Survival, growth and reproductive performance in F1 crossbred cattle produced and managed on station in the Gambia

A Diack, F B Sanyang and N Corr

International Trypanotolerance Centre, PMB 14, Banjul,
The Gambia, West Africa
a.diack@itc.gm  ;  adiack89@yahoo.com

Abstract

In a trial whereby a large number of cows were needed to calve at approximately the same time, opportunity was taken to establish a crossbred cow population at the International Trypanotolerance Centre (ITC).

A slight improvement in the traditional husbandry system revealed a great productivity potential of these crossbreds. Their survival rate to one year (i.e., 90.0 % for the Jersey x N'Dama (J x N) and 71.2 % for the Friesian x N'Dama (F x N)) was proved satisfactory in the local environment, though conclusions are that more attention is needed for rearing Friesian type F1 calves in the tropical environment. With an overall mean birth weight of 17.7 ± 4.1 kg and an overall mean daily weight gain (DWG) of 0.220 ± 0.104 kg they attained an average weight of 100.6 ± 29.9 kg at one year. Their relatively retarded growth recommended a better management. Puberty was attained at 478.2 ± 13.9 days, age at first calving 970.5 ± 94.1 days and the overall mean calving interval and open period were 400 ± 82.5 and 117 ± 83.2 days, respectively.

These reproduction data showed that the crossbreds mature earlier and have shorter calving intervals than the N'Dama breed.

Key words: Crossbreds, Friesian, Jersey, N'Dama, growth, reproduction

Introduction

In 1994, at the International Trypanotolerance Centre (ITC) a disease-nutrition trial (Bennison 1997) was planned in which a large number of cows which had to calve at the same time were needed. This could only be achieved by synchronising all open N'Dama cows available at the time. It was then decided that this opportunity be taken to use semen from exotic dairy breeds in order to produce F1 animals for the purpose of peri-urban milk production. The programme envisioned was a continuous F1 production scheme as proposed by Madalena (1993). The resulting males would just be a by-product and therefore destined to slaughter or used for draught purpose after castration. At that time the methods of synchronising N'Dama cows were still not perfect and as a consequence quite a few twin births resulted, something which naturally occurs extremely rarely in N'Dama cows. In order to get a reasonable number of F1 cows the synchronisation and insemination was then repeated in 1995 and to a lesser degree in 1996. The first phase of that scheme focussed on producing, rearing and managing F1 crosses on station to evaluate their productivity and adaptability to the peri-urban small-scale farms. The data generated are analysed here so as to constitute a reference for small-scale farmers involved in producing and exploiting F1 crossbreds.

Materials and methods

F1 production and rearing

The production of the F1 population was done by artificial insemination following oestrus synchronisation of the N'Dama cows. Deep-frozen semen of the Jersey type was obtained from New Zealand and that of Holstein-Friesian through FAO from an AI station in Italy. In both cases semen from test bulls was requested, since the aim was to determine the value of the breed and not of any individual sire. The synchronisation was done so that the calves were born at the end of the rains when feeding for both calf and dam was optimal. Out of the synchronised N'Dama cows 142 crossbred calves were obtained of which 77 of the Friesian type (43 males and 34 females) and 65 of the Jersey type (30 males and 35 females).

The new-born calf was allowed to suck colostrum and milk ad libitum during the first week. The calves, until weaning at ten months, were raised in the traditional way. They were used to stimulate the milk let down effect and were allowed to feed on residual milk left after milking during mornings and evenings. The calves were then reared as a group in a single pen and offered groundnut hay and water ad libitum. At weaning, males were castrated to be sold when they attained a 100-kg target live weight. The heifers were removed from their male counterparts by twelve months of age and reared as a separate group. Dry season feed comprised groundnut hay offered ad libitum and a supplement consisting of a mixture of groundnut cake, rice bran and cottonseed. During the rainy seasons the animals grazed the natural pastures within the station premises. The same feeding system was applied for the rest of the station herd. When the heifers reached the age of 20 months, a N'Dama service bull was introduced and stayed with the herd throughout. Prophylactic treatment for control of gastrointestinal parasites was given twice during the rainy seasons (from June to October) to calves and heifers and acaricide treatment for tick control applied to all categories throughout the year. Vaccination was done against anthrax, black quarter and haemorrhagic septicaemia, and all clinical cases were attended.

Data collection and analysis

All animals were identified using ear tag numbers at birth and their birth weights were recorded in the herd book. All animals were weighed monthly. All matings and calvings were recorded based on the observations of the herdsmen. Thus, mating and calving dates were used to compute gestation lengths and open periods from calving intervals. Calving interval was determined as the number of days between two consecutive calvings for the same cow. Records of matings were reviewed to calculate the gestation length and open period in each calving interval. In case the service date was unknown, only the calving interval was considered. Therefore, the data set used to determine open periods and gestation lengths represent only a subset of data used to calculate calving intervals. Therefore, unequal numbers of records were used for computing the measurements of the various traits.

For the analysis of gestation length, birth weight and mortality rates the following model was used:

y = year_i + sex_j + type of birth_k + breed_l + ε_ijklm

For weight development, the same linear model was applied but included in addition herd, month and age.

Calving interval was analysed with the following model:

Y_ijkl = breed_i + birthtype_j + year_k + ε_ijkl

Results

Birth types in the F1 cattle herd

A total of 142 crosses was born in three crops from 1995 and 1997 (Table 1). There were more multiple births in 1995 and 1996 than in 1997 (P<0.001)..

Gestation length and birth weights

In cattle, the gestation length is largely determined by the genotype of the foetus. In this study, gestation time was known for 117 pregnancies which had a mean gestation time of 279.6 days with a standard deviation = 5.7 days. There were 133 available birth weights of the crossbreds of which the overall mean was 17.7 kg with a standard deviation of 4.1 kg (Table 2).

As a baseline value the 1995 born (F x N) single males were carried 284.1 ±1.8 days and had a mean birth weight of 22.2 ± 0.8 kg.The different contrasts obtained between levels of major factors and their respective significance are summarised in Table 3 for gestation length and birth weights.

Mortality

Out of the total of crossbreds born 18 animals (13.1%) died at or shortly after birth; therefore, there were 124 animals left. Mortality was significantly higher (P<0.0004) in males than females, and in the group born in 1996 (P<0.02) compared to the others. For the factor breed type only a tendency could be suspected (P<0.08). Up to one year the mortality of (J x N) was 10.0% and that of (F x N) was 28.79%, a difference that was significant by Fisher's exact test (P<0.013). The most frequent cause of death was diarrhoea. All other causes arose only sporadically.

Growth

There were great differences in weights between breeds and sexes. Live weights at specific ages are shown in Table 4 whereas the weight development expressed as daily weight gain at specific periods is illustrated in Graphs 1 and 2.