Introduction
Management practices at Chizombezi and Tuchila
Calf performance at Chizombezi
Comparison between cow performance at Tuchila and on smallholder farms
As was observed in Section 2, the exact breed composition of the 'off-type' female cattle that were used to produce the crossbred calves was not known but was believed to be a mixture of Sussex, Brahman-type and Africander-cross cattle. In this section the birth weight of F1 female calves produced from Friesian bulls and 'off-type' females, and their growth rate from birth to weaning are analysed. Crossbred cows, mainly 3/4, 7/8 and higher-grade Friesians, are kept at Tuchila to provide milk for growing calves left behind by the F1 heifers sold to smallholders, and their performance is also summarized. The number of records at Tuchila did not warrant detailed analysis. However, the means presented are the best available figures from a station-type operation with which performance of the crosses at the smallholder farms can be compared.
The two main breeding seasons at Chizombezi were from the middle of May to August and from December to March. 'Off-type' heifers at Chizombezi were put to a number of Friesian bulls from Mikolongwe at 2 to 21/2 years old or at a breeding weight of about 300 kg.
Pregnant heifers were steamed up by feeding a production ration from the seventh month of pregnancy. The production ration was usually compounded from soya bean, pigeon pea, maize, maize bran and cottonseed cake, depending on the availability of these materials on the market. Pregnant heifers were separated from the rest of the females about two weeks before calving, and were introduced to milking-shed practices. After parturition calves stayed with the dams for 24 to 48 hours, after which they were placed in a calf pen and bucket fed milk diluted with increasing amounts of water over a period of 10 weeks and then weaned. The male 3/4-Friesian calves were castrated at 4 to 6 weeks old. Females were inseminated with Friesian semen at 21/4 years old to produce 7/8-Friesian calves. Half- and 3/4 Friesian cows were usually sold to smallholder farmers while 7/8-Friesians and higher grades were kept at Tuchila.
In the absence of a weighing scale approximate birth and weaning weights were obtained for calves by the use of a weigh-band. All animals at the station were dipped in Supona solution every week and were drenched regularly.
Birth weight, daily weight gain and actual and adjusted weaning weights
On the basis of the frequency of births in the various months at Chizombezi, four seasons of calving were created for the analyses of the birth-weight and growth-rate data on 1/2-Friesian female calves. These seasons were November to March, April to May, June to August and September to October, and comprise the two main breeding seasons and accidental breedings occurring between the main breeding seasons.
Analyses of variance of calf birth weight, actual weaning weight, 200-day adjusted weaning weight and daily weight gain up to weaning are presented in Table 12.
Table 12. Analyses of variance of female calf birth weight, actual and 200-day adjusted weaning weights and daily weight gain of 1/2-Friesian calves at Chizombezi multiplication centre, 1974-83.
|
Source |
d.f. |
Birth wt. |
d.f. |
Weaning wt. |
200-day weaning wt. |
Daily wt. gain |
|
MS |
MS |
MS |
MS x 103 |
|||
|
Season of calving |
3 |
130.9** |
3 |
2 422** |
5 701** |
173** |
|
Year of calving |
8 |
230.4** |
6 |
2 548** |
3 930** |
81** |
|
Remainder |
568 |
13.2 |
313 |
508 |
491 |
11 |
** = P<0.01
Season of birth and year of birth had significant effects (P < 0.01) on all four traits (Table 12).
The estimated least squares means for the four traits are hid out in Table 13.
Birth weight: The mean calf birth weight for 580 female calves was 30.1 ± 3.6 kg with a CV of 12%. Calves born between April and August were significantly heavier than those born between September and March (P < 0.05).
With the exception of 1983, calf birth weight at Chizombezi has been declining since 1974 (Table 13). A regression of female calf birth weight on years (coded 1 through 9) from 1974 to 1983 indicated that birth weight has been decreasing by 0.16 kg per year, although the regression coefficient was not statistically significant.
200-day adjusted weaning weight and daily weight gain: The mean 200-day adjusted weaning weight and daily weight gain for 323 female calves were 136.2 ± 22 kg and 0.53 ± 0.11, respectively. The respective CVs were 16 and 21%. Calves born in September through March were significantly heavier (150.5 kg vs 134.2 kg) than calves born in April through August at 200-days postpartum, despite the heavier birth weights of the latter. Similarly calves born in September through March on average gained 0.1 kg per day more than calves born in April through August.
Table 13. Estimated least squares means for calf birth weight, actual and 200-day adjusted weaning weights and daily weight gain of 1/2-Friesian calves at Chizombezi multiplication centre, 1974-83.
|
|
No. |
Birth weight |
No. |
Actual weaning wt. |
200-day adjusted wt. |
Daily wt. gain |
|
(kg) |
(kg) |
(kg) |
(kg) |
|||
|
Overall |
580 |
30.5 |
323 |
135.1 |
142.3 |
0.56 |
|
Season of birth |
||||||
|
Nov.-March |
62 |
29.8a |
33 |
131.7a |
151.4a |
0.61a |
|
April-May |
279 |
30.9b |
183 |
131.0a |
131.5b |
0.50b |
|
June-Aug. |
73 |
31.8b |
39 |
133.2a |
135.9b |
0.52b |
|
Sept.-Oct. |
166 |
29.3a |
68 |
144.3b |
149.6a |
0.60a |
|
Year of birth |
||||||
|
1974 |
31 |
31.0a |
31 |
142.1 acd |
146.3a |
0.57a |
|
1975 |
16 |
29.6a |
16 |
135.2 acd |
145.9a |
0.58a |
|
1976 |
31 |
33.9c |
30 |
147.1 ac |
161.5b |
0.64b |
|
1978 |
31 |
31.0a |
29 |
115.0b |
140.2c |
0.55 ac |
|
1979 |
127 |
29.9 a |
121 |
135.6 ce |
141.7 ae |
0.56 a |
|
1980 |
104 |
29.5 bd |
42 |
136.4 ae |
133.7 cef |
0.52 ce |
|
1981 |
99 |
29.5 bd |
54 |
134.0 de |
127.0 df |
0.49 de |
|
1982 |
73 |
27.0 b |
- |
- |
- |
- |
|
1983 |
68 |
33.0c |
- |
- |
- |
- |
Within variable groups, row means followed by the same letter do not differ significantly (P < 0. 05). No letter following indicates that the variable group did not show a significant difference in the analysis of variance.
The 200-day adjusted weaning weight and daily weight gain of calves decreased between 1974 and 1981 (Table 13). The regressions of 200-day weaning weight and daily weight gain on years indicated that these characters had been decreasing by 3.6 and 0.16 kg/year, respectively. The regressions were significant at the 10% level of probability.
The seasonal effects on calf birth weight, 200-day adjusted weaning weight and daily weight gain follow the patterns of rainfall and availability of feed. Calves born after the major rainy season were heavier as a result of more green feed being available to their dams during the later phases of pregnancy, while calves born in September through March were lighter at birth due to poor nutrition of dams in the dry season which begins in June. However, the calves born at this time benefited from the increased feed availability during the next rainy season and hence weaned 15 kg heavier than calves born in other seasons.
The unadjusted means of reproductive parameters calculated for crossbred cows kept at Tuchila are given in Table 14. The few data available suggest that age at first calving has been increasing over the years. This is contrary to the trend found with data from the smallholder farms. On the other hand the mean calving interval of 432 ± 16 days and the mean days open of 154 ± 16 days found for 60 cows at Tuchila were much lower than figures estimated for smallholder herds (510 and 231 days). There do not seem to be any year trends in calving interval and days open at Tuchila.
The mean total lactation milk yield for 52 crossbred cows at Tuchila was 3121 ± 211 kg (Table 15). A breakdown of milk yield by breed of cow gave figures of 1240 kg for 1/2 Friesians, 3850 kg for 3/4 Friesians, 2962 kg for 7/8 Friesians and 4840 kg for 15/16 Friesians. The higher mean total lactation yield observed at Tuchila compared with the mean for smallholder herds (2225 kg) is the result of the higher percentage of high-grade cattle and the better feeding strategy at Tuchila. The lower mean yield for the 1/2 Friesians at Tuchila compared with 1/2 Friesians on smallholder farms (1950 kg) could be explained by the fact that the 1/2 Friesians kept at Tuchila were those that failed the minimum milk yield standard of 5 kg per day during the first 3 weeks postpartum and hence were not sold to smallholders.
The milk yield per day of lactation in Tuchila was fairly stable from 1977 to 1980 but fell in 1981. This trend was also observed in the smallholder herds, which suggests that the government farms and research stations also suffered from feed shortages as a result of the poor weather in 1981.
Table 14. Raw means and standard deviations (SD) of reproduction parameters at Tuchila, 1976-82.
|
Year |
Age at first calving (months) |
Calving interval (days) |
Days open |
|||
|
No. |
Mean ± SD |
No. |
Mean ± SD |
No. |
Mean ± SD |
|
|
Overall |
23 |
38.9 ± 1.8 |
60 |
432 ± 15.5 |
60 |
154 ± 15.5 |
|
1976 |
5 |
34.0 ± 2.1 |
4 |
413 ± 22.0 |
4 |
135 ± 22.0 |
|
1977 |
10 |
34.7 ± 3.2 |
9 |
433 ± 23.3 |
10 |
150 ± 24.4 |
|
1978 |
5 |
35.1 ± 1.5 |
10 |
415 ± 19.3 |
10 |
137 ± 19.3 |
|
1979 |
3 |
50.1 ± 1.8 |
8 |
367 ± 15.2 |
8 |
87 ± 15.2 |
|
1980 |
- |
- |
15 |
469 ± 43.9 |
14 |
198 ± 46.5 |
|
1981 |
- |
- |
8 |
406 ± 27.9 |
8 |
128 ± 27.9 |
|
1982 |
- |
- |
5 |
431 ± 26.4 |
5 |
153 ± 26.3 |
Table 15. Raw means and standard deviations (SD) of production parameters at Tuchila, 1977-81.
|
Year |
No. |
Lactation yield (kg) |
Lactation length (days) |
Yield/lact. Day (kg) |
|
Mean ± SD |
Mean ± SD |
Mean ± SD |
||
|
Overall |
52 |
3121 ± 211 |
327 ± 13.5 |
9.1 ± 0.5 |
|
1977 |
4 |
2816 ± 899.5 |
267 ± 65.5 |
8.8 ± 2.3 |
|
197x |
13 |
3605 ± 426.0 |
357 ± 23.8 |
10.0 ± 0.8 |
|
1979 |
10 |
3579 ± 384.8 |
343 ± 14.8 |
10.3 ± 0.8 |
|
1980 |
6 |
3166 ± 555.6 |
291 ± 23.7 |
10.7 ± 1.3 |
|
1981 |
17 |
2643 ± 413.5 |
322 ± 31.3 |
7.4 ± 0.8 |
