Responses to a Pennisetum purpureum (Napier grass) basal diet harvested at two different heights and fed with three levels of Leucaena forage to crossbred dairy cows in the subhumid tropics

R W Muinga ¹, W. Thorpe ², J. H Topps ³ and J G. Mureithi ¹

¹ Kenya Agricultural Research Institute (KARI)
PO Box 16, Kikambala, Kenya

² International Livestock Centre for Africa (ILCA)
PO Box 80147, Mombasa, Kenya

³ School of Agriculture
581 King Street, Aberdeen, Scotland, UK

ABSTRACT

Smallholder dairy production based on zero-grazed Napier grass (Pennisetum purpureum cv Bana) fed to crossbred Bos taurus x Bos indicus cows has been introduced to tropical subhumid East Africa. Leucaena leucocephala forage offers a cheap, convenient source of supplementary protein. Thirty-six Ayrshire/Brown Swiss x Sahiwal cows with one to four previous lactations and which calved during the period 26 March to 2 August 1990 were stall-fed individually to evaluate the effects of harvesting height of Napier grass (1.0 or 1.5 m) and level of Leucaena supplement (0, 4 or 8 kg fresh weight) on dry-matter (DM) intake of Napier grass, total DM intake, liveweight change and milk yield. The study began on day 15 of lactation and lasted 98 days. Average daily milk yield and liveweight during the second week of lactation were covariates for milk yield, and for DM intake and liveweight change, respectively. Harvesting height of Napier grass significantly (P<0.001) affected Napier fodder and total DM intakes, liveweight losses and average daily milk yield. Supplementation with Leucaena tended to increase Napier fodder intake, significantly (P<0.001) increased total DM intake and reduced liveweight loss, and increased (P<0.05) milk yield. The results indicate the importance of stage of harvesting of Napier fodder and the benefits from Leucaena supplementation in attaining an acceptable level of performance from crossbred dairy cows in the subhumid tropics.

RESUME

Effet sur des vaches laitières métisses d'un aliment de base de Pennisetum purpureum (herbe à éléphant) récolté à deux hauteurs de coupe complémenté avec trois niveaux de fourrage de Leucaena

L'alimentation à l'auge de vaches métisses Bos taurus x Bos indicus avec des rations de base composées d'herbe à éléphant (Pennisetum purpureum) a été récemment introduite dans les petites exploitations laitières de la zone tropicale subhumide de l'Afrique de l'Est. Les fourrages de Leucaena leucocephala constituent une source bon marché de complémentation protéique. 36 vaches Ayrshire/Brown Swiss x Sahiwal qui avaient connu de une à quatre lactations dans le passé et avaient vêlé entre le 26 mars et le 2 août 1990 avaient été individuellement alimentées à l'auge en vue d'évaluer l'effet de la hauteur de coupe de l'herbe d'éléphant (1 m et 1,5 m) et du niveau de complémentation de Leucaena (0,4 et 8 kg de fourrage) sur la consommation de matière sèche de Pennisetum, la consommation totale de matière sèche, les variations de poids vif et la production de lait. L'expérience a démarré au 15^e jour de lactation et a duré 98 jours. La production moyenne de lait par jour et le poids vif enregistrés au cours de la deuxième semaine de lactation étaient les covariables respectivement de la production de lait d'une part et de la consommation de matière sèche et des variations du poids vif de l'autre. La hauteur de coupe avait un effet significatif (P<0,001) sur la consommation de matière sèche totale et de matière sèche d'herbe d'éléphant. L'apport de Leucaena se traduisait par un accroissement de la consommation d'herbe d'éléphant, une augmentation significative (P<0,001) de la consommation totale de matière sèche, une baisse significative (P<0,001) des pertes de poids et un accroissement (P<0,05) de la production de lait. Ces résultats font ressortir l'importance du stade de coupe de l'herbe d'éléphant et les avantages d'une complémentation de Leucaena pour les performances des vaches laitières métisses en zone tropicale subhumide.

INTRODUCTION

A major constraint on dairy development in coastal subhumid Kenya is the inadequacy of feed resources available on the mixed crop-livestock smallholder farms targeted in the Ministry of Livestock Development's National Dairy Development Programme (NDDP). Soils are free-draining and low in organic matter and fertility, factors which limit the productivity of forages.

Natural pasture is scarce and of poor quality, and its availability in the future may be further restricted by subdivisions of farms into smaller units. Land tenure is freehold. Significant quantities of crop byproducts, with the exception of copra cake and maize bran, are not available. Cash shortages often limit the purchase of these concentrates by smallholder farmers.

To address these problems the Kenya Agricultural Research Institute and the International Livestock Centre for Africa carry out collaborative research on feed resources at the Regional Research Centre, Mtwapa, near Mombasa. The research focuses on developing systems with minimal purchased inputs which can intensify and sustain the production and utilisation of forages. The zero-grazing package extended by the NDDP to smallholders is the target, and the objective is to have profitable milk production through producing, on-farm, adequate quantities of good quality dry matter for feeding throughout the year.

A review of past on-station forage research at the coast indicated the potential of Napier grass (Pennisetum purpureum cv Bana), the legume shrub Leucaena and some herbaceous legumes. Experiences with these forages on farms supported by the NDDP, and the absence of research-based management recommendations, showed that on-station agronomic trials were required. The agronomy research concentrates on improving soil fertility and water-holding capacity through growing the Napier grass in an alley farming system utilising Leucaena hedgerows, combined with intercropped herbaceous legumes and the application of slurry (manure) (Mureithi, 1990).

The animal nutrition research is integrated closely with the forage agronomy programme. Its objective is to develop feeding systems for zero-grazed cows utilising the forage species from the agronomy programme. The experiments have measured feed intakes, liveweight changes and lactation performance of dairy cows fed a basal forage (Napier grass) diet supplemented with protein using locally produced feeds, especially legume forages, and the local crop byproducts copra cake and maize bran.

An experiment in 1989 with Jersey cows supplemented with 300 g crude protein (CP) showed that dry-matter (DM) intakes and milk yields were similar whether the protein supplement was supplied by copra cake or fresh Leucaena forage. This result suggested that reasonable performance could be achieved by supplementing a Napier basal diet with only a legume forage, which could be produced cheaply and conveniently on-farm. Consequently during 1990 an experiment was carried out to evaluate the effects on cow performance of level of Leucaena supplement and of the harvesting height of the Napier basal fodder.

MATERIALS AND METHODS

Study site

The experiment was carried out at the Regional Research Centre, Mtwapa, Kenya, 20 km north-west of Mombasa in the coastal lowland coconut-cassava agro-ecological zone (Jaetzold and Schimdt, 1983). During the study period, March to November 1990, mean monthly minimum and maximum temperatures were 20-24 and 24-27°C, respectively, and relative humidity was high. During most of the experiment there was good rainfall and fast Napier grass growth.

Animals

Thirty-six Ayrshire/Brown Swiss x Sahiwal cows of known breed composition, previous performance and service dates were purchased from a large local dairy farm. They were representative of the crossbred dairy population found on smallholder farms at the Kenya coast. They had had one to four previous lactations. The cows were housed in a well ventilated zero-grazing unit where they were fed chopped Napier fodder and some copra cake and maize bran until calving. They were treated with the trypanocidal prophylactic drug isometamidium chloride (Samorin), and drenched with levamisole hydrochloride/oxyclozanide (Nilzan) against internal parasites. They were sprayed weekly with a diamidide acaricide (Triatix) to control tick-borne diseases.

Diets

Napier grass (Pennisetum purpureum cv Bana) was harvested daily at heights of 1.0 or 1.5 m, chopped with a motorised chopper into pieces about 20-50 mm long and mixed thoroughly before feeding. Leucaena forage (about 280 g crude protein/kg DM, 250 g DM/kg fresh matter) was harvested from well-established hedgerows of the variety K28. It was cut in the evening for morning feeding and in the morning for the afternoon feeding. Stems thicker than 5 mm in diameter were removed from the forage before feeding.

Experiment procedure

The 36 cows were allocated to two groups with greater or less than 50% Sahiwal genes. Cows from each group were then assigned at calving to treatment groups in a 2 x 3 factorial design to evaluate the effects of harvesting height of Napier (1.0 or 1.5 m) and level of Leucaena supplement (0, 4 or 8 kg fresh weight). Where possible the six treatment groups were balanced for postpartum body weight. All cows had good body condition. The cows calved between 26 March and 2 August and the experiment began on day 15 of lactation and lasted 98 days.

The cows were confined in individual stalls in the zero-grazing unit. Body weights were recorded the day after calving, and weekly thereafter before morning feeding. The cows were hand-milked at about 0500 and 1500 hours and the milk production recorded. Water and mineral lick (19.95% Ca, 11.76% P. 10.26% Na, 0.16% Cu) were available at all times. Napier fodder was offered at least twice daily to ensure constant availability of the fodder for ad libitum feeding. From day 15 of lactation, the cows were fed according to treatment group, the ad libitum Napier fodder, harvested at a height of 1.0 or 1.5 m, supplemented with 0, 4 or 8 kg fresh weight of Leucaena forage. Feed refusals were weighed and recorded before milking on the following day. There were no Leucaena refusals. The Leucaena forage offered and the Napier fodder offered and refused were sampled weekly on consecutive days; half of each sample was dried at 85°C for laboratory analysis and the other half at 105°C for dry-matter determination. Blood was sampled every fortnight to screen for trypanosomes, and other health measures were taken as necessary.

Statistical analysis

Dry-matter (DM) intake of Napier, total DM intake, body weight change and milk yield were analysed using the General Linear Model (GLM) for covariance analysis of the SAS (1987) computer package. The linear model included the independent variables, calving period (before or after the end of May), breed group, Napier harvesting height, level of Leucaena supplement and the interaction of the latter two factors. Second-week body weight was a covariate in the analyses of DM intake and liveweight change. Average daily milk yield in the second week of lactation was a covariate for milk yield.

RESULTS

Only results for the production traits are presented here. Laboratory analyses giving the digestibility, metabolisable energy and protein levels of the forage samples are not yet available. These laboratory results will determine the final interpretation of, and conclusions from, the results for the production traits.

All cows were in good health throughout the experiment, with the exception of one cow which had to be replaced early in the experiment because of severe mastitis, and another two cases of metritis which responded quickly to treatment.

Feed intake

Dry-matter intake of the basal Napier fodder was significantly (P<0.001) affected by the harvesting height of the Napier grass (Table 1). The provision of the Leucaena forage supplement did not significantly affect Napier dry-matter intake. Not only was there no substitution effect, but there was an indication of some stimulation of Napier intake when cows received the Leucaena supplement. Consequently total DM intake was significantly affected (P<0.001) both by harvesting height of Napier and by level of Leucaena supplement.

Despite the large effects of Napier harvesting height and level of Leucaena supplement there was no significant harvesting height x supplement interaction. However, there were indications in the latter period of the experiment that interactions may have been important.

When expressed as a proportion of body weight, total DM intake for the six dietary combinations ranged from 1.8 to 2.8%.

Table 1. Mean daily Napier fodder and total (Napier plus Leucaena) dry-matter intakes of lactating crossbred cows fed ad libitum Napier fodder harvested at 1.0 or 1.5 m supplemented with 0.4 or 8 kg fresh Leucaena forage from day 15 to day 112 of lactation

Treatment	n	Mean dry-matter intake (kg/day)
		Napier	Total (Napier plus Leucaena)
Napier harvest height (m)
1.0	18	9.3	10.5
1.5	17	6.8	7,9
SE		0.29	0.29
F-test of probability		P<0.001	P<0.001
Leucaena supplement (kg)
0	12	7.8	7.8
4	11	8.2	9.3
8	12	8.2	10.4
SE		0.35
F-test of probability		ns	P<0.001

Body weight changes

Body weight losses occurred in all treatment groups, but the losses were more marked in weeks 3 to 9 of lactation than later (Table 2).

There were no significant, nor apparently important, harvest height x Leucaena supplement interactions for body weight change.

Milk production

Over the 14 weeks of the experiment both harvest height of Napier and level of Leucaena supplement had significant effects (P<0.001 and P<0.05, respectively) on mean daily milk yield (Table 3). Napier fodder harvested at 1.0 m rather than 1.5 m gave on average 1.7 kg (25%) per day more milk, with a greater advantage (32% compared to 18%) in the second half of the experiment. Similarly there was a differential response to level of Leucaena supplement during the two halves of the experiment. The supplement did not affect mean daily milk yield during weeks 3 to 9 of lactation when body weight losses (Table 2) were marked, but it did have a significant (P<0.01) effect on milk yields in weeks 10 to 16 when body weight losses were lower. In the latter period, each 4 kg of fresh Leucaena (about 1 kg DM) gave a response of about 0.8 kg more milk.

There were no significant Napier grass harvest height x level of Leucaena supplement interactions, but there were indications that in the latter half of the experiment responses to Leucaena supplementation were higher in cows fed Napier fodder harvested at 1.5 m.

Table 2. Mean body weight changes for lactating crossbred cows fed ad libitum Napier fodder harvested at 1.0 or 1.5 m supplemented with 0,4 or 8 kg fresh weight Leucaena forage from day 15 to day 112 of lactation

Treatment	Mean body weight change (kg)
	Days 15-63		Days 64-112		Overall
	n	Mean	n	Mean	n	Mean
Napier harvest height (m)
1.0	18	-8	18	-8	18	-16
1.5	18	-30	17	-18	17	-48
SE		6.3		4.4		7.1
F-test of probability		P<0.01		P<0.05		P<0.001
Leucaena supplement (kg)
0	12	-37	12	-18	12	-55
4	12	-10	11	-10	11	-20
8	12	-10	12	-10	12	-20
SE		7.9		5.5		9.0
F-test of probability		P<0.01		ns		P<0.01

Table 3. Mean daily milk yield for lactating crossbred cows fed ad libitum Napier fodder harvested at 1.0 or 1.5 m supplemented with 0,4 or 8 kg fresh weight Leucaena forage from day 15 to day 112 of lactation

Treatment	Mean milk yield (kg/day)
	Days 15-63		Days 64-112		Overall
	n	Mean	n	Mean	n	Mean
Napier harvest height (m)
1.0	18	9.4	18	7.8	18	8.5
1.5	18	8.0	17	5.9	17	6.8
SE		0.30		0.35		0.30
F-test of probability		P<0.001		P<0.001		P<0.001
Leucaena supplement (kg)
0	12	8.6	12	6.0	12	7.2
4	12	8.7	11	6.8	11	7.6
8	12	8.9	12	7.7	12	8.3
SE		0.36		0.42		0.36
F-test of probability		ns		P<0.01		P<0.05

DISCUSSION

This work set out to test the hypothesis that reasonable dairy cow performance could achieved by supplementing a basal diet of Napier fodder with only a legume forage. Major improvements in performance were observed in cows fed Napier fodder harvested at 1.0 m height, supplemented with 4 or 8 kg fresh weight of Leucaena Cows fed this diet had high DM intakes (approaching 3% of body weight) which enabled them to maintain body weight and produce about 1000 kg milk in less than the first three months of lactation. With reasonable subsequent nutrition a total lactation yield of at least 2000 kg could be expected.

The results highlight the important contribution legume forages can make to achieving reasonable performance and to improving the utilisation of basal forage diets. The higher level of Leucaena supplement gave on average 15% more milk over the period of the experiment. The lack of response in the earlier months may be explained by the greater mobilisation of body reserves by cows not receiving Leucaena compared with those that were given the supplement. Thus the main effect of Leucaena in early lactation was to reduce the loss of body weight. In the third and fourth months of lactation the effect of the supplement on milk production was large, with each 1 kg of Leucaena DM stimulating the production of about 0.8 kg of milk. Thus Leucaena supplementation can make a very efficient contribution, both biologically and economically, towards improving cow performance.

In the absence of laboratory analyses of the forages used in the experiment, calculations based on expected values indicated that the diets were deficient in energy. A small quantity of an energy-rich concentrate, maize bran, for example, would therefore allow cows supplemented with Leucaena to utilise the available protein more efficiently and produce more milk very cost-effectively. This hypothesis was tested in a subsequent experiment which is now being analysed.

In the context of the smallholder, the legume is also expected to play an important complementary role in improving the stability and sustainability of Napier yields. As mentioned in the introduction, the agronomic studies, which run concurrently with the nutrition research, evaluate the productivity and sustainability of fodder production systems combining shrub and herbaceous legumes grown in association with Napier grass. These studies will quantify the output per unit area of sole stands of Napier grass and Leucaena and of their mixed stands and intercrops with herbaceous legumes.

The importance of these agronomic studies is emphasised by the large effect on cow performance of the harvesting height of the Napier fodder. By quantifying the yields of Napier harvested at different heights throughout the year, and then feeding those Napier fodders to cows in experiments similar to that reported here, it will be possible to assess the relative productivities of the systems in terms of output per area and per cow. When labour inputs are included in the calculations, an economic evaluation can be applied and recommendations developed.

REFERENCES

Jaetzold R and Schmidt H. 1983. Farm management of Kenya. Vol. 11 C, National conditions and farm management information. East Kenya (Eastern and Coast Provinces). Farm Management Branch, Ministry of Agriculture, Nairobi, Kenya. pp. 332-333.

Mureithi J G. 1990. Research on feed resource development. Working Document 1 (rune 1990). KARI/ILCA [Kenya Agricultural Research Institute/International Livestock Centre for Africa] Collaborative Research on Smallholder Dairy Production in the Coastal Subhumid Zone. ILCA, Mombasa, Kenya. 30 pp.

SAS (Statistical Analysis Systems Institute Inc). 1987. SAS/STAT: Guide for personal computers, version 6 edition. SAS, Cary, North Carolina, USA. pp. 551-640.