Effects of seasonal forage supply on some fertility parameters in the Small East African goat in northern Kenya

T. Rutagwenda, H.J. Schwartz, A.B. Carles & A.N. Said

Department of Animal Production
University of Nairobi
P.O. Box 29053 Nairobi Kenya

Introduction
Materials and methods
Results
Discussion

Summary

Various fertility parameters are under investigation in the Small East African goat at Isiolo, northern Kenya. A programme of aseasonal breeding is used and parameters are examined in relation to the quantity and quality of forage available. Breeding groups consisting of 18 females each are used: bucks stay with one group for two months and are then transferred to another group. Records are taken for mating, abortions, birth weights, weaning weights and pre- and post-partum weights of dams. Preliminary results from the first four breeding groups indicate high conception rates in animals mated during the rainy season and low rates in those mated during the dry season. Weights were higher for kids born at the start of and weaned after the long rains when forage was good. High kid survival rates were recorded for animals born at the start of the long rains.

Introduction

The Small Ruminant Research Unit in the Department of Animal Production of the University of Nairobi carries out investigations of behavioural, physiological and morphological adaption of indigenous sheep and goats to seasonal changes of forage availability and forage quality on semiarid and arid rangelands in northern Kenya. This paper reports preliminary results of a study of the effects of seasonal changes in forage supply on some fertility parameters in Small East African (SEA) goats kept on a semi-arid thornbush savanna pasture in Isiolo District. The breeding programme with the SEA goats was initiated in January 1984: the results reported' below have not been subjected to detailed statistical analysis and only reflect rather general trends.

Materials and methods

EXPERIMENTAL ANIMALS

In early 1983 a herd of SEA goats comprising some 60 each mature and immature females was provided by the Research Division of the Ministry of Livestock Development. By culling unsuitable animals and further local purchases, 90 mature does and 50 immature females were present at the start of the breeding programme. The majority of the animals had age and previous birth records and if not, were tooth-aged. Ages ranged from one to six years. From this herd, breeding groups with a balanced age structure were established numbering 18 animals each. A systematic, aseasonal breeding programme was designed. Into one breeding group at a time a buck was introduced for two months and after that transferred to the next breeding group to achieve year round mating, kidding and weaning in the experimental herd.

EXPERIMENTAL PASTURES AND HERD MANAGEMENT

The studies were carried out at a small research station situated on a holding ground of the Livestock Marketing Division, Ministry of Agriculture and Livestock Development near Isiolo, 300 km north of Nairobi. The altitude is 1100 m a.m.s.l. and the mean annual rainfall is 510 mm in two rainy seasons (March to May and October-November). The soils are volcanic in origin with some alluvial floodplains along seasonal watercourses. The main vegetation type is a thornbush savannah dominated by various Acacia species with a sparse ground cover of annual grasses, herbs and dwarf shrubs. Along the seasonal watercourses Acacia woodland and dense bush dominated by Grewia species occur and perennial grassland is found on the floodplains.

For most of the year the holding ground is understocked and consequently most of the range is in good condition. The animals are watered from a deep borehole which is part of the station.

There are no fenced paddocks and animals are herded throughout the year. A normal grazing day starts at 07h00, is interrupted for watering at the station with a midday rest between 13h00 and 15h00 and ends at 18h00, when the animals return to the night enclosure. During a grazing day the animals walk 5-10 km, longer distances being travelled during the dry season.

The animals are drenched twice a year with an anthelminthic prior to the rainy season and are vaccinated once a year against Contagious Caprine Pleuro-Pneumonia. Injuries are treated as they occur and an acaricide is applied whenever necessary. A mineral lick is supplied in the night enclosure.

DATA COLLECTION

All events such as mating, abortion, birth and death were recorded continuously: liveweights and milk yields were measured regularly every two weeks. All dead animals were subjected to post-mortem examination to establish the cause of death. Pasture condition was judged every two weeks using a simple classification with four grades incorporating forage availability and greenness (Table 1).

Table 1. Criteria for the classification of pasture condition

Notes:

a) Excluding browse
^b) crude fibre < 30%
^c) crude fibre 30-60%
^d) Crude fibre > 60%

Results

The results reported refer to the first four breeding groups only, which at the time of writing had already completed the weaning stage. Figure 1 shows the dates of mating, kidding and weaning for the four groups in relation to the prevalent pasture condition. Table 2 summarises the observed fertility parameters. Group 1, which was mated prior to the long rains 1984 and kidded at the beginning of the long dry season, showed the highest conception and kidding rates. No abortions were observed. Group 4, mated at the end of the long dry season had the lowest conception and kidding rate combined with the highest abortion rate. The reverse trend was observed for the weaning rate which was highest in group 4 and lowest in group 1.

Figure 1. Reproductive events for four breeding groups of SEA goats related to pasture condition (Table 1 describes pasture condition categories)

Table 2. Fertility parameters observed in four breeding groups of Small East African goats (18 does per group)

Figure 2 shows the number of kids born and surviving to weaning age in the four groups. Lowest survival was observed in group 1 (30 per cent of kids born) with kidding at the beginning of the long dry season and pasture condition 1 prevalent throughout lactation. Survival rate was better in group 2 (45 per cent) with kidding prior to the short rains and in group 3 (63 per cent) which kidded during the short dry season 1984-1985. Survival rate in group 4, where kidding took place at the onset of the long rains 1985, was highest (100 per cent). In all groups the survival rate of single kids was higher than that of twins.

The same trend as in survival to weaning was reflected in the liveweights of the kids from birth to weaning (Figure 3). Lowest mean weights at weaning (5 kg) were observed in group 1 and highest in groups 3 and 4. The lowest individual weaning weight (2.1 kg) was recorded in group 1 and the highest (19.5 kg) in group 4. In all groups mean live weights of singles were higher than those of twins for the whole of the pre-weaning period, although the difference was significant only in group 3.

Figure 2. Survival to weaning in relation to kids born in four breeding groups of SEA goats (18 does per group)

Figure 3. Growth of kids to weaning in four groups of SEA goats

The overall productivity of does in terms of total liveweight of kids at weaning relative to total liveweight of does after parturition (n=18) was lowest in group 1 and highest in group 3 as shown in Table 3. That this ratio is less favourable for group 4 than for group 3 is due to the fact that does in group 4 were much heavier after parturition (37.3 kg) than those in group 3 (30.9 kg) because pasture was good throughout the pregnancy period.

Discussion

The few preliminary results from this investigation demonstrate that the realisation of the productive potential is affected differently by the prevailing pasture condition at different stages in the reproductive cycle. High conception and high kidding rates do not necessarily result in high flock productivity and vice versa. Based on the present results only, one would find it difficult to make recommendations for a restricted breeding season. Further exploration of different combinations of prevailing pasture conditions with varying stages of the reproductive cycle are needed and are currently being carried out. Lines of investigation other than the present one will have to be followed before all mechanisms involved can be determined. It is, for example, not clear if the low conception rates in groups 3 and 4 were caused by low ovulation rates in the females or by reduced semen quality in the male. Such information would be necessary before a feasible supplementation system for breeding stock could be designed. The effects of increased veterinary inputs on fertility under semi-arid range feeding conditions are also still largely unknown. Such studies should be initiated in future.

Table 3. Survival rate of kids and total kid weight at weaning in four breeding groups of Small East African goats (18 does per group)