbred Sahiwal calves, and weaning weights were recorded on 48 Sahiwal × East African Zebu cross calves and 75 straightbred Sahiwal calves, born from 1974 through 1978. Weaning weights were adjusted to 240 days.
All characters were analyzed by least-squares fixed-model procedures (Harvey, 1972). As appropriate for each character involved, the model was varied in regard to the factors included. The specific factors included in the model for the analysis of each character will be evident when results are presented and discussed for the specific characters.
6.2.1 Reproductive characters
6.2.2 Milk production
6.2.3 Growth characters
6.2.4 Viability
6.2.5 Index of cow productivity
6.2.6 General remarks
The dates of birth of the East African Zebu cows included in the study were not known, so it was not possible to analyze differences between the East African Zebus and the Sahiwals in terms of age at first calving The age at first calving for 40 of the Sahiwal cows included in the study, whose birth dates were known, averaged 1147 days.
Calving intervals recorded from 1974 through 1976 averaged 473 days. Calving interval was significantly influenced by year of calving, averaging 358 days in 1974, 456 days in 1975 and 604 days in 1976. The month of calving did not influence calving interval significantly, however (P > .05) Parturition number was a significant influence: calving intervals averaged 546 days after the first parturition, 462 days after the second and 411 days after the third parturition. The two breeds did not differ significantly in terms of calving interval, nor was the interaction of breed with year significant. However, the straightbred Sahiwal cows averaged a 38-day shorter calving interval than the East African Zebus (Table 15).
Table 15. Least-squares breeding group means and standard errors for maternal characters, Ilkerin Project
|
|
1974 - 76a |
|
1978b |
|||||||
|
|
Lactation yield |
Lactation length |
Daily milk yield |
Calving interval |
Lactation yield |
Lactation length |
Daily milk yield |
|||
|
N |
kg |
days |
kg |
N |
days |
N |
kg |
days |
kg |
|
|
East African Zebu |
29 |
34c ± 95 |
111c ± 31 |
0.7c +0.2 |
22 |
492c ± 47 |
37 |
244c ± 57 |
176c ± 21 |
1.4c ± 0.2 |
|
Sahiwal |
102 |
595d ± 56 |
222d ± 18 |
2.5d ± 0.1 |
102 |
454c ± 28 |
53 |
420d ± 37 |
146c ± 14 |
2.7d ± 0.2 |
a Cows milked once a day and suckled once a day for the first 2.5 months, then milked twice a day with limited suckling by calf.
b Cows fully milked out with limited suckling by calf.
cd Means with no superscript letter in common differ at the P £ .05 level.
6.2.2.1 Lactation yield.
6.2.2.2 Lactation length.
6.2.2.3 Daily milk yield.
Lactation yields were not significantly influenced by year of calving among the cows analyzed for the period 1974 through 1976, but the effect of month of calving was significant (P < .05). Cows calving from January through April produced an average of 142 kg more milk per lactation than the overall average. Neither parturition number nor the interaction of breed with year were important (P > .05) for lactation yield, but the effects of breed on lactation yield were significant: when suckled by their calves and milked once a day, the East African Zebu cows produced an average of 34 kg of milk per lactation, while the Sahiwal cows averaged 595 kg (P < .01).
Among the cows analyzed for 1978, month of calving did not significantly influence lactation yield, but parturition number had a significant effect. The effect of parturition number on lactation yield was not consistent, however: lactation yield was highest, at 522 kg on average, following the third parturition and lowest, averaging 204 kg, following the fourth. Lactation yields averaged 244 kg for the 37 East African Zebu cows and 420 kg for the 53 Sahiwals (P < .01), with both breeds fully milked out twice a day (Table 15).
The average length of lactations recorded in 1974, 1975 and 1976 was 166 days. Neither the effects of year or month of birth, parturition number nor the interaction of breed with year was significant for lactation length. The mean lactation length was 111 days for the East African Zebu cows and 222 days for the Sahiwals (P <.01) (Table 15). For cows that were fully milked out in 1978, neither month of birth of calf, parturition number nor breed significantly influenced lactation length.
For the data collected from 1974, 1975 and 1976, neither year of birth, parturition number nor the interaction of breed with year was significant for daily milk yield. The effects of month of calving were important (P < .05): cows calving during January-February and March-April averaged 0.4 kg more milk a day than the overall average. The East African Zebu cows averaged 0.7 kg milk per day and the Sahiwals 2.5 kg (P < .01).
Month of birth did not significantly influence daily milk yield for the cows recorded in 1978. Parturition number did influence (P < .01) daily- milk yields for this sample, however: daily production following the first and fourth parturitions averaged 0.3 kg less than the overall average. The East African Zebu cows averaged 1.4 kg milk per day, while the Sahiwals averaged 2.7 kg (P < .01) (Table 15)
Birth weight records were analyzed for 53 Sahiwal × East African Zebu calves and 106 Sahiwal calves born from 1975 through 1978. The effects of year of birth were significant: calves born in 1976 and 1977 averaged 3.2 kg lighter at birth than calves born in 1975 and 1978. Month of birth was also significant (P < .01): calves born from September through December averaged 1.9 kg lighter at birth than the average for all calves of 19.8 kg. Parturition number did not have a major influence on birth weight, however (P > .05) The influence of sex was significant: male calves weighed on average 2.2 kg more at birth than female calves, or 20.9 vs 18.7 kg. Straightbred Sahiwal calves were significantly heavier at birth than Sahiwal × East African Zebu cross calves (Table 16).
Weaning weight records were analyzed on 48 Sahiwal × East African Zebu calves and 75 straightbred Sahiwal calves born from 1974 through 1978 during the months of March through September. The average weight at weaning for the entire sample was 100 kg. Year of birth had an important effect on weaning weight (P < .01): calves born in 1978 averaged 14 kg heavier at weaning than the overall average for all calves. Neither month of birth nor parturition number significantly influenced weaning weight, but the effects of sex of calf on weaning weight were important (P < .01): male calves averaged 10 kg more at weaning than female calves. The difference between breeding groups was also significant: straightbred Sahiwal calves averaged 16 kg more at weaning than Sahiwal × East African Zebu calves (Table 16).
Table 16. Least-squares breeding group means and standard errors for growth characters, Ilkerin Project
|
|
Birth weight |
Weaning weight |
Calf survival |
|||
|
N |
kg |
N |
kg |
N |
% |
|
|
Sahiwal × East African Zebu |
53 |
19.2a ± 0.73 |
48 |
92a ± 3.8 |
83 |
95a |
|
Sahiwal |
106 |
20.5b ± 0.49 |
75 |
108b ± 3.0 |
187 |
96a |
ab Means with no superscript letter in common differ at the P £ .05 level.
Similar proportions of Sahiwal calves and Sahiwal × East African Zebu calves survived to 12 months. Calf survival to approximately 12 months was 96% for the Sahiwals and 95% for the East African Zebus (Table 16).
Mortality was greater among Sahiwal than among East African Zebu cows. A total of 14 Sahiwal cows died out of the 242 cow-years analyzed, giving an annual mortality rate of 6%. Only 3 East African Zebu cows died out of 108 cows-years, giving a 2.8% annual mortality rate. Standard errors are large for these values, however, so the difference between breed groups is not significant.
The characters of reproductive performance, cow and calf viability, milk production, growth and cow weight are combined in Table 17 to build up an index of the total weight of 1-year-old calf plus the liveweight equivalent of milk produced, both per cow per year and finally per 100 kg of cow maintained per year. As in the other production situations, the cow productivity index is computed as the product of cow viability (%) × calving percentage (%) × calf viability (%) × calf weight at one year (kg) + cow viability (%) × calving percentage (%) × lactation milked-out yield (kg)/9.
The cow weights provided in Table 17 are estimates based on data from other sources, as the actual cows for which productivity data were obtained were not weighed. According to this index, the Sahiwal cows were 77% more productive than the East African Zebus per cow per year. However, when the productivity index is expressed on the basis of estimated weight of cow maintained per year, the difference in favour of the Sahiwal cow is reduced to 24% (Table 17).
Table 17. Productivity estimates of cows by breed group, Ilkerin Project
|
Character |
East African Zebu |
Sahiwal |
|
Cow viability (%) |
97.2 |
94.2 |
|
Calving percentage (%) |
74.2 |
80.4 |
|
Calf survival (%) |
95.2 |
95.7 |
|
Calf weight at 1 year (kg) |
128.0 |
152.0 |
|
Lactation milked-out yield (kg) |
34 |
595 |
|
Productivity index per cow per yeara (kg) |
90.6 |
160.3 |
|
Cow weight (kg) (estimated) |
(280) |
(400) |
|
Productivity index per 100 kg of cow maintained per yeara (kg) (estimated) |
(32.4) |
(40.1) |
a Total weight of 1-year-old calf plus liveweight equivalent of milk produced.
The results from this study comparing lactation characteristics show the Sahiwal breed to be greatly superior to the East African Zebu breed for characters that contribute to milk production. Also, straightbred Sahiwal calves are significantly heavier at birth and at weaning than Sahiwal × East African Zebu cross calves, even though the crosses have the benefit of heterosis for growth rate. Survival rates are similar for straightbred Sahiwal and East African Zebu cross calves. Thus, the Sahiwal breed is superior to the East African Zebu breed in transmitted effects for lactation and growth-related characters. The 38-day advantage in calving interval in favour of the straightbred cows indicates that they are at least equally we'll adapted to the environment.
The conditions under which these comparisons were made at the site of the Ilkerin Project are classified as harsh in regard to nutritional environment. It is concluded that the Sahiwal breed has potential for use in both milk and beef production programmes under adverse environmental conditions as found at this site. The potential of the Sahiwal breed under such conditions would appear to be greatest in organized crossbreeding programmes or as a contributor to composite breeds, rather than as a straightbred
