Citation of this paper |
Data on body dimensions were collected from 257 purebred N’Dama calves at 12 months of age at Fashola stock farm in a southwestern zone of Nigeria. Measurements considered were Head to Shoulder (HDS), Shoulder to Tail Drop (STD), Body Length (BLT), Height at Withers (HTW), and Heart girth (HGT).
On subjecting the data to analysis of variance it was
found that all the five body dimensions were strongly influenced (p<001) by
calf sex and birth season. Birth year also affected all the body dimensions
significantly (p<001) except HDS. Calf sire had no effect (p>001) on any
of the body measurements.
Over the years, emphasis has shifted from subjective methods of appraising cattle to more objective methods like the use of linear measurements of different body parts. Linear measurements can be used in assessing growth rate, weight, feed utilization, and carcass characteristics in farm animals (Brown et al 1973). Linear measurements can be taken at relatively lower costs with a high relative accuracy and consistency. Gilbert and Gregory (1952) noted that linear body measurements describe an animal more completely than conventional methods of weighing and grading.
Linear measurements are divided into two groups, which include skeletal and tissue measurements. Skeletal measurements include all the height and length measurements while tissue measurements include heart girth, chest depth, punch girth, and width of hips (Blackmore et al 1995). These body measurements can be further divided into horizontal measurements like body length (BLT) and head to shoulder (HDS) and vertical measurements like height at withers (HTW) and chest depth.
In skeletal development, there is a faster bone growth in length than in width and circumference (Brown et al 1956). In Angus cattle, wither height was found to be about 50% matured at birth and skeletal growth ceases at 30-40months (Brown et al 1956). Orheruata (1988) also observed that body length, height at withers and shoulder to tail drop were about 40-50% matured in N’Dama cattle at birth. Brown et al (1983) in a study of skeletal pattern in Angus heifers showed that linear measurements in this breed matured in the following order: hip height, shoulder width, hip width, wither height, heart girth, chest depth, body length, and loin width. Orheruata (1988) put forward the following order of maturity among five body dimensions: head to shoulder, height at withers, heart girth, shoulder to tail drop, and body length in birth sexes of N’Dama cattle.
Sex differences have been observed in the developmental pattern of linear measurements in certain breeds. Walker (1964) working with East African and shorthorn cattle, observed a higher level of development in female than in males of same breed. In their own study, Green and Carmen (1978) showed that skeletal development within a population became relatively more uniform with age. Certain body dimensions can be helpful in evaluating the pattern of development of the skeletal frame. As weight increases, bone and muscle develop first (Berg 1978; Berg and Butterfield 1976). As maturity for bone and muscle is approached, the fattening process increases. Monitoring these changes objectively with body measurements can aid in guiding a breeding programme, as the fattening process is synonymous with a decline in the efficiency of food use (Berg and Butterfield 1976).
A number of studies have been carried out on linear measurements in several African cattle breeds. For instance, Spencer and Eckert (1988) working with Gambian N’Dama derived production equations for weight, taking sex and seasonal variations into consideration. Orheruata (1988) found that in beef cattle, a high girth measurement meant more muscle in meat. A study of linear measurements in this part of the world is important because most traditional African farmsteads lack a weighing machine and adequate knowledge to understand its manipulation. The use of the calibrated weigh band which is very common in developed countries, is not common in the developing world because their calibrations are based on temperate breeds of cattle. But simple linear measuring devices will be easy to handle and will assist in selecting animals to become the parents of the next generations. This study therefore investigates the relationship between body dimension and environmental characteristics of N’Dama cattle in a humid tropic zone of Nigeria.
N’Dama cattle kept at the Fashola stock farm were used in this study. The farm was established in 1947 as a multiplication and improvement center for N’Dama cattle to be distributed to local farmers and for research purposes. The farm is situated within the tsetse fly belt where Trypanosoma vivax is the most prevalent trypanosome. This is the reason why only trypano-tolerant breeds like N’Dama are kept on the farm. The climatic conditions prevalent on the farm are more typical of the forest zone due to its location at the fringe of the forest region. The rainfall pattern is bimodal with two maximal regimes, in June and September, with a short break in August.
The mean monthly rainfall for the years 1947 to 1953 were recorded and the different seasons were categorized into four namely January to March (Season 1), April to June (Season 2), July to September (Season 3), October to December (Season 4).
For the purpose of this study, 257 offspring of the N’Dama breed kept at the Fashola stock farm situated in Oyo State, in a humid tropic zone of Southern Nigeria were used. Linear measurements were taken originally on 270 calves at 12 months. After the elimination of sires with less than 5 progenies, there were 9 sires for analysis, the number of calves therefore reduced to 257 (121 males and 136 females).
Data were analyzed using the least squares and maximum likelihood procedure of Harvey (1987)
The model used was:
YIJKLM = U + YI + SJ
+ CK + RM + eijklm
Where YIJKLM = observed linear measurement
U = common mean
YI = Effect of birth year
SJ = Effect of season
CK = Effect of Sex
RM = Effect of Calf size
eijklm = Uncontrolled environmental and genetic deviations attributable to the individuals within Sire group
The results (Table 1) reveal that Calf Sire and Birth year had no effect (p>001) on Head to Shoulder (HDS) measurement. However, Calf sex and Birth season strongly affected HDS (p<001). The HDS lengths of male calves were generally longer than the corresponding measurement in female calves by about 37%, 5% higher than the 32% reported by Alade (1990). Calves born in April-June had the longest HDS measurements while calves born in October-December had the shortest HDS measurement.
|
Table 1 Least square analysis of variance of five linear
body measurements of N’Dama calves at 12 months |
||||||
|
Sources of variation |
Df |
HDS |
STD |
HTW |
HGT |
BLT |
|
Calf Sire |
8 |
1016 |
255 |
234 |
795 |
373 |
|
Calf Sex |
1 |
245** |
338** |
355** |
364** |
1179** |
|
Birth year |
3 |
474 |
1699** |
845** |
6528** |
2248** |
|
Birth season |
3 |
151** |
169** |
173** |
992** |
620** |
|
Remainder |
241 |
2691 |
2179 |
1924 |
4568 |
6019 |
|
HDS = Head to Shoulder; STD = Shoulder to Tail Drop; HTW = Height at
Withers; HGT = Height girth; BLT = Body length |
||||||
All the sources of variation had strong effects on Shoulder to Tail Drop (STD), except Calf Sire Male calves STD measurements were about 326% longer than the STD measurements taken on their female counterparts. Calves born in season 2 of 1960 had the largest STD while calves born in season 1 of 1953 had the lowest STD.
Calf sex, calf year and calf season significantly influenced (p<001) Height at Withers (HTW). Male calves were taller than their female counterparts. The tallest calves were born in season 2 of 1952 while the smallest calves were born in season 1 of 1953.
All sources of variation except Calf Sire greatly affected (p<001) Heart Girth (HGT) This agrees with results of Alade (1990). The Heart girth measurements taken on the males were higher than those taken on female calves. The calves with the largest heart girths were born in season 2 of 1950 while the those with lowest heart girth were born in season 4 of 1951.
Birth year, birth season and calf sex all strongly influenced (p<001) body length (BLT). Calf Sire had no effect on BLT. This finding is in agreement with Orheruata (1988) and Alade (1990). Male calves were longer than female calves. The longest calves were born in season 2 of 1950 while the shortest calves were born in season 4 of 1951.
The differences in the measurements obtained between the sexes can most probably be attributed to the fact that the gestation period of the male foetus is often a little longer than that of the female. The different developmental rates between males and females with regard to the effect of season on linear measurement is most probably hinged on the fact that annual rainfall affects pasture availability, diseases, changes in management techniques and genetic progress (Fall et al 1982). It can also be explained by the findings of Egbunike and Ologun (1993) that calving in the rainy season promotes better growth rate from birth to weaning and up to puberty.
Findings of this study revealed that linear body measurements of N’Dama calves were predominantly influenced by calf sex, birth year and birth season. However, calf sire showed no significant effect on any of the linear body measurements at 12 months.
It is therefore recommended that in
selecting for linear measurements, calf sex, birth season and birth year should
be given serious consideration at 12 months. In deriving prediction equations
for weight and other growth traits, appropriate adjustment factors for birth
year and birth season should be introduced into the equation.
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Received 31 March 2003; Accepted 12 May 2003