| Livestock Research for Rural Development 13 (5) 2001 | Citation of this paper |
Data from the Small-scale Dairy Project were analyzed to compare the reproductive performance of Simmental × Tswana crosses and purebred Tswana milking cows from smallholder farms. The effects of season (dry and wet), breed group (Tswana and Simmental crosses) and their interaction on calving interval and days open were determined. The effects of breed and year and their interaction on calving rate were determined. Correlation of monthly calving and monthly rainfall was computed.
There was no
difference in calving interval and days open between Tswana (576±11.3 and 296± 11.3
days) and Simmental crosses (584± 22.3 and 303± 22.3 days) cows. There were no effects
of season on the calving interval and days open. There was also no breed x season
interaction. Peak calving occurred between October and January (52.3%) while between May
and June 15.3% of cows calved. The mean calving rate of Tswana cows (68.2%) tended to be
higher than that of. Simmental crosses (62.5%) cows. There was a significant effect of
year on calving rate. The implications of the results are discussed in relation to the
effects of breed and season on the reproductive performance of these breeds.
The Dairy Research Program of the
Department of Agricultural Research has investigated smallholder milk production around
peri-urban areas of Gaborone since 1985. When the project started in 1985 it was envisaged
that the adoption of improved dairy husbandry techniques by the traditional farmers would
increase milk production and consequently diversify rural economic activities, improve
human nutrition at household level and reduce the country’s dependence on
imported fluid milk. It was found consistently that Simmental crosses produce more milk
than the Tswana cows on the same management regime. During the 1989/90 lactation periods,
the Simmental × Tswana crosses produced twice the amount of milk as Tswana cows (806 vs.
462 kg/lactation) (APRU 1990). The difference in milk yield was attributed to the
difference in the genetic potential of the genotypes.
The National Development Plan 6
(1985-91) recognized the need to increase milk production by peri-urban small-scale
farmers for home consumption and surpluses for sale to the rapidly growing urban
population. Crop-livestock systems are such that cattle provide draft, meat and milk
products. In Botswana cattle depend on natural pasture for their nutritional requirements
and often experience nutritional deficiencies especially in the dry season. These
nutritional stresses often lead to loss in weight and delayed reproductive activities,
which further contributes to fluctuations in milk supply.
Due to shortage of feed supply and
reduction in the area available for grazing, nutrition has become a major constraint to
animal productivity in many parts of Africa (Mukasa-Mugerwa et al1992). This limitation can manifests itself in both beef
and milking herds in terms of longer calving interval and reduced milk off take. According
to Voh and Otchere (1989) the percentage calf crop is crucial for herd replacement while
milk off take for calf and human is dependent on reproduction.
The importance of regular calving
interval in a milking herd is emphasized by the fact that it costs money in lost income
for each day the calving interval is prolonged beyond 365 days. A significant increase to
productivity could therefore be feasible by paying attention to problems of reproductive
inefficiency (Mukasa-Mugerwa et al 1992). Hence
an important starting point in any animal improvement package is to assess the
reproductive performance of the herd (Voh and Otchere 1989).
Though the major aim of the smallscale
dairy project was to increase milk production through improved nutrition and
crossbreeding, it was hoped that other important parameters like reproductive wastage due
to nutritional stress would be reduced. It was thus deemed necessary to investigate the
effects of improved feeding and cow genotype on the reproduction of the participating
herds.
The objective of this study was to
assess breed differences under improved feeding during the dry season on the reproductive
performance of cows kept by smallholder milk producers around the peri-urban areas of
Gaborone.
Farmers participating in the Smallscale
Dairy Project on average cultivated 6 ha of land and practiced a mixed crop and livestock
system within the communal grazing lands (APRU 1986). In Botswana grazing pasture is not
improved and its seasonal variation in quantity and quality follows the annual rainfall
pattern. The most widely reared cattle are the Tswana, which belong to the humped Sanga
type. The rearing system operates on a communal use of grazing land and thus natural
mating is not controlled. However, the participating farmers observed cows that were
on heat and confined them with a Simmental or crossbred Simmental bull in a kraal. The wet season covered the months of November to
April and the dry season covered the months of May to October. Generally cows calve during
the wet season to take advantage of abundant feed supply which promotes better milk
production hence a better chance of survival of the calf. However, some animals tend to
calveduring the dry season.
The data were obtained from pooled
records kept by the small-scale dairy research project participants located within a
radius of about 20 km from Gaborone. The records cover a seven-year period (1985 to the
1992). Forty-five farmers participating in
the project, each with an average of 16 cattle were selected. They fed cereal crop
residues, Lablab (Lablab purpureus) hay, sorghum
bran, bone meal and salt during the dry season . However, the number of animals per farm per
year varied as farmers could sell or slaughter their animals at will. During the wet
season, feed resources were natural grazing, sorghum bran, bone meal and salt. To date
most of the original farmers who participated in the on-farm research are keeping and
milking their crossbred cows (mainly Simmental x Tswana crosses) and Tswana cows.
The cows were milked either twice or
once a day depending on either the managerial capacity of the farmer, the needs of the
calves or the availability of feeds. The calves were allowed to suckle their dams before
milking for a few minutes to stimulate milk letdown. After milking, the calves were
allowed to suckle again to draw residual milk for 30 minutes.
Calving interval was taken as the
period between two consecutive calvings and was not adjusted. The total number of records
included in the analysis when calving rate was the dependent variable was 502, whilst 387
records were included in the analysis when calving interval and days open were dependent
variables. Observations that had less than 325 days (gestation and uterus involution)
between two consecutive calving were excluded. The effects of season, (dry and wet), breed group
(Tswana and crosses) and their interaction on calving interval and days open were
determined using General Linear Model procedures
(SAS ).Differences
between means in interaction subclasses were tested by least significant difference (LSD).
Cows that had three or more consecutive calvings were included in the analysis for the
calving interval. Monthly calving frequencies were computed as percentages of the total
number of calves born. The relationship between rainfall and monthly calving frequencies
after a delay of 9, 10 and 11 months were established by means of calculating correlation
coefficients (r). The calving rates between the two genotypes were compared using
Chi-Square test. Calving rates were calculated for each year starting from 1986 to 1991.
The effects of year on calving rates were tested using GLM procedure and means separation
was achieved using Duncan multiple range test. Results are reported as least square means ± standard error.
Within the period 1985 to 1992 the mean calving interval for the cows (n =387) was 577 days. Tswana cows tended to have a shorter calving interval and days open, compared to Simmental crosses (Table 1). This difference was not significant (p> 0.05).
Table 1. Mean calving
interval and days open of Simmental × Tswana crosses and Tswana cows. |
|||
Genotype |
No of cows | Calving
interval (days) |
Days
open (days) |
Simmental Cross |
78 |
584±22.3 |
304±22.3 |
Tswana |
309 |
576±11.3 |
296±11.3 |
Level of significance |
|
0.750 |
0.750 |
There were no effects (p> 0.05) of season on the calving interval and days open (Table 2).
Table 2. The effects of season on the calving interval
and days open |
|||
Season |
No of cows |
Calving interval
(days) |
Days open (days) |
Dry |
173 |
570±18.2 |
290±18.2 |
Wet |
204 |
589±17.1 |
309±17.1 |
Level of
significance |
|
0.453 |
0.453 |
Simmental × Tswana crosses that
calved during the dry season tended to have a shorter mean calving interval than Tswana
cows. Days open followed the same trend as calving interval (Table 3). Among the cows that
calved during the wet season Simmental crosses tended to have a longer calving interval
compared with Tswana cows. Days open had a similar trend as calving interval.
Table 3.
Interaction of season and breed on calving interval and days open |
||||||
Parameter |
Dry |
|
Wet |
P |
||
Simmental cross |
Tswana |
|
Simmental cross |
Tswana |
||
Calving
interval |
561.1±32.3 |
579.2±16.9 |
|
606.0±30.7 |
571.9±14.9 |
|
Days
open |
281.1±32.3 |
299.2±16.9 |
|
326.0±30.7 |
291.9±15.0 |
0.297 |
Monthly calving
frequencies as percentage of the total number of calves born showed a bimodal calving
pattern with peak calving occurring during October to January representing 52.3% of the
calvings. The small peak occurred in May to June
representing 15.3% of the calving (Figure 1).
The calving rates for the years 1986,
1988, 1989, 1990, and 1991 tended to be higher for Tswana cows than Simmental × Tswana
crosses. However, the differences were not significant except for the year 1987 (Table 4).
The mean calving rate of Tswana cows was slightly higher (p=0.330) than that of Simmental
× Tswana crosses. The highly significant difference between breeds in calving rates
during the year 1987 cannot be explained.
Table 4. Mean
calving rates (%) of Simmental crosses and Tswana cows |
|||||
Year |
n |
Simmental
x Tswana |
Tswana |
Prob. |
|
1986 |
28 |
54.6 |
56.7 |
0.88 |
|
1987 |
90 |
50.0 |
84.4 |
0.005 |
|
1988 |
95 |
63.0 |
66.7 |
0.71 |
|
1989 |
125 |
75.6 |
79.3 |
0.67 |
|
1990 |
103 |
63.0 |
67.7 |
0.63 |
|
1991 |
61 |
52.6 |
53.1 |
0.97 |
|
Mean |
84 |
62.5 |
68.2 |
|
|
There was a significant (p<0.001)
effect of year on calving rate (Table 5). Strong
correlation was observed between calving and the previous monthly rainfall at 9 (r= 0.58;
p<0.05), 10 (r=0.84; p<0.001) and 11 (r=0.72; p<0.01) months.
Table 5: The
effect of year on the calving rates |
||
Year |
n |
|
1986 |
28 |
55.0±0.84c |
1987 |
90 |
76.2±0.50a |
1988 |
95 |
63.4±0.50b |
1989 |
125 |
76.0±0.43a |
1990 |
103 |
64.1±0.47b |
1991 |
61 |
50.2±0.60d |
abc Figures
with different superscript are different: p<0.05 |
||
Butterfield and Lishman (1990)
attributed low fertility to deficiencies in management programs including feeding regimes.
In the present study calving interval between Simmental × Tswana crosses and Tswana cows
was similar though Tswana cows tended to have a shorter calving interval. However in a
typical traditional setup where no supplementary feeding is practiced, difference in
performance between the indigenous and temperate breeds would be expected. It has been
observed that under nutritional stress the temperate breeds succumb more than indigenous
breeds. Peters (1984) attributed prolonged anoestrus when Bos taurus animals are introduced in the tropics to
malnutrition. However, in the present study, cows were offered supplements, which perhaps
explains the lack of difference between the genotypes. It is also possible that crossing
Simmental with Tswana introduced traits into Simmental crosses, which enables them to
withstand stress conditions. van Zyl et al (1992) found that cows with more than 50%
Afrikaner breeding (Sanga type cattle of South Africa)
had longer calving intervals than Hereford and Bonsmara but not Simmentaler.
Ideally the calving interval should be as near to 365 days as possible. However the values
reported here are higher than 365 days for both genotypes, indicating that regardless of
the supplementary feeding, reproduction was not optimal. Assuming that the gestation
period is 280 days and then adding 45 days for uterus involution, the long calving
interval is explained by the long period to conception (days open), which had a mean of
297 days. According to Peters (1984), to achieve a 365-day calving interval,
calving-to-conception interval should not be more than 85 days. Reasons for a long
re-conception period are nutrition, reproductive diseases and heat stress. In on-station
studies, APRU (1991, 1992) reported calving interval for Simmental × Tswana crosses of
385 and 400 days, respectively. These figures are closer to the 365 days than the values
reported in the present study. This difference is indicating variation in management
levels between on-station trials and on-farm situation. The implication therefore is that
smallholder farmers face difficulties in attaining managerial levels found in the research
station.
The lack of seasonal effect on calving
interval may imply that supplementary feeding obviated the effects of season. Often,
during the wet season there is sufficient dry matter from grazing and nutrient supply is
adequate for reproductive activities. During a prolonged dry season, nutritional
deficiencies cause cows to lose weight resulting in post-partum anoestrus and delayed
re-conception (Rennie et al 1977).
Voh and Otchere (1989) estimated a
calving interval of 730 days for Zebu cattle under traditional agro pastoral management in
Northern Nigeria. This is higher than the value found in the present study (563 days).
Citing other workers (Pullan 1979; Wheat et al 1972; Oyedipe 1982), Voh and Otchere (1989)
indicated that under improved nutritional conditions calving interval is shorter than 546
days. In the present study supplementary feeding probably played an important role in
shortening the calving interval. The insignificant effects of interaction between season
and genotype on calving interval suggest that both breeds may be responding the same to
the effects of season.
The slight difference in the calving rates indicate that slightly more Tswana cows were able to calve than Simmental crosses regardless of the same feeding management. These values are higher than those reported by Rennie et al (1977) of 46% in Botswana, or by Gubbins and Prankerd (1983) in Zimbabwe (40-52%) for cows kept as communally managed herds. The difference between these reports and the present study may be attributed to the supplements fed in our study. Rainfall data indicates a high amount of rain was recorded in the rainy season 1987/88 and 1988/89. However, high calving rates were observed in the years 1987 and 1989 followed by the years 1988 and 1990. The trends in calving follow the trends in rainfall that fell in the study area. However, the bimodal pattern reflects the benefits of supplementary feeding. Butterworth (1983) attributed the bimodal calving distribution in the Lowveld of Swaziland to the similarities in the nutritional levels of the forage during the dry and wet months. According to Martin et al (1992), a seasonal pattern of food availability has resulted in an evolution of the reproductive mechanism of herbivore animals in which plentiful supply of nutrients is a cue to initiating reproductive function. In the present study the initiation of breeding activities was started after the rain due to abundance of feed but was only reflected through calving 10 months later (Figure 1). This observation was confirmed by Butterworth (1983) in which monthly calving of Nguni cattle was highly correlated with rainfall that fell 10 months earlier. The rainy season 1985/86 and 1989/1990 were drought years (Boitumelo, personal communication) and thus their effect on calving rate was reflected 10 months later in 1986 and 1991 respectively. Thorpe and Cruickshank (1980) attributed the effect of year on calving rate of Zebu and Sanga cattle of Zambia to the variation in quantity and quality of forage between years.
According to van Niekerk (1982) low
calving percentages can often be ascribed to poor nutrition at critical stages of the
cow’s reproduction cycle.
Inefficiency in reproductive
performance is caused by many factors and often it is difficult to identify which one
contributes more to inefficient reproduction. However, in the tropics, under-nutrition
plays a major role in depressing reproduction. In the present study it was postulated that
dry season supplementary feeding of cereal by-products and home grown fodder to Simmental
× Tswana crosses and Pure Tswana will improve their reproductive performance. This
appears to have been the case, since animal performance between the dry season and the wet
season were similar, indicating that nutrient supply for reproduction during the dry
season may have equaled nutrient supply during the wet season. However, reproduction was
not optimal, probably indicating other problems such as diseases, which were not
investigated in this study.
The authors wish to thank B M
Mosimanyana for his comments and the Biometrics staff for helping with statistical
analysis. B Mabechu and S Tshenyo provided
technical assistance. The International Development Research Centre (IDRC) and Botswana
Government sponsored the Small-scale Dairy Project.
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Received 29 July 2001